Palygorskite-Sepiolite: Occurrences, Genesis and Uses (Developments in Sedimentology)

DEVELOPMENTS IN SEDIMENTOLOGY 37

PACYGORSKITE - SEPlOllTE Occurrences, Genesis and Uses

FURTHER TITLES IN THIS SERIES VOLUMES 1.2.3.5.8 and 9 are out of print 4 F.G. T I C K E L L THE TECHNIQUES O F SEDIMENTARY MINERALOGY 6 L. V A N D E R PLAS T H E IDENTIFICATION O F DETRITAL FELDSPARS 7 S. D Z U L Y N S K I and E.K. W A L T O N SEDIMENTARY FEATURES O F FLYSCH AND GREYWACKES 10 P.McL.D. D U F F , A. H A L L A M and E.K. W A L T O N CYCLIC SEDIMENTATION 11 C.C. REEVE'S Jr. INTRODUCTION T O PALEOLIMNOLOGY 12 R.G.C. B A T H U R S T CARBONATE SEDIMENTS AND THEIR DIAGENESIS 13 A.A. M A N T E N SILURIAN R E E F S O F GOTLAND 14 K.W. G L E N N I E DESERT SEDIMENTARY ENVIRONMENTS 1 5 C.E. W E A V E R and L.D. P O L L A R D THE CHEMISTRY O F CLAY MINERALS 16 H.H. R I E K E III and G . V . C H I L I N G A R I A N COMPACTION O F ARGILLACEOUS SEDIMENTS 11 M.D. P I C A R D and L.R. HIGH Jr. SEDIMENTARY STRUCTURES O F EPHEMERAL STREAMS 18 G . V . C H I L I N G A R I A N and K.H. W O L F , Editors COMPACTION O F COARSE-GRAINED SEDIMENTS 19 W. S C H W A R Z A C H E R SEDIMENTATION MODELS AND QUANTITATIVE STRATIGRAPHY 20 M.R. W A L T E R , E d i t o r STROMATOLITES 21 B. V E L D E CLAYS AND CLAY MINERALS I N NATURAL AND SYNTHETIC SYSTEMS 22 C.E. W E A V E R and K.C. B E C K MIOCENE O F THE SOUTHEASTERN UNITED STATES 23 B.C. H E E Z E N , Editor INFLUENCE O F ABYSSAL CIRCULATION O N SEDIMENTARY ACCUMULATIONS IN SPACE AND TIME 24 R.E. G R I M and G U V E N BENTONITES 25A G. L A R S E N and G . V . C H I L I N G A R , Editors DIAGENESIS I N SEDIMENTS AND SEDIMENTARY ROCKS, I 26 T.S U D O and S. S H I M O D A , Editors CLAYS AND CLAY MINERALS O F JAPAN 21 M.M. M O R T L A N D and V.C. F A R M E R , Editors INTERNATIONAL CLAY CONFERENCE 1978 28 A . N I S S E N B A U M , Editor HYPERSALINE BRINES AND EVAPORITIC ENVIRONMENTS 29 P. T U R N E R CONTINENTAL R E D BEDS 30 J . R . L . A L L E N SEDIMENTARY STRUCTURES 31 T.S U D O , S. S H I M O D A , H . Y O T S U M O T O and S . A I T A ELECTRON MICROGRAPHS OF CLAY MINERALS 32 C.A. N I T T R O U E R , E d i t o r SEDIMENTARY DYNAMICS O F CONTINENTAL SHELVES 33 G.N. B A T U R I N PHOSPHORITES ON THE SEA FLOOR 34 J.J. F R I P I A T . E d i t o r ADVANCED TECHNIQUES F O R CLAY MINERAL ANALYSIS 36 H . V A N O L P H E N and F . V E N I A L E , Editors INTERNATIONAL CLAY CONFERENCE 1981 36 A. I I J I M A , J.R. H E I N and R. S I E V E R . E d i t o r s SILICEOUS DEPOSITS IN T H E PACIFIC REGION

DEVELOPMENTS IN SEDIMENTOLOGY 37

PALYGORSKITE - SEPlOLlTE Occurrences, Genesis and Uses Edited by

A. SINGER The Hebrew University o f Jerusalem, Seagram Centre f o r Soil & Water Sciences, Rehovot 76-100 (Israel) and

E. GALAN Departamento de Geologia, Facultad de Quimica, Palos de la Frontera 1, Universidad d e Sevilla, Sevilla (Spain)

ELSEVIER Amsterdam - Oxford -New York - Tokyo

1984

ELSEVIER SCIENCE PUBLISHERS B.V. Molenwerf 1 P.O. Box 211,1000 AE Amsterdam, The Netherlands Distributors for the United States and Canada: ELSEVIER SCIENCE PUBLISHING COMPANY INC. 52, Vanderbilt Avenue New York, N.Y. 10017

Library of Congress Cataloging i n Publication D a t a

Main e n t r y under t i t l e : P a l y g o r s k i t e - s e p i o l i t e occuri-CLICC - , pcni.7 i s , ;Ind

URII;.

(Dtvelopments i n s e d i m e n t o l o a ; 37) Bibliosraphy: p. Includcs indexes. 1. P a l y g o r s k i t e . 2. Meerschau?:. I . Singer, A. 11. Galan, E. III. S e r i e s . $E391.P34P34 1gL4 >JI~ .I> ' ;4-59,7 ISBN 0-444-4;337-0

ISBN 0-444-42337-0 (Vol. 37) ISBN 0-444-41238-7 (Series) Elsevier Science Publishers B.V., 1984 All rights reserved. N o part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording o r otherwise, without the prior written permission of the publisher, Elsevier Science Publishers B.V., P.O. Box 330, 1000 AH Amsterdam, The Netherlands 0

Printed in The Netherlands

V PREFACE The p a l y g o r s k i t e - s e p i o l i t e c l a y m i n e r a l group, a l s o known as t h e h o r m i t e group, f i b r o u s c l a y m i n e r a l s , o r c h a i n p h y l l o s i l i c a t e s , has r e c e i v e d f a r l e s s a t t e n t i o n than o t h e r major c l a y minerals.

This neglect p a r t l y

r e f l e c t s t h e f a c t t h a t t h e s e c l a y m i n e r a l s a r e l e s s common t h a n t h e l a y e r phyllosilicates.

D i f f i c u l t i e s i n i d e n t i f i c a t i o n , p a r t i c u l a r l y during rou-

t i n e XRD i d e n t i f i c a t i o n procedures f o r g e o l o g i c a l surveys, may a l s o have c o n t r i b u t e d t o t h e s c a r c i t y o f i n f o r m a t i o n a v a i l a b l e on t h i s c l a y m i n e r a l group. D e s p i t e t h i s , however, t h e p a l y g o r s k i t e - s e p i o l i t e c l a y group has been known t o , and used by mankind f o r c e n t u r i e s because o f i t s many d i v e r s e and u s e f u l p r o p e r t i e s , and makes i n t e r e s t i n g h i s t o r y .

Pre-Columbian I n d i a n s

f r o m t h e Yucatan p e n i n s u l a c a l l e d p a l y g o r s k i t e c l a y "Sac l u ' u m " (Maya f o r "White E a r t h " ) and used i t i n t h e p r o d u c t i o n o f ceramics, as f a r back as

800 y e a r s ago.

When mixed w i t h i n d i g o i t produced t h e h i g h l y p r i z e d o r g a -

n i c pigment known as "Maya B l u e " .

" T i e r r a del Vino", a mixture o f c a l c i t e

and s e p i o l i t e has been used f o r t h e p u r i f i c a t i o n o f w i n e i n L e b r i j a , a p r o v i n c e o f Spain, f o r hundreds o f y e a r s and s e p i o l i t e , mined i n Spain s i n c e t h e b e g i n n i n g o f t h e 1 7 t h C e n t u r y i s used i n t h e manufacture o f p i p e s and c i g a r e t t e f i l t e r s , and was a l s o used f o r c e r a m i c s d u r i n g t h e l a t e 1 9 t h Century. These c l a y s today, because o f t h e i r c o l l o i d a l - r h e o l o g i c a l p r o p e r t i e s , have a wide range o f i n d u s t r i a l a p p l i c a t i o n s and a r e c o n s i d e r e d t o be one o f t h e most i n t e r e s t i n g m i n e r a l groups used i n i n d u s t r y . Many new o c c u r r e n c e s o f c h a i n - p h y l l o s i l i c a t e s ,

p a r t i c u l a r l y palygorskite,

which i s more abundant t h a n s e p i o l i t e , have been r e p o r t e d d u r i n g t h e p a s t few y e a r s and l a r g e amounts o f i n f o r m a t i o n on t h e i r e n v i r o n m e n t a l c h a r a c t e r i s t i c s have r e s u l t e d .

The l a b o r a t o r y s y n t h e s i s o f c h a i n p h y l l o s i l i c a t e s under con-

t r o l l e d c o n d i t i o n s , however, has encountered d i f f i c u l t i e s and t h e r e s u l t i n g hypotheses on t h e g e n e s i s o f t h e s e c l a y s a r e t h e r e f o r e f a i r l y s p e c u l a t i v e . I n a d d i t i o n , r e p o r t s on p a l y g o r s k i t e - s e p i o l i t e occurrences a r e w i d e l y d i s s e m i -

VI n a t e d t h r o u g h o u t t h e many e a r t h - s c i e n c e d i s c i p l i n e s of geology, m i n e r a l o g y , s o i l s c i e n c e and oceanography.

I t i s t h e r e f o r e a p p a r e n t t h a t a comprehensive

r e v i e w i s l o n g overdue.

I n response t o t h e i n i t i a t i v e o f one o f t h e e d i t o r s , a symposium e n t i t l e d "Occurrences and Genesis o f S e p i o l i t e / P a l y g o r s k i t e Sediments" was o r g a n i z e d d u r i n g t h e 7 t h I n t e r n a t i o n a l C l a y Conference, h e l d i n I t a l y i n 1981.

Nine

papers were p r e s e n t e d a t t h i s sympsoium and i n a d d i t i o n , s i n c e t h e o r g a n i z e r s f e l t t h a t t h i s s u b j e c t deserved more comprehensive monographic coverage, cont r i b u t i o n s f r o m well-known s p e c i a l i s t s i n t h i s f i e l d were s o l i c i t e d .

The

r e s u l t i n g volume, which i n c l u d e s e i g h t o f t h e papers p r e s e n t e d a t t h e I n t e r n a t i o n a l Clay Conference, i s t h e outcome o f t h i s i n i t i a t i v e . F o l l o w i n g an i n t r o d u c t i o n on t h e d i s t r i b u t i o n o f p a l y g o r s k i t e i n space and t i m e , t h e c o n t r i b u t i o n s a r e a r r a n g e d a c c o r d i n g t o t h e t y p e s o f e n v i r o n ment a s s o c i a t e d w i t h t h e o c c u r r e n c e s .

These i n c l u d e c o n t i n e n t a l ( s u b d i v i d e d

i n t o l a c u s t r i n e and pedogenic) and p e r i m a r i n e environments.

The hydrothermal

environment i s r e p r e s e n t e d by o n l y one c o n t r i b u t i o n f r o m Japan, and one sect i o n i n c l u d e s n o t e s on d e p o s i t s f r o m U.S.S.R.,

o f China.

I n d i a and t h e P e o p l e ' s R e p u b l i c

The volume c l o s e s w i t h a d i s c u s s i o n on t h e i n d u s t r i a l a p p l i c a t i o n s

o f p a l y g o r s k i t e - s e p i o l i t e minerals.

Two appendices i n c l u d e d e t a i l s o f DSDP

occurrences o f t h e s e m i n e r a l s , i n a d d i t i o n t o a c o m p l e t e l y u p - t o - d a t e b i b 1 i o graphy.

The r e v i e w e d and e d i t e d m a n u s c r i p t s were t y p e d by t h e a u t h o r s i n

camera-ready f o r m and t h e volume was produced by p h o t o - o f f s e t . due t o t h e a u t h o r s and r e v i e w e r s .

A. S i n g e r , E. Galan Editors

Thanks a r e

VII

TABLE OF CONTENTS

v

PREFACE INTRODUCTION: DISTRIBUTION OF PALYGORSKITE-SEPIOLITE IN SPACE AND TIME

Clays of the palygorskite-sepiolite group: depositional environment, age and distribution 1 R.A. CALLEN,' SECTION I.

DEPOSITS IN PERI-MARINE ENVIRONMENTS

Origin and geologic implications of the palygorskite of the S.E. United States 39 C.E. WEAVER The clays of Yucatan, Mexico: a contrast in genesis W.C. 1SPHORDING

59

Palygorskite in the Tertiary deposits of the Armorican Massif J. ESTEOULE-CHOUX

75

SECTION 11.

DEPOSITS AND OCCURRENCES IN CONTINENTAL ENVIRONMENTS: LACUSTRINE

Sepiolite-palygorskite in Spanish Tertiary Basins: genetical patterns in continental environments E. GALAN AND A. CASTILLO

87

Sepiolite in the Amboseli Basin of Kenya: a new interpretation 125 R.L. HAY AND R.K. STOESSEL Sepiolite in Pleistocene Lake Tecopa, Inyo County, California H.C. STARKEY AND P.D. BLALKMON

137

Diagenetic palygorskite in marginal continental detrital deposits located in the south of the Tertiary Duero Basin (Segovia, Spain) S. LEGUEY, J. MARTIN DE VIDALES AND J. CASAS 149 Ballarat sepiolite, Inyo County, California J.L. POST AND C . JANKE SECTION 111.

159

DEPOSITS AND OCCURRENCES IN CONTINENTAL ENVIRONMENTS: PEDOGEPTIC

Pedogenic palygorskite in the arid environment A. SINGER

169

Origin of palygorskite in some soils of the Arabian Peninsula R.C. MACKENZIE, M.J. WILSON AND A.S. MASHHADY

177

Occurrence of palygorskite in the soils and rocks of the Jordan Valley H. SHADFAN AND J.B. DIXON 187 Occurrence of palygorskite in ground-water rendzinas (Petrocalcic Calciaquolls) in south-east South Australia T. HODGE, L.W. TURCHENEK AND J.M. OADES

199

VIII

SECTION I V . DEPOSITS AND OCCURRENCES I N CONTINENTAL ENVIRONMENTS: HYDROTHERMAL S e p i o l i t e and p a l y g o r s k i t e i n Ja p a n N. IMAI AND R. OTSUKA SECTION V.

21 1

NOTES ON THE OCCURRENCES AND USES OF PALYGORSKITESEPIOLITE I N THE USSR, I N D I A AND P.R. OF C H I N A

P a l y g o r s k i t e and s e p i o l i t e d e p o s i t s i n t h e USSR and t h e i r u s e s P.D. OVCHARENKO AND Y E . G . KUKOVSKY

233

O c c u r r e n c e of p a l y g o r s k i t e i n t h e Deccan T r a p F o r m a t i o n i n I n d i a M . K . HASNUDDIN SIDDIQUI

243

S e p i o l i t e c l a y d e p o s i t s i n South China ZHANG R E N J U N

25 1

SECTION V I .

INDUSTRIAL USES OF SEPIOLITE

S e p i o l i t e : p r o p e r t i e s and u s e s A. ALVAREZ SECTION V I I .

253

APPENDICES

A p p e n d i x I , 1-3: D e t a i l s of Deep Sea D r i l l i n g P r o j e c t o c c u r r e n c e s ; 4: Details of l a n d o c c u r r e i c e s R . CALLEN, c o m p i l e r 289 Appendix 11: B i b l i o g r a p h y R. CALLEN, c o m p i l e r

315

AUTHOR I N D E X

337

SUBJECT I N D E X

339

1

CLAYS O F THE PALYGORSKITE-SEPIOLITE GROUP: DEPOSITIONAL ENVIRONMENT, AGE AND DISTRIBUTION*

ROGER A. CALLEN Eastwood, S.A.

Department of Mines and Energy, South A u s t r a l i a ,

Box 151,

5063.

ABSTRACT Major d e p o s i t s of p a l y g o r s k i t e - s e p i o l i t e

g r o u p m i n e r a l s were i n i t i a l l y

formed i n t h r e e e n v i r o n m e n t s of d i f f e r e n t c h a r a c t e r

-

( 1 ) i n epicontinental

and i n l a n d seas and l a k e s as c h e m i c a l s e d i m e n t s , o r by r e c o n s t i t u t i o n of former c l a y s d u r i n g e a r l y d i a g e n e s i s ;

( 2 ) i n t h e open o c e a n s i n a s s o c i a t i o n

w i t h f o r e - a r c b a s i n s and ocean rises by h y d r o t h e r m a l a l t e r a t i o n of b a s a l t i c q l a s s , v o l c a n i c s e d i m e n t s or c l a y s ;

( 3 ) i n c a l c a r e o u s s o i l s by d i r e c t

S u b s e q u e n t l y marine d e p o s i t s w e r e a l s o formed by slumping

crystallization.

and t u r b i d i t y c u r r e n t t r a n s p o r t of n e a r s h o r e m a t e r i a l s ,

and from windblown

dust. Palygorskite-sepiolite

group m i n e r a l s which formed i n s o i l s , l a k e s or

s h a l l o w seas w e r e m o s t l y a s s o c i a t e d w i t h a M e d i t e r r a n e a n t o s e m i - a r i d

climate.

T h i s i s r e f l e c t e d i n t h e i r d i s t r i b u t i o n i n low l a t i t u d e s .

These

climatic c o n d i t i o n s were p r e s e n t d u r i n g t h e L a t e Devonian and C a r b o n i f e r o u s and L a t e Permian t o T r i a s s i c i n t h e n o r t h e r n h e m i s p h e r e , and i n t h e E a r l y and

L a t e Eocene, L a t e O l i g o c e n e and l a t e Neogene, and p o s s i b l y Late C r e t a c e o u s i n b o t h hemispheres. marine o r i g i n .

The L a t e C r e t a c e o u s d e p o s i t s are l a r g e l y of h y d r o t h e r m a l

Some of t h e Devonian d e p o s i t s a r e a s s o c i a t e d w i t h b a s a l t s , and

t h e i r mode of o c c u r r e n c e s u g g e s t s t h e y may be h y d r o t h e r m a l o c e a n i c t y p e s . These c o n c l u s i o n s were r e a c h e d by e x a m i n i n g P l i o - P l e i s t o c e n e distributions,

l i t h o f a c i e s a s s o c i a t e s and occurrence d i s t r i b u t i o n s , p l o t t e d on

p a l a e o c o n t i n e n t a l maps.

when the o r i g i n a l d i s t r i b u t i o n - b i a s i n DSDP d a t a

( c o i n c i d e n t a l l y i n similar l a t i t u d e s to c o n t i n e n t a l d a t a ) w a s e l i m i n a t e d , t h e r e was l i t t l e e v i d e n c e f o r l a t i t u d i n a l c o n c e n t r a t i o n i n t h e oceans. Sampling b i a s on l a n d is d i f f i c u l t to assess, b u t t h e r e a p p e a r s t o be a c o n c e n t r a t i o n between 30° and 40° N and S . between 20°-400N

and 10°-350S

There is a d i s t i n c t concentration

i n t h e l a t e Neogene,

f o r b o t h l a n d and sea

deposits.

*Presented at the International Clay Conference 1981.

2 M TRODUCTI (El The p a l y g o r s k i t e - s e p i o l i t e ( p a l y g o r s k i t e o r a t t a p u l q i te,

etc.

-

g r o u p m i n e r a l s o r f i b r o u s magnesium c l a y s

s e p i o l ite, p i l o l i te, l o u g h l i n i te, f r a n c l a n d i te,

h e n c e f o r t h r e f e r r e d to as p a l y g o r s k i t e s ) were once r e g a r d e d as rare

m i n e r a l s , r e s t r i c t e d t o h y d r o t h e r m a l v e i n s and ore-body a l t e r a t i o n z o n e s . They are now known to be widespread i n marine and non-marine e s p e c i a l l y i n t h e oceans.

s e d i m e n t s , and

The p a l y q o r s k i t e s are s t r o n g l y a b s o r b e n t , v e r y

l i g h t , and p o r o u s , which makes them much sough+ a f t e r as F u l l e r ' s E a r t h , meerschaum and s i m i l a r materials, f o r i i d u s t r i a l a b s o r b a n t s , c a t a l y s t s and

ceramics.

S t r u c t u r e and c o m p o s i t i o n are summarized i n Zelazny and Calhoun

( 1 9 7 7 ) who g i v e a d e q u a t e r e f e r e n c e s of d e t a i l e d s t r u c t u r a l s t u d i e s . The g e o l o g y of t h e s e c l a y s h a s s u g g e s t e d t h e y c o u l d b e good p a l a e o c l i m a t i c i n d i c a t o r s (e.g.

Weaver and Beck,

1977, M i l l o t ,

1964, Wiersma,

1970, S i n g e r , 1979, 1980. 1981, Chamley, 1979, Chamley e t a l , 1977, LOmova, 1979, among o t h e r s ) .

Hence a n e a r l i e r c o n t r i b u t i o n o f C a l l e n ( 1 9 7 7 ) h a s been

e x t e n d e d t o i n c l u d e t h e l a r g e amount of Deep Sea D r i l l i n g P r o j e c t (DSDP)

material, and many new i n v e s t i g a t i o n s of l a n d d e p o s i t s .

METHODS The l i t h o l o g i c a l a s s o c i a t i o n of each d e p o s i t w a s r e c o r d e d , and t h e l o c a t i o n p l o t t e d on p a l a e o c o n t i n e n t a l maps.

For t h e o l d e r d e p o s i t s ,

E c k e r t p r o j e c t i o n s of Kanasewich e t a1 (1978) are used ( F i g . 4 ) .

the

a s it i s

easier t o p l o t on t h e s e , and t h e y show t h e d i s t r i b u t i o n of l a n d and s h e l f sea.

More recent p a l a e o c o n t i n e n t a l maps, u s i n g s e d i m e n t a r y palaeoclimatic

i n d i c a t o r s i n a d d i t i o n t o i n d e p e n d e n t p a l a e o m a g n e t i c d a t a , have been p r e p a r e d by Z i e g l e r e t a l . ( 1 9 7 9 ) .

The l a t t e r place Devonian European R u s s i a j u s t

n o r t h of t h e e q u a t o r and C a r b o n i f e r o u s R u s s i a f u r t h e r s o u t h t h a n t h e maps o f Kanasewitch e t al. (19781, b o t h b e i n g i m p o r t a n t areas and t i m e s of palygorskite deposition. For o c e a n i c o c c u r r e n c e s the polar p r o j e c t i o n r e c o n s t r u c t i o n s of Firstbrook et al.

( 1 9 7 9 ) are used ( F i g s . 5-9).

They have t h e a d v a n t a g e o f

b e i n g a t 10 Ma i n t e r v a l s , w i t h DSDP h o l e s p l o t t e d .

They are similar t o t h e

Smith and Briden ( 1 9 8 0 ) maps w i t h respect to c o n t i n e n t a l p o s i t i o n s .

The S m i t h

and B r i d e n mercator p r o j e c t i o n s are u s e d t o p l o t c o n t i n e n t a l p a l y g o r s k i t e s and

summarize oceanic occurrences ( F i g s . 1 , 4 , 1 0 - 1 2 ) , view o f l a t i t u d i n a l d i s t r i b u t i o n , well-defined

because they g i v e a b e t t e r

and the a g e of land-based

t h a t narrower t i m e i n t e r v a l s can be c o n s i d e r e d .

d e p o s i t s is n o t so

3 The comments of S c o t e s e ( 1 980) concerning a l t e r n a t i v e c o n t i n e n t a l c o n f i g u r a t i o n s must be c o n s i d e r e d with respect to t h e r e c o n s t r u c t i o n s of Smith and Briden (1980) and F i r s t b r o o k e t a1 ( 1 9 7 9 ) .

The p o s i t i o n of N e w Zealand on

t h e Mercator p r o j e c t i o n s h a s been a d j u s t e d a p p r o x i m a t e l y , i n l i n e with t h e s u g g e s t i o n s of Scotese ( 1 9 8 0 ) . reconstructions.

Smith (1981) h a s r e c e n t l y updated some of h i s

The work o f Veevers e t a l . (1980) s u g g e s t s a somewhat

d i f f e r e n t h i s t o r y f o r t h e s o u t h e r n I n d i a n Ocean and t h e p o s i t i o n of It i s s u g g e s t e d t h a t Madagascar w a s a t t a c h e d to A u s t r a l i a ,

Madagascar.

r e a c h i n g a ?re

n o rth erl y l o cat io n a t an e a r l y stage.

Basically, these

a d j u s t m e n t s make no major changes i n t h e d i s t r i b u t i o n p a t t e r n s ( F i g s . 5-6). D a t a f o r DSDP c r u i s e s and onshore s t u d i e s has been o b t a i n e d from t h e

p r o j e c t volumes (see r e f e r e n c e s ) , though t h e r e are some i m p o r t a n t a d d i t i o n a l a n a l y s e s p u b l i s h e d e l s e w h e r e (Appendix 1.1 and r e f e r e n c e s ) .

The d a t a used are

e s s e n t i a l l y t h a t of o r i e n t e d < 2 ~ )c l a y a n a l y s e s ; o t h e r u n o r i e n t e d < 2 ~ )a n a l y s e s a r e recorded and p l o t t e d b u t n o t used i n t h e p e r c e n t a g e c a l c u l a t i o n s .

A few

p a p e r s p u b l i s h e d o u t s i d e t h e DSDP series, b u t u s i n g t h e p r o j e c t cores, do n o t

state t h e a n a l y t i c a l method, b u t i t is assumed t h e s e are o r i e n t e d

(211) samples.

D a t a from t h e South A t l a n t i c Ocean and 1982 onwards has n o t y e t

been i n c o r p o r a t e d i n t h e p e r c e n t a g e abundance s t u d i e s , p a r t l y due t o l a c k of s u f f i c i e n t d e t a i l i n some r e p o r t s . D a t a from DSDP s t u d i e s were s u f f i c i e n t t o r e c o r d t h e approximate

abundance o f p a l y g o r s k i t e p l u s s e p i o l i t e ( F i g s . 2-6) i n each h o l e f o r each 10 My t i m e s l i c e .

The scheme used t o show this on t h e polar p l o t s i s e s s e n t i a l l y

q u a l i t a t i v e , and i s e x p l a i n e d i n t h e f i g u r e c a p t i o n . %

A l l t h e d a t a used i n t h e

abundance and a v e r a g e c a l c u l a t i o n s ( F i g . 1 3 and Appendix 1.2) are t a b u l a t e d

(Appendix 1 . 3 i n c l u d e s a d d i t i o n a l d a t a o b t a i n e d s i n c e these c a l c u l a t i o n s w e r e made

.

PREVIOUS WORK M o s t s i g n i f i c a n t p r e v i o u s work is summarized and a d e q u a t e l y d i s c u s s e d i n

t h e reviews by S i n g e r (1979, 19801, Weaver and Beck (1977) and Lomova ( 1 9 7 9 ) . S i n g e r (1980) concluded that p a l y g o r s k i t e s a r e t y p i c a l of a r i d and s e m i a r i d s o i l s , and one of t h e few u s e f u l palaeoclimatic i n d i c a t o r s among t h e c l a y minerals.

S i n g e r (1979) also s p e c i f i e d the c o n d i t i o n s of f o r m a t i o n of

p a l y g o r s k i t e and s e p i o l i t e , b e i n g a l k a l i n e pH, h i g h S i grid Mg, and l o w A 1 activity. diagenesis.

H e demonstrated t h a t most data s u g g e s t e d neoformation r a t h e r t h a n

S o l i d state t r a n s f o r m a t i o n o f smectite to p a l y g o r s k i t e as

proposed by Weaver and Beck (1977) i s n o t f a v o r e d as a major mechanism.

4 S i n g e r proposed a n e s s e n t i a l l y d e t r i t a l o r i g i n f o r deep marine p a l y g o r s k i t e , w i t h some o f h y d r o t h e r m a l o r i g i n , and most d e p o s i t s b e i n g neoformed i n t h e perimarine environment. Weaver and Beck (1977) i n c l u d e a summary of p e r i m a r i n e e n v i r o n m e n t s i n t h e i r p a p e r on t h e G e o r q i a - F l o r i d a p a l y g o r s k i t e mines o f U.S.A.,

concluding

t h e y a r e dominant e n v i r o n m e n t s of n e o f o r m a t i o n . Lomova (1979) summarizes* some of t h e DSDP and o t h e r c o r i n g p r o j e c t s i n t h e oceans a s well as much data from t h e c o n t i n e n t s , and d i v i d e s d e p o s i t s i n t o the followinq types:

t e r r i g e n o u s c l a s t i c ' , chemogenic e v a p o r i t i c , p y r o c l a s t i c ,

v o l c a n i c h y d r o t h e r m a l , pedogenic,

h y d r o t h e r m a l v e i n s , and c o n t a c t metamorphic

o r a l t e r a t i o n zones around o r e b o d i e s .

This a u t h o r i n c l u d e s playa-lake

and

s h a l l o w l a c u s t r i n e t y p e s i n t h e p e d o g e n i c group, and f a v o u r s widespread neoformation i n o c e a n s from v o l c a n i c d e t r i t u s and h y d r o t h e r m a l a c t i v i t y .

An

a r i d e n v i r o n m e n t f o r c o n t i n e n t a l d e p o s i t s i n R u s s i a i s emphasized and m o s t of t h e major R u s s i a n d e p o s i t s a r e d i s c u s s e d i n some d e t a i l .

Lomova b e l i e v e s

p a l y g o r s k i t e s can form i n humid a r e a s , p r o v i d e d t h e r e i s an abundance of basic volcaniclastics

o v e r a l l t h e r e is a g r e a t e r emphasis on h y d r o t h e r m a l and

v o l c a n i c i n f l u e n c e i n g e n e s i s t h a n i s g i v e n most " w e s t e r n " l i t e r a t u r e . b r i e f r e v i e w by Gradusov ( 1 9 7 6 ) , however,

p l a c e s more emphasis on a d e t r i t a l

o r i g i n i n t h e o c e a n s , w i t h n e o f o r m a t i o n i n s o i l s and p e r i - m a r i n e C o u t u r e (1977,a,b)

The

environments.

s t u d i e d o c e a n i c d e p o s i t s , and s u g g e s t e d d i a q e n e s i s

from smectite and v o l c a n i c d e t r i t u s ,

though t h e e v i d e n c e f o r t h i s i s n o t

c o n v i n c i n g (Beck and Weaver, 1978).

Decarreau e t a l . ( 1 9 7 5 ) , on t h e o t h e r

hand, p r o v i d e some e v i d e n c e s u p p o r t i n g d i a g e n e s i s from degraded f e r r i f e r o u s b e i d e l l i t e i n r e s t r i c t e d m a r g i n a l marine c o n d i t i o n s .

A g r i c u l t u r a l i n v e s t i g a t i o n s have p r o v i d e d l a r g e numbers of c l a y a n a l y s e s , r e s u l t i n g i n t h e d i s c o v e r y of h i g h - p e r c e n t a g e s of p a l y g o r s k i t e s i n c a l c a r e o u s s o i l s and calcretes over a wide area ( F i g . 1 1.

Many of t h e s e c o n t a i n

p a l y g o r s k i t e as c u t a n i c f i l m s o f o r i e n t e d f i b r e s on s k e l e t o n g r a i n s or j o i n t ( p e d ) s u r f a c e s , i n d i c a t i n g n e o f o r m a t i o n i n t h e s o i l (Perelman, 1950, van den Heuvel,

1966, S i n g e r and N o r r i s h ,

1981, Hutton and Dixon,

1981).

1974,

Eswaran and B a r z a n j i , 1974, W a t t s ,

Many o t h e r s are s a i d to be i n h e r i t e d from

* c o m m e n t s b a s e d on p a r t i a l t r a n s l a t i o n f r o m R u s s i a n t e x t by W.V. P r e i s s , S o u t h A u s t r a l i a n D e p a r t m e n t of M i n e s a n d E n e r g y .

5

PALYGORSKITES 0 m.y. LATE PLIOCENE

- HOLOCENE

Fig. 1 . L a t e P l i o c e n e - Holocene p a l y g o r s k i t e s e p i o l i t e o c c u r r e n c e s . Dots a r e g e n e r a l i z e d DSDP and o c e a n i c o c c u r r e n c e s , d i a g o n a l s h a d i n g i s c o n t i n e n t a l d a t a . P r e f i x D i n d i c a t e s s o i l or c a l c r e t e . Cross-hatched a r e a s a r e s o i l s superposed on sedimentary b a s i n s w i t h p a l y g o r s k i t e . See Appendix 11.3 f o r r e f e r e n c e s . I s r a e l i occurrences are D3, D24, D25, D30, D31, Lebanon D13A. u n d e r l y i n g material, or added by a e o l i a n t r a n s p o r t , though t h i s i s l i k e l y to have been overemphasized i n e a r l y s t u d i e s through l a c k o f knowledge of t h e submicroscopic d i s t r i b u t i o n w i t h i n the s o i l f a b r i c .

The d e r i v e d s o i l s a t

l e a s t demonstrate p a l y g o r s k i t e s are s t a b l e i n t h e s e environments, though a few show evidence of p r e s e n t day d e g r a d a t i o n (e.g.

Nahon and R u e l l a n , 1975, Bigham

e t al., 1980). The v a l u e o f the l a t e Neogene p a l y g o r s k i t e o c c u r r e n c e s i n t h e p r e s e n t s t u d y is to i d e n t i f y t h e climatic zone i n which p a l y g o r s k i t e s are p r e s e r v e d , and demonstrate t h a t many such o c c u r r e n c e s were neoformed w i t h i n c e r t a i n latitudinal l i m i t s .

They also show t h a t t h e s e s o i l s are a major s o u r c e o f

f i b r o u s c l a y m i n e r a l s f o r t h e oceans, through e r o s i o n .

The plots show t h a t

a l l of t h e s o i l s l i e w i t h i n t h e p r e s e n t day d r y Mediterranean to a r i d climatic

belts.

A non-random

d i s t r i b u t i o n of o r i g i n a l c l a y sample p o i n t s can be

reasonably assumed, as r o u t i n e c l a y a n a l y s e s o f s o i l s are undertaken by most c o u n t r i e s , e x c e p t perhaps i n some c e n t r a l A f r i c a n n a t i o n s , South and C e n t r a l America and s o u t h e a s t A s i a .

Frozen ground a t l a t i t u d e s h i g h e r t h a n 80° would

also be a f a c t o r p r e v e n t i n g sampling.

Many of t h e s o i l s and c a l c r e t e s c o n t a i n i n g p a l y g o r s k i t e s are p r o b a b l y quite old. Australia,

1981) i n

The calcretes of t h e Murray B a s i n ( H u t t o n and Dixon,

f o r example are most l i k e l y s e v e r a l hundred thousand y e a r s o l d

(Cook e t a l . ,

1976, and u n p u b l i s h e d work o f t h e a u t h o r ) .

Thus, a l t h o u g h many

of these s o i l s are now a t the E a r t h ' s s u r f a c e and even used i n a g r i c u l t u r e , t h e y are l i k e l y t o be relic, and may n o t have formed under t h e c l i m a t i c c o n d i t i o n s of t h e p r e s e n t .

Calcrete d e p o s i t s were p r o b a b l y common i n t h e more

a n c i e n t p a s t ; Watts ( 1 9 7 6 ) h a s d e m o n s t r a t e d t h e p r e s e n c e of p a l y g o r s k i t e i n T r i a s s i c calcretes.

Pre-Neogene

c a l c r e t e and s o i l o c c u r r e n c e s have n o t o f t e n

been r e c o r d e d , p r o b a b l y because o f t h e s m a l l volume o f s u c h materials p r e s e r v e d i n t h e s e d i m e n t a r y r e c o r d compared w i t h s e d i m e n t s , and also b e c a u s e

of t h e l a c k of c l a y m i n e r a l s t u d i e s on s u c h materials and d i f f i c u l t y i n r e c o g n i t i o n of a n c i e n t s o i l s .

Only r e c e n t l y h a s i t been r e a l i z e d t h a t t h e y

can be a major p a l y g o r s k i t e - f o r m i n g environment. Large amounts of p a l y g o r s k i t e s are p r e s e n t i n P l i o - P l e i s t o c e n e

sediments

around t h e A t l a n t i c Ocean i n t h e same l a t i t u d e s as t h e s o i l s and p l a y a s .

In

t h e n o r t h e r n I n d i a n o c e a n , Goldberg and G r i f f i n (1970, p. 532), from comprehensive c o r i n g of bottom s e d i m e n t s , s u g g e s t e d p a l y g o r s k i t e w a s a n a e o l i a n i n p u t from N.

I f t h i s e v i d e n c e is coupled

Africa and S o u t h Arabia.

w i t h t h a t o f windblown d u s t , t o t h e p r e s e n c e o f i n t e r c a l a t e d r e d d e s e r t s a n d s and p a l y g o r s k i t e c l a y i n t h e A t l a n t i c a d j a c e n t t o n o r t h e r n A f r i c a (Chamley e t al.,

1 9 7 7 ) , and t o e v i d e n c e from t h e N.

P a c i f i c Ocean ( L e i n e n and Heath,

19811, it i s c l e a r t h a t many of t h e l a t e Neogene o c e a n i c d e p o s i t s are c l o s e l y

related t o l a t i t u d e s i n which d r y windy c o n d i t i o n s and p a l y g o r s k i t e - b e a r i n g soils prevail. I t i s known from d u s t a n a l y s e s t h a t p a l y g o r s k i t e s c a n be c a r r i e d i n s i g n i f i c a n t q u a n t i t i e s over long d i s t a n c e s (e.g.

Bain and T a i t ,

19771, hence

t h e e r o s i o n of p a l y g o r s k i t i c soils i n t h e a r i d zones and r e d e p o s i t i o n i n t h e o c e a n s i s a phenomenum of p r e s e n t - d a y Soil-derived

environments.

d e p o s i t s , whether from windblown d u s t o r stream erosion, a r e

t r a n s p o r t e d i n t o d e e p e r waters by t u r b i d i t y c u r r e n t s and slumps (Chamley, 1979, Melieres, 1978, Chamley e t a l . ,

1979).

The d i s t r i b u t i o n of

p a l y g o r s k i t e s w i t h age s h o u l d t h e r e f o r e give s o m e i n d i c a t i o n o f t h e d r i e r

climatic r e g i o n s i n t h e g e o l o g i c a l r e c o r d , f o r b o t h non-marine environments.

and marine

I n marine c o n d i t i o n s a much more c r u d e d i s t r i b u t i o n would be

e x p e c t e d b e c a u s e o f the e f f e c t s of ocean c u r r e n t s . A number o f p l a y a d e p o s i t s

s t i l l forming (McLean e t a l . ,

are of c o m p a r a t i v e l y r e c e n t o r i g i n , or are

1972, S t o e s s e l and Hay, 1978, Kautz and P o r a d a ,

1 9 7 6 ) , and t h e s e a l s o f a l l w i t h i n t h e same l a t i t u d i n a l b e l t .

Occurrences

neoformed i n l a k e s and p l a y a s are much commoner i n many C a i n o z o i c and o l d e r s e d i m e n t s ( C a l l e n , 1977, V e r z e l i n e t a l . ,

1973).

7

L ~ ~ h o f a c ~ e . - o f _ o l d e g_oEkit-es r~~Y Land - b a s e d d e p o s i t s The l i t h o f a c i e s a s s o c i a t e s of past p a l y g o r s k i t e s s h o u l d r e v e a l whether c o n d i t i o n s o u t l i n e d above a p p l y t h r o u g h o u t t h e g e o l o g i c r e c o r d .

There i s one

o b v i o u s d i f f e r e n c e which i s i m m e d i a t e l y d i s c e r n e d ; t h e p e r i - m a r i n e environment has been an i m p o r t a n t environment o f g e n e s i s i n t h e p a s t (Appendix 1 . 4 ) , b u t

i s p o o r l y r e p r e s e n t e d i n modern t i m e s .

The s t u d y of Weaver and Beck ( 1 9 7 7 ) o f

i s t h e b e s t known

m a r g i n a l marine f a c i e s i n F l o r i d a and G e o r g i a , U . S . A . example a n d : i n c l u d e s a world-wide

summary of p e r i - m a r i n e

deposits.

Readers

a r e r e f e r r e d t o t h e i r report f o r f u r t h e r d e t a i l s . A l l t h e d e p o s i t s ( m a r i n e and nonmarine) on p r e s e n t landmasses a r e

dominated by d o l o m i t e s ,

limestones,

f i n e o r sometimes coarse c l a s t i c s , and are

o f t e n a s s o c i a t e d w i t h e v a p o r i t e s , or p h o s p h a t e s ,

and c h e r t .

Palygorskites

a p p a r e n t l y p r e c i p i t a t e o r form w i t h i n t h e s e d i m e n t i n c o n d i t i o n s less s a l i n e t h a n t h o s e conducive to gypsum p r e c i p i t a t i o n .

The magnesium- c l a y s are o f t e n

found p e r i p h e r a l to e v a p o r i t e d e p o s i t s , o r above o r below such d e p o s i t s (Chamley e t a l . , Gradusov,

1976).

1978, HSU e t a l . ,

1973, C i t a , 1979, V e r z e l i n e t al.,

1973,

Other d e p o s i t s a r e a s s o c i a t e d w i t h p h o s p h a t e s , p a r t i c u l a r l y

i n A f r i c a n e p e i r i c seas of L a t e C r e t a c e o u s t o Eocene a g e , and i n t h e Gulf of Mexico r e g i o n ( M i l l o t , 1964, I s p h o r d i n g ,

1972, Weaver and Beck, 1 9 7 7 ) .

These

p h o s p h a t e s are of t h e s h a l l o w w a r m s h e l f t y p e , where n u t r i e n t s f o r t h e p h o s p h a t i c o r g a n i s m s are r e p l e n i s h e d by wind-induced

u p w e l l i n g s n e a r t h e edge

of t h e c o n t i n e n t a l s h e l f ( B i r c h , 1980. Giresse, 1980, Boujo e t a l . , The m a j o r i t y of non-marine d o l o m i t e (e.g.

1980).

p a l y g o r s k i t e s are i n t i m a t e l y r e l a t e d to

S i t t l e r , 1964, Suguio, 1975, C a l l e n , 1 9 7 7 ) . and are o f t e n

a s s o c i a t e d w i t h anomalous barium and s t r o n t i u m values.

. These d o l o m i t e s are

f r e q u e n t l y of t h e t y p e formed i n t h e zone of mixing between Mg-charged w a t e r s and s a l i n e l a k e s

CI

p l a y a s (Muir e t al.,

i n a Coorong-type environment.

1980, C a l l e n ,

fresh

19771, p e r h a p s

R e c e n t l y Turchenek and Oades ( t h i s volume) and

Hutton and Dixon ( 1 9 8 1 ) have shown p a l y g o r s k i t e forms up t o 75% of t h e f i n e f r a c t i o n ( o f t e n n e a r 1 0 0 % ) of s o i l samples and calcretes i n the palaeo-Coorong s e t t i n g of t h e s o u t h e a s t d i s t r i c t of S o u t h A u s t r a l i a . Turchenek and Oades are, however, o l d P l e i s t o c e n e beach r i d g e s .

l a t e Holocene.

The s o i l s d e s c r i b e d by

They are l o c a t e d between t h e

Thus t h e s u g g e s t i o n of W i e r s m a (1970) t h a t t h i s

is a p a l y g o r s k i t e - b e a r i n g environment i s correct.

However, it was found that

i n t h e Coorong, p a l y g o r s k i t e s do n o t occur where carbonates are p r e s e n t l y being p r e c i p i a t e d communication).

( C a l l e n , u n p u b l i s h e d a n a l y s e s , von d e r Borch, personal P a l y g o r s k i t e i s a l s o found i n v a l l e y s between t h e b e a c h

r i d g e s of t h e M e d i t e r r a n e a n coast of Egypt, which r e s e m b l e s t h e s i t u a t i o n i n s o u t h e a s t e r n S o u t h A u s t r a l i a (Hassouba and Shaw, 1 9 8 0 ) .

8

Few s t u d i e s of modern sabkha e n v i r o n m e n t s have l o c a t e d p a l y g o r s k i t e s , and i n t h e s e t h e c l a y s are b e l i e v e d to have been t r a n s p o r t e d from e l s e w h e r e (Seibold e t al.,

1973).

Oceanic d e p o s i t s I n the p r e s e n t open marine s i t u a t i o n p a l y g o r s k i t e s a r e found i n t h r e e t y p i c a l s e d i m e n t a r y a s s o c i a t i o n s i n waters of v a r y i n g d e p t h :

(il

With d i s t u r b e d s e d i m e n t s or t u r b i d i t e s .

(ii)

P e r i m a r i n e f a c i e s which have s,ubsided i n t o d e e p w a t e r (Enos and

(iii

With c h a l k o r t h e " c a l c a r e o u s ooze" f a c i e s o f Kidd and Davies

Freeman, 1 9 7 9 ) , or formed i n t h e e a r l y s t a g e s of opening of o c e a n s .

(1978).

The f i r s t a s s o c i a t i o n i s t y p i c a l of A t l a n t i c Ocean p a l y g o r s k i t e s .

There

is no d o u b t t h a t slumps and t u r b i d i t e s p l a y a major r o l e i n r e d i s t r i b u t i n g s h a l l o w c o n t i n e n t a l s h e l f material i n t o d e e p e r waters.

P a l y g o r s k i t e s i n such

d e p o s i t s are d i s c u s s e d i n t h e r e f e r e n c e s g i v e n e a r l i e r . The second a s s o c i a t i o n needs no f u r t h e r comment e x c e p t to .suggest t h a t c o n d i t i o n s i n t h e e a r l y o c e a n s would p r o b a b l y have been similar to t h e M e d i t e r r a n e a n Sea d u r i n g and j u s t a f t e r t h e M e s s i n i a n s a l i n i t y e v e n t (Chamley

e t al.,

1978, HSU e t a l . ,

1973, Rouchy, 1 9 8 0 ) .

The t h i r d a s s o c i a t i o n i s c l e a r l y shown by an example from the I n d i a n P l o t t i n g p a l y g o r s k i t e z o n e s ( F i g . 2 ) on t h e f a c i e s - t i m e - d e p t h

Ocean.

curves

of Kidd and D a v i e s (1978) d e m o n s t r a t e s the i n t e r v a l s o f p a l y g o r s k i t e s e d i m e n t a t i o n c o i n c i d e w i t h calcareous ooze (or sometimes " o t h e r c l a y s " o f Kidd and D a v i e s , 1 9 7 8 ) , d e p o s i t e d i n water of v a r i a b l e d e p t h , i n c l u d i n g v e r y d e e p waters.

Thus, as f o r l a n d d e p o s i t s ,

the carbonate facies.

ther e i s a general associ at i on with

A s i m i l a r a s s o c i a t i o n i s r e p o r t e d f o r the S h a t s k y rise

o f t h e n o r t h w e s t e r n P a c i f i c Ocean ( Z e m m e l s , 1976, Matti e t a l . ,

1973, Gorbunova, 1 9 7 2 ) .

1973, Z e m m e l s and Cook, 1973, W e s h a l l see l a t e r when

c o n s i d e r i n g t h e i r o r i g i n , t h a t t h e s e d e p o s i t s f r e q u e n t l y overlie e x t e n s i v e b a s a l t i c f l o w s of s i m i l a r age (Despraires, 1 9 8 2 ) .

-----SUlnUG3I-y The Plio-Holocene

d e p o s i t s d e m o n s t r a b l y formed i n a l k a l i n e - b r a c k i s h

waters i n a M e d i t e r r a n e a n / a r i d climate, and i n s o i l s and c a l c r e t e s , h e n c e o l d e r d e p o s i t s may have also formed under s i m i l a r c i r c u m s t a n c e s .

The a r i d

climatic a s s o c i a t i o n i s confirmed from t h e l i t h o f a c i e s o f o l d e r p a l y g o r s k i t e s , hence p a l a e o l a t i t u d i n a l p l o t s might be e x p e c t e d to reveal past d i s t r i b u t i o n of 'arid'

climatic b e l t s .

The g r e a t e r e x t e n t of p e r i m a r i n e d e p o s i t s p r i o r t o t h e

Neogene i n d i c a t e s that p a l a e o c o n t i n e n t a l p l o t s of r e s u l t s from the Deep Sea D r i l l i n g P r o j e c t would assist i n d e f i n i n g l a t i t u d i n a l d i s t r i b u t i o n s .

9

TIME (m.v.)

12561

PALYGORSKITES EASTERN INDIAN

1212)

WESTERN INDIAN

1214

z ~ o

GAPS REPRESENT HIATUSES

Drn 1 t

Fig. 2. P a l y g o r s k i t e s i n the I n d i a n O c e a n - p a l a e o d e p t h c u r v e s , a d a p t e d from f i g . 5 o f Kidd & D a v i e s , 1978. N o t e l a c k of r e l a t i o n s h i p between p a l y g o r s k i t e and depth. P a l y g o r s k i t e s are a s s o c i a t e d w i t h " c a l c a r e o u s ooze" f a c i e s , e x c e p t i n 250, 252 ( " o t h e r t y p e s " - Cretaceous d e e p sea c l a y ) , 223 (Neoqene " t e r r e g i n o u s s e d i m e n t s " ) , and 213, 215, 220, 221, 256 (small amounts i n Neogene " o t h e r t y p e s " o f c l a y , " t e r r e g i n o u s s e d i m e n t s " and " s i l i c e o u s ooze" 1. Windblown d u s t is e s s e n t i a l l y d e r i v e d from a r i d a r e a s , and many deep ocean d e p o s i t s come from slumping of p e r i m a r i n e o c c u r r e n c e s ( i n c l u d i n g d u s t d e p o s i t s ) hence even t h e d e e p ocean p l o t s might show a l a t i t u d i n a l distribution related to ' a r i d i t y ' ,

p r o v i d M t h e r e are no problems w i t h sample

distribution.

LATITUDINAL DISTRIBUTICN Sampling Bias --_ --- -____ The s i g n i f i c a n c e of t h e d i s t r i b u t i o n s can o n l y be a s s e s s e d a f t e r d e t e r m i n i n g whether t h e o r i g i n a l samples w e r e randomly d i s t r i b u t e d or not. Both l a n d and DSDP o c c u r r e n c e s are a f f e c t e d by d i f f i c u l t y of access i n t h e

polar r e g i o n s due to ice, hence t h e s e zones are n o t c o n s i d e r e d i n t h e s t u d y . A second factor is i n t r o d u c e d by t h e change i n area of e a c h l a t i t u d i n a l slice,

which d e c r e a s e s by a b o u t 4x p r o c e e d i n g from e q u a t o r to p o l e .

Thus a s p e c i f i c

number of samples i n t h e h i g h e r l a t i t u d e s are of more s i g n i f i c a n c e w i t h respect to c o n c e n t r a t i o n t h a n t h e same number n e a r t h e e q u a t o r .

10

Deposits on land must be a s s e s s e d s e p a r a t e l y from DSDP r e s u l t s f o r t h e

following reasons: D e p o s i t s on p r e s e n t landmasses are p l o t t e d i n terms of b a s i n s ,

to

a v o i d t h e b i a s t h a t would be caused by r e p e a t e d s t u d i e s of t h e same

s o r t i n one series of r e l a t e d beds.

Any area once s t u d i e d t e n d s t o

a t t r a c t f u r t h e r s t u d i e s and r e f i n e m e n t s .

DSDP h o l e s on t h e o t h e r

hand, are s i n g l e s p o t o c c u r r e n c e s . The o r i g i n a l sample d i s t r i b y t i o n i s known f o r DSDP h o l e s , whereas i t

i s n o t f o r land-based d e p o s i t s .

For

the l a t t e r , one must assume an

even coverage o f r o c k s o f a l l a g e s i n a l l c o u n t r i e s , o b v i o u s l y a r a t h e r i d e a l i s t i c assumption (see ( 3 ) ) . The d i s t r i b u t i o n of land d e p o s i t s 'depends on t h e i n d i v i d u a l e f f o r t s o f c e r t a i n groups, o f t e n working w i t h i n c e r t a i n t e r r i t o r i a l l i m i t s , and a l s o i n f l u e n c e d by a c c e s s i b i l i t y .

DSDP r e s u l t s are a n

i n t e r n a t i o n a l e f f o r t , w i t h c o m p a r a t i v e l y u n l i m i t e d access.

Accepting t h a t t h e two sets of d a t a must be c o n s i d e r e d s e p a r a t e l y , a n o t h e r problem arises. and t i m e .

The d i s t r i b u t i o n of l a n d and sea v a r i e s with l a t i t u d e

For example t h e r e i s much more l a n d i n t h e n o r t h e r n m i d - l a t i t u d e s ,

hence one would e x p e c t more r e s u l t s from t h i s area.

-

A few o c c u r r e n c e s i n a

b e l t w i t h l i t t l e l a n d are more s i g n i f i c a n t t h a n t h e same number i n a b e l t w i t h much l a n d , and c o n v e r s e l y f o r t h e oceans.

Then, phenomena such as t h e

northward d r i f t o f I n d i a and A u s t r a l i a s i g n i f i c a n t l y change t h e d i s t r i b u t i o n o f l a n d and sea w i t h t i m e . Taking l a n d d e p o s i t s f i r s t , a n estimate of t h e r e l a t i v e c o n c e n t r a t i o n per l a t i t u d e w a s made by d i v i d i n g t h e number o f o c c u r r e n c e s , i n t e r m s of b a s i n s , by t h e area of each 10'

l a t i t u d i n a l belt.

This was a d j u s t e d c r u d e l y f o r land

area by d i v i d i n g by t h e f r a c t i o n of l a n d i n each b e l t , e s t i m a t e d by eye from mercator p r o j e c t i o n s of each t i m e i n t e r v a l ( u s i n g t h e maps of Smith and Briden, 1 9 8 0 ) .

D i f f e r e n t f a c t o r s w e r e t h e r e b y d e r i v e d f o r Oo-30°

i n t h e n o r t h and s o u t h hemispheres.

and 30°-60'

A more a c c u r a t e r e s u l t could be o b t a i n e d

by t a k i n g 10' b e l t s and c a l c u l a t i n g by p l a n i m e n t r y , b u t t h i s i s h a r d l y j u s t i f i e d c o n s i d e r i n g the number of d a t a p o i n t s and the o t h e r u n c e r t a i n t i e s . A d i f f e r e n t and perhaps more r e l e v a n t approach could be made by i n c o r p o r a t i n g

d a t a on e p i c o n t i n e n t a l seas, which could change t h e f a c t o r s s i g n i f i c a n t l y , b u t t h i s h a s n o t been accomplished a t t h i s s t a g e . Adding t h e r e s u l t i n g f i g u r e s f o r each t i m e i n t e r v a l , and p l o t t i n g by l a t i t u d e , g i v e s Fig.

3A.

The r e s u l t i s o b v i o u s l y non random, d e m o n s t r a t i n g a

c o n c e n t r a t i o n i n l a t i t u d e s 1 0'-40°N, Pliocene-Holocene

e s p e c i a l l y 30'-40°N,

and 3Oo-4O0S.

The

r e s u l t s are n o t i n c l u d e d because o f t h e i m p o s s i b i l i t y o f

11

t

I

400

Lend deDosits 0

300 c

0 I

A

100

-L

I

$ u0

100

r 50

20 Lal

N

I

-TT-+ de

1 50

S

300

B

50 Latitude

N

60

S ~

-

8

Palygorskite in

DSDP holes

0 Lalntude

N Drn JPV

80

82-34

S

5 A Department of Mmes and Energy

Fig. 3. L a t i t u d i n a l d i s t r i b u t i o n of p a l y g o r s k i t e s i n terms of 1 O o i n t e r v a l s . A. C o n t i n e n t a l r e c o r d s i n terms of b a s i n s . C o n c e n t r a c t i o n f a c t o r approximately a d j u s t e d for l a t i t u d e and l a n d area. P l i o - P l e i s t o c e n e o c c u r r e n c e s n o t i n c l u d e d . See t e x t f o r method of e s t i m a t i o n . B. A l l DSDP h o l e s i n terms of 1 0 M a t i m e slices, t o t a l l e d . C. P a l y g o r s k i t e s r e c o r d e d on p r e s e n c e or absence b a s i s f o r each s i t e per 10 Ma t i m e slices. Shaded area r e p r e s e n t s sites shown as l a r g e d o t s on d r i f t maps (*: greatest c o n c e n t r a t i o n i n < 2 u f r a c t i o n ) .

r e c o r d i n g t h e e x t e n s i v e s o i l o c c u r r e n c e s as s i n g l e b a s i n s .

The s i g n i f i c a n c e

o f t h e s e younger d e p o s i t s h a s a l r e a d y been d i s c u s s e d . Taking t h e o c e a n i c o c c u r r e n c e s , 3B i s obtained.

on Fig.

e s s e n t i a l l y from DSDP r e s u l t s ,

the plot

The p a l y g o r s k i t e o c c u r r e n c e s have been r e c o r d e d

a g a i n s t l a t i t u d e on a h i s t o g r a m ( F i g . 3C), f o r DSDP h o l e s , by t o t a l l i n g a l l h o l e s c o n t a i n i n g p a l y g o r s k i t e s f o r e a c h 1 0 My t i m e s l i c e i n e a c h 10' l a t i t u d i n a l belt. hemisphere, However,

The d i s t r i b u t i o n i s s t r o n g l y skewed toward t h e n o r t h e r n

w i t h zones of most abundance between 1 0'-30°N

F i g . 38

and 30'-40°S.

d e m o n s t r a t e s t h a t t h e o r i g i n a l sample d i s t r i b u t i o n is b i a s e d

i n t h e same way towards c e r t a i n l a t i t u d e s , t h e s e b e i n g e s s e n t i a l l y t h e same o n e s as f ? r l a n d - d e p o s i t s

( F i g s 1 , 10-12) by c o i n c i d e n c e .

Thus t h e r e is no

proof t h a t o c e a n i c o c c u r r e n c e s are s i g n i f i c a n t l y c o n c e n t r a t e d i n c e r t a i n l a t i t u d e s , e x c e p t p o s s i b l y i n 20-30°N and 30-40's.

'Ancient' D e p o s i t s

This latter concentration

d e p o s i t s i n t h e s e same l a t i t u d e s .

may be t h e r e s u l t of e r o s i o n o f t h e ' l a n d ' ( F i g . 4).

The s c a r c i t y of r e s u l t s from pre-Mesozoic l a c k of o c e a n f l o o r of t h i s age.

t i m e s i s p a r t l y t h e r e s u l t of

I n a d d i t i o n , v e r y few d e e p ocean d e p o s i t s

have been r e c o g n i z e d i n p r e s e n t c o n t i n e n t a l areas, which i s s u r p r i s i n g c o n s i d e r i n g t h e g r e a t e x t e n t o f t h e p a l a e o - P a c i f i c Ocean.

Those d e e p s e a

s e d i m e n t s t h a t have been r e c o g n i z e d have no d e t a i l e d c l a y mineralogy.

Lack of

o l d e r d e p o s i t s i s a l s o caused by t h e loss of h y d r o x y l water above 40OoC and d i s s o l u t i o n of p a l y g o r s k i t e above 800°C

( K u l b i c k i , 1959.

Thus p r i m a r y

p a l y g o r s k i t e o r s e p i o l i t e would n o t s u r v i v e h i g h g r a d e metamorphism. A l l b u t one of t h e ' A n c i e n t '

occurrences

30° o f t h e e q u a t o r i n s h a l l o w land-locked

Russia.

(Fig. 4 ) a r e concentrated within

seas of c e n t r a l and w e s t e r n

The a p p a r e n t l y anomalous S i b e r i a n o c c u r r e n c e may be of marine

h y d r o t h e r m a l o r i q i n ( D i v i n a e t al.,

19781, p e r h a p s d e p o s i t e d i n a f o r - a r c

t r o u g h l i k e t h e p a l y g o r s k i t e of t h e Marianas t r e n c h ( D e s p r a i r e s , 19821, though t h e s e d i m e n t s d o n o t seem to f i t t h i s model.

The most e x t e n s i v e d e p o s i t s are

Devonian t o Permian i n a g e , a s s o c i a t e d w i t h p l a t f o r m d o l o m i t e s and o t h e r carbonates. I t i s l i k e l y t h a t o t h e r s u c h d e p o s i t s w i l l be d i s c o v e r e d , b e c a u s e t h e r e

are few a d e q u a t e s t u d i e s of t h e c l a y m i n e r a l o g y of s u c h s e q u e n c e s .

These

c o u l d r a d i c a l l y a l t e r t h e p a t t e r n of t h i s d i s t r i b u t i o n . Mesozoic and C a i n o z o i c D e p----osits ___________________-----P a l y g o r s k i t e s are widely,

though d i f f u s e l y s p r e a d t h r o u g h t h e a r i d

T r i a s s i c r o c k s o f n o r t h A f r i c a and Europe, ( F i g . 4, t o p l e f t ) , r e a c h i n g c o n c e n t r a t i o n s of 50% o r more i n t h e p h o s p h a t i c r o c k s of tbrocco (Krumm, 1969).

As f o r many of t h e C a r b o n i f e r o u s occurrences o f R u s s i a ,

they w e r e

r e s t r i c t e d t o a series of s h a l l o w l a n d l o c k e d seas and s a l i n e l a k e s , c l o s e t o t h e equator.

13

TRIASSIC 190 M a

//-\

PERMOCARBONIFEROUS 280 M a

N

DEVONIAN

Land---)rn

Marine Shelf

-

CAMBRIAN

B m 82-70 SADME

J.PV

Fig. 4. ‘Ancient’ and T r i a s s i c occurrences ( p l o t t e d on Eckert P r o j e c t i o n s simplified from Kanasewick, e t a l . (1978). There a r e few records from t h e J u r a s s i c t o Early Cretaceous ( F i g s 5 , 6 and

l o ) , though Early J u r a s s i c and Aptian-Albian

d e p o s i t s a r e prominent i n t h e

newly opened North A t l a n t i c Ocean northwest of Austral-Antartica, proto-Pacific

Ocean.

and i n t h e

Environments i n t h e A t l a n t i c Ocean probably resembled

those of the Triassic s e a s and t h e Late Miocene of t h e Mediterranean Sea (Hsu e t al.,

1973).

Chamley (1979) has given a d e t a i l e d h i s t o r y of t h e development

14 of t h e A t l a n t i c Ocean deposits through t o modern t i m e s ,

emphasizing t h e role

of t h e p e r i m a r i n e environment, and d e s c r i b i n g how t h i s r e t r e a t e d from t h e c e n t r a l ocean area as r i f t i n g developed.

I

PORTLANDIAN TO MIDDLE BERRIASIAN

MIDDLE OXFORDIAN TO KlMMERlDGlAN ,900 , ,150my

-.

42% P+S or isolated high % samples - - 2-10% P+S in beds of decimetricthickness - -A

)lo%

P+S in bedsof decimetric thickness--

DSDP drillhole number

r.e.

- - - - - ---

-0

-223

Fig. 5

81-493

SADME

F i g s 5-9. DSDP o c c u r r e n c e s p l o t t e d on p o l a r p r o j e c t i o n s of F i r s t b o o k e t a l . , (1979). See Fig. 5, f o r abundance key. S i t e numbers shown. Key t o r e f e r e n c e s appendix 1-1, 1-3 f o r % abundance i n t2 v f r a c t i o n . P o s i t i o n s approximate f o r 29; 10 Ma 87, 88, 139, t h e f o l l o w i n g : 40 Ma - 138, 171, 288, 460,459; 5 Ma 171,, 323, 333. S i t e 462 n o t p l o t t e d ( M a r s h a l l I s l a n d s - Nauru B a s i n ) .

-

-

Neoformation l a t e r became c o n c e n t r a t e d i n s h a l l o w seas l i k e t h e Gulf of Mexico and S t r a i t s of G i b r a l t a r ( F i g s 7, 8, lo), from which t r a n s p o r t i n t o t h e deep oceans w a s e f f e c t e d by t u r b i d i t y c u r r e n t s .

Such t r a n s p o r t methods

prevented s e v e r e breakage of t h e long p a l y g o r s k i t e and s e p i o l i t e f i b r e s . P r e v i o u s l y t h e p r e s e n c e of such f i b r e s had been a c c e p t e d a s evidence of "IN SITW'genesis (e.g.

Gorbunova, 1973).

Large amounts o f p a l y g o r s k i t e d u s t w e r e

probably a l s o f i n d i n g t h e i r way i n t o t h e seas a t t h i s t i m e (though t h e s e would be expected t o have much s h o r t e r f i b r e s , a f a c t o r which can be t e s t e d ) .

In

t h e s o u t h e r n I n d i a n ocean, t h e d i s t r i b u t i o n s ( F i g s 6-9, 10-12) s u g g e s t wind t r a n s p o r t from A f r i c a , and t h e r e are some d e p o s i t s i n t h e a d j a c e n t east A f r i c a n landmass which c o u l d have provided t h i s material.

15

900

LATE CENOMANIAN TO TURONIAN

LATE ALBIAN TO EARLY CENOMANIAN

goo

16

90'

PALEOCENE

90'

900

CAMPANIAN TO MAASTRICHTIAN

900

goo

rn T E

SANTONIAN TO CONlAClAN

Fig. 7

900

81-491

SADME

17

LATE EOCENE TO EARLY OLIGOCENE

my

90"

Drn TE

EARLY TO MIDDLE EOCENE

Fig. 8

90'

81-490

SADMI

18

I

LATE MIDDLE MIOCENE

SO"

Dm TE.

EARLY MIOCENE TO EARLY MIDDLE MIOCENE

Fig. 9

900

81-489

SADW

19 I n the c e n t r a l S o u t h A t l a n t i c , a b e l t of h i g h l y c o n c e n t r a t e d p a l y g o r s k i t e s may be r e l a t e d to s e d i m e n t s o f similar a g e on t h e a d j a c e n t c o n t i n e n t s ( F i g s 7-8, and t h e P o i n t - N o i r e Cretaceous

, India

10-111,

b e i n g the Bauru Basin ( S u g u i o , 1975) o f B r a z i l ,

Basin (Giresse, 1980) o f t h e Congo.

I n the Late

had d r i f t e d i n t o t h i s same l a t i t u d i n a l b e l t ( F i g . 1 0 ) and

p a l y g o r s k i t e s w e r e d e p o s i t e d i n a l k a l i n e l a k e s i n d e p r e s s i o n s i n t h e Deccan t r a p s (Aneesuddin, 1971 )

.

The Campanian was one of the main p e r i o d s of p a l y g o r s k i t e d e p o s i t i o n i n t h e o c e a n s , r g a c h i n g up t o 80% or more of t h e c l a y f r a c t i o n (Appendix 1 . 2 ; Fig.

1 3 ) i n e x t e n s i v e t h i c k c l a y - r i c h beds ( F i g s 7 , 1 0 ) .

T h i s w a s t h e t i m e of

major d e p o s i t i o n , e s p e c i a l l y i n t h e r e g i o n e q u i v a l e n t to t h e S h a t s k y R i s e i n t h e proto-Pacific Ocean.

A t t h e same t i m e ,

major nonmarine and m a r g i n a l

marine d e p o s i t s w e r e forming i n t h e Fergana t r o u g h of K h u r g i z s t a n , a r e g i o n which h a s a l o n g h i s t o r y o f p a l y g o r s k i t e d e p o s i t i o n from L a t e J u r a s s i c t o Pliocene.

N o r t h e r n hemisphere o c c u r r e n c e s o f t h e s e t i m e s e x t e n d t o 4OoN o f

t h e e q u a t o r , and are d i s t r i b u t e d m a i n l y beween 25'

and 40°.

T h i s w a s also t h e

b e g i n n i n g of e x t e n s i v e s h a l l o w marine e p i c o n t i n e n t a l sea d e p o s i t i o n i n North A f r i c a , where p h o s p h a t e s were p r o m i n e n t s e d i m e n t a r y a s s o c i a t e s of p a l y g o r s k i t e and s e p i o l i t e .

These e p i c o n t i n e n t a l seas w e r e comparable to t h o s e o f

A u s t r a l i a i n t h e L a t e J u r a s s i c to E a r l y C r e t a c e o u s , and y e t A u s t r a l i a h a s no

Mesozoic p a l y g o r s k i t e s .

T h i s is a t t r i b u t e d t o i t s h i g h - l a t i t u d e p o s i t i o n a t

this time. I n t h e M a a s t r i c h t i a n t o E a r l y EOcene ( F i g s 7-8,

10 t o p ) , zonal

d i s t r i b u t i o n i s n o t as clear, and o c c u r r e n c e s s p r e a d f u r t h e r n o r t h and s o u t h

t o l a t i t u d e s 45ON and 55's.

The l a c u s t r i n e d e p o s i t s of B r a z i l and s o u t h e r n

France w e r e p r o m i n e n t , as w e r e t h e I n d i a n Ocean and n o r t h w e s t A u s t r a l o -

Antarctica d e p o s i t s . The Middle Eocene t o E a r l y O l i g o c e n e map ( F i g . latitudinal distribution.

11, t o p ) shows a n a p p a r e n t

Non marine l a c u s t r i n e d e p o s i t s became more

a b u n d a n t , i n s i m i l a r l a t i t u d i n a l belts.

The main sites of d e p o s i t i o n were

around t h e Tethyan margin and i n t h e Gulf o f Mexico area. During the Middle Miocene, t h e l a t i t u d i n a l d i s t r i b u t i o n resembled t h a t of t h e L a t e P l i o c e n e to p r e s e n t day.

There w e r e e x t e n s i v e l a c u s t r i n e beds i n

A u s t r a l i a , Europe and A s i a ( F i g s . 11 top, and 1 2 ) . The i n t e r p l a y between marine and non-marine

environments is w e l l

d i s p l a y e d by t h e d e p o s i t s of the M e d i t e r r a n e a n Sea.

Here, p a l y g o r s k i t e c l a y s

are i n t e r b e d d e d w i t h some of t h e M e s s i n i a n e v a p o r i t e - d o l o m i t e (Chamley e t al.,

1978).

sequences

These were l a i d down i n b r a c k i s h l a k e waters of the

d r y o c e a n i c d e p r e s s i o n , which c o n t a i n e d a v a r i e t y of s h a l l o w s a l i n e e n v i r o n m e n t s a t t h i s t i m e (Rouchy, 1 9 8 0 ) .

After c o n n e c t i o n w i t h the A t l a n t i c

20

PALYGORSKITES 60 m.y. MAASTRICHTSAN - EARLY EOCENE

PALYGORSKITES 80 m.y. CONlAClAN

Fig. 10

- CAMPANIAN

21

PALYGORSKITES 20 m.y. LATE OLIGOCENE

- MIDDLE MIOCENE

PALYGORSKITES 40 m.y. MIDDLE EOCENE - EARLY OLIGOCENE

Fig. 11

22

PALYGORSKITES 10 m.y. MIDDLE MIOCENE - EARLY PLIOCENE

Fig. 12 F i g s 10-12. General d i s t r i b u t i o n , p l o t t e d as b a s i n s on Mercator p r o j e c t i o n s m o d i f i e d from Smith E B r i d e n , 1977. See a p p e n d i x 1 1 . 2 and 1.4 f o r d e t a i l s . D o t s are g e n e r a l i z e d DSDP and'oceanic'occurrences, d i a g o n a l s h a d i n g is c o n t i n e n t a l d a t a ( M : p a r t l y m a r i n e ) . Some'oceanic'occurrences p a r t l y nonsee t e x t ) . marine (e.9. M e d i t e r r a n e a n Sea Some d a t a from t h e c o n t i n e n t s a p p e a r on more t h a n one map by r e a s o n of l a c k o f a g e d e f i n i t i o n r a t h e r t h a n d e p o s i t i o n o v e r a l o n g t i m e span.

-

Ocean w a s r e - e s t a b l i s h e d

in t h e P l i o c e n e , t h e r e w a s a sudden i n c r e a s e i n

p a l y g o r s k i t e i n p e l a g i c oozes and t u r b i d i t e s of t h e c e n t r a l b a s i n s .

These

younger c l a y s are p r o b a b l y d e t r i t a l (Chamley e t a l , m 1978). d e r i v e d e i t h e r from eroded M e s s i n i a n

and p o s s i b l y o l d e r d e p o s i t s of t h e a d j a c e n t landmasses,

o r neoformed n e a r s h o r e and carried i n t o d e e p w a t e r d u r i n g t h e P l i o c e n e .

The

former is most l i k e l y as m a r g i n a l M e d i t e r r a n e a n s e d i m e n t a t i o n d i d n o t i n c l u d e s u i t a b l e environments f o r neoformation i n Late P l i o c e n e e x c e p t i n s o i l s a l o n g the A f r i c a n and I s r a e l i

-

-

Pleistocene t i m e s ,

Lebanon Coasts.

-__-__ SUmmaLy A l a t i t u d i n a l d i s t r i b u t i o n is recognizeable

p r o j e c t i o n p l o t s ( F i g s 1 , 10-12).

i n n e a r l y a l l t h e Mercator

The L a t e P l i o c e n e to p r e s e n t d a y

l a t i t u d i n a l p a t t e r n persists back i n t i m e a t l e a s t t o t h e L a t e O l i g o c e n e , and

i s also v i s i b l e i n t h e L a t e C r e t a c e o u s .

A l s o , p r i o r to t h e L a t e O l i g o c e n e ,

t h e r e is a t e n d e n c y f o r a g r e a t e r s p r e a d towards t h e e q u a t o r i n the d e p o s i t s

23 on p r e s e n t day landmasses.

C o n f i r m a t i o n of t h e s o u t h e r n hemisphere

l a t i t u d i n a l b e l t i s o b s c u r e d by l a c k of r e c o r d s from S o u t h A m e r i c a and South Africa. There a p p e a r s t o be a r e a l c o n c e n t r a t i o n of p a l y g o r s k i t e s on ' l a n d ' , between 30-40°

i n b o t h hemispheres.

The f a c t t h a t many of t h e s e are a c t u a l l y

p e r i m a r i n e o c c u r r e n c e s s u g g e s t s a s i m i l a r d i s t r i b u t i o n o u g h t t o be v i s i b l e i n the oceans.

T h i s i s d i f f i c u l t t o d e t e r m i n e b e c a u s e m o s t DSDP d r i l l i n g was

done, c o i n c i d e n t a l l y , i n t h e s e same l a t i t u d e s , c r e a t i n g a n i n i t i a l b i a s i n t h e sample p a t t e r n .

The o c e a n i c DSDP d i s t r i b u t i o n t h e r e f o r e S u g g e s t s a n even

s c a t t e r i n most l a t i t u d e s , g i v i n g no f i r m s u p p o r t from t h i s s t a t i s t i c a l basis t o t h e h y p o t h e s i s t h a t many o c e a n i c d e p o s i t s w e r e d e r i v e d by e r o s i o n from However, g e o l o g i c a l c r i t e r i a may s u g g e s t o t h e r w i s e , as

'land' deposits.

d i s c u s s e d , f o r example, i n t h e A t l a n t i c Ocean. Non-marine d e p o s i t s are most e v i d e n t from t h e Eocene t o P l i o c e n e .

T I K S OF PALYGORSKITE ABUNDANCE The age d i s t r i b u t i o n of p a l y g o r s k i t e - s e p i o l i t e abundance i n t h e o c e a n s is d e m o n s t r a t e d by F i g .

13, a h i s t o g r a m of t o t a l and a v e r a g e p e r c e n t a g e of Table 1 summarizes t h e times of greatest

p a l y g o r s k i t e s and s e p i o l i t e .

abundance of d e p o s i t s on t h e c o n t i n e n t s and o c e a n s a s d e t e r m i n e d from F i g . 1 3 and Appendix 1.4.

The DSDP r e s u l t s show t h a t t h e p e a k s of s i m p l e a g g r e g a t e

percentage f o r a l l t h e h o l e s f o r each t i m e - s t r a t i g r a p h i c w i t h t h e a v e r a g e p e r c e n t a g e peaks.

Age u n i t c o i n c i d e s

~ are used, and Only o r i e n t e d < 2 samples

some d a t a w e r e n o t i n c l u d e d (see Methods s e c t i o n ) . from many a n a l y s e s i n one or two h o l e s ;

Some d a t a d e r i v e l a r g e l y

t h e c a p t i o n t o t h e g r a p h shows which

peaks come i n t o t h i s c a t e g o r y . I n t h e L a t e Miocene-Holocene,

t o t a l abundance i s h i g h , b u t a v e r a g e

p e r c e n t a g e l o w , and p e r u s a l o f t h e o r i g i n a l d a t a c o n f i r m s a l a r g e number of samples of l o w p e r c e n t a g e .

This i s t h e r e s u l t of t h e l a r g e number of bores,

t h e Q u a t e r n a r y sediments being t h e m o s t widespread,

t o g e t h e r with the l a r g e

number of c l o s e l y spaced samples from t h e s e b o r e i n t e r s e c t i o n s . s u i t a b l e l a t e Neogene p e r i - m a r i n e

e n v i r o n m e n t s may b e t h e r e a s o n f o r t h e low

a v e r a g e p e r c e n t a g e of p a l y g o r s k i t e s i n t h e s e o c c u r r e n c e s . have fewer p a l y g o r s k i t e - s e p i o l i t e

The l a c k of

The o l d e r s e d i m e n t s

b e a r i n g i n t e r v a l s b e c a u s e t h e amount of

ocean f l o o r d i m i n i s h e s t o z e r o i n t h e T r i a s s i c . Examination o f t h e d a t a of R o b e r t ( 1 9 8 1 ) and Chamley and R o b e r t ( 1 9 7 9 ) f o r t h e S o u t h A t l a n t i c , which is n o t i n c l u d e d i n t h e c a l c u l a t i o n s , coupled w i t h d a t a from h o l e s w i t h b u l k a n a l y s e s or n o n - o r i e n t a t e d (Appendix 1.31,

< 2 p samples

shows t h e same d i s t r i b u t i o n a s t h e h i s t o g r a m .

c o n f i r m s t h e e x i s t e n c e of t h e A l b i a n peak.

It a l s o

24

TOTAL %

""""4

5200 PLI LK

4800

TOTAL % PALYGORSKITE A N 0 SEPlOLlTE

_______

TOTAL % PALYGORSKITE A N 0 SEPlOLlTE AGGREGATED FOR EPOCHS

4400

________

4000

I

r P--

3600

I

AVERAGE % PALYGORSKITE AND SEPlOLlTE

________

3200

I

I

2800 P

AVE %

9

2400

50;

2000

40;

1600

n 0

1200

30: I

20j

800

I

400

10: I

0:

0

0

10

20 30 40 50

so

m TE

Fig. 1 3 . Age Ages, Epochs estimation. from 1 h o l e ,

70 80 90 100 110 t i 0 130 140 150 160 AGE 1m.y.) 82-26

SADME

d i s t r i b u t i o n of p a l y g o r s k i t e s : t o t a l and average % p l o t t e d by and P e r i o d s , f o r DSDP d r i l l i n g . See t e x t f o r method o f 10: Mainly from two h o l e s , 1E: m o s t l y 1 h o l e , Camp.: 50% d a t a Albian: dashed peak = d a t a from 1 h o l e . Data from appendix 1.3.

Some of t h e marine d e p o s i t s , such as t h o s e of t h e Mediterranean L a t e Miocene, and e a r l y oceans, are b e s t r e g a r d e d as l a c u s t r i n e whereas many of t h e d e p o s i t s on p r e s e n t landmasses are m a r g i n a l marine o r s h e l f environments.

The

r e s u l t s show t h a t from t h e L a t e C r e t a c e o u s onwards t h e main i n t e r v a l s o f d e p o s i t i o n c o i n c i d e f o r marine and non-marine p r e s e n t day oceans o r on landmasses.

d e p o s i t s , whether l o c a t e d i n

The p a l y g o r s k i t e L a t e C r e t a c e o u s -

Paleocene "event" of C a l l e n (1978, see a l s o S i n g e r , 1980) h a s been r e s o l v e d i n t o s e v e r a l e v e n t s , one of which (Campanian) is e s s e n t i a l l y o c e a n i c , and t h e importance of three earlier i n t e r v a l s o f d e p o s i t i o n i s recognized.

25

TABLE I

Major I n t e r v a l s of Abundance

DSDP

'LAND'

Cambrian Devonian Permian

-

-

Carboniferous Triassic

Late C r e t a c e o u s , e s p e c i a l l y Albian and Campanian L a t e C r e t a c e o u s t o Eocene ( e s p e c i a l l y Eocene). Eocene, e s p e c i a l l y E a r l y and L a t e Late O l i g o c e n e t o Middle Miocene

Late O l i g o c e n e to Middle Miocene, e s p e c i a l l y Middle Miocene

Pliocene t o P l e i s t o c e n e

Pliocene t o P l e i s t o c e n e

V E I N DEPOSITS Vein o c c u r r e n c e s are p l o t t e d i n F i g .

14.

M o s t are a s s o c i a t e d w i t h

basalts, serpentinites or other related basic r o c k s , and a r e g e n e r a l l y r e g a r d e d as h y d r o t h e r m a l i n o r i g i n .

The age of most

is d i f f i c u l t to e s t a b l i s h , and l i t t l e i n f o r m a t i o n is g i v e n a b o u t o v e r l y i n g rocks. e t al.

The s t u d i e s of Watts ( 1 9 8 0 ) , Haranczyk and Prochazka ( 1 9 7 4 ) and Barnes ( 1 9 7 8 ) s u g g e s t t h a t some c o u l d be t h e r e s u l t of w e a t h e r i n g or

p e d o g e n e s i s i n a high-Mg2+ environment,

s u c h as f a v o u r e d by Muller-Vonmoos

and

Schindler (1973) i n a d e p o s i t i n Switzerland. Occurrences i n caves a r e also informative.

Such d e p o s i t s , f o r example

those d e s c r i b e d by Lowry (1964) and Urbani (1975 l i m e s t o n e , w i t h p a l y g o r s k i t e c o a t i n g s on calcite

are j o i n t i n f i l l i n g s i n The former i s i n E a r l y t o

Middle O l i g o c e n e s h e l f l i m e s t o n e of n o r t h e r n N e w Zealand and i s t h o u g h t t o have been d e p o s i t e d under p h r e a t i c c o n d i t i o n s .

The d e p o s i t d e s c r i b e d by

Urbani i s i n l a t e J u r a s s i c d o l o m i t e o f Venezuela and w a s d e r i v e d by w e a t h e r i n g of t h e c a r b o n a t e .

Both p l o t w i t h i n the same l a t i t u d i n a l p o s i t i o n as

s e d i m e n t a r y d e p o s i t s o f t h e i r age. I t i s n e c e s s a r y t o i n v e s t i g a t e whether or n o t t h e p r e s e n c e of t h e v e i n s i n d i c a t e s t h e p r e s e n c e of s e d i m e n t a r y

26 p a l y g o r s k i t e i n t h e h o s t rocks.

It is suggested that o t h e r vein d e p o s i t s

could a l s o be t h e r e s u l t of r e c o n s t i t u t i o n of p a l y g o r s k i t e s from s u r r o u n d i n g rocks,

and t h i s a l s o needs to be t e s t e d by s u i t a b l e a n a l y s e s .

A number of o c c u r r e n c e s

are o f undoubted h y d r o t h e r m a l o r i g i n , w i t h

s u i t a b l y zoned c r y s t a l l i z a t i o n s e q u e n c e s , i n c r a c k s r e l a t e d to i g n e o u s b o d i e s

or hydrothemal v e i n s .

PALY GORSKITES "VEIN" DEPOSITS

I 82-25 I

SADME

1 Y uo

180"

0"

90"

180"

F i g . 14. Vein d e p o s i t s , p l o t t e d on p r e s e n t day map. FD = f a l c o n d i t e . See a p p e n d i x 1 1 . 4 r e f e r e n c e s .

D I SCUSSICN Latitudinal Distribution --_-----------__________ The l a t i t u d i n a l d i s t r i b u t i o n of p a l y g o r s k i t e s w i t h i n the p r e s e n t c o n t i n e n t a l areas

(e.

between 20-40°N

and S ) i s u n l i k e l y t o be t h e r e s u l t o f

b i a s e d s a m p l i n g , though the n a t u r e of that s a m p l i n g p r e c l u d e s r i g o r o u s

statistical t e s t i n g .

I n t h e n o r t h e r n hemisphere, e x t e n s i v e s t u d i e s o f c l a y s

from r o c k s of a l l a g e s have been made by the d e v e l o p e d n a t i o n s e x i s t i n g i n these regions.

The e x t e n t o f l a n d a t l a t i t u d e s greater t h a n 4OoN is g r e a t ,

and y e t v e r y few p a l y g o r s k i t e d i s c o v e r i e s ( a p a r t f r o m vein d e p o s i t s : compare Fig.

1 4 w i t h F i g s 1 a n d 10-12) have been made i n r o c k s younger t h a n

Triassic.

Thus the ' l a n d ' d e p o s i t s (as a g a i n s t

DSDP d e p o s i t s )

are

27 l a t i t u d i n a l l y c o n t r o l l e d f o r the younger d e p o s i t s and are t h o u g h t to r e f l e c t

past mild climatic ' a r i d i t y ' .

I t is u n c e r t a i n what t y p e of a r i d i t y i s

i n v o l v e d , though a climate similar t o t h a t of s o u t h e r n S o u t h A u s t r a l i a , M e d i t e r r a n e a n to s e m i - a r i d

&.

type, is l i k e l y .

The e x i s t e n c e of a c l i m a t i c b e l t conducive t o p a l y g o r s k i t e f o r m a t i o n i s i n d i c a t e d by e v e n t s i n A u s t r a l i a and I n d i a .

F i g u r e s 10-11 show t h a t a s

A u s t r a l i a d r i f t s n o r t h w a r d s p a l y g o r s k i t e s are d e p o s i t e d , f i r s t l y i n t h e n o r t h d u r i n g t h e O l i g o c e n e and t h e n i n s o u t h e r n A u s t r a l i a n i n t h e Miocene. S i m i l a r l y d e p o s i t i o n does n o t b e g i n i n I n d i a u n t i l t h e L a t e C r e t a c e o u s t o E a r l y Eocene, when it had d r i f t e d i n t o l a t i t u d e 2OoS (see Powell e t a l . , f o r d e t a i l s of the northward d r i f t of A u s t r a l i a and I n d i a ) .

1981,

However t h e

s i t u a t i o n i n I n d i a i s c o m p l i c a t e d by a s s o c i a t i o n w i t h b a s a l t s , and p o s s i b i l i t y of h y d r o t h e r m a l a d d i t i o n of Mg2+. The c o n c l u s i o n i s t h a t t h e climate of t h e Late C r e t a c e o u s was ' a r i d ' , which c o r r e s p o n d s w i t h t h e o b s e r v a t i o n s o f F r a k e s ( 1 9 7 9 ) . C a r b o n i f e r o u s and Eocene -re a c c e p t e d views.

That t h e

also ' a r i d ' i s i n some c o n f l i c t w i t h p r e s e n t l y

Perhaps ' a r i d i t y '

may have been a g r e a t e r f a c t o r i n c e r t a i n

l a t i t u d e s a t t h e s e times t h a n has g e n e r a l l y been a c c e p t e d , p a r t i c u l a r l y f o r t h e s o u t h e r n hemisphere.

Some of t h e major Devonian-Carboniferous

deposits i n

n o r t h e r n R u s s i a may r e p r e s e n t d e e p sea h y d r o t h e r m a l d e p o s i t s a s s o c i a t e d w i t h

basalts, t h u s n o t b e i n g connected w i t h p a r t i c u l a r c l i m a t i c c o n d i t i o n s . The r e s u l t s of t h e Deep Sea D r i l l i n g P r o j e c t s u g g e s t p a l y g o r s k i t e s are probably f a i r l y u n i f o r m l y d i s t r i b u t e d i n t h e o c e a n s , and d o n o t r e f l e c t t h e l a t i t u d i n a l c o n s t r a i n t s a p p a r e n t i n t h e Neogene. palygorskite-bearing

d i s t r i b u t i o n of a l l h o l e s d r i l l e d .

t o 110 M a .

The d i s t r i b u t i o n of

DSDP h o l e s i s v i r t u a l l y t h e same as t h e o v e r a l l T h i s a p p l i e s f o r a l l t i m e i n t e r v a l s back

P l o t t i n g t h e h i g h e s t c o n c e n t r a t i o n of p a l y g o r s k i t e r a t h e r t h a n

s i m p l y i t s p r e s e n c e o r a b s e n c e p r o d u c e s t h e same r e s u l t ( F i g . 3C), e x c e p t t h a t t h e r e i s a somewhat more e x c e p t i o n a l c o n c e n t r a t i o n i n t h e 0-20' w i t h t h e 20-40°

belt.

b e l t compared

I n s p e c t i o n of t h e p l o t s shows that it i s t h e n o r t h

I n d i a n Ocean, Red Sea and P a c i f i c Ocean d e p o s i t s t h a t have t h e g r e a t e s t i n f l u e n c e on t h i s , r a t h e r t h a n t h e M e d i t e r r a n e a n and p r o t o - A t l a n t i c S e a s . Thus t h e dominant ocean o c c u r r e n c e s are n o t d i s t r i b u t e d i n t h e same l a t i t u d e s

as t h e ' l a n d ' d e p o s i t s .

The e v a p o r i t e - a s s o c i a t e d

p a l y g o r s k i t e s of the

Mediterranean and p r o t o - A t l a n t i c are, however i n t h e same l a t i t u d e s a s t h e peri-marine

'land'

deposits.

The i n i t i a l s u g g e s t i o n t h a t o c e a n i c d e p o s i t s w u l d r e f l e c t t h e z o n a t i o n a p p a r e n t on l a n d d u r i n g t h e Neogene i s n o t s u p p o r t e d by t h e d i s t r i b u t i o n

statistics.

I f most oceanic d e p o s i t s are d e t r i t a l , whether t h e y be d e p o s i t e d

from t u r b i d i t e s or from a e o l i a n d u s t , t h e n o c e a n c u r r e n t s have a p p a r e n t l y

28 produced a v e r y even r e d i s t r i b u t i o n .

Although g e o l o g i c a l e v i d e n c e i n t h e

d e p o s i t s themselves s t r o n g l y s u g g e s t s many are d e r i v e d from land d e p o s i t s , o r formed i n n e a r s h o r e s h a l l o w marine o r l a g o o n a l environments, a d i f f e r e n t o r i g i n f o r many o t h e r s must be proposed t o a c c o u n t f o r t h e d i s t r i b u t i o n statistics. Such i s s u g g e s t e d f o r some of t h e major d e p o s i t s , R i s e i n t h e P a c i f i c Ocean ( F i g 7 ) .

f o r example t h e Shatsky

These d e p o s i t s are n o t i n t u r b i d i t e s , and

t h e r e were no l a r g e ' l a n d ' d e p o s i t s nor s u i t a b l e p e r i m a r i n e environments known around t h e margins of t h e p r o t o - P a c i f i c Ocean t o a c t as a d e t r i t a l s o u r c e . Even if such s o u r c e s f o r t h e s e d e p o s i t s were found i n t h e f u t u r e , t h e d i s t a n c e of t h e S h a t s k y R i s e from land i s such t h a t one would have t o e n t e r t a i n a d i f f e r e n t s p r e a d i n g h i s t o r y (Woods and Davies, 19821, or e a r t h expansion s i n c e t h e Campanian ( S h i e l d s , 1 9 7 9 ) , to a c c o u n t f o r t h e i r p r e s e n t p o s i t i o n . Gorbunova (1972, 1 9 7 3 , ) h a s s u g g e s t e d t h e y a r e hydrothermal, a h y p o t h e s i s s u p p o r t e d by t h e oxygen isotope s t u d i e s of Church and Velde ( 1 9 7 9 ) . An a l t e r n a t i v e

i s t h e d i a g e n e s i s of m o n t m o r i l l o n i t e and r e l a t e d m i n e r a l s ,

s u g g e s t e d by Couture ( 1 9 7 7 a ) . d i f f i c u l t , however,

Conversion o f smectite to p a l y g o r s k i t e i s

though Giresse e t a 1 ( 1 9 8 0 ) p r o p o s e it f o r p r o d u c t i o n of

p a l y g o r s k i t e i n t h e P a r i s b a s i n , from b e i d e l l i t e .

The c r y s t a l l i n i t y and

a g g r e g a t i o n of p a l y g o r s k i t e f i b r e s i n t o bundles was i n v e s t i g a t e d by S i n g e r ( 1 9 8 1 ) f o r t h e Jordan r i f t v a l l e y d e p o s i t s .

H e found p a l y g o r s k i t e w a s

d i s c r e t e , w i t h no s i g n s of t r a n s i t i o n t o m o n t m o r i l l o n i t e ,

i n d i c a t i n g it was

n o t d e r i v e d from t h e l a t t e r m i n e r a l b u t w a s p r o b a b l y a d i r e c t p r e c i p i t a t e from solution. The r e c e n t d i s c o v e r i n g of abundant p a l y g o r s k i t e i n t h e Marianas Trench, a forearc basin, i s of considerable i n t e r e s t .

D e s p r a i r i e s (1982) and Natland

and Mahoney ( 1 9 8 2 ) p r e s e n t s t r o n g e v i d e n c e f o r a hydrothermal s o u r c e of Mg2+, and massive a l t e r a t i o n of b a s a l t i c g l a s s , v o l c a n o c l a s t i c sediments and b e i d i l l i t e clays.

The Mg2+ w a s d e r i v e d from p r o c e s s e s a s s o c i a t e d w i t h t h e

earlier b a s a l t i c o u t p o u r i n g s .

The p r o c e s s i s similar to t h a t s u g g e s t e d by

Russian w r k e r s (Gorbunova, 1973, Kurnusov and Shevchenko, 19821, f o r o t h e r l a r g e o c c u r r e n c e s i n t h e P a c i f i c Ocean.

This d e m o n s t r a t e s t h a t marine

d e p o s i t s of d e e p o c e a n i c o r i g i n c a n be d e r i v e d from processes independent of l a t i t u d i n a l constraints. A n a l y s i s of a e o l i a n components i n t h e c e n t r a l P a c i f i c Ocean ( R e a and Jancock, 1981) r e v e a l t h e Aptian/Albian c o n t r i b u t i o n h e r e w a s e s s e n t i a l l y v o l c a n i c d u s t ; and show the Coniacean and L a t e Campanian were t i m e s of l o w a e o l i a n i n p u t froni the land.

This r e i n f o r c e s t h e i d e a o f an e s s e n t i a l l y

d i a g e n e t i c o r i g i n f o r the Campanian p a l y g o r s k i t e peak, and a l s o s u g g e s t s it

w a s n o t d e r i v e d from v o l c a n i c d u s t .

The o t h e r e v i d e n c e from t h i s s t u d y d o e s

29

n o t s u p p o r t a windblown c a l c a r e o u s d u s t o r i g i n f o r P a c i f i c p a l y g o r s k i t e i n t h e A p t i a n / A l b i a n and Coniacean.

T h i s i s d e s p i t e t h e f a c t t h a t t h e s e were a n o x i c

e v e n t s i n t h e o c e a n s , when c a r b o n a c e o u s matter was h i g h . form r e a d i l y i n t h e p r e s e n c e of o r g a n i c matter.

P a l y g o r s k i t e s do n o t

This i s compatible with

formation a t a l a t e r s t a g e through d i a g e n e s i s o r

palygorski te-sepiolite a 1t e r a t i o n .

Agewise d i s t r i b u t i o n The DSDP r e s u l t s s u g g e s t a broad a g e w i s e c o i n c i d e n c e w i t h ' l a n d ' deposits,

though t h e main Campanian peak i s l a r g e l y an o c e a n i c f e a t u r e .

the four 'land'

d e p o s i t s r e c o r d e d i n t h e Campanian-Maastrichtian,

Of

o n l y one i s

d e f i n i t e l y o f t h i s age. The a g e w i s e l i n k f o r o t h e r t i m e s of p a l y g o r s k i t e abundance c a n be e x p l a i n e d by t h e i n f l u x o f d e t r i t a l p a l y g o r s k i t e s t o t h e o c e a n s d u r i n g ' a r i d '

times,

i n t h e manner d e s c r i b e d e l s e w h e r e i n this p a p e r , supplemented by I f o c e a n i c d e p o s i t s c o u l d be more c l e a r l y i d e n t i f i e d a s d e t r i t a l ,

diagenesis.

d i a g e n e t i c or h y d r o t h e r m a l , and t h e r e s u l t s p l o t t e d , t h e age d i s t r i b u t i o n might prove d i f f e r e n t f o r each t y p e . I n the s e a r c h f o r g o s s i b l e e x p l a n a t i o n s of t h e a p p a r e n t agewise l i n k , C a l l e n ( 1 9 7 8 ) s u g g e s t e d Mg2+ i n t r o d u c e d t h r o u g h v o l c a n i s m c o u l d be a c o n t r i b u t i n g f a c t o r , though t h e r e i s no o b v i o u s c o r r e l a t i o n between v o l c a n i c e f f u s i v e p h a s e s ( f i g . 7, Ronov e t a l . ,

1980) and p a l y g o r s k i t e ' e v e n t s ' .

There

i s an a p p r o x i m a t e c o r r e l a t i o n of p a l y g o r s k i t e ' e v e n t s ' w i t h the a l p i n o t y p e o r o g e n i c e v e n t s o f Schwan (19801, e x c e p t f o r t h e Campanian phase.

This

i m p l i e s v o l c a n i c d u s t i n t h e oceans is n o t n e c e s s a r i l y a p r e c u r s o r f o r p a l y g o r s k i t e ; i n t r o d u c t i o n of hydrothermal Mg2+ the continental deposits, d u s t or b a s a l t s .

r i c h solutions is likely.

t h e r e i s f r e q u e n t l y no s o u r c e of Mg2+

In

from v o l c a n i c

D e p o s i t s l i k e t h o s e o f t h e Miocene i n South A u s t r a l i a

( C a l l e n , 1 9 7 7 ) have no l i n k t o r o c k s of this k i n d .

A similar problem e x i s t s

i n t h e s o u t h e a s t of t h e S t a t e of South A u s t r a l i a , where t h e e x t e n s i v e d o l o m i t e s of t h e modern and a n c i e n t "Coorong" e n v i r o n m e n t s (Muir e t a l . , 19801, and t h e p a l y g o r s k i t e s of t h e calcretes ( H u t t o n and Dixon,

1981) and

modern s o i l s (Turchenek and Oades, t h i s volume) need more t h a n a series of i s o l a t e d b a s a l t i c volcanoes ( M t . groundwa ters

.

Gambier, etc.) to p r o v i d e Mg2+ i o n s i n t h e

Lack of p a l y g o r s k i t e s i n c e r t a i n i n t e r v a l s i n t h e oceans, e s p e c i a l l y the Maastrichtian

-

E a r l y P a l e o c e n e and E a r l y O l i g o c e n e , i s p a r t l y a r e f l e c t i o n of

climatic c o n d i t i o n s .

These were t i m e s of w i d e s p r e a d l o w s e d i m e n t a t i o n rates

and a b u n d a n t h i a t u s . e s (Moore e t a l . ,

1978, Worsley and D a v i e s , 1 9 7 9 ) ,

30

connected t o c i r c u l a t i o n of c o l d ocean c u r r e n t s .

Such c u r r e n t s are u n l i k e l y

to a f f e c t s h e l f s e d i m e n t a t i o n and o b v i o u s l y n o t non-marine

sedimentation, b u t

t h e e v e n t s which g e n e r a t e d them may do so. The abundance of p a l y g o r s k i t e s i n n e a r s h o r e marine environments i m p l i e s peaks i n c o n c e n t r a t i o n might c o i n c i d e w i t h t h e s p r e a d of e p e i r i c seas.

Ronov

e t a l . ( 1980) summarized world sediment volumes i n g e o s y n c l i n e s and s h e l v e s , s e d i m e n t a t i o n rates, and o t h e r f a c t o r s of r e l e v a n c e .

Comparing t h e s e r e s u l t s

t h e r e i s no o b v i o u s correspondence between peaks i n p a l y g o r s k i t e s e d i m e n t a t i o n , r e g r e s s i o n s and t r a n s g r e s s i o n s , or e x t e n t of seas and platforms.

The main peak i n abundance i n t h e Campanian i s t h e o n l y one which

correlates w i t h a major i n t e r v a l of s h e l f s e d i m e n t a t i o n and e x t e n t , and y e t most d e p o s i t s o f t h i s t i m e are o c e a n i c .

I

Jenkyns ( F i g . 3, 1980) p l o t s g l o b a l t r a n s g r e s s i o n c u r v e s .

These do show

a c r u d e correspondence between t r a n s g r e s s i o n s and p a l y g o r s k i t e peaks, more p r e c i s e l y j u s t b e f o r e and a f t e r t h e maximum t r a n s g r e s s i v e phase of t h e Santonian

- Coniacean.

However, most of t h e p a l y g o r s k i t e s o f t h e s e times were

forming i n t h e open oceans, n o t i n e p i c o n t i n e n t a l seas.

More d e t a i l e d

s t u d i e s , such a s t h o s e of Cooper (1977) are u n h e l p f u l as t h e age r a n g e s o f p a l y g o r s k i t e peaks are n o t known w i t h enough accuracy.

The g e n e r a l l a c k of

c o r r e l a t i o n i n d i c a t e s t h a t o t h e r f a c t o r s are more i m p o r t a n t t h a n t h e e x t e n t o f e p e i r i c seas.

The p r e v a l e n c e of

'aridity'

within the continents a t these

times may be one such f a c t o r .

(i)

Late P l i o c e n e to Holocene p a l y g o r s k i t e - s e p i o l i t e

l o c a t e d mainly between 20°-40°N

and 1 0°-350S

M e d i t e r r a n e a n t o a r i d climatic belts.

m i n e r a l d e p o s i t s are

latitudes in the

Oceanic d e p o s i t s of these

t i m e s are probably l a r g e l y d e r i v e d from windblown d u s t , w i t h some slumped material and t u r b i d i t e s .

Neoformation took p l a c e e x t e n s i v e l y

i n c a l c a r e o u s s o i l s and pedogenic c a l c r e t e s , and minor p l a y a s and springs. ( i i ) The l a t i t u d i n a l p a t t e r n i n t h e Pliocene-Holocene t h r o u g h o u t t h e Cretaceous and T e r t i a r y . between 30°-400N

and South.

is present

C o n c e n t r a t i o n is l a r g e l y

That p a r t of the d i s t r i b u t i o n

c o n t r i b u t e d by t h e oceans, d e r i v e d from DSDP r e s u l t s , i s e s s e n t i a l l y c o i n c i d e n t a l with t h a t determined from onshore d e p o s i t s , b u t i s t h e r e s u l t of i n i t i a l sample d i s t r i b u t i o n and c a n n o t t h e r e f o r e be used as s u p p o r t f o r a l a t i t u d i n a l d i s t r i b u t i o n i n t h e oceans.

31 P r i o r t o t h e C r e t a c e o u s , t h e m a j o r i t y of d e p o s i t s are i n t h e n o r t h e r n hemisphere, w i t h i n l a t i t u d e 4S0, the equator.

b u t are most abundant n e a r

P r e - J u r a s s i c c o n t i n e n t a l r e c o n s t r u c t i o n s are somewhat

s p e c u k a t i v e and n o t independent of s e d i m e n t a r y environmental d a t a . ( i i i )P a l y g o r s k i t e - s e p i o l i t e

m i n e r a l s i n p e r i m a r i n e and i n t r a c o n t i n e n t a l

s i t u a t i o n s are i n d i c a t o r s of semi-arid or s e a s o n a l l y a r i d c o n d i t i o n s , b u t n o t g e n e r a l l y a s extreme a s f o r sand dune d e s e r t formation and This i s i n d i c a t e d by t h e l a t e Neogene

evaporite deposition.

d i s t r i b u t i o n , p a r t i a l c o i n c i d e n c e i n l a t i t u d i n a l and agewise d i s t r i b u t i o n between marine and non-marine C a i n o z o i c , and the l i t h o f a c i e s associates.

deposi t s during t he D e p o s i t i o n took p l a c e i n

b r a c k i s h a l k a l i n e waters. (iv)

Some c o n t i n e n t a l l a c u s t r i n e d e p o s i t s , such a s t h e e x t e n s i v e A u s t r a l i a n o c c u r r e n c e s , are n o t a s s o c i a t e d with v o l c a n i c a s h , n o r w e r e there any basic r o c k s or metamorphic r o c k s of any e x t e n t i n t h e

s u r r o u n d i n g catchments.

Such d e p o s i t s d e m o n s t r a t e o t h e r s o u r c e s o f

magnesium i o n s are s u f f i c i e n t f o r palyqorskite-sepiolite g e n e s i s ( i n t h e South A u s t r a l i a n b a s i n s f o r example, t h e o n l y o t h e r s o u r c e are t h e e x t e n s i v e m o n t m o r i l l o n i t i c c l a y s of t h e C r e t a c e o u s ) . (v)

S e v e r a l l a r g e deep ocean d e p o s i t s have a hydrothermal o r i g i n , which b e s t e x p l a i n s t h e Campanian peak i n t h e P a c i f i c Ocean, similar p r o c e s s e s may e x p l a i n some o f t h e l a r g e P a l a e o z o i c d e p o s i t s o f northern Russia, a s s o c i a t e d with b a s a l t s .

A l t e r a t i o n could have

o c c u r r e d some t i m e a f t e r d e p o s i t i o n , which might e x p l a i n t h e r a t h e r poor c o r r e l a t i o n w i t h worldwide c l i m a t i c and t e c t o n i c e v e n t s . O t h e r s were d e r i v e d from s o i l s t h r o u g h windblown d u s t i n t h e t r a d e wind belts, and from n e a r s h o r e o c c u r r e n c e s by slumping and turbidity currents.

Some r e p r e s e n t foundered peri-marine

environments l e f t behind as t h e c o n t i n e n t s d r i f t e d a p a r t . There i s no r e l a t i o n s h i p between p d y ~ s k i t e - ~ p i o l i t e d e p o s i t i o n and water d e p t h i n t h e oceans. (vi)

Vein d e p o s i t s are m o s t l y hydrothermal i n o r i g i n , and are c h a r a c t e r i z e d by a p r e v a l e n c e o f s e p i o l i t e and r e l a t e d m i n e r a l s . Some are p r o b a b l y pedogenic c r a c k or j o i n t i n f i l l s , some from s p r i n g a c t i o n , or r e s u l t from t h e w e a t h e r i n g of a l t e r a t i o n zones around ore b o d i e s and igneous rocks.

( v i i ) P e r i o d s when p a l y g o r s k i t e - s e p i o l i t e are: Cambrian L a t e Devonian and C a r b o n i f e r o u s

group m i n e r a l s are m o s t abundant

32

L a t e Permian and T r i a s s i c

?Late Jurassic Late Cretaceous,

e s p e c i a l l y A l b i a n , Campanian and p o s s i b l y

Coniacian. E a r l y Eocene ( F i r s t major widespread non marine d e p o s i t s ) L a t e Eocene L a t e Oligocene Middle Miocene t o P l i o c e n e

ACKNOWLEDGEMENTS The d a t a a r e p r e s e n t e d w i t h t h e p e r m i s s i o n of t h e D i r e c t o r G e n e r a l of The m a n u s c r i p t w a s r e a d by B. G.

Mines and Energy, South A u s t r a l i a . and G .

W.

K r i e g , W.V.

P r e i s s i s s i n c e r e l y thanked f o r t r a n s l a t i o n of German

and R u s s i a n l i t e r a t u r e , t o which D.

Gravestock h a s a l s o c o n t r i b u t e d .

C a l l e n h a s t r a n s l a t e d French l i t e r a t u r e .

bibliography.

( l i b r a r i a n ) was i n v a l u a b l e f o r

A l l b u t J.H.C.

J.H.

T h i s p a p e r m u l d have been

i m p o s s i b l e t o produce w i t h o u t t h e i r g e n e r o u s h e l p . McKellar-Stewart+

Forbes

The a s s i s t a n c e of N. c o m p i l a t i o n of t h e e x t e n s i v e

(my w i f e ) are of t h e Dept.

of Mines and Energy,

South A u s t r a l i a . Correspondence w i t h A.

S i n g e r (Hebrew U n i v e r s i t y , J e r u s a l e m ) , C. Weaver

( G e o r g i a I n s t i t u t e of Technology, U.S.A.), U t v i n n i n g s a v d e l i n g e n , Norway) and R. U.S.A.)

L.

Watts (Norske S h e l l ,

Couture (Argonne N a t i o n a l L a b o r a t o r y ,

i s acknowledged.

L i l i a n Musich, S c r i p p s I n s t i t u t e of Oceanography, La J o l l a , C a l i f o r n i a i s thanked f o r p r i n t o u t s o f p a l y q o r s k i t e a n a l y s e s n o t i n DSDP volumes ( c u r r e n t t o

1978). A.

S i n g e r and two unknown r e f e r e e s are thanked f o r r e v i e w i n g this

manuscript.

Angeli ( S . A u s t . k p t . Mines thanked for typing this offset. Miss F. de

& m rgy) is

Sincerely

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39

O R I G I N AN0 GEOLOGIC IMPLICATIONS OF THE PALYGORSKITE DEPOSITS OF S.E. STATES

UNITED

CHARLES E. WEAVER Georgia I n s t i t u t e o f Technology ABSTRACT

This paper i s a p a r t i a l summary of a d e t a i l e d i n v e s t i g a t i o n of t h e Miocene of t h e S.E.

U n i t e d States by Weaver and Beck (1977).

P a l y g o r s k i t e formed i n

shallow s c h i z o h a l i n e lagoons, l a r g e l y by t h e a l t e r a t i o n of m o n t m o r i l l o n i t e . The temporal ' d i s t r i b u t i o n of p a l y g o r s k i t e seems c o n t r o l l e d l a r g e l y by c l i m a t e which i n t u r n i s r e l a t e d t o t h e p a t t e r n of c o n t i n e n t a l d r i f t . GEOLOGIC SETTING The Miocene sediments of t h e southeastern United States c o n t a i n commerci a1 deposits of p a l y g o r s k i t e - s e p i o l i t e and phosphate.

These minerals, i n a d d i t i o

t o carbonates, o p a l - c r i s t o b a l i t e , z e o l i t e , and some of t h e smectites, had an orthochemical o r i g i n . The m i n e r a l s were deposited i n a peri-marine environment where c o n d i t i o n s favored t h e growth of m i n e r a l s f r o m s o l u t i o n . Sediments were deposited i n shallow water i n a m i l d l y t e c t o n i c a l l y a c t i v e hinge area separating t h e A t l a n t i c Ocean and t h e Gulf of Mexico.

An isopoch

map of t h e Miocene and Upper Oligocene Tampa Formation ( F i g u r e 1) shows t h e major s t r u c t u r a l f e a t u r e s i n t h e area.

M o n t m o r i l l o n i t e i s t h e dominant c l a y

mineral i n t h e T e r t i a r y o f t h e A t l a n t i c and Gulf Coastal P l a i n s except f o r t h e Upper Oligocene and Lower and Middle Miocene of n o r t h e r n F l o r i d a , Georgia, southern South Carol i na, Georgia Shelf and B1ake P1atdau, where p a l y g o r s k i t e and s e p i o l i t e are commnly dominant.

A marine channel o r trough extended through southern Georgia and connected t h e A t l a n t i c Ocean and t h e Gulf o f Mexico f r o m Cretaceous through Oligocene time. The F l o r i d a p l a t f o r m was an i s l a n d . During t h e Miocene t h e platform was j o i n e d w i t h t h e mainland.

During l a t e Oligocene (Tampa) t h e sea t r a n s -

gressed over an eroded k a r s t l a n d s u r f a c e and t i d a l and l a c u s t r i n e carbonates ( l a r g e l y dolomite) and p a l y g o r s k i t e were deposited.

This i s t h e f i r s t

occurrence of p a l y g o r s k i t e and s e p i o l i t e i n t h e area. General t r a n s g r e s s i o n continued d u r i n g much o f t h e Lower Miocene (Torreya and Chipola) f o l l o w e d by a r e g r e s s i o n c u l m i n a t i n g i n t h e development of an extensive s o i l and reworked ( c l a y , phosphate and quartz pebbles) h o r i z o n near During t h e Lower

t h e end of Lower Miocene and t h e beginning o f Middle Miocene.

Miocene p a l y g o r s k i t e and s e p i o l i t e formed throughout t h e r e g i o n i n b r a c k i s h Formation of these c l a y s ceased a t t h e end of lagoon and t i d a l environments. t h e Lower Miocene ( a t a s o i l -reworked horizon).

40

LATERAL PATTERN F i g u r e 2 i s a c r o s s - s e c t i o n i n t h e n o r t h e r n p a r t of t h e area, p a r a l l e l i n g t h e Savannah River.

P a l y g o r s k i t e and s e p i o l i t e are r e s t r i c t e d t o Lower

Miocene and stop a b r u p t l y a t t h e Middle-Lower Miocene boundary.

Numerous o t h e r

cross-sections show t h a t t h e bedded p a l y g o r s k i t e i s r e s t r i c t e d t o t h e Lower Miocene and Tampa.

The Middle Miocene sediments are c h a r a c t e r i z e d by t h e

Fig. 1. Generalized Miocene paleogeographic map based on thickness o f Miocene. Two p o s i t i v e areas separated by two depocenters. The Suwannee U p l i f t i s an o l d e r f e a t u r e than t h e Ocala U p l i f t . The A t l a n t i c and Appalachicola Embayments were i n t e r m i t t e n t l y connected by a trough.

41 presence o f m a r i n e diatoms and o p a l - c r i s t o b a l i t e ( F i g u r e 3).

Phosphate pebbles

a r e c o n c e n t r a t e d a t t h e Lower-Middle Miocene boundary and mark t h e b e g i n n i n g of t h e M i d d l e Miocene t r a n s g r e s s i o n .

T h i s boundary, c h a r a c t e r i z e d by phosphate

and c l a y pebbles, c a n b e t r a c e d o v e r much of t h e area.

T h i s i s t h e p e r i o d of

t i m e when much of' t h e phosphate was c o n c e n t r a t e d i n t h e c o a s t a l area. F i g u r e 4 i s a s o u t h w e s t - n o r t h e a s t c r o s s - s e c t i o n down t h e c e n t e r of t h e Trough.

P a l y g o r s k i t e is p r e s e n t i n t h e Upper Oligocene and Lower Miocene.

The commercial p a l y g o r s k i t e c l a y beds o c c u r i n b o t h t h e Lower Miocene and Middle Miocene sediments ( s o u t h e r n p a r t of s e c t i o n ) .

The l a t t e r d e p o s i t s a r e

d e t r i t a l and 'were d e r i v e d f r o m t h e Lower Miocene d e p o s i t s .

Fig. 2. Northwest-southeast c r o s s - s e c t i o n a l o n g t h e Savannah R i v e r e x t e n d i n g 80 km t o t h e coast. The M i d d l e Miocene-Lower Miocene boundary c o i n c i d e s w i t h t h e change f r o m m o n t m o r i l l o n i t e (M) t o p a l y g o r s k i t e p l u s s e p i o l i t e (P and S). K = k a o l i n i t e , z = z e o l i t e , B = b i o t i t e , 0 = no samples, b l a c k c i r c l e s = phosphate pebbles, open c i r c l e s = c l a y c l a s t s .

42

The general lithologic units of t h e Lower Miocene are shown in Figure 5. Coarse, high energy, gravelly deposits occur in the center of the Atlantic Embayment. These were deposited in an estuarine environment a t the m o u t h of t h e ancestral Altamaha and Sewanee Rivers. The deposits are flanked by shallow brackish dolomite (limpid variety) and dolomitic palygorskite beds. Relatively pure clay beds occur t o the northwest of the Ocala High and extend t o the southwest. The environment was shallow water marine t o brackish.

B PL

C L A Y MI NERALOG Y

x

f

L

-

0 0

te

iL -S

Fig. 3. Core hole Effingham No. 3 showing lithology, mineralogy and phosphate content. I = i l l i t e ; B = b i o t i t e ; K = kaolinite; M = montmorillonite; P = palygorskite; S = s e p i o l i t e ; P.M. = post Miocene; and BPL = bone phosphate of lime. Core also shown i n Figure 2.

43

The d i s t r i b u t i o n of p a l y g o r s k i t e and s e p i o l i t e i n t h e Lower Miocene i s q u i t e extensive ( F i g u r e 6).

S e p i o l i t e i s concentrated shoreward of t h e p a l y g o r s k i t e

and was apparently formed under l e s s s a l i n e c o n d i t i o n s .

The A t l a n t i c Embayment

and Trough c o n t a i n d e t r i t a l p a l y g o r s k i t e . Thin, r e l a t i v e l y pure p a l y g o r s k i t e c l a y beds, 1 t o 5 m t h i c k , a r e concent r a t e d i n an area from s l i g h t l y n o r t h of t h e Georgia-Florida border t o 60 km t o t h e south of t h e s t a t e l i n e .

S i m i l a r beds are present i n o t h e r areas b u t have

not been mined. The main commercial i n t e r v a l commonly c o n t a i n s two c l a y beds separated by a sand, s h e l l , dolomite, o r s o i l bed of v a r i a b l e thickness.

These two c l a y beds

appear t o be r e l a t i v e l y continuous throughout t h e n o r t h F l o r i d a area of t h e Trough.

Thin, discontinuous beds occur above and below t h e main c l a y h o r i z o n

b u t they g e n e r a l l y c o n t a i n abundant m o n t m o r i l l o n i t e .

Fig. 4. Southwest-northeast ( r i g h t ) c r o s s - s e c t i o n extending f r o m northwest F l o r i d a through Embayment and Trough t o Savannah River. Section shows d i s t r i b u t i o n of c l a y minerals. White areas i n lower p a r t of s e c t i o n i n d i c a t e no data; i n t h e upper p a r t of s e c t i o n w h i t e i n d i c a t e s where k a o l i n i t e i s t h e predominant clay. Authigenic Lower Miocene commercial c l a y beds occur between sections W6890 and 665494; d e t r i t a l Middle Miocene commercial c l a y beds between GGS205 and 665175. S t i p p l e = p a l y g o r s k i t e , h o r i z o n t a l = montmoril l o n i t e .

44 VERTICAL PATTERN L i t h o l ogy A c o r e ( 9 m) from t h e La Camelia p a l y g o r s k t e mine

Engel h a r d M i n e r a l s and

Chemical Corp.) i n n o r t h F l o r i d a was s t u d i e d i n d e t a i l t o d e t e r m i n e t h e v e r t i c a l v a r i a b i l i t y and t h e r e l a t i o n s of t h e v a r i o u s parameters.

The s t r u c t u r a l ,

t e x t u r a l , m i n e r a l o g i c a l and chemical d a t a i n d i c a t e t h e r e a r e two m a j o r d e p o s i t i o n a l cycles represented within t h e minable i n t e r v a l .

The sediments d e p o s i t e d

d u r i n g t h e two c y c l e s d i f f e r i n d e t a i l b u t i n g e n e r a l a r e s i m i l a r .

The

environments of d e p o s i t i o n grade f r i m s h a l l o w m a r i n e t o l a g o o n a l t o t i d a l f l a t t o soil. F i g u r e 7 shows t h e c o r e l i t h o l o g y and c l a y m i n e r a l c o m p o s i t i o n .

There a r e

t w o p u r e c l a y beds (0.5 t o 1.5 m and 6.0 t o 7.3 m) t h a t c o n s i s t of r e l a t i v e l y pure, p a r a l l e l l a m i n a t e d c l a y .

The c l a y beds were d e p o s i t e d d u r i n g two p e r i o d s

o f r e g r e s s i o n s e p a r a t e d by a p e r i o d of t r a n s g r e s s i o n . The l o w e r i n t e r v a l s t a r t s w i t h a c l a y e y sand.

T h i s i s f o l l o w e d by a t h i n

i n t e r v a l o f mud-cracked c l a y i n f i l l e d w i t h a c o a r s e r sandy c l a y . c l a s t s a r e p a r t i a l l y dolomitized.

Some of t h e

There i s a t h i n sand zone i n t h e m i d d l e of

t h e c l a y bed and some worm burrows n e a r t h e top.

F i g . 5. D i s t r i b u t i o n of m a j o r l i t h o l o g i c u n i t s i n t h e Lower Miocene. Mixed a r e a t o t h e southwest c o n t a i n s beds of p a l y g o r s k i t e b u t o v e r a l l l i t h o l o g y i s complex. P a l y g o r s k i t e i s m a j o r c l a y i n t h e d o l o m i t i c sediments. The High F o r o r i e n t a t i o n see F i g u r e 1. ( O c a l a ) was an a r e a of non-deposition.

45

This i s followed by another bed of mud-cracked and s l i g h t l y reworked clay c l a s t s in a matrix of c o a r s e r sandy clay. Round sand-size clay grains a r e a l s o abundant in t h i s bed. This bed i s overlain by a sandy clay bed with a v e r t i c a l , s l i g h t l y slickensided f r a c t u r e pattern. Many f r a c t u r e s a r e coated with a t h i n f i l m o f glossy clay t h a t resembles cutans (clay skins) found i n s o i l . The lower half contains organic s t a i n s and clay g r a i n s and the upper half burrows. This interval i s a soil zone which occurs a t t h e top of a sequence of sediments deposited during a regression. This interval i s overlain by a sandy bed which i s a greenish clayey sand with i r r e g u l a r mottles of white sand and worm tubes. Over t h i s i s a white sand containing pelecypod s h e l l s . The mixing i n the lower p a r t of the sand is apparently due t o both burrowing and c u r r e n t action.

PALVGORSIITE

LOWER MIOCENE C L A Y S

20 K Y

Fig. 6. Map showing d i s t r i b u t i o n of palygorskite and s e p i o l i t e i n the Lower Miocene. Montmorillonite i s t h e dominant clay in unlabeled areas. Dotted l i n e indicates l o c a t i o n of concentration of d e t r i t a l palygorskite in Middle Miocene sediments. For o r i e n t a t i o n see Figure 1.

46

There i s a gradual t r a n s i t i o n from sand t o dolomitic clay ( 3 m). A pure clay bed containing patches of dolomite extends up t o 2.4 m. Dolomite then becomes predominant and t h e r e i s 0.9 m of clayey dolomite. The dolomitic bed i s overlain by 1 m of pure clay. The lower one-third has an i r r e g u l a r , massive appearance with some i r e g u l a r v e r t i c a l f r a c t u r e surf aces. This clay bed grades i n t o an interval which c o n s i s t s l a r g e l y of t h e same type of c l a y , b u t i s heavily burrowed and i t i f i l l e d w i t h a coarser clayey sand. This i s the top o f the core. I t i s overlain by a clayey marine sand s i m i l a r t o t h e type t h a t occurs in t h e burrows in t h e top of t h e core. WLVGORSKITE

Meters

MONTMORILLDNITE

SEPIOLITE

Marine Clay Burrowed

Lagoona I

TI do I

Marine Sand

Sail

Supra Tidal

Lagoona I

Tidal Marine Sand

Fig. 7. Lithology and mineralogy of MC-1 core from La Camelia Mine, Florida. Two cycles of regression and transgression a r e evident.

47

Thus, on gross l i t h o l o g y , t h e r e appear t o be two s i m i l a r , b u t d i s t i n c t depositional u n i t s .

Both u n i t s appear t o b e topped by a h i a t u s , and b o t h s t a r t

w i t h a sand bed of p r o b a b l y m a r i n e ( l i t t o r a l ) o r i g i n .

The l o w e r u n i t i s

c h a r a c t e r i z e d by mud c r a c k e d and l o c a l l y reworked sediments and t h e upper u n i t by d o l o m i t i c beds. The t e x t u r a l d a t a i n d i c a t e t h e l a g o o n a l p a l y g o r s k i t e c l a y s c o n t a i n l e s s t h a n

10%sand and have a mean g r a i n s i z e (MZ) l e s s t h a n 3.04.

Marine m o n t m o r i l l o n i t e

c l a y s and c l a y e y sands c o n t a i n more t h a n 30% sand and t h e MZ i n c r e a s e s as t h e percent sand increases.

Reworked samples and s o i l samples have i n t e r m e d i a t e

values. Mineralogy P a l y g o r s k i t e i s t h e predominant c l a y i n t h e s e c t i o n .

Montmorillonite i s

I l l i t e and mica a r e p r e s e n t i n second i n abundance, f o l l o w e d by s e p i o l i t e . .The e s t i m a t e d r e l a t i v e c l a y m i n e r a l

minor amounts t h r o u g h o u t t h e s e c t i o n .

content, based on x - r a y p a t t e r n s o f o r i e n t e d s l i d e s , i s shown i n F i g u r e 7. The c l a y m i n e r a l s u i t e i s c l o s e l y r e l a t e d t o t h e l i t h o l o g y and t h u s presumably d e p o s i t i o n a l environments.

I n addition, there are s i g n i f i c a n t

d i f f e r e n c e s between t h e upper and l o w e r d e p o s i t i o n a l u n i t s . I n t h e p e b b l y zone ( 6 t o 5 m) t h e pebbles have a h i g h p a l y g o r s k i t e c o n t e n t . The c l a y e y sand m a t r i x i s composed l a r g e l y o f m o n t m o r i l l o n i t e ( F i g u r e 7).

Small

(2 t o 5 mn) rounded t a n c l a y g r a i n s a r e s i m i l a r i n c o m p o s i t i o n t o t h e l a r g e S e p i o l i t e i s present throughout t h i s

blocks o f apparent mud-crack o r i g i n .

i n t e r v a l i n t h e c l a y pebbles and g r a i n s b u t n o t i n t h e m a t r i x .

The c l a y s u i t e

o f t h e m a t r i x i s s i m i l a r t o t h a t of t h e o v e r l y i n g m o n t m o r i l l o n i t i c sandy s o i l . M o n t m o r i l l o n i t e comprises o v e r 90% o f t h e c l a y s u i t e i n t h e s o i l zone. S e p i o l i t e has a maximum c o n c e n t r a t i o n a t t h e b o t t o m of t h e s o i l zone and i s n o t present i n t h e o v e r l y i n g sediments.

This i s t h e only i n t e r v a l t h a t contains

more s e p i o l i t e t h a n p a l y g o r s k i t e .

A d e t a i l e d s t u d y o f t h e b o t t o m p a r t of t h e s o i l zone i n d i c a t e s t h a t t h e c l a y m i n e r a l s a r e inhomogeneously d i s t r i b u t e d .

The g r e e n i s h sandy c l a y i s composed

almost e n t i r e l y o f m o n t m o r i l l o n i t e , w i t h some b i o t i t e .

Some small w h i t e

pebbles have a c o m p o s i t i o n s i m i l a r t o t h e u n d e r l y i n g l a r g e pebbles (palygorskite

>

montmorillonite

>

sepiolite).

A l s o p r e s e n t a r e some small

t a n n i s h g r a i n s ( 2 t o 5 mn) and a t h i n t a n n i s h c o a t i n g on t h e v e r t i c a l f r a c t u r e surfaces.

I n b o t h of t h e s e t y p e s of samples m o n t m o r i l l o n i t e i s t h e dominant

c l a y and s e p i o l i t e i s more abundant t h a n p a l y g o r s k i t e . s u i t e has a d i s t i n c t i v e occurrence.

Thus t h e " s e p i o l i t e - r i c h "

The d i s t r i b u t i o n suggests t h e c l a y may be

secondary and has formed by p o s t - d e p o s i t i o n a l s o i l i n t e r v a l and growth i n t h e bottom.

l e a c h i n g of t h e upper p a r t of t h e

48

Tannish g r a i n s i n t h e upper p o r t i o n of t h e s o i l zone a r e composed almost e n t i r e l y o f p a l y g o r s k i t e , sometimes w i t h d o l o m i t e .

These g r a i n s must have been

added f r o m a d j a c e n t o v e r l y i n g sediments. Burrows i n t h e 4 t o 4.8 m m o n t m o r i l l o n i t e - r i c h i n t e r v a l a r e f i l l e d by p a l y g o r s k i t e , i n d i c a t i n g c l a y has been worked down f r o m as much as 1.5 m above. I n t h e o v e r l y i n g s h e l l y sand zone p a l y g o r s k i t e i n c r e a s e s and becomes r e l a t i v e l y abundant w i t h i n t h e sand.

However, t h e m o t t l e s and p e b b l e s of

g r e e n i s h c l a y e y sand i n t h i s i n t e r v a l have a h i g h m o n t m o r i l l o n i t e c o n t e n t s i m i l a r t o t h a t of t h e underlying i n t e r v a l .

Thus some o f t h e m i x i n g i s p r o b a b l y

due t o c u r r e n t r e w o r k i n g o f t h e l o w e r m a t e r i a l i n t o t h e upper, r a t h e r t h a n b u r r o w i n g which would cause a downward m i x i n g .

The l a r g e s h e l l s i n t h i s

i n t e r v a l (3.3 t o 3.6 m) have been c o n v e r t e d t o d o l o m i t e and much o f t h e p a l y g o r s k i t e i s secondary. upper c l a y bed.

P a l y g o r s k i t e i s a t a maximum (90%) i n t h e d o l o m i t e and

There i s a s l i g h t decrease i n p a l y g o r s k i t e i n t h e c l a y s of t h e

uppermost burrowed zone.

The burrows a r e f i l l e d w i t h a sandy m o n t m o r i l l o n i t e

clay derived from t h e overlying montmorillonite. Texture TEM and SEM p i c t u r e s show a number of i n t e r e s t i n g f e a t u r e s .

S h o r t , 1 pm

f i b e r s comprise t h e bulk o f t h e p a l y g o r s k i t e - s e p i o l i t e clay b u t long ( g r e a t e r t h a n 10 pm) f i b e r s a r e l o c a l l y abundant.

Long f i b e r s o c c u r i n s m a l l areas w i t h

d e s i c c a t i o n f e a t u r e s , i n d i c a t i n g t h e y grew f r o m r e s i d u a l f l u i d s when d e h y d r a t i o n was n e a r l y complete.

These o c c u r i n a m a t r i x of s h o r t f i b e r s .

Long f i b e r s o c c u r i n t h e s o i l samples where t h e y f o r m mats and a r e a l s o aligned perpendicular t o v e i n walls. S h o r t f i b e r s were observed f o r m i n g f r o m m o n t m o r i l l o n i t e , r e p l a c i n g q u a r t z and c a l c i t e f o s s i l s , and by t h e c o a l e s c i n g o f s m a l l o p a l i n e spheres.

Much o f

t h e c l a y o c c u r s as t h i n , p a r a l l e l laminae, s u g g e s t i n g a p e r i o d i c s u p p l y o f d e t r i t u s ( m o n t m o r i l l o n i t e ) t o t h e lagoon. Environment

I t i s e v i d e n t from t h e s t u d y o f t h i s one c o r e (and many o t h e r s ) t h a t t h e s e Miocene sediments were d e p o s i t e d i n a s h a l l o w w a t e r environment near t h e s t r a n d 1i n e . I n g e n e r a l t h e m o n t m o r i l l o n i t i c sandy i n t e r v a l s appear t o be o f s h a l l o w marine o r i g i n .

The h o r i z o n t a l -bedded, c l a y - r i c h p a l y g o r s k i t e beds must have

been d e p o s i t e d i n a q u i e t lagoon.

The d o l o m i t i c beds were d e p o s i t e d i n a simi,

l a r environment, though some i s replacement d o l o m i t e and p r o b a b l y formed e p i g e n e t i c a l ly. The p e b b l e and mud-crack beds r e p r e s e n t l a g o o n a l d e p o s i t s t h a t were l a t e r reworked by c u r r e n t s coming f r o m e i t h e r t h e seaward o r landward d i r e c t i o n .

The

v e r t i c a l l y - o r i e n t e d m o n t m o r i l l o n i t i c , o r g a n i c , sandy c l a y bed i s a s o i l f o r m e d

49

on f l u v i a t i l e sediments.

Burrowing i s evident throughout, b u t i s p a r t i c u l a r l y

i m p o r t a n t i n t h e sediments c l o s i n g t h e end o f each d e p o s i t i o n a l c y c l e . The d e p o s i t i o n a l c y c l e s s t a r t e d o f f w i t h a sand o r sandy s h e l l bed which acted as b a r r i e r s . thin barriers.

S h a l l o w w a t e r lagoons developed b e h i n d t h e s e r e l a t i v e l y

I n t h e o l d e r c y c l e t h e lagoon was sometimes evaporated t o n e a r

dryness and mud c r a c k s developed.

D u r i n g t h e e a r l y s t a g e t h e b a r r i e r was

breached and c l a y e y m a r i n e sands were mixed w i t h t h e mud c l a s t s . seemed t o b e c h a r a c t e r i s t i c o f t h e l o w e r d e p o s i t i o n a l u n i t .

Near t h e end

This s i t u a t i o n

o f t h e c y c l e f r e s h w a t e r c u r r e n t s p r o b a b l y d i d t h e reworking.

This lower u n i t i s

topped by a s o i l zone developed on f l u v i a t i l e sediments, s u g g e s t i n g t h e o v e r a l l u n i t i s regressive.

T h i s r e g r e s s i o n i s f o l l o w e d by an a b r u p t t r a n s g r e s s i o n

( s h e l l y m a r i n e sand) which m i g h t r e f l e c t o n l y a m i n o r l a t e r a l s h i f t of environments. The upper d e p o s i t i o n a l u n i t shows l i t t l e r e w o r k i n g and a r e l a t i v e l y t h i c k lagoonal sequence ( d o l o m i t e and p a l y g o r s k i t e c l a y bed), which suggest a more permanent b a r r i e r p l u s a decrease i n a v a i l a b l e S i and A l .

This i n t e r v a l

appears t o end i n a s h a l l o w i n g r e g r e s s i v e environment (burrows and r e w o r k i n g )

,

f o l l o w e d by a r e l a t i v e l y a b r u p t m a r i n e t r a n s g r e s s i o n . Thus, b o t h d e p o s i t i o n a l u n i t s appear t o r e p r e s e n t a seaward m i g r a t i o n of a shallow water f l u v i a t i l e - l a g o o n - b a r r i e r

sequence.

Whenever t h e m i g r a t i o n was

i n t e r r u p t e d by a s u s t a i n e d m a r i n e t r a n s g r e s s i o n a new c y c l e began. The l i t h o l o g y i n d i c a t e s t h a t t h e l o w e r u n i t was p r o b a b l y more e f f e c t e d by p h y s i c a l energy ( c l a y c l a s t ) and t h e upper by chemical energy ( d o l o m i t e ) .

The

d e t a i l e d m i n e r a l and chemical d i f f e r e n c e s between t h e two u n i t s l i k e l y r e f l e c t o n l y m i n o r e n v i r o n m e n t a l and s o u r c e d i f f e r e n c e s ; however, f r o m a p r a c t i c a l s t a n d p o i n t t h e s e d i f f e r e n c e s can b e used t o i d e n t i f y t h e d i f f e r e n t c l a y beds. The presence of l i m p i d d o l o m i t e , f a u n a l data, l o w L i c o n t e n t (average 24 ppm) and l a c k o f h y p e r s a l i n e f e a t u r e s suggests t h e w a t e r i n t h e lagoons was b r a c k i s h , probably schizohaline.

The presence of m o n t m o r i l l o n i t e i n b o t h m a r i n e and

c o n t i n e n t a l sediments i n d i c a t e s i t was p r o b a b l y a l s o p r e s e n t i n t h e s h a l l o w w a t e r lagoons.

Chemistry F i g u r e 8 shows t h e d i s t r i b u t i o n o f A1203, MgO and Fe203 i n t h e c l a y f r a c t i o n o f t h e MC-1 core.

I n g e n e r a l t h e A1203 and MgO a r e i n v e r s e l y r e l a t e d and

r e f l e c t v a r i a t i o n s i n t h e m o n t m o r i l l o n i t e ( A l ) and p a l y g o r s k i t e (Mg) c o n t e n t . Fe203 f o l l o w s A1203 and has a maximum v a l u e n e a r t h e base of t h e s o i l zone where

i t was a p p a r e n t l y c o n c e n t r a t e d by o r g a n i c l e a c h i n g o f t h e s o i l .

The K20 (mica)

values (0.5 t o 1.7%) c l o s e l y f o l l o w A1203. Chemical a n a l y s e s and s t r u c t u r a l f o r m u l a ( T a b l e 1 ) o f p u r e m i n e r a l concent r a t e s i n d i c a t e t h e m a r i n e m o n t m o r i l l o n i t e s have a r e l a t i v e l y u n i f o r m

50

Meters

-

0-

I-

2-

3-

4-

D L

0 5-

6-

7-

8-

Fig. 8. Mine.

L

Chemical data of c l a y f r a c t i o n of samples from MC-1 core, La Camelia

composition.

The s o i l smectite has a r e l a t i v e l y high content of Fe and Mg.

Approximately h a l f t h e octahedral p o s i t i o n s of t h e p a l y g o r s k i t e are occupied by Al.

I f i t i s assumed t h a t t h e p a l y g o r s k i t e i n p a l y g o r s k i t e

+ smectite mixtures

has t h e same composition as pure p a l y g o r s k i t e , t h e composition of t h e smectite

(Si02 = 68.3%. Fe20j = 7.4%, MgO = 2 4 . X ) i s more s i m i l a r t o s t e v e n s i t e than t o montmorillonite. Chemical c a l c u l a t i o n s tend t o confirm t h a t most of t h e palyg o r s k i t e formed by t h e d i r e c t a l t e r a t i o n of montmoril l o n i t e w i t h s t e v e n s i t e - l i k e

51

Table 1.

S t r u c t u r a l Formula.

MONTMORILLONITE Marine Soil EC-2-32 F5-13 FF-1 FH-12 FF-18 Octahedral A1 Fe3+ Mg

z

PALYGORSKITE FE-21

FE-17

1.49

1.43

1.46

1.51

1.24

1.66

1.58

.24 .28 2.01

.33 .25 2.01

.28 .28 2.02

.25 .22 1.98

.42 .41 2.07

.36 1.83 3.85

.40 1.79 3.77

.ll 3.89

-11 3.89

.03 3.97

.ll 3.89

.19 7.81

.40 7.60

.01 .45

.24 .40

Tetrahedral A1 .09 Si 3.91 Exchange Cations Ca Na

MIXED FF-54'

MC1-S3 ~ C 1 - 2 3 ~

.79

1.20

1.32

1.33

.55 2.23 3.57

.38 2.15 3.73

.43 2.08 3.83

.38 2.01 3.72

.47 7.53

-39 7.61

.36 7.64

.53 .39

.31 .39

.52 .17

FE-80' Octahedral A1 Fe3+ Mg

c

Tetrahedral .71 A1 Si 7.29 Exchange Cations Ca .57 Na .20 1. 2. 3. 4.

P>Sp>M P >> M P >> M,Qtz P >> M

material being a by-product. The A1 and Fe remained constant and a d d i t i o n a l S i , Mg and H were obtained f r o m s o l u t i o n . When t h e S i and Mg content of t h e solut i o n i s s u f f i c i e n t l y h i g h and t h e pH i s i n t h e range of 8 t o 9 m o n t m o r i l l o n i t e w i l l convert t o p a l y g o r s k i t e . When montmoril l o n i t e i s not present s e p i o l i t e

w i l l precipitate.

Dolomite i s commonly formed contemporaneously w i t h both C a l c i t e i s commonly deposited o u t of phase w i t h t h e

s e p i o l i t e and p a l y g o r s k i t e . Mg minerals.

Though most of t h e p a l y g o r s k i t e formed by d i r e c t replacement of

mantmorillonite, i t i s evident f r o m t h e c o n f i g u r a t i o n t h a t some of t h e long f i b e r p a l y g o r s k i t e grew f r o m s o l u t i o n ( F i g u r e 9).

The l a t t e r t y p e i s most

commonly found i n areas where voids probably existed. DOLOMITE Shells i n sands u n d e r l y i n g t h e lagoonal c l a y have been replaced by p a l y g o r s k i t e and dolomite.

Seeping Mg-rich waters f r o m t h e lagoon e s t a b l i s h e d

F i g . 9. P a l y g o r s k i t e t r e e a s s o c i a t e d w i t h d o l o m i t i c s h e l l (3.4 m i n F i g u r e 7 ) White b a r equals 1 pm.

53

a d o l o m i t i z a t i o n gradient.

The deepest s h e l l s a r e c o n v e r t e d t o d o l o m i t e ( p r o t o -

d o l o m i t e ) p r e s e r v i n g t h e p l a t e t e x t u r e of t h e c a l c i t e . r i c h i n Ca r e l a t i v e t o t h e i n t e r i o r .

The o u t e r s u r f a c e s a r e

T h i s i s t r u e of most of t h e dolomites.

Once t h e p l a t e s achieve a p r o t o d o l o m i t e c o m p o s i t i o n , g r o w t h s t a r t s a t t h e edges and two- and t h r e e - s i d e d rhombs and e v e n t u a l l y s i x - s i d e d h o l l o w rhombs a r e formed ( v e r t i c a l sequence).

P l a t e s arranged i n v a r i o u s s u b s p h e r i c a l f o r m s a r e

present i n some d o l o m i t e l e n s e s and beds.

D o l o m i t e rhombs i n t h e c l a y beds have

o v e r l a p p i n g , t h i n , f l ame-shaped l a y e r s s u g g e s t i n g a slow sheet-by-sheet growth r a t h e r t h a n replacement o r a b r u p t p r e c i p i t a t i o n .

D o l o m i t e f o r m a t i o n precedes

p a l y g o r s k i t e i h some s i t u a t i o n s and f o l l o w s i n o t h e r s .

I n some areas i t appears

t h a t m o n t m o r i l l o n i t e r e a c t s w i t h d o l o m i t e o r Mg c a l c i t e t o f o r m p a l y g o r s k i t e and c a l c i t e ( f i n e disks). OETRITAL DEPOSITS The commercial c l a y d e p o s i t s 40 km n o r t h e a s t of t h e s e p r i m a r y d e p o s i t s were d e p o s i t e d i n t h e narrow M i d d l e Miocene Trough on t o p of t h e s o i l zone s e p a r a t i n g t h e Lower and M i d d l e Miocene.

Diatoms and sponge s p i c u l e s , p r e s e n t i n amounts

up t o 30%, i n d i c a t e a r e s t r i c t e d m a r i n e environment becoming m r e m a r i n e t o t h e n o r t h e a s t (seaward).

The p a l y g o r s k i t e and s e p i o l i t e ( 2 0 t o 70% of t h e c l a y

s u i t e ) i s d e t r i t a l and d e r i v e d from Lower Miocene c l a y s on t h e f l a n k o f t h e u p l i f t e d Ocala High ( t o t h e e a s t and s o u t h e a s t ) . t a i n i n g a p p r e c i a b l e a p a t i t e a r e abundant.

Clay g r a i n s and pebbles con-

T h i s c l a y i s o v e r l a i n by b r a c k i s h

w a t e r ( d i a t o m s ) , m o n t m o r i l l o n i t i c c l a y and sand ( K - f e l d s p a r ) d e r i v e d f r o m t h e west f l a n k and d e p o s i t e d d u r i n g t h e f i n a l m a r i n e r e g r e s s i o n i n t h e area. The p a l y g o r s k i t e - s e p i o l i t e c l a y ( F i g u r e 10) o c c u r s as l e n s e s (10 t o 50 f e e t t h i c k ) and were d e p o s i t e d i n s h e l t e r e d depressions between Lower Miocene b a r r i e r i s l a n d , beach, and c h e n i e r sand r i d g e s when t h e a r e a was t r a n s g r e s s e d by t h e M i d d l e Miocene seas.

The d e p o s i t s a r e r e s t r i c t e d t o t h e southwest p o r t i o n of

t h e Trough w h i c h e x i s t e d as a s i l l .

The s i l l e f f e c t was produced by t h e u p l i f t

o f t h e f l a n k i n g Ocala High; t h i s u p l i f t a l s o a f f o r d e d t h e p a l y g o r s k i t e s e p i o l i t e source.

F a r t h e r t o t h e n o r t h e a s t t h e Trough deepens and

m o n t m o r i l l o n i t i c c l a y s were deposited. There i s a c o m p l e t e c o m p o s i t i o n a l g r a d u a t i o n between c l a y pebbles and phosp h a t e pebbles.

During periods of weathering a p a t i t e replaces a d d i t i o n a l c l a y

and d i a t o m s i n t h e pebbles.

Most o f t h e a p a t i t e o c c u r s as s h o r t r o d s b u t t h a t

r e p l a c i n g diatoms has shapes r a n g i n g f r o m s p h e r i c a l t o p r i s m a t i c c r y s t a l s . O p a l - c r i s t o b a l i t e formed f r o m d i s s o l v e d diatoms and sponge s p i c u l e s i s r e l a t i v e l y abundant.

I t i s commonly massive b u t o c c u r s as b l a d e d s p h e r u l e s

and we1 1 -rounded o p a l ine spheres.

54

STABILITY RELATIONSHIPS Thermodynamic c a l c u l a t i o n s (25°C) have been made f o r t h r e e r e a c t i o n s of d i r e c t concern: montmorillonite-palygorskite, palygorskite-aqueous s o l u t i o n , and sepiolite-aqueous s o l u t i o n .

The s t a b i l i t y f i e l d boundaries f o r these r e a c t i o n s

a r e d e f i n e d by: l o g [Mg++] + 2 pH + 2 l o g [H,SiO;]

+ 0.76 pH + 2.6 l o g [ H 4 S i O i l t 0.62 l o g [ A l ( O H ) i I = -10.70,

0.69 l o g [Mg"]

+2

l o g [Mg"]

= 5.75,

respectively.

pH + 1.5 l o g [H4SiOi]:

and

= 7.95,

I n a l l cases t h e c h a i n s i l i c a t e s are f a v o r e d by an increase i n

one o r more of [Mg

++1,

pH, and CH4SiO;l.

P a l y g o r s k i t e also r e q u i r e s an appro-

p r i a t e i n p u t of A1 (and Fe), e i t h e r i n h e r i t e d d i r e c t l y from t h e precursor c l a y o r taken f r o m s o l u t i o n .

Sepiolite requires l o g [H4SiOi]

B

C

A

_ . ... . .

.

6 0

-. . . .. .. .

, ..

.

. -.

.

. _ .

. . ..

'

= 4.25

(around 3.0

ppm

0

. . . . . ..I ._ ... ' . . . . . , .1 . . ._' . . .. . .. .- . . . . _ . . ,_ . . . . . .- . _. .- . . ' .

MONTMORILLON IT€

0

0

a W n

orskite and Sepiolile

'

i'

'

CHEROKEE CO.

MINE

Fig. 10. North-south l i n e of s e c t i o n ( 4 c o r e s ) through Cherokee Company Mine, NW Thomay County, Georgia. Lower t a n sand u n i t i s Lower Miocene sand w i t h s o i l zone. O v e r l a i n by Middle Miocene, d e t r i t a l p a l y g o r s k i t e c l a y bed, a. m o n t m o r i l l o n i t e c l a y bed, and a m o n t m o r i l l o n i t e sand. Both c o n t a i n marine diatoms and sponge spicules.

55

Si02 i n

sea

w a t e r , assuming H4SiO:

aqueous s o l u t i o n . l o g [H,SiOi]

1. -4.29

= 1.13) f o r s t a b i l i t y w i t h r e s p e c t t o

P a l y g o r s k i t e should f o r m f r o m m o n t m o r i l l o n i t e a t ( a r o u n d 2.7 ppm S i 0 2 ) .

Thus, f r o m t h e p o i n t of view of

thermodynamic c a l c u l a t i o n s , o n l y s l i g h t m o d i f i c a t i o n s of normal sea w a t e r c o n d i t i o n s a r e r e q u i r e d t o f o r m s e p i o l i t e and p a l y g o r s k i t e .

However, i f t h i s were

t r u e t h e s e m i n e r a l s s h o u l d be more common. The c a l c u l a t i o n s i n d i c a t e t h e c h a i n s i l i c a t e s a r e f a v o u r e d by an i n c r e a s e i n [Mg"],

pH, and [ H 4 S i O i ] .

F i e l d o b s e r v a t i o n s i n d i c a t e they a r e a l s o f a v o r e d by

l e s s t h a n normal s a l i n i t y and by h i g h temperature. C a l c u l a t e d s t a b i l i t y f i e l d b o u n d a r i e s between p a l y g o r s k i t e , m o n t m o r i l l o n i t e , and a s e r i e s of d i f f e r e n t c o r r e n s i t e s ( F i g u r e ll), show t h a t r e g a r d l e s s of t h e c h o i c e o f c o r r e n s i t e c o m p o s i t i o n , i t i s f a v o r e d o v e r m o n t m o r i l l o n i t e by h i g h e r [Mg"]

The [ H 4 S i O i l e f f e c t i s m i n o r .

and pH.

r e a c t i o n t h e i m p o r t a n c e o f [Mg++] c o r r e n s i t e composition. gorskite.

For t h e corrensite-palygorskite

and pH i s v a r i a b l e depending on t h e c h o i c e of

However, i n a l l cases h i g h [ H 4 S i O i l f a v o r s p a l y -

These c a l c u l a t i o n s t e n d t o c o n f i r m t h e i d e a t h a t c o r r e n s i t e i s more

-6

-5

-4

-3

-2

log H SiOo [ 4 41

F i g . 11. S t a b i l i t y r e l a t i o n s among s i m p l i f i e d ( F e - f r e e ) p a l y g o r s k i t e and m o n t m o r i l l o n i t e and v a r i o u s c o r r e n s i t e s a t 2 5 T . Continuous l i n e s ( " i d e a l " c o r r e n s i t e ; dashed l i n e s (----------), B r a d l e y and Weaver c o r r e n s i t e ; d o t t e d l i n e s (. .), h y p o t h e t i c a l c o r r e n s i t e .

....

1,

56 abundant i n t h e P a l e o z o i c and e a r l y Mesozoic because e v a p o r a t i c environments w i t h h i g h pH were abundant. TEMPORAL FACTORS Small e v o l u t i o n a r y o r p e r i o d i c f l u c t u a t i o n s i n t h e c o m p o s i t i o n of t h e ocean may have i n c r e a s e d t h e p o s s i b i l i t y o f M g - s i l i c a t e v e r s u s Mg-carbonate f o r m a t i o n

i n t h e younger Phanerozoic.

The f i r s t appearance o f p a l y g o r s k i t e i n t h e e a r l y

Mesozoic may b e r e l a t e d t o t h e i n i t i a t i n g o f sea f l o o r s p r e a d i n g and a t t e n d a n t i n t r o d u c t i o n of s i l i c a (and perhaps Mg) i n t o t h e oceans.

Development may have

been f u r t h e r enhanced i n t h e Upper CFetaceous by t h e p r o l i f e r a t i o n of diatoms. I n t h e G e o r g i a - F l o r i d a a r e a p a l y g o r s k i t e and l i m p i d d o l o m i t e developed i n s h a l l o w , c o a s t a l b r a c k i s h t o s c h i z o h a l i n e waters. h i g h pH.

Warm t e m p e r a t u r e caused a

Both i n c r e a s e d t h e s o l u b i l i t y o f , s i l i c a ( l a r g e l y f r o m d i a t o m s ) .

C o o l e r c o n d i t i o n s d u r i n g t h e M i d d l e Miocene made c o n d i t i o n s u n f a v o r a b l e f o r t h e development of p a l y g o r s k i t e .

Magnesium was o b t a i n e d f r o m sea water.

There i s a mutual a n t i p a t h y between p a l y g o r s k i t e and c l i n o p t i l o l i t e , w i t h p a l y g o r s k i t e b e i n g t h e f r e s h e r w a t e r m i n e r a l and c l i n o p t i l o l i t e t h e more s a l i n e equivalent.

The r e s u l t s of thermodynamic c a l c u l a t i o n s a r e c o m p a t i b l e w i t h t h i s

distribution. The phosphate d e p o s i t s a r e l a r g e l y r e s t r i c t e d t o t h e A t l a n t i c f a c i e s .

Much

o f t h e phosphate was p r o b a b l y d e r i v e d f r o m diatoms i n s h a l l o w c o a s t a l w a t e r s and c o n c e n t r a t e d by r e p l a c i n g c l a y pebbles and c l a y - r i c h f e c a l p e l l e t s .

A r e v i e w o f t h e l i t e r a t u r e on "marine" p a l y g o r s k i t e s i n d i c a t e s t h e r e i s l i t t l e , i f any, p o s i t i v e d a t a t o i n d i c a t e t h e y formed i n a normal m a r i n e environment.

P a l y g o r s k i t e i s r e l a t i v e l y abundant i n some deep sea cores.

Most

o f t h e d e s c r i p t i v e d a t a i n d i c a t e s i t i s d e t r i t a l o r hydrothermal i n o r i g i n .

It

i s suggested t h a t p e r i - m a r i n e p a l y g o r s k i t e d e p o s i t s f o r m o n l y i n b r a c k i s h w a t e r and m o n t m o r i l l o n i t e (and g l a u c o n i t e ) i s u s u a l l y t h e s t a b l e c l a y i n t h e normal m a r i n e waters.

C h l o r i t i c c l a y s (mixed-layer chlorite-montmoril l o n i t e ) are t h e

common s t a b l e phase under h y p e r s a l i n e c o n d i t i o n s . F i g u r e 12 shows t h e g e n e r a l d i s t r i b u t i o n of some a u t h i g e n i c m i n e r a l s t h r o u g h time.

C o r r e n s i t e and d o l o m i t e a r e abundant i n t h e P a l e o z o i c and e a r l y Mesozoic.

As Mg-rich c o r r e n s i t e decreases i n abundance M g - r i c h p a l y g o r s k i t e i n c r e a s e s i n abundance, as does k a o l i n i t e .

V a r i o u s s t u d i e s i n d i c a t e t h a t i n N o r t h America,

Europe and presumably N o r t h A f r i c a t h e P a l e o z o i c and E a r l y Mesozoic c l i m a t e was warmer and much d r i e r t h a n t o d a y ' s .

T h i s would f a v o r t h e development of evapo-

r i t i c c o n d i t i o n s , t h e c o n c e n t r a t i o n of Mg and t h e f o r m a t i o n of c o r r e n s i t e . B e g i n n i n g i n t h e L a t e Mesozoic, r a i n f a l l increased.

This increased r a i n f a l l

caused more i n t e n s e w e a t h e r i n g and t h e f o r m a t i o n of k a o l i n i t e .

I t apparently

a l s o c r e a t e d m r e b r a c k i s h w a t e r c o n d i t i o n s i n t h e f r i n g i n g m a r i n e environments. T h i s f a v o r e d t h e f o r m a t i o n of p a l y g o r s k i t e i n environments where c o r r e n s i t e formed i n d r i e r p e r i o d s .

57

TIME (MY.)

Fig. 12. Estimate of r e l a t i v e abundance of some authigenic minerals through a p o r t i o n of geologic time.

Coastal marine p a l y g o r s k i t e deposits range i n age from T r i a s s i c t o Miocene. Most deposits f r i n g e t h e Tethys and south A t l a n t i c Oceans.

Phosphate deposits

show a s i m i l a r d i s t r i b u t i o n and commonly are associated w i t h p a l y g o r s k i t e deposits.

Upwelling c o l d ocean waters are assumed t o be t h e source of t h e P;

i t would a l s o be a source of S i f o r t h e formation of palygorskite.

The temporal data suggest climate, t h a t i s , temperature and, possibly more important, humidity, determines whether o r n o t p a l y g o r s k i t e w i l l form.

The global d i s t r i b u t i o n of t h e major p a l y g o r s k i t e deposits i n d i c a t e s they are r e s t r i c t e d t o t h e b e l t of t r o p i c a l - s u b t r o p i c a l temperatures.

To a l a r g e extent

t h e d i s t r i b u t i o n was c o n t r o l l e d by t h e p a t t e r n of t h e warm Tethys currents. During t h e Mesozoic coastal p a l y g o r s k i t e was formed along t h e warm margins of t h e Tethys and South A t l a n t i c .

During t h e e a r l y Cenozoic t h e westward f l o w i n g

Tethys c u r r e n t s supplied warm waters t o t h e Caribbean region. The A f r i c a n and Eurasian p l a t e s converged i n t h e Late Oligocene and e a r l y Miocene and allowed these c u r r e n t s t o swing t o t h e n o r t h and increase temperatures i n t h e coastal waters of t h e southeastern United States, presumably c r e a t i n g t h e subtropical humid c o n d i t i o n s t h a t allowed p a l y g o r s k i t e t o form. The c o l l i s i o n of Europe and North A f r i c a a t G i b r a l t a r a t t h e beginning of t h e Middle Miocene modified t h e

58 A t l a n t i c c i r c u l a t i o n pattern, a l l o w i n g c o l d a r c t i c waters t o enter t h e western North A t l a n t i c .

T h i s caused a decrease i n t e m p e r a t u r e and h u m i d i t y and t h e

growth of p a l y g o r s k i t e ceased. i n t h e faunal s u i t e .

The i n c r e a s e d coolness

is c o n f i r m e d by a change

Low r a i n f a l l is i n d i c a t e d by t h e presence o f an abundance

o f opal p h y t o l i t h s c h a r a c t e r i s t i c o f p r a i r i e grasses. I n c o n c l u s i o n we contend t h a t c o a s t a l p a l y g o r s k i t e d e p o s i t s f o r m l a r g e l y f r o m rnontmoril l o n i t e i n p r o t e c t e d q u i e t w a t e r environments and under c l i m a t i c c o n d i t i o n s t h a t produce h i g h r a i n f a l l , b r a c k i s h w a t e r s and s u b t r o p i c a l temperatures. REFERENCE

Weaver, C. E. and Beck, K. C., 1977. Miocene of t h e S.E. U n i t e d S t a t e s : A model f o r chemical s e d i m e n t a t i o n i n a p e r i - m a r i n e environment, Sedimentary Geol., 17, 234 pp., and Developments i n Sedimentology, 22, E l s e v i e r , 234 pp.

59

THE CLAYS OF YUCATAN, M E X I C O :

A CONTRAST I N GENESIS

WAYNE C. ISPHORDING Department of Geology-Geography, U n i v e r s i t y o f South Alabama, Mobile, AL

36693

ABSTRACT The Yucatan P e n i n s u l a o f Mexico p r o v i d e s an e x c e l l e n t s i t e t o examine t h e formation of c l a y m i n e r a l s by pedogenic processes, d e t r i t a l s e d i m e n t a t i o n and direct crystallization.

Clays formed b y each o f these mechanisms a r e widespread

and can be found i n a l l s t a g e s o f m a t u r i t y , depending upon c l i m a t e and t h e geomorphic age o f t h e s i t e .

P o o r l y c r y s t a l l i z e d k a o l i n i t e , boehmite, t a l c and

c h l o r i t e c h a r a c t e r i z e t h e most y o u t h f u l c l a y s , whereas those i n an advanced stage o f m a t u r i t y c o n s i s t a l m o s t e n t i r e l y o f w e l l c r y s t a l l i z e d k a o l i n i t e . t r i t a l clays, i n contrast,

De-

a r e uncommon on t h e n o r t h e r n p e n i n s u l a , because o f

an almost complete l a c k o f s u r f a c e streams and, f o r t h e most p a r t , a r e r e s t r i c t e d t o t h e E a s t e r n B l o c k F a u l t D i s t r i c t and a number o f o l d b a s i n - l i k e areas.

S m e c t i t e c l a y s a r e abundant i n t h e s e b a s i n s and g i v e evidence o f h a v i n g

been d e p o s i t e d i n m a r g i n a l lagoons t h a t were l a t e r t r a n s f o r m e d i n t o s a l i n e lakes by t e c t o n i c u p l i f t .

The u l t i m a t e s o u r c e o f t h e d e t r i t a l m a t e r i a l appears

t o be r e l a t e d t o p y r o c l a s t i c d e b r i s c a r r i e d n o r t h w a r d f r o m B e l i z e and Guatemala. Tnlc, c : i l o r i t e ,

p a l y g o r s k i t e - s e p i o l i t e , and m i x e d - l a y e r k a o l i n i t e - m o n t m o r i l -

1!1niL? c w s t i t u t e t h e t h i r d g e n e r i c t y p e o f c l a y s found on t h e p e n i n s u l a and a l l a r e b e l i e v e d t o be r e l a t e d t o an o r i g i n b y d i r e c t c r y s t a l l i z a t i o n .

These

clays a r e e s s e n t i a l l y r e s t r i c t e d t o t h e n o r t h e r n r e g i o n o f t h e p e n i n s u l a and have c r y s t a l l i z e d e i t h e r d i r e c t l y f r o m m a r i n e w a t e r s o f e l e v a t e d s a l i n i t y o r have formed d i a g e n e t i c a l l y by a l t e r a t i o n o f d o l o m i t e . INTRODUCTION The Yucatan P e n i n s u l a o f Mexico extends n o r t h w a r d f r o m t h e Chiapas Laramide deformation b e l t o f C e n t r a l America and c o n s i s t s o f a massive c a r b o n a t e p l a t f o r m t h a t has, o n l y r e c e n t l y , p a r t i a l l y emerged f r o m t h e sea ( F i g . 1 ) .

The l i m e -

stones, d o l o m i t e s and e v a p o r i t e s t h a t c h a r a c t e r i z e t h e r e g i o n range i n age f r o m

Cretaceous t o Recent and a r e something o v e r 3,000 m e t e r s i n t h i c k n e s s near t h e northern shoreline.

Data f r o m deep w e l l s i n d i c a t e t h a t t h e carbonates r e s t

A detailed g e o l o g i c map o f t h i s 80,000 square k i l o m e t e r r e g i o n has y e t t o be compiled, non-conformably on a n d e s i t e s and metamorphics o f Pennsylvanian age.

however g e o l o g i c i n v e s t i g a t i o n s have i n c r e a s e d m a r k e d l y d u r i n g t h e p a s t 10 years as a d i r e c t consequence o f t h e r e q i o n ' s boom i n t o u r i s m .

The l a r q e

60

F i g . 1. Map o f t h e Yucatan P e n i n s u l a showing t h e m a j o r geomorphic ( p h y s i o graphic) provinces. number o f t o u r i s t s t h a t a n n u a l l y v i s i t t h e p e n i n s u l a have caused t h e government t o c o n s t r u c t numerous new r o a d s i n t o t h e i n t e r i o r w i t h t h e r e s u l t t h a t many exposures a r e now a c c e s s i b l e t h a t have h e l p e d c l a r i f y t h e r e g i o n a l geology.

A

number o f b a s i c g e o l o g i c q u e s t i o n s s t i l l r e m a i n t o be answered, however, and c o n t r o v e r s i e s abound i n t h e l i t e r a t u r e c o n c e r n i n g t h e p e n i n s u l a ' s s t r a t i g r a p h y , s t r u c t u r a l geology, and even t h e genesis o f i t s c l a y m i n e r a l s .

The l a t t e r i s

o f e s p e c i a l i n t e r e s t because, u n l i k e most o t h e r l o c a t i o n s i n t h e w o r l d where t h e r e s i d e n t c l a y s have formed d o m i n a n t l y by one s i n g l e process, t h o s e i n Yucatan f a l l i n t o t h r e e d i s t i n c t groups.

These i n c l u d e :

( 1 ) pedogenic c l a y s , ( 2 )

d e t r i t a l c l a y s , and ( 3 ) d i r e c t c r y s t a l l i z a t i o n ( " p r i m a r y " ) c l a y s .

Each o f

these has developed i n response t o a p a r t i c u l a r c o m b i n a t i o n o f c l i m a t i c , env i r o n m e n t a l and d i a g e n e t i c c o n d i t i o n s and, i n a g e n e r a l way, i s c h a r a c t e r i s t i c o f a p a r t i c u l a r area o f t h e peninsula.

61

PEDOGENIC CLAYS General D i s c u s s i o n With t h e exception o f smectite c l a y s found i n t h e eastern block f a u l t basins and i n s e v e r a l " p o l j e - l i k e "

basins i n t h e i n t e r i o r , c l a y s containing s i g n i f i -

c a n t d e t r i t a l components a r e e s s e n t i a l l y l a c k i n g elsewhere i n Yucatan.

North

o f t h e Champoton R i v e r a l l d r a i n a g e i s s u b t e r r a n e a n and, e x c l u d i n g a few t i d a l channels t h a t e x t e n d i n t o t h e Coastal Zone, s u r f a c e streams a r e c o m p l e t e l y lacking.

The s i m i l a r absence i n deep p e t r o l e u m t e s t w e l l s o f any i d e n t i f i a b l e

c l a s t i c s i n t e r b e d d e d w i t h t h e carbonates i n d i c a t e s t h a t such c o n d i t i o n s p e r s i s t e d t h r o u q h o u t t h i s r e g i o n from e a r l y T e r t i a r y t i m e .

Though c l a y s o r i g i n a t -

i n g by a l t e r a t i o n o f v o l c a n i c d e t r i t u s have n o t been u n e q u i v o c a l l y i d e n t i f i e d i n t h e n o r t h e r n p e n i n s u l a , u n - a l t e r e d ash i s d e s c r i b e d f r o m a t l e a s t one l o c a t i o n i n t h e Central H i l l D i s t r i c t ( a small lens, several centimeters thick, t h e Maya ceremonial cave a t L o l t u n ) .

Small amounts o f ash may, t h e r e f o r e ,

in

be

p r e s e n t as m i n o r components i n t h e s e s o i l s and i n t h e u n d e r l y i n g p a r e n t c a r bonate r o c k s . M i n e r a l o g y and Chemistry Quinones (1975) p r o v i d e d an e x c e l l e n t d e s c r i p t i o n o f s e v e r a l sol'l p r o f i l e s f r o m t h e n o r t h e r n p e n i n s u l a o f Yucatan and d e s c r i b e d two o f t h e more y o u t h f u l s o i l s as " O r t h i c U s t o c h r e p t s " and " O r t h i d i c H a p l u s t o l l s " , u s i n g t h e 1960 Comp r e h e n s i v e System t e r m i n o l o g y .

X-ray d i f f r a c t o g r a m s 1 t h r o u g h 4 ( F i g . 2 ) a r e

r e p r e s e n t a t i v e o f e a r l y pedogenic s o i l development and i n d i c a t e t h a t t h e s e s o i l s a r e l a r g e l y composed o f p o o r l y c r y s t a l l i z e d k a o l i n i t e , boehmite and t r a c e amounts o f t a l c and c h l o r i t e .

M i c r o s c o p i c e x a m i n a t i o n d i s c l o s e d t h a t most of

these s o i l s c o n s i s t e d l a r g e l y o f weathered l i m e s t o n e fragments, o r g a n i c d e b r i s , and l e s s e r amounts o f s o i l c l a y s and o x i d e s .

Quinones (1975) n o t e d t h a t if

i r o n o x i d e s were e l i m i n a t e d b y d i t h i o n a t e t r e a t m e n t , t h a t sand-sized p a r t i c l e s were p r a c t i c a l l y n o n - e x i s t e n t ( a l l s a n d - s i z e d p a r t i c l e s a r e e s s e n t i a l l y composed

o f i r o n o x i d e and h y d r o x i d e a g g r e g a t e s ) . F u r t h e r , though a l l o p h a n e was n o t i d e n t i f i e d i n any analyses performed by t h e a u t h o r , Quinones r e p o r t e d i t s l i k e l y presence as an amorphous s o i l c o n s t i t u e n t on t h e b a s i s o f p o s i t i v e sodium

fluoride tests.

I n view o f t h e f a c t t h a t amorphous i r o n o x i d e s were i d e n t i f i e d

by t h e w r i t e r as common c o n s t i t u e n t s o f t h e pedogenic s o i l s , i t seems l i k e l y t h a t amorphous forms o f aluminum s h o u l d a l s o be p r e s e n t . Chemical a n a l y s e s o f t h e s e s o i l s i n d i c a t e d t h a t t h e y were l o w e r i n s i l i c a , alumina and i r o n o x i d e s t h a n more mature pedogenic s o i l s and c o n s i d e r a b l y h i g h e r i n l i m e (as a r e s u l t o f i n c l u d e d , p a r t i a l l y weathered l i m e s t o n e f r a g m e n t s ) . A n a l y s i s 3, T a b l e 1 i s t y p i c a l o f t h i s s t a g e o f development.

The s o i l s o f t h e

N o r t h e a s t e r n Coastal P l a i n were s i m i l a r t o t h o s e i n N o r t h w e s t e r n Yucatan, except

62 t h a t t h e y were somewhat deeper, c o n t a i n e d f e w e r l i m e s t o n e fragments and were composed o f b e t t e r c r y s t a l l i z e d k a o l i n i t e ( d i f f r a c t o g r a m 5, F i g , 2 ) .

Analyses

4 and 5 on T a b l e 1 show t h a t t h e i r more advanced s t a g e o f development i s a l s o r e f l e c t e d i n h i g h e r s i l i c a , alumina, and i r o n c o n t e n t s and l o w e r c a l c i u m l e v e l s . Quinones (1975) r e p o r t e d c a t i o n exchange c a p a c i t i e s f o r t h e s e s o i l s a t a p p r o x i m a t e l y 30 meq/100 g and d e s c r i b e d them as " O r t h i c R h o d u s t a l f s " ( V e r t i c L u v i sols).

These s o i l s have developed i n a r e g i o n o f h i g h e r r a i n f a l l , g r e a t e r

t o p o g r a p h i c r e l i e f and where d i a g e n e t i c processes have a c t e d t o t r a n s f o r m t h e c l a y s t o more p e r f e c t l y c r y s t a l l i n e k a o l i n i t e and t o e l i m i n a t e l e s s s t a b l e cons t i t u e n t s ( t a l c , boehmite and c h l o r i t e ) .

I n t h e C e n t r a l H i l l D i s t r i c t , where

r e l i e f i s g r e a t e s t and r a i n f a l l somewhat h i g h e r , a c c u m u l a t i o n o f pedogenic c l a y s f r e q u e n t l y exceeds 20 meters and t h e most advanced s t a t e o f s o i l m a t u r i t y f o r t h e r e g i o n i s found.

X-ray a n a l y s e s ( d i f f r a c t o g r a m 1, F i g . 3 ) r e v e a l e d

t h a t t h e o n l y c r y s t a l l i n e phase p r e s e n t i s k a o l i n i t e and, i n a l l cases, t h i s m i n e r a l i s p r e s e n t as t h e w e l l c r y s t a l l i z e d f o r m t h a t c h a r a c t e r i z e s pedogenic l i m e s t o n e s o i l s i n an advanced s t a g e o f development. OriginBecause o f t h e l a c k o f c l a s t i c m a t e r i a l s i n t e r b e d d e d w i t h t h e Yucatan l i m e stones, t h e pedogenic c l a y s o f t h e n o r t h e r n p e n i n s u l a can o n l y owe t h e i r o r i g i n t o t h e a c c u m u l a t i o n and a l t e r a t i o n o f t r a c e q u a n t i t i e s o f i m p u r i t i e s t h a t were

w

n

'

h

"

'

F i g . 2. X-ray d i f f r a c t o g r a m s o f r e s i d u a l s o i l s f r o m N o r t h w e s t e r n Coastal P l a i n ( a n a l y s e s 1 t h r o u g h 4) and N o r t h e a s t e r n Coastal P l a i n ( a n a l y s i s 5 ) . O r i e n t e d s l i d e s , copper K-alpha r a d i a t i o n .

63 TABLE 1 Chemical analyses o f Yucatan d e t r i t a l , pedogenic and d i r e c t c r y s t a l l i z a t i o n c l a y s . A l s o shown a r e p a l y g o r s k i t e and s e p i o l i t e analyses from o t h e r l o c a t i o n s . O e t r i t a l Clays

Res idua 1

Palygorskite-Sepiolite

OXIDE

1

2

3

4

5

6

7

8

9

Si02

45.09

47.28

20.70

30.39

40.40

45.20

62.60

60.00

61;OO

A1203

14.91

14.50

12.80

34.21

27.80

28.80

9.40

9.50

9.80

3.80

FeO +

3.68

13.10

4.40

8.92

6.70

6.20

2.50

3.70

2.70

2.3C

Fe203 CaO

7.09

3.15

21.50

1.42

2.00

0.56

0.13

0.24

0.60

0.37

MgO Na20

2.18 0.40

0.90

1.00

0.79

0.60

0.35

11.00

10.60

11.20

17.30

2.50

0.06

nr

0.05

0.05

0.03

0.02

0.03

0.34

KZO T i O2

1.26

nr

0.29

0.30

0.48

0.52

0.71

0.14

0.80

nr

0.53

1.28

1.20

1.30

0.38

0.40

0.20

0.05

42.50

21.11

20.00

18.50

20.50

20.60

20.50

22.60

L.O.I.

24.11

18.49

Mixed Layer OXIDE Si02 2'3 FeO +

Non-Yucatan P a l y g o r s k i t e - S e p i o l i t e

11

12

13

14

15

16

17

53.5

45.0

59.53

G1.60

59.09

53.98

53.03

28.0

26.3

11.58

6.82

6.84

0.20

3.34

4.28

4.34

3.47

0.87

4.21

0.01

1.67

Fe203 CaO

0.92

0.54

2.31

0.67

0.01

0.04

0.89

MgO Na20

1.2

1.8

9.63

14.22

14.12

22.80

23.43

0.15

0.50

0.35

nr

nr

0.58

1.44

0.63

0.45

0.25

nr

nr

0.16

nr

0.34

0.49

nr

nr

1.66

14.16

14.18

K20 Ti02 L.O.I.

0.43 21.0

10 64.00

21.5

nr

nr 20.00

16.15

fl (1971)

( a ) K a o l i n i t e - M o n t m o r i l o n i t e ( m o d i f i e d a f t e r Schultz, ( b ) Attapulgus, Georgia (Robertson, 1961) ( c ) P a l y g o r s k i t e , South A f r i c a (Heystek and Schmidt, 1953) ( d ) P a l y g o r s k i t e , A u s t r a l i a (Rogers,

3 aJ,

1954)

( e ) S e p i o l i t e , Nevada (Post, 1978) ( f ) S e p i o l i t e , U.S.S.R. present i n t h e p a r e n t limestones.

(Teodorovitch, 1961) X-ray d i f f r a c t i o n and i n s o l u b l e r e s i d u e

analyses have shown t h a t t h e o n l y p o s s i b l e source m a t e r i a l s were t h e m i n e r a l s talc,

c h l o r i t e , and t r a c e amounts o f s m e c t i t e and mixed-layer c l a y s .

Some

v o l c a n i c ash may a l s o have been p r e s e n t as i s ( i n d i r e c t l y ) i n d i c a t e d by t h e abundant i r o n oxides present i n these s o i l s (Quinones, 1975).

The o r i g i n s o f

t h e m i n e r a l s t a l c and c h l o r i t e a r e more f u l l y discussed i n t h e s e c t i o n d e a l i n g

64 w i t h " p r i m a r y " ( d i r e c t c r y s t a l 1 i z a t i o n ) c l a y s b u t , based on abundance5 i n t h e i n s o l u b l e r e s i d u e s , i t seems l i k e l y t h a t c h l o r i t e and p o s s i b l e s m e c t i t e c l a y s have served as t h e source m a t e r i a l f o r t h e b u l k o f t h e pedogenic c l a y s now found on t h e p e n i n s u l a .

The development o f k a o l i n i t e would p o s s i b l y a r i s e as a

consequence o f a r e a c t i o n s i m i l a r t o t h a t d e s c r i b e d by B e r n e r (1971): (smectite)

(Kaol i n i t e )

( 1 ) 4NaA1MgSi4010(OH)2 + 6H2C03%=3A14Si4010(OH)4

+ 2Mgf2 + 2Na' +6HC03- +

1OH4S iO4 The r e a c t i o n shows t h a t t h e f o r m a t i o n o f k a o l i n i t e i s f a v o r e d where t h e HC03-/ H2C03 r a t i o i s low, whereas t h e r e a c t i o n proceeds t o t h e l e f t where t h e r a t i o i s high.

The f o r m e r would be t h e expected r e s u l t i n an a r e a o f r e c e n t l y u p l i f t e d

l i m e s t o n e s undergoing chemical w e a t h e r i n g b y t h e a c t i o r l o f m e t e o r i c ( i .e., Yucatan P e n i n s u l a ) .

the

The a c t u a l f o r m a t i o n o f k a o l i n i t e f r o m e i t h e r c h l o r i t e o r

smectite parent c l a y s i s thus c o n t r o l l e d b y reactions i n v o l v i n g carbonic a c i d which, i n l i m e s t o n e t e r r a n e s , a r e e s s e n t i a l l y " s e l f b u f f e r i n g " ( s e e G a r r e l s and Dreyer, 1952).

The c o n t r o l o f pH a c t s t o moderate t h e r a t e a t w h i c h breakdown

o f t h e l i m e s t o n e and a c c u m u l a t i o n o f t h e pedogenic s o i l m a t e r i a l o c c u r s and may f u r t h e r a c t t o r e t a r d t h e a c c u m u l a t i o n o f alumina d u r i n g t h e d i s s o l u t i o n of p r i mary a l u m i n o - s i l i c a t e s ( c h l o r i t e and s m e c t i t e ) .

Under such c o n d i t i o n s , any

alumina l i b e r a t e d w i l l l i k e l y r e a c t w i t h d i s s o l v e d s i l i c a t o i n i t i a l l y form

30

20

10

F i g . 3. X-ray d i f f r a c t o g r a m s o f r e s i d u a l s o i l s f r o m C e n t r a l H i l l D i s t r i c t ( a n a l y s i s 1 ) and E a s t e r n B l o c k F a u l t D i s t r i c t ( 2 and 3 ) . O r i e n t e d s l i d e s , copp e r K-alpha r a d i a t i o n .

65 amorphous o r p o o r l y c r y s t a l l i n e k a o l i n i t e by t h e r e a c t i o n proposed b y B e r n e r (1971):

(Kaol i n i t e )

+

( 2 ) 2A1 (OH) 3amorp,

2H4Si0 5 A1 S i 0 (OH) 4aq. lo 4amorp.

For r e a c t i o n ( 2 ) t o proceed t o t h e r i g h t , maintenance o f s u f f i c i e n t c o n c e n t r a t i o n s of s i l i c a a r e r e q u i r e d , o t h e r w i s e t h e f o r m a t i o n o f k a o l i n i t e i s i n h i b i t e d and Al(OH),

persists.

I n t h e N o r t h w e s t e r n and, t o a l e s s e r e x t e n t , t h e N o r t h -

e a s t e r n Coastal P l a i n o f Yucatan where r e l i e f i s l o w and t h e r a i n f a l l l e s s t h a n one m e t e r per: y e a r , s i l i c a has been p a r t i a l l y removed and t h e r e a c t i o n has t a k e n place sluggishly w i t h the r e s u l t t h a t the s o i l s contain a mixture o f poorly c r y s t a l l i z e d k a o l i n i t e and boehmite.

I n areas o f t h i c k e r s o i l s and i n h i b i t e d

drainage, s i l i c a a c t i v i t i e s a r e m a i n t a i n e d a t h i g h e r l e v e l s t h a t i n s u r e t h a t r e a c t i o n ( 2 ) w i l l proceed t o t h e r i g h t .

Hence t h e s o i l s o f t h e C e n t r a l H i l l

D i s t r i c t l a c k boehmite and c o n s i s t , a l m o s t w h o l l y , o f w e l l c r y s t a l l i z e d k a o l i n i t e ( s e e I s p h o r d i n g , 1974). DETRITAL CLAYS Clays i n t h i s c a t e g o r y a r e l a r g e l y r e s t r i c t e d t o t h e E a s t e r n B l o c k F a u l t D i s t r i c t ( F i g . 1 ) and t o s c a t t e r e d " p o l j e - l i k e " b a s i n s t h a t l i e s o u t h o f t h e S i e r r a de T i c u l and e a s t o f Campeche.

E x c e l l e n t exposures o f t h e s e c l a y s may

a l s o be seen i n t h e S t a t e o f Q u i n t a n a Roo a l o n g t h e Escarcega-Chetumal highway. Abundant sand and s i l t - s i z e d q u a r t z , as w e l l as t h e b l a c k opaque m i n e r a l s m a g n e t i t e and i l m e n i t e , c l e a r l y r e f l e c t a d e t r i t a l o r i g i n f o r t h e s e sediments. I n c o n t r a s t t o t h e f r i a b l e t o s l i g h t l y p l a s t i c , r e d o r reddish-brown c o l o r of t h e p r e v i o u s l y d e s c r i b e d pedogenic c l a y s , t h e s e c l a y s a r e h i g h l y p l a s t i c and a r e c h a r a c t e r i s t i c a l l y g r a y , d a r k brown o r b l a c k i n c o l o r .

The l a c k o f an i d e n -

t i f i a b l e C - h o r i z o n would cause many o f t h e s e c l a y s t o b e d e s c r i b e d as "rendzinas" ("Rendolls",

u s i n g t h e 1960 Comprehensive System t e r m i n o l o g y ) .

Mineral-

o g i c a l l y , t h e s e s o i l s were dominated by s m e c t i t e , b u t a l s o c o n t a i n e d l e s s e r amounts o f k a o l i n i t e ( s e e d i f f r a c t o g r a m s 2 and 3, F i g . 3 ) .

Chemically, t h e s e

were l o w e r i n alumina and i r o n o x i d e s and h i g h e r i n a l k a l i s , l i m e , and magnesia when compared w i t h t h e pedogenic c l a y s .

T y p i c a l a n a l y s e s a r e presented i n

Table 1 ( a n a l y s e s 1 and 2 ) . Origin The o b v i o u s c l a s t i c components t h a t make up t h e s e c l a y s s t r o n g l y suggests t h a t t h e y were d e r i v e d f r o m a i r - b o r n e and sea-borne d e t r i t u s t h a t was c a r r i e d n o r t h w a r d f r o m v o l c a n i c s o u r c e l a n d s t o t h e s o u t h i n B e l i z e and C e n t r a l Guatemala.

D e p o s i t i o n l a r g e l y t o o k p l a c e i n l a k e s and i n f r i n g i n g lagoons p r i o r t o

u p l i f t o f t h e n o r t h e r n p e n i n s u l a d u r i n g t h e l a t e Neogene.

U p l i f t o f t h e east-

e r n s i d e o f t h e p e n i n s u l a and c o n c u r r e n t down-to-the-basin

faulting

trapped

66 marine w a t e r s i n b l o c k f a u l t b a s i n s , f o r m i n g s a l i n e l a k e s .

Climatic conditions

o v e r t h e p e n i n s u l a were p r o b a b l y s i m i l a r t o t h o s e c h a r a c t e r i z i n g t h e a r e a a t p r e s e n t i n t h a t a r a i n y season o f r e l a t i v e l y s h o r t d u r a t i o n ( 3 t o 4 months) was f o l l o w e d by a l o n g d r y season.

Such c o n d i t i o n s a c t e d t o p r e v e n t t h e r a p i d

transformation o f t h e smectite c l a y s t o k a o l i n i t e (formation o f t h e smectite c l a y s , themselves, i s t h o u g h t t o have l a r g e l y t a k e n p l a c e i n t h e s o u r c e l a n d s by a l t e r a t i o n o f v o l c a n i c a s h ) .

I n areas o f t h e p e n i n s u l a where r a i n f a l l was

g r e a t e r , t h e poor d r a i n a g e a s s o c i a t e d w i t h t h e s e c l a y s c r e a t e d seasonal swamps o r savannas, p e r m i t t i n g t h e c l a y s t o remain s a t u r a t e d f o r l o n g e r p e r i o d s o f time.

Such c o n d i t i o n s s i m i l a r l y r e s t r i c t t h e removal o f c a t i o n s and l e a d t o

t h e meta-stable persistence o f smectite.

No such s m e c t i t e c l a y s a r e p r e s e n t

i n t h e modern l a k e s o f t h e p e n i n s u l a (Lake B a c a l a r , Lake Chichankanab, e t c . ) r e f l e c t i n g t h e absence o f a s u i t a b l e source m a t e r i a l ( i . e . ,

volcanic ash).

These l a k e s a r e composed o f b o t t o m sediments dominated b y c a r b o n a t e s and m i n o r 9Y PS um * PRIMARY CLAYS (DIRECT CRYSTALLIZATION) W i t h o u t q u e s t i o n , t h e most unusual m i n e r a l s f o u n d on t h e Yucatan P e n i n s u l a a r e v a r i o u s forms o f magnesium s i l i c a t e s and a l u m i n o - s i l i c a t e s t h a t a r e b e s t i n t e r p r e t e d as h a v i n g Yormed by processes i n v o l v i n g d i r e c t c r y s t a l l i z a t i o n . S p e c i f i c a l l y , these include:

c h l o r i t e , t a l c , p a l y g o r s k i t e , s e p i o l i t e and mont-

morillonite. T a l c and C h l o r i t e Bodine (1972) i d e n t i f i e d t a l c and c h l o r i t e as a u t h i g e n i c p r o d u c t s i n marine, h y p e r s a l i n e sediments i n t h e e a s t e r n Caribbean.

T h e i r presence was a t t r i b u t e d

t o t h e h y p e r h a l m y r o l i c response o f t e r r i g e n e o u s sediments t o t h e h i g h magnesium a c t i v i t i e s o f hypersaline waters.

I n Yucatan, n e i t h e r t a l c n o r c h l o r i t e has

been i d e n t i f i e d i n macroscopic f o r m b u t b o t h a r e commonly d e t e c t e d i n X-ray a n a l y s e s o f b o t h t h e c a r b o n a t e r o c k s and t h e pedogenic s o i l s o f t h e n o r t h e r n p e n i n s u l a ( e s p e c i a l l y i n t h e N o r t h w e s t e r n Coastal P l a i n D i s t r i c t ) .

Their close

a s s o c i a t i o n w i t h d o l o m i t i c r o c k s s t r o n g l y suggests t h a t t h e y have formed b y d i r e c t c r y s t a l l i z a t i o n as a consequence o f t h e d i a g e n e t i c a l t e r a t i o n o f t h e d o l o mite.

S u p p o r t f o r t h i s i s seen i n t h e X-ray d i f f r a c t o g r a m s w h i c h possess s t r o n g

f i r s t and t h i r d o r d e r r e f l e c t i o n s , i n d i c a t i n g t h a t t h e c h l o r i t e i s an i r o n - p o o r (magnesium-rich) v a r i e t y .

Two p o s s i b l e r e a c t i o n s a r e suggested b y t h e w r i t e r

t o e x p l a i n t h e presence o f t a l c : (1)

4H4Si04 + H20 + 3 C a M g ( C 0 3 ) 2 ~ M g 3 S i , 0 1 0 ( O H ) 2

A

FR = -13.35

+ 3CaC03 + 3C02

67 (2)

3Mg+2 + H20

+

6HC03-l

+

4H4Si04S=izMg3Si4010(OH)2 + 3H20 + 6H2C03

A F = ~-25.8 Reaction ( 1 ) forms t a l c by t h e a c t i o n o f s i l i c a - b e a r i n g groundwaters on d o l o mite; r e a c t i o n ( 2 ) d e r i v e s t h e m i n e r a l b y d i r e c t c r y s t a l l i z a t i o n f r o m groundwater s o l u t i o n s .

Because no t h i n s e c t i o n e v i d e n c e has been observed showing

d o l o m i t e a l t e r i n g t o t a l c , i t i s l i k e l y t h a t t h e m i n e r a l has formed by a r e action s i m i l a r t o (2).

The d i a g e n e t i c i n v e r s i o n o f h i g h naonesium c a l c i t e t o

low magnesium c a l c i t e would s u p p l y t h e needed magnesium which, i n t u r n , would r e a c t w i t h s i l i c a and c a r b o n i c a c i d i n t h e p o r e waters t o f o r m t a l c .

The f o r -

mation o f t h e magnesium c h l o r i t e s c o u l d i n v o l v e a s i m i l a r process and d i f f e r o n l y i n t h e r e q u i r e d a c t i v i t i e s o f magnesium, s i l i c a and alumina.

The j o i n t

occurrence o f t h e two m i n e r a l s i n d i a g e n e t i c a l l y a l t e r e d d o l o m i t e s t h r o u g h o u t the northern peninsula a l s o supports t h i s conclusion.

The p e r s i s t e n c e of b o t h

m i n e r a l s i n t h e y o u t h f u l pedogenic s o i l s o f t h e N o r t h w e s t e r n Coastal P l a i n can probably be a t t r i b u t e d t o t h e l o w r a i n f a l l e x p e r i e n c e d by t h i s p a r t of t h e peninsula.

To t h e south, and e a s t , where r a i n f a l l l e v e l s a r e g r e a t e r , b o t h

m i n e r a l s a r e absent as s o i l c o n s t i t u t e n t s . Palygorskite-Sepiolite C l a y s Occurrence.

Unlike the "attapulgite" (palygorskite) deposits o f the

G e o r g i a - F l o r i d a r e g i o n o f t h e U n i t e d S t a t e s , t h e p a l y g o r s k i t e and p a l y g o r s k i t e s e p i o l i t e c l a y s o f Yucatan o c c u r as i s o l a t e d , r e l a t i v e l y t h i n l e n s e s t h a t a r e r a r e l y t r a c e a b l e f o r more t h a n a few t e n s o f meters, l a t e r a l l y ( s e e l o c a t i o n map, F i g . 4 ) .

Further, i n c o n t r a s t t o t h e deposits i n eastern United States,

those i n Yucatan a r e n o t f o u n d i n t e r b e d d e d w i t h p h o s p h a t i c sediments and smect i t e c l a y s b u t r a t h e r o c c u r as c o n f o r m a b l e l e n s e s o r " p l u g l i k e " d e p o s i t s w i t h i n dolomites.

I n appearance, t h e s e c l a y s a r e w h i t e t o t a n i n c o l o r , range f r o m a

few m i l l i m e t e r s t o o v e r one m e t e r i n t h i c k n e s s and do n o t c o n t a i n any macroscopic d e t r i t a l components.

Schultz,

g fi (1971)

have r e p o r t e d t h e presence

o f rounded g r a i n s o f q u a r t z i n t h e f i n e s i l t f r a c t i o n o f s p a t i a l l y r e l a t e d clays, thus i t i s possible t h a t f u t u r e d i l i g e n t searching might a l s o reveal similar material i n t h e palygorskite clays. History.

Van Olphen (1966) f i r s t n o t e d t h a t c e r t a i n c l a y s i n Yucatan

were used as components i n an unusual pigment known a s "Maya B l u e " t h a t was manufactured by t h e pre-Columbian I n d i a n s o f t h e r e g i o n .

A r n o l d (1967, 1971)

l a t e r i d e n t i f i e d t h e m i n e r a l as " a t t a p u l g i t e " and f u r t h e r commented on i t s i m portance as an i n g r e d i e n t i n pre-Columbian ( a n d p r e s e n t day) ceramicware.

The

m i n e r a l was t h u s known t o t h e Maya I n d i a n s hundreds o f y e a r s b e f o r e t h e coming o f t h e f i r s t Europeans and was termed Sac l u ' u m (Maya f o r " w h i t e e a r t h " ) by t h e indigenous p o t t e r s .

Because of i t s l i m i t e d w a t e r a b s o r b i n g p r o p e r t i e s i t was

68 mixed w i t h o t h e r c l a y s t o add s t r e n g t h t o ceramicware; when mixed w i t h i n d i g o , i t produced a d i s t i n c t i v e , h i g h l y p r i z e d , o r g a n i c pigment (Maya B l u e ) which was

w i d e l y disseminated t h r o u g h o u t t h e r e g i o n as a t r a d e w a r e i t e m .

One v i l l a g e i n

t h e a o r t h e r n p e n i n s u l a , Sacalum ( a Spanish c o r r u p t i o n o f Sac l u ' u m ) , has appar e n t l y served as a major source o f t h i s c l a y f o r o v e r 800 y e a r s !

Here t h e c l a y

occurs as a l e n s a p p r o x i m a t e l y one meter t h i c k and i s l o c a t e d a t t h e b o t t o m of a large

c e n o t e some 15 meters below t h e ground s u r f a c e .

Access t o t h e d e p o s i t

i s p r o v i d e d b y means o f s t a i r s c a r v e d i n t o t h e s i d e o f t h e c e n o t e and an e x c e l l e n t d e s c r i p t i o n o f t h e s i t e may be f o u n d i n t h e d i s c u s s i o n by Bohor ( 1 9 7 5 ) .

It

i s i n t e r e s t i n g t o n o t e t h a t a l t h o u g h p a l y g o r s k i t e was a v a l u a b l e t r a d e i t e m , p r i z e d by a n c i e n t Maya p o t t e r s , t h e y d i d n o t , i n f a c t , c o n s i d e r i t as a t r u e "clay".

The Maya word f o r c l a y i s

k'at and,

a l t h o u g h t h e p a l y g o r s k i t e does be-

come s o f t and p l i a b l e when wet, i t a p p a r e n t l y possessed o t h e r p h y s i c a l p r o p e r t i e s t h a t p e r m i t t e d i t s d i s t i n c t i o n f r o m o t h e r c l a y s t h a t were r o u t i n e l y used f o r ceramic purposes ( A r n o l d , 1 9 6 7 ) .

F i g . 4. G e o l o g i c map o f t h e Yucatan P e n i n s u l a showing l o c a t i o n o f p a l y g o r s k i t e and s e p i o l it e c l a y s .

69

M i n e r a l o g y and Chemistry.

X-ray d i f f r a c t i o n a n a l y s e s c a r r i e d o u t on

c l a y s c o l l e c t e d a t Sacalum c o n f i r m e d A r n o l d ' s c o r r e c t i d e n t i f i c a t i o n o f t h e m i n e r a l as p a l y g o r s k i t e ( s e e I s p h o r d i n g , 1973).

Though n o t r e p o r t e d by Arnold,

t h e m i n e r a l s e p i o l i t e was a l s o p r e s e n t i n one sample c o l l e c t e d near t h e base o f the lens.

T h i s m i n e r a l , w h i l e u s u a l l y encountered o n l y i n t r a c e amounts, d i d

c o n s t i t u t e t h e dominant m i n e r a l i n s e v e r a l samples c o l l e c t e d n e a r t h e Maya r u i n s o f Etzna.

Where p a l y g o r s k i t e was t h e c h i e f m i n e r a l , t h e c l a y s were s o f t ,

p l a s t i c when wet, and l a c k e d any appearance o f bedding; where s e p i o l i t e was dominant, t h e : c l a y s were t o t a l l y n o n p l a s t i c and c o n s i s t e d o f p a p e r - t h i n l a y e r s . Chemical a n a l y s e s o f t h e Yucatan p a l y g o r s k i t e - s e p i o l i t e c l a y s a r e p r e s e n t e d i n Table 1.

Analyses 7, 8, and 9 a r e t y p i c a l o f t h e p a l y g o r s k i t e - r i c h c l a y s

whereas 10 i s f r o m t h e s e p i o l i t e l e n s n e a r Etzna.

When compared w i t h analyses

f r o m elsewhere i n t h e w o r l d , t h e Yucatan p a l y g o r s k i t e c l a y s a r e seen t o be s i m i l a r , c h e m i c a l l y , whereas t h e Yucatecan s e p i o l i t e ( w h i c h c o n t a i n e d some p a l y g o r s k i t e ) was r i c h e r i n s i l i c a and alumina and l o w e r i n magnesia.

D e t a i l e d de-

s c r i p t i o n s and l i t h o l o g i c s e c t i o n s o f s e v e r a l o f t h e p a l y g o r s k i t e l o c a l i t i e s i n n o r t h e r n Yucatan may be f o u n d i n Bohor ( 1 9 7 5 ) . Origin.

E x c l u d i n g t h e p r e v i o u s l y d i s c u s s e d pedogenic and d e t r i t a l

c l a y s , a l l o t h e r s on t h e p e n i n s u l a a r e l i k e l y t o have formed b y d i r e c t c r y s t a l l i z a t i o n e i t h e r from marine waters o r during diagenesis o f dolomites.

T h i s con-

c l u s i o n has been s u p p o r t e d b y a number o f p r i o r i n v e s t i g a t i o n s , most o f which were d i r e c t e d toward t h e genesis o f t h e p a l y g o r s k i t e c l a y s ( s e e I s p h o r d i n g , 1973; Bohor, 1375; DePablo, 1976).

One c o n t r o v e r s y s t i l l e x i s t s , however, and

i n v o l v e s a mixed l a y e r kaolinite-montmorillonite t h a t was i d e n t i f i e d by S c h u l t z , _ et _ a1 (1971) f r o m t h r e e l o c a t i o n s i n t h e n o r t h e r n p e n i n s u l a .

These c l a y s were

d e s c r i b e d as o c c u r r i n g i n l e n s e s 1 t o 2 m e t e r s t h i c k w i t h i n e n c l o s i n g l i m e stones, c o n t a i n e d l i t t l e q u a r t z and were o f h i g h p u r i t y ( a n a l y s e s 11 and 12, Table l ) , and were a t t r i b u t e d an o r i g i n by t h e w e a t h e r i n g o f v o l c a n i c ash. Though S c h u l t z , _ et_ a1 _(1971) concede t h a t such an o r i g i n i s " h i g h l y s p e c u l a t i v e ; t h e y l i s t s e v e r a l l i n e s o f e v i d e n c e t h a t , t h e y b e l i e v e , s u p p o r t such an o r i g i n . If t h e s e mixed l a y e r c l a y s are, i n f a c t , d e r i v e d by a l t e r a t i o n o f v o l c a n i c ash,

i t would have an i m p o r t a n t b e a r i n g on t h e o r i g i n o f t h e p a l y g o r s k i t e - s e p i o l i t e c l a y s because:

( 1 ) a t l e a s t i n one case p a l y g o r s k i t e c l a y s a r e f o u n d i n c l o s e

p r o x i m i t y t o one o f . t h e m i x e d - l a y e r s i t e s and ( 2 ) i t has been argued t h a t some p a l y g o r s k i t e s elsewhere i n t h e w o r l d have formed by a l t e r a t i o n o f p y r o c l a s t i c m a t e r i a l s ( s e e G r i m , 1933; G r e m i l l i o n , 1965). One s t r o n g argument a g a i n s t a v o l c a n i c o r i g i n f o r t h e m i x e d - l a y e r c l a y s (and t h e p a l y g o r s k i t e - s e p i o l i t e c l a y s ) i s t h e l a c k o f any s i g n i f i c a n t amount o f ash i n t h e rocks o f t h e northern peninsula.

A s e a r c h f o r t h i s m a t e r i a l has been

c a r r i e d on f o r y e a r s , p r i n c i p a l l y by a r c h a e o l o g i s t s i n t e r e s t e d i n e s t a b l i s h i n g

70 t h e o r i g i n o f " v o l c a n i c ash" temper t h a t has been i d e n t i f i e d i n p o t t e r y f r a g ments from some s i t e s i n t h e r e g i o n . that

...."The

B r a i n e r d (1958) a d m i t t e d , however, ( p . 70)

sources o f v o l c a n i c ash temper i n Yucatan have n o t been l o c a t e d "

and . . . . I ' t h e q u a n t i t i e s o f t h i s m a t e r i a l which must have been used . . . . . p r e c l u d e t h e p o s s i b i l i t y of i m p o r t a t i o n o f v o l c a n i c ash f r o m t h e n e a r e s t a r e a s where volcanism now occurs, a d i s t a n c e o f some 509 k i l o m e t e r s . "

F u r t h e r , Shepard

(1952), i n a d i s c u s s i o n o f l o c a l Yucatecan p o t t e r y , n o t e d ( p . 264-265).

..."The

ash i n a l l these s e c t i o n s i s comparable i n f o r m and i n sparseness and f i n e n e s s of mineral i n c l u s i o n s

.....As

t y p e o f ash i n Yucatan."

o f y e t we:have no c l u e t o t h e o c c u r r e n c e o f t h i s

As n o t e d i n an e a r l i e r paper ( I s p h o r d i n g and W i l s o n ,

1974), because t h e presence o f any s i g n i f i c a n t q u a n t i t i e s o f ash i s d o u b t f u l , either:

( 1 ) t h e m a t e r i a l i d e n t i f i e d by v a r i o u s a r c h a e o l o g i s t s as ash i f i n d i -

genous i s , i n f a c t , some o t h e r m a t e r i a l ( t h e f i n e g r a i n e d p a l y g o r s k i t e s o r t h e m i x e d - l a y e r c l a y s a r e l i k e l y c a n d i d a t e s ) o r ( 2 ) t h e p o t t e r y i s non-indigenous tradeware. F u r t h e r arguments a g a i n s t a v o l c a n i c o r i g i n can be r a i s e d by examining e v i dence used b y S c h u l t z , eJaJ

(1971) and t h e n c o n s i d e r i n g p o s s i b l e a l t e r n a t i v e s .

F o r example, t h e y proposed t h a t a v o l c a n i c ash f a l l d u r i n g t h e Eocene ( p . 139)

...."seems

t h e most l i k e l y p r e c u r s o r o f t h e c l a y beds because ( 1 ) v o l c a n i c ash

o r m o n t m o r i l l o n i t e derived from i t i s the parent m a t e r i a l o f t h e mixed-layer

kaolinite-montmorillonite i n F l o r i d a and Japan, ( 2 ) many v o l c a n i c ashes and b e n t o n i t e 5 d e r i v e d t h e r e f r o m a r e v e r y l o w i n q u a r t z , as a r e t h e Yucatecan c l a y s , ( 3 ) much v o l c a n i c d e b r i s o c c u r s i n t h e T e r t i a r y r o c k s o f t h e G u l f o f Mexico r e g i o n , and ( 4 ) because an ash f a l l i s one o f t h e few r e a s o n a b l e mechanisms f o r i n t r o d u c i n g n e a r l y p u r e a l u m i n o - s i l i c a t e m a t e r i a l i n t o a s e d i m e n t a r y sequence dominated b y carbonate r o c k s .

I'

Regarding p o i n t (l), t h e w r i t e r knows o f no m i x e d - l a y e r c l a y s i n F l o r i d a w i t h a proven v o l c a n i c o r i g i n .

On t h e c o n t r a r y , most e v i d e n c e t o d a t e has

argued a g a i n s t any m a r i n e o r a i r b o r n e t r a n s p o r t o f v o l c a n i c ash f r o m sources i n western U n i t e d S t a t e s o n t o t h e F l o r i d a P l a t f o r m .

Strong supporting evidence

f o r t h i s i s f o u n d i n t h e s t r i k i n g l y d i f f e r e n t m i n e r a l s u i t e s found i n e a s t e r n , c e n t r a l and western G u l f Coast Miocene sediments (see I s p h o r d i n g , 1971, 1973). I t would be d i f f i c u l t , a t b e s t , t o e x p l a i n how w e s t e r n - d e r i v e d v o l c a n i c d e b r i s

c o u l d be d e p o s i t e d on t h e F l o r i d a P l a t f o r m and subsequently "weather" t o p a l y g o r s k i t e , s e p i o l i t e and m i x e d - l a y e r c l a y s , w h i l e b e i n g c o m p l e t e l y a b s e n t i n contemporaneous sediments i n e a s t e r n M i s s i s s i p p i , Alabama and w e s t e r n F l o r i d a . S i m i l a r l y , p o i n t (2),

t h e l o w q u a r t z c o n t e n t o f Yucatecan c l a y s , c o u l d a l s o

be e x p l a i n e d b y t h e f o r m a t i o n o f t h e s e m i n e r a l s i n an area c h a r a c t e r i z e d by n e g l i g i b l e c l a s t i c sedimentation.

Such i s f r e q u e n t l y t h e case where m i n e r a l s

a r e formed by d i r e c t c r y s t a l l i z a t i o n on a submerged c a r b o n a t e s h e l f environment.

71 As a case i n p o i n t , t h e b o t t o m sediments o f t h e p r e s e n t submerged p o r t i o n o f t h e Yucatan P l a t f o r m c o n t a i n n e g l i g i b l e amounts o f q u a r t z because t h e y l i e a g r e a t d i s t a n c e f r o m any source o f such m a t e r i a l .

F u r t h e r t o t h e south, as t h e d e l t a

o f t h e Usumacinta R i v e r i s approached, q u a r t z becomes i n c r e a s i n g l y more common and c a r b o n a t e sediments l a r g e l y d i s a p p e a r . The abundance o f v o l c a n i c ash i n G u l f Coast T e r t i a r y sediments ( p o i n t 3 ) i s n o t argued by t h e w r i t e r .

Numerous s t u d i e s have c l e a r l y i d e n t i f i e d v o l c a n i c

sources f o r s p e c i f i c G u l f Coast f o r m a t i o n s ( s e e McBride, Lindemann and Freeman, 1968).

The w r i t e r would, however, argue t h e e x i s t e n c e o f any such m a t e r i a l e a s t

o f t h e S t a t e o f M i s s i s s i p p i f o r reasons a l r e a d y s t a t e d .

F u r t h e r , assuming t h a t

p a s t wind d i r e c t i o n s were n o t g r e a t l y d i f f e r e n t from t h o s e o f t h e p r e s e n t , t h e p r i n c i p a l sources f o r such p y r o c l a s t i c d e b r i s on t h e Yucatan P l a t f o r m would l i e hundreds o f m i l e s t o t h e e a s t , i n Jamaica, H i s p a n i o l a and t h e A n t i l l e s .

I n the

e v e n t t h a t such t r a n s p o r t d i d t a k e place, t h e n o t h e r s u p p o r t i n g e v i d e n c e should a l s o be p r e s e n t .

T h i s would i n c l u d e g l a s s shards, m i c r o l i t e s o r c r y s t a l l i t e s ,

as w e l l as s i l t - s i z e d , pyroxene o r z i r c o n .

euhedral o r subhedral g r a i n s o f amphibole, p l a g i o c l a s e , These m a t e r i a l s a r e a b u n d a n t l y p r e s e n t i n o l d e r T e r t i a r y

f o r m a t i o n s i n t h e w e s t e r n G u l f Coast o f t h e U n i t e d S t a t e s t h a t a r e known t o have been, i n p a r t , d e r i v e d f r o m v o l c a n i c sources (see Swineford, F r y e and Leonard, 1955; McBride, Lindemann and Freeman, 1968). R e f e r r i n g t o p o i n t ( 4 ) , and ash f a l l i s

not

t h e o n l y " r e a s o n a b l e mechanism"

f o r i n t r o d u c i n g p u r e a l u m i n o - s i l i c a t e m a t e r i a l i n t o a sedimentary b a s i n domin a t e d by c a r b o n a t e r o c k s .

Jeans (1971) n o t e d t h a t each y e a r an e s t i m a t e d 475

m i l l i o n t o n s o f alumina and s i l i c a a r e c a r r i e d i n s o l u t i o n and d e p o s i t e d i n t r a n s i t i o n a l m a r i n e environments.

Areas a d j a c e n t t o t e r r a c e s

undergoing t r o p i -

c a l w e a t h e r i n g r e c e i v e a d i s p r o p o r t i o n a t e s h a r e o f t h i s t o t a l because o f t h e r i g o r o u s w e a t h e r i n g regimen t h a t c h a r a c t e r i z e s such r e g i o n s .

The a l k a l i n e pH

o f t h e m a r g i n a l m a r i n e w a t e r s t h e n i n s u r e s t h a t a s i z e a b l e p r o p o r t i o n of t h e i o n s w i l l be p r e c i p i t a t e d i n t h e f o r m o f alumina and s i l i c a h y d r o x i d e g e l s and colloids.

Such c o n d i t i o n s c o u l d , t h u s , e x p l a i n t h e h i g h p u r i t y o f t h e "source

m a t e r i a l s " o f t h e m i x e d - l a y e r (and p a l y g o r s k i t e - s e p i o l i t e ) c l a y s of Yucatan and would a v o i d problems i n e x p l a i n i n g t h e l a c k o f any s i g n i f i c a n t q u a n t i t i e s o r known d e p o s i t s o f remnant ash on t h e p e n i n s u l a .

Even where ash has been t h o u g h t

t o be o f importance.as an u l t i m a t e s o u r c e m a t e r i a l (such as t h e d e t r i t a l c l a y s

o f t h e E a s t e r n B l o c k F a u l t D i s t r i c t ) , t h e m a t e r i a l d e p o s i t e d i s b e l i e v e d t o have a l r e a d y been t r a n s f o r m e d t o s m e c t i t e c l a y p r i o r t o i t s d e p o s i t i o n (and c o n t a i n s abundant q u a r t z and heavy m i n e r a l s as " i m p u r i t i e s " ) . Conclusions.

Based on t h e p r e c e e d i n g evidence, t h e w r i t e r b e l i e v e s

t h a t t h e p a l y g o r s k i t e - s e p i o l i t e c l a y s of Yucatan and t h e p a r e n t m a t e r i a l f o r t h e m i x e d - l a y e r c l a y s formed by d i r e c t c r y s t a l l i z a t i o n i n m a r g i n a l b a s i n s and lagoons, a d j a c e n t t o a l i m e s t o n e t e r r a c e t h a t was s l o w l y emerging from t h e sea.

72 D i r e c t c r y s t a l l i z a t i o n as a mechanism f o r t h e f o r m a t i o n o f such c l a y s i s n o t without precedent.

M c C l e l l a n (1964) argued a g a i n s t a v o l c a n i c o r i g i n f o r t h e

F l o r i d a - G e o r g i a " F u l l e r s E a r t h " d e p o s i t s as d i d a l s o Post (1978) f o r f o u r s e p i o l i t e d e p o s i t s near Las Vegas, Nevada.

S i m i l a r l y , M i l l o t (1970) c a l l e d

upon d i r e c t c r y s t a l l i z a t i o n t o e x p l a i n a seaward s u c c e s s i o n o f m o n t m o r i l l o n i t e , p a l y g o r s k i t e and s e p i o l i t e t h a t o c c u r s i n T e r t i a r y b a s i n s i n West A f r i c a . M i l l o t n o t e d t h a t as l o n g as s u f f i c i e n t a l u m i n a was p r e s e n t , m o n t m o r i l l o n i t e was t h e s t a b l e phase t o c r y s t a l l i z e .

F u r t h e r seaward i n t h e b a s i n , where

alumina a c t i v i t i e s were lower, m o n t m o r i l l o n i t e was r e p l a c e d b y p a l y g o r s k i t e and, f i n a l l y , s e p i o l i t e where alumina was absent.

The e x p l a n a t i o n o f f e r e d by M i l l o t ,

i n which t h e f o r m a t i o n o f t h e t h r e e m i n e r a l s i s a f u n c t i o n o f magnesium, s i l i c a , and a l u m i n a a c t i v i t i e s , i s e s p e c i a l l y a t t r a c t i v e f o r t h e Yucatan c l a y s because i t e l i m i n a t e s t h e problem o f e x p l a i n i n g why m i x e d - l a y e r c l a y s formed by weatheri n g o f ash a t one s i t e w h i l e a s h o r t d i s t a n c e away n e a r l y p u r e p a l y g o r s k i t e was f o r m i n g i n contemporaneous sediments b y w e a t h e r i n g o f t h e same " a s h " .

Bohor

(1975) has e l e g a n t l y e x p l a i n e d t h e c l o s e s i m i l a r i t y between Yucatecan and F l o r i d a p a l y g o r s k i t e c l a y s by u t i l i z i n g a model t h a t p o s t u l a t e s t h a t Yucatan and F l o r i d a were once i n c l o s e p r o x i m i t y d u r i n g t h e Mesozoic.

A s t h e two a r e a s

s l o w l y began t o move away f r o m each o t h e r , as a consequence o f p l a t e movement, s i m i l a r t y p e s o f sediments were f o r m i n g i n t h e two a r e a s i n b a c k - r e e f , environments.

lagoonal

The m i x e d - l a y e r k a o l i n i t e - m o n t m o r i l l o n i t e c l a y s may have o r i g i -

n a l l y p r e c i p a t e d as m o n t m o r i l l o n i t e s ( i n response t o l o c a l l y h i g h e r a l u m i n a c o n c e n t r a t i o n s ) whereas t h e p a l y g o r s k i t e c l a y s (and s e p i o l i t e s ) r e p r e s e n t e d l o w e r a c t i v i t i e s of alumina.

The t r a n s f o r m a t i o n o f m o n t m o r i l l o n i t e t o t h e

m i x e d - l a y e r s t r u c t u r e may have o c c u r r e d a t a l a t e r t i m e ( d i a g e n e t i c a l l y ) by t h e a c t i o n o f a c i d groundwaters,

by t h e mechanism suggested f o r s i m i l a r c l a y s

i n F l o r i d a b y G r e m i l l i o n (1965). REFERENCES

Arnold, D., 1967. Sak Lu'um i n Maya c u l t u r e : and i t s p o s s i b l e r e l a t i o n t o Maya B l u d . U n p u b l i s h G d - P m T h e s i s , Dept. o f Anthropology, U n i v . o f I l l i n o i s , 53 p. A r n o l d , D., 1971. Ethnomineralogy o f T i c u l Yucatan p o t t e r s . Am. A n t i q u i t y , 36: 20-40. Berner, R., 1971. P r i n c i p l e s o f Chemical S e d i m e n t a t i o n . McGraw-Hill, New York, 191 p. Bodine, M., 1972. Layer s i l i c a t e s i n t h e modern m a r i n e h y p e r s a l i n e environment. Abs., 2 1 s t Clay M i n e r a l s Conf., 9 t h Ann. Mtg., Clay M i n e r a l s SOC., p. 19. Bohor, 8. F., 1975. A t t a p u l g i t e i n Yucatan. In: Guidebook FT-4, 1975 I n t . C l a y Conf., I n s t . Geol., Univ. Nat. de Mexico, L. DePablo, Ed., p. 95-125. B r a i n e r d , G., 1958. The a r c h a e o l o g i c a l ceramics o f Yucatan. U n i v . o f Cal i f o r n i a , A n t h r o p o l o g i c a l Records: 36, 374 p. DePablo, L., 1976. A t a p u l g i t a s e d i m e n t a r i a m a r i n a de Yucatan, Mexico. I n s t . de Geologia, B o l e t i n 96, Univ. Nac. Autonoma de Mexico, 3-30. G a r r e l s , R. and R. Dreyer, 1952. Mechanism o f l i m e s t o n e r e p l a c e m e n t a t l o w temp e r a t u r e s and p r e s s u r e s . B u l l . Geol. SOC. Amer., 63:325-380.

73 Heystek, H. and E. Schmidt, 1953. The m i n e r a l o g y o f t h e a t t a p u l g i t e - m o n t m o r i l l o n i t e d e p o s i t s i n t h e Springbok F l a t s , T r a n s v a a l . Trans. Geol. SOC. Amer., 56: 99-115. I s p h o r d i n g , W . C., 1971. Provenance and p e t r o g r a p h y o f G u l f Coast Miocene s e d i ments. I n : G e o l o g i c a l Review o f N o r t h F l o r i d a M i n e r a l Resources. Southe a s t e r n Geol. Zoc. 1 5 t h F i e l d Conf., 43-54. I s p h o r d i n g , W. C., 1973. D i s c u s s i o n o f t h e o c c u r r e n c e and o r i g i n o f sedimentary p a l y g o r s k i t e - s e p i o l i t e d e p o s i t s . Clays Clay M i n e r . , 21: 391-401. I s p h o r d i n g , W. and E. Wilson, 1974. The r e l a t i o n s h i p of " v o l c a n i c ash", Sak Lu'um and p a l y g o r s k i t e i n n o r t h e r n Yucatan Maya ceramics. Am. A n t i q u i t y , m83-488. Jean, C., 1971. The n e o f o r m a t i o n o f c l a y m i n e r a l s i n b r a c k i s h and m a r i n e e n v i ronments. : C l a y s Clay Miner., 9: 209-217. McBride, E., W. Lindemann and P. Freeman, 1968. L i t h o l o g y and P e t r o l o g y o f t h e Guedan ( C a t a h o u l a ) F o r m a t i o n i n South Texas. Bur. Econ. Geol. I n v e s t . 63, 122 p. M c C l e l l a n , G., 1964. P e t r o l o g y o f A t t a p u l g u s Clay i n N o r t h F l o r i d a and Southwest Georgia. Unpublished Ph.D. Thesis, Dept. o f Geology, U n i v . o f I l l i n o i s , 127 p. M i l l o t , G., 1970. Geology o f Clays. S p r i n g e r - V e r l a g , New York, 429 p. Post, J . , 1978. S e p i o l i t e d e p o s i t s o f t h e Las Vegas, Nevada area. Clays C l a y Miner., 26: 58-64. Quinones, H., 1975. S o i l s t u d y area 4. I n t r a z o n a l s o i l s o f n o r t h e r n Yucatan P e n i n s u l a . I n : Guidebook FT-4, 1975 I n t . Clay Conf., I n s t . Geol., U n i v . Nat. de Mexico, L. DePablo, Ed., 70-93. Robertson, R., 1961. The o r i g i n o f E n g l i s h F u l l e r s E a r t h s . Min. Mag., 4: 282'287. P a l y g o r s k i t e f r o m Queensland. Rogers, L., A. M a r t i n and K. N o r r i s h 1954. Min. Mag., 30: 534-540. S c h u l t z , L., A. Shepard, P. Blackmon and H. Starkey, 1971. M i x e d - l a y e r k a o l i n i t e - m o n t m o r i l l o n i t e f r o m t h e Yucatan Peninsula, Mexico. Clays Clay Miner., 19: 137-150. Shepard, A., 1952. Ceramic t e c h n o l o g y . Carnegie I n s t i t u t i o n o f Washington Yearbook 51, 263-266. Swineford, A., J. F r y e and A. Leonard, 1955. P e t r o g r a p h y o f t h e l a t e T e r t i a r y v o l c a n i c ash f a l l s i n t h e c e n t r a l G r e a t P l a i n s . Sed. P e t r o l . , 54: 829-838. A u t h i g e n i c M i n e r a l s i n Sedimentary Rocks ( T r a n s l a t i o n ) . T e o d o r o v i t c h , G. 1961. C o n s u l t a n t s Bureau, New York, 120 p. Van Olphen, H., 1966. Maya Blue: c l a y - o r g a n i c pigment. Science., 154: 645467.

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75

PALYGORSKITE IN THE TERTIARY DEPOSITS OF THE ARMORICAN MASSIF *

J.

ESTEOULE-CHOUX

Laboratoire de Gdologie G. 4 , UniversitP de RENNES I, Campus de Beaulieu, Avenue du General Leclerc 35042 RENNES C6dex - FRANCE ABSTRACT I n the Armorican Massif, palygorskite has been found in Eocene and Oligo-

cene deposits, in marine, transitional marine and lacustrine depositional environments.

The palygorskite occurs in layers containing either exclusively

clays or carbonates (dolomite, or calcite).

The palygorskite is sometimes

alone, sometimes closely associated with a ferriferous illite, and most rarely with smectite. When palygorskite is associated with iron rich illites, the genesis of these two minerals can be considered as a manifestation of the antagonism A1-Mg, and this paragenesis is regulated by the iron content of the depositional environment. When palygorskite is associated with smectite, transitional textures were never identified by electron microscopy.

This suggests that

palygorskite has formed by precipitation from solution. I n all the cases, palygorskite is formed by direct precipitation in lagoons and in shallow marine waters of elevated salinity: the chemical character

cf the sedimentation is determined by water depth, a climate favourable to an intense evaporation and the absence of tectonic activity, prohibiting the arrival of coarse terrigenous material.

The source of the necessary ions was the

deep lateritic weathering of the different rocks of the Armorican Massif. INTRODUCTION Palygorskite has been identified in many Tertiary deposits of the Armorican Massif (Estgoule-Choux, 1 9 6 7 ) . and at Stampian (Fig. 1 ) .

It appears at Upper Lutetian, at Bartonian

At Upper Lutetian and at Bartonian, palygorskite

occurs in the clayey beds and also in the marly beds which complete the filling of the Campbon basin.

This basin seems to have behaved itself like a residual

shallow gulf: in this continually subsiding gulf the sea has deposited thirty meters of sediments without any detrital particles. basin became continental. in.

During the Bartonian the

In the Oligocene deposits, palygorskite appears aga-

It is a constituent of the clayey beds interbedded in the limestones of

the Upper serie of the Stampian of Saffrg. Palygorskite is also present in the "Calcaires a Archiacines" where it is associated with a smectite, and in the clays of the Stampian of Langon, St. SBglin and Loutehel. * Presented at the International Clay Conference 1981

I n these three ba-

76

Fig. 1.

Localisation and age of the palygorskite deposits of the Armorican Massif.

77

sins, palygorskite is closely associated with iron-rich illite (this illite contains between 10 and 15pb of Fe 0 ) . This paragenesis of palygorskite-ferri2 3 ferous illite is present in all the samples but the proportions of each of these two minerals vary. These basins mark out the traces of an old marine g u l f oriented SouthEast, North-West, exZending from the Basse Loire to the Bay of St. Brieuc.

In

this gulf, the subsidences were localized but important and they allowed the deposition of sediments many maters thick: 331 m for instance at SaffrE (Borne, 1978) where the age of the bottom layers is Upper Lutetian.

These Eocene and Oligocene palygorskites are either marine or continental, but always littoral: fresh water swamps of the Bartonian of Campbon (OllivierPierre, 1980).

In the lacustrine Sannoisian of Landean, palygorskite is pre-

sent in minor amounts together with a great quantity of smectite. The discovery of a new deposit (The Bohu-Robien) shows that palygorskite may also be associated in the Armorican Massif with small amounts of smectites. THE BOHU-ROBIEN DEPOSIT This deposit is located 8 km to the North of the Oligocene basin of Quessoy, the extension of which was suspected long ago (Est6oule-Choux, 1967).

The age

of this new deposit cannot be specified because the sediments are azoic.

But

compared to other Tertiary basins and particularly to the basin of Quessoy, one may suppose that parts of the sediments of the Bohu-Robien belong. to the Stampian. Palygorskite has been found only in one bore-hole, which has given the sequence outlined in Table 1 . Table 1 - Mineralogical composition of the bore-hole of Le Bohu-Robien; in capital letters, the dominant minerals, in italic, the minerals in very small amounts. 1,50 m

ochreous clay

2,OO m

ochreous and greenish clay

SMECTITE, k a o l i n i t e , micaceous clay SMECTITE, k a o l i n i t e , t r a c e s of micaceous

clay 2,70 m

ochreous clay

SMECTITE, KAOLINITE, t r a c e s of micaceous

clay 3,20 m

green clay

SMECTITE, k a o t i n i t e , t r a c e s of micaceous

clay 3,50 m

friable grey clayey limestone (72% of C03-Ca)

4,OO m

ochreous clay

SMECTITE, palygorskite

5.20 m

grey and ochreous clay

SMECTITE, t r a c e s ,of k a o l i n i t e

SMECTITE

=

PALYGORSKITE

,

6.60 m

light grey clay

SMECTITE, trmces of k a o l i n i t e

7.60 m

light grey clay

MICACEOUS CLAY, k a o l i n i t e , smectite

8.60 m

grey and white clay

KAOLINITE, micaceous c l a y , smectite

9.60 m

grey and pink clay

KAOLINITE, micaceous c l a y

78

Compared to what can be seen in the basin of Quessoy, it is possible to associate the two bqttom layers where kaolinite is dominant with the detritic sedimentation of the Upper Eocene now recognized in the Armorican Massif. Above, the sediments with smectite, and smectite with palygorskite may be regarded as belonging to the Stampian. GENESIS OF THE PALYGORSKITE AND OF THE ASSOCIATED CLAY MINERALS Palygorskite is closely associated with either an iron-rich illite, or a smectite: it is not possible to discuss the genesis of the first without considering the two others. The problem of the origin of the smectites of the Paleogene of the Armorican Massif has already been studied (Est&ule-Choux,

1967).

These smectites

cannot be detrital because during the Cretaceous and the beginning of the Tertiary the continents were kaolinised (EstGoule-Choux, 1967, Louail, 1981). Hydromorphous tropical soils on the other hand, were never identified.

Even

if such soils had developed, some traces must have remained in low lying grounds that are preserved from erosion.

An origin from volcanic ashes

is also ex-

cluded. Moreover, the absence of coarse detrital material (sands, silts) is an additional support for a chemical sedimentation which developed while the continents were lateritised. The green iron-rich illites of the Stampian have been regarded as formed by direct precipitation; they cannot have formed from smectites because there are not smectites

on

the nearby continent and in the basins with illite smec-

tites were never identified: the illite i s either pure or associated with palygorskite in greater or lesser amounts. When illite is dominant, the carbonates are ankeritic; when palygorskite is dominant, carbonates are calcite and/or dolomite.

The constant paragenesis palygorskite-iron-rich illite seems to be

directed by the iron content of the sedimentary environment, which controls the formation of illite. When iron is absent, aluminium and magnesium remain and palygorskite forms by direct precipitation with no ferriferous carbonates. The genesis of palygorskite and of illite could be considered a s a manifestation of the antagonism A1-Mg;

It can be concluded from this, that paly-

gorskite was neoformed whether in its pure form (basin of Campbon, upper part of Saffr6 and in certain beds of the basin of Langon and the basin of S t . Seglin) or associated with iron-rich illite (Estgodle-Choux, 1967).

Once neoformation

was nearly the only mode of possible genesis envisaged for palygorskite and sepiolite deposits.

However, palygorskite was found in soils (Vanden Heuvel,

1966; Millot, et al., 1969; Lamouroux, 1971) and it has been considered

as

detrital in origin in the sediments of the North-East of the Persian gulf (Estioule, et al., 1970).

More recently, its formation by diagenetic alteration

of smectite has been suggested sy some authors, especially Decarreau et al.,

79

PLATE I C a p t i o n on p . 8 2 .

80

PLATE I1

81

PLATE I I1 Caption on next page.

82

PLATE I P a l y g o r s k i t e o f l e Bohu-Robien ( S t a m p i a n ) a s s o c i a t e d w i t h s m e c t i t e 1 and 3 : S.E.M.

o f t h e l i m e s t o n e a t 3.50 m s h o w i n g t h e d e l i c a t e meshworks o f

palygorskite coating carbonate grains.

2 and 4 : T.E.M.

o f d i s p e r s e d c l a y samples s e p a r a t e d f r o m t h e a c i d - i n s o l u b l e

r e s i d u e o f t h e same l i m e s t o n e .

5 and 6 : S.E.M.

and T.E.M.

o f t h e o c h r e o u s c l a y a t 4 m.

The l i t t l e p a r t i c l e s w i t h b l u r r e d o u t l i n e s v i s i b l e o n t h e f i g . 6 a r e smectite. PLATE I 1

1 and 2 : S.E.M.

and T.E.M.

o f t h e s m e c t i t e ( g r e e n c l a y e y bed a t 3 , 2 0 m) w h i c h

l i e s on t h e p a l y g o r s k i t e r i c h 1imestone. 3 and 4 : S.E.M.

and T.E.M.

o f t h e s m e c t i t e ( g r e y and o c h r e o u s c l a y a t 5 . 2 0 m)

under t h e p a l y g o r s k i t e c l a y e y bed. 5 and 6 : T.E.M.

o f t h e t w o c l a y e y beds o f S a n n o i s i a n o f Landean where s m e c t i t e

i s a s s o c i a t e d t o some l a t h s o f p a l y g o r s k i t e .

PLATE I 1 1 P a l y g o r s k i t e a s s o c i a t e d w i t h i r o n - r i c h i l l i t e (S.E.M.

and T.E.M.)

1 and 2 : P a l y g o r s k i t e o f Campbon ( B a r t o n i a n ) : r e m a r k some p a r t i c l e s o f f e r r i f e r o u s i11 it e .

3 and 4 : P a l y g o r s k i t e o f L o u t e h e l ( S t a m p i a n ) a s s o c i a t e d t o some p a r t i c l e s o f ferriferous i l l i t e . 5 and 6 : P a l y g o r s k i t e and f e r r i f e r o u s i l l i t e i n e q u a l q u a n t i t i e s i n a bed o f t h e S t a m p i a n o f Langon.

83 (1975) or by Trauth (1977).

This last hypothesis cannot be considered for the

palygorskite of Le Bohu-Robien.

Indeed, when one studies the two beds of this

deposit in the transmission electron microscope, one cannot identify transitional phases between smectites and palygorskite

Smectites look like isometric

particles with blurred contours and palygorskite shows aggregates of laths (Pl. I, fig. 2,4,6).

Never could laths of palygorskite growing from the par-

ticles of smectites such as those described by Trauth ( 1 9 7 7 ) be observed. On the other hand, in the calcareous bed the scanning electron microscope shows palygorskite fibres coating carbonate or aggregates of carbonate grains. Fig. 3 (Pl. I) is similar to the figure published by Hassouba and Shaw (1980): for these two authors "the delicate meshworks of palygorskite in these marl sediments strongly suggest an authigenic rather than a detrital origin for the palygorskite, as it is difficult to envisage how such delicate fabrics could have been preserved during transport and deposition"

(p. 8 0 ) .

Moreover, there

is no transition between the two palygorskite rich beds, the lower ochreous smectite rich bed and the upper green smectite rich bed.

In micrographs 1,2,3

and 4 (Pl. 11) not one lath of palygorskite can be observed and the smectite shows the same form as when it is associated with palygorskite. Galan et al., (1975) who observed similar features think that "the absence of a transition

between the two excludes the possible alteration in place of montmorillonite to palygorskite in the magnesium-rich environment" ( p . 93). Figs. 5 and 6 (Pl. 11) show some laths of palygorskite associated with the smectites of the Sannoisian of Landean.

On plate 111, palygorskite asso-

ciated with some ferriferous illite can be seen. ENVIRONMENT, PALEOGEOGRAPHY The characteristics of the deposits, as well as the data obtained from laboratory studies, particularly electron microscope observations, permit us to propose for the palygorskite associated with smectites the same authigenic origin as that which had been given for other Breton palygorskite deposits: the problem of the genesis of these minerals must be considered on a large scale. All the Tertiary basins are located in areas which were subsident as far back as the Eocene and which are limited by N-NW, S-SE faults (fault of Quessoy Nort-sur-Erdre, fault of Pont-Rean and little grabens of Landean and of Laval-Thevalles) (fig. I).

Moreover, they are situated in a lateritic land-

scape: lateritised antecambrian shales (Langon, St-S6glin for instance), kaolinised granite and schists (Quessoy, Le Bohu-Robien).

The sediments are

characterized by the absence of associated detrital constituents even at Quessoy, Le Bohu-Robien, where the granite and the schists are very rich in coarse quartz.

The absence of tectonic activity during Palaeogene favoured

84

the action of wet and warm tropical climates,s~p?ortinglateritic weathering which supplied the basins with elements necessary to form calcite, dolomite, palygorskite, ferrifereous illites, smectites and sometimes gypsum.

It must

be noted that the smectites-palygorskite deposits are less numerous than those composed of iron rich illites and/or palygorskite: sepiolite has never been identified

.

This occurence of palygorskite in marine, non-marine or sometimes brackish deposits, going from Upper Lutetian to Stampian (with a period of uniquely kaolinitic sedimentation at the end of the Upper Eocene) in always subsident basins results from the combination of several ideal conditions for direct precipitation: the source of the necessary ions was the Armorican Platform undergoing rigorous tropical weathering and the concentration of the solutions in low-lying areas communicating with the open sea intermittently, and resembling salt marshes, was favoured by the climate becoming relatively drier. CONCLUSION While palygroskite may form by a variety of processes

-

direct precipi-

tation, alteration of volcanic ashes, detrital, transformation of smectites

-

the palygorskite of the Tertiary deposits of the Armorican Massif is the result of direct precipitation in shallow, marginal seas or lakes adjacent to areas undergoing tropical weathering.

Such an origin had been proposed by

Isphording (1973) for the Georgia-Florida deposits in southeastern United States. REFERENCES Borne, V., 1978. Etude d'un sondage profond dans le bassin tertiaire de Saffrg ( 4 4 ) . (Si?dimentologie, biostratigraphie, Paleoecologie). D.E.A. Univ. Nantes, 46 pp. Decarreau, A., Sautereau, J.P. and Steinberg, M. 1975. GSn'ese des mineraux argileux du Bartonien moyen du Bassin de Paris. Bull. SOC. fr. Mineral, Cristallogr., 98: 142-151. EstGoule-Choux, J., 1967. Contribution a l'itude des argiles du Massif Armoricain. Argiles des alterations et argiles des bassins ssdimentaires tertiaires. Thkse Sci., Rennes, 319 pp. Estgoule, J., Esteoule-Choux, J., Melquen, M. and Seibold, E., 1970. Sur la pr6sence d'attapulgite dans les se'diments recents du Nord-Est du Golfe Persique. C.R. Acad. Sc. Paris, 274: 1153-1156. Galan, E., Brell, J.M., La Iglesia, A. and Roberton, R.H.S., 1975. The Caceres palygorskite deposit, Spain. Proceedings of the Intern. Clay Conf. Mexico, July, 16-23, 1975: 81-94. Hassouba, H. and Shaw, H.F., 1980. The occurence of palygorskite in Quaternary sediments of the coastal plain of North-West Egypt. Clay Minerals, 15: 77-83.

Isphording Wayne, C., 1973. Discussion of the occurence and origin of sedimentary palygorskite-sepiolite deposits. Clays and Clay Minerals 21: 391-401. Lamouroux, M., 1971. Etude de sols formgs sur roches carbonatges. Pidoghese fersiallitique au Liban. Th6se Sc., Strasbourg et Mgm. O.R.S.T.O.M., 56 (1972), 245 pp.

85

Louail, J., 1981. L a transgression cretacee au Sud du Massif armoricain. CCnomanien de 1'Anjou et du Poitou, CretacZ supzrieur de Vendsee. Etude stratigraphique, skdimentologique et minsralogique. ThSse Sci. Rennes, 456 pp. Millot, G., Paquet, J. and Ruellan, A., 1 9 6 7 . Ngoformation de l'attapulgite dans les s o l s a carapaces calcaires de l a Basse-Moulouya (Maroc oriental). C.R. Acad. S c , , Paris, 2 6 8 : 2771-2774. Ollivier-Pierre, M.F., 1980. Etude palynologique (spores et pollens) de gisements paliogsnes du Massif Armoricain. Hem. SOC. Giol. Min. Bretagne, 25: 239 pp. Trauth, N., 1977. Argiles gvaportiques dans la sedimentation carbonatgee continentale et Gpicontinentale tertiaire. Bassin de Paris, Mormoiron et Salinelles (France), Ibel Ghassoul (Maroc). Sciences G6ologiques. Kem. 49: 695 pp. Vanden Heuvel, R.C., 1 9 6 7 . The occurence of sepiolite and attapulgitein the calcareous zone of a soil near Las Cruces, New Mexico, Clays and Clay Min., 13: 193-207.

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87

SEPIOLITE

-

PALYGORSKITE I N SPANISH TERTIARY BASINS: GENETICAL PATTERNS I N

CONTINENTAL ENVIRONMENTS* EMILIO GALAN ( * ) and ANTONIO CASTILLO (**)

(*) Dept. of Geology, F a c u l t y o f Chemistry, U n i v . o f S e v i l l a , Spain

(**) TOLSA, S . A . Nunez de Balboa 51, Madrid, Spain

ABSTRACT Spanish T e r t i a r y d e p o s i t s o f s e p i o l i t e and p a l y g o r s k i t e a r e formed i n l a c u s t r i n e o r p e r i m a r i n e environments. A c c o r d i n g t o t h e i r g e o l o g i c a l s e t t i n g and mineralogy t h e y can be grouped i n t o f o u r fundamental types, w i t h t h e f o l l o w i n g p r i n c i p a l f e a t u r e s : 1 ) T a j o b a s i n t y p e ; s e p i o l i t e formed i n d i s t a l zones o f a l l u v i a l - f a n s , o r i n p e r e n n i a l l a c u s t r i n e zones, by p r e c i p i t a t i o n f r o m a S i and M g - r i c h s o l u t i o n w i t h a pH between 8 and 9. Other a u t h i g e n i c m i n e r a l s formed i n t h i s environment were Mg-smectite, p a l y g o r s k i t e , carbonates and c h e r t . 2 ) T o r r e j o n t y p e ; p a l y g o r s k i t e formed i n t e c t o n i c b a s i n s on s l a t y basement from p a r t i a l l y d i s s o l v e d c h l o r i t e , and a l s o by d i r e c t p r e c i p i t a t i o n i n an a l k a l i n e environment. 3) Benfica-San M a r t i n de Pusa t y p e ; p a l y g o r s k i t e appears as t h e p r i n c i p a l c l a y m i n e r a l i n t h e cement o f conglomerates and sandstones, formed by d i a g e n e s i s i n t h e s e d e t r i t a l sediments, i n a s l i g h t l y a1 k a l i n e environment r i c h i n magnesium. 4) L e b r i j a t y p e ; p a l y g o r s k i t e - s e p i o l i t e m a r l s formed i n a p e r i m a r i n e b r a c k i s h l a c u s t r i n e environment r i c h i n S i and Mg. P a l y g o r s k i t e i s a l s o t h o u g h t t o be a t r a n s f o r m e d m i n e r a l f r o m i l l i t e . I n a l l these patterns t h e sedimentation o f authigenic c l a y minerals occurred under s e m i - a r i d o r seasonably a r i d c l i m a t i c c o n d i t i o n s d u r i n g p e r i o d s o f t e c t o n i c calm. INTRODUCTION S e p i o l i t e and p a l y g o r s k i t e a r e commonly found i n Spain, o c c a s i o n a l l y i n abundant amounts.

Some d e p o s i t s have g r e a t economic importance.

One o f these, i n V a l l e c a s , Madrid, was mined by means o f w e l l s and g a l l e r i e s during t h e l a t e 1600's.

The s e p i o l i t e was used i n t h e "manufacture of p i p e s

and c i g a r e t t e f i l t e r s " ( t h e s o f t e r v a r i e t y ) and as "a b u i l d i n g m a t e r i a l i n r u s t i c houses" ( V i l a n o v a , 1875).

Used p r i m a r i l y i n t h e manufacture of l i g h t

w a l l s d u r i n g t h e second h a l f o f t h e 1 9 t h c e n t u r y , i t was r e f e r r e d t o as "crazy r o c k " i n t h a t r e g i o n . lite.

Small l a b o r a t o r y ovens were a l s o made o f s e p i o -

V i l a n o v a (1875) i n t h a t paper d e s c r i b e d i n d e t a i l t h e s e p i o l i t e d e p o s i t s

i n Cabanas de l a Sagra and Yepes, Toledo. Between 1735 and 1808 t h e V a l l e c a s s e p i o l i t e was mixed w i t h c l a y f r o m Capodimonte, I t a l y , i n t h e ceramic p a s t e o f t h e famous p o r c e l a i n s o f t h e Buen R e t i r o i n M a d r i d (Prado, 1864).

In 1830 B e r t h i e r conducted t h e f i r s t known a n a l y s i s o f V a l l e -

*

Presented a t t h e I n t e r n a t i o n a l C l a y Conference 1981.

88 cas s e p i o l i t e . Mg0=23.8%;

ThE c o m p o s i t i o n was S i 0 2 = 5 3 . 8 % ;

A1203=1.2%;

H20=20%.

Spanish contributions t o the study o f these p h y l l o s i l i c a t e s have been v e r y i m p o r t a n t . mineralogists,

F o r more t h a n t h i r t y y e a r s ,

h a v e c o m p l e t e d n u m e r o u s s t u d i e s on t h e s t r u c t u r e , morphology,

physico-chemical

these minerals.

properties,

diffraction;

and Robertson (1971),

Huertas e t a l .

(19751, Galan (1979), La I g l e s i a (1977,

(1970,

on t h e r m a l a n a l y s i s ;

on e l e c t r o n m i c r o s c o p y a n d

1971 a n d 1 9 7 4 ) , G a l a n e t a l .

Fernandez A l v a r e z (1970,

on q e n e s i s ;

on s y n t h e s i s a t room t e m p e r a t u r e ;

M a r t i n V i v a l d i and L i n a r e s (1962),

and

Fenoll and M a r t i n V i v a l d i

1978), Serna (1973),

and Serna and Vanscoyoc (1978), physico-chemical

(1970),

and Galan and F e r r e r o (1982),

1978),

include:

on t h e m i n e r a l o g i c a l f o r m u l a o f

M a r t i n V i v a l d i and Ferioll

Martin Vivaldi

composition,

genesis and s y n t h e s i s o f

The m o s t r e l e v a n t S p a n i s h c o n t r i b u t i o n s

M a r t i n V i v a l d i a n d Cano ( 1 9 5 6 ) , sepiolite;

Spanish c l a y

e s p e c i a l l y M a r t i n V i v a l d i and h i s c o l l a b o r a t o r s ,

Serna e t a l .

(1968)

(1975),

on v a r i o u s s t r u c t u r a l a s p e c t s a n d

properties.

The c o m m e r c i a l i z a t i o v o f s e p i o l i t e i n S p a i n began i n 1945, a t which t i m e i n v e s t i g a t i o n s o f p o s s i b l e d e p o s i t s and t h e i r m i n e r a l o g i c a l c h a r a c t e r i s t i c s were c a r r i e d o u t (Lacazette, Vivaldi

a n d Cano,

1947; M a r t i n

1953).

S e p i o l i t e and p a l y g o r s k i t e a r e found as m i n o r components i n various types o f rocks.Reoorts

o f these minerals being found i n

Cambrian and S i l u r i a n s l a t e s a r e d o u b t f u l .

More f r e q u e n t and c r e d i -

b l e a r e r e p o r t s o f s e p i o l i t e i n Keuper c l a y s and m a r l s . Occurrences on p e r i d o t i t e s and b a s i c v o l c a n i c r o c k s ,

as w e l l as i n J u r a s s i c

dolomitic rocks are a l s o described (Alonso, Martin Vivaldi,

1972; O o r r o n s o r o ,

1970;

1978; G a l a n ,

C a b a l l e r o and

1979).

However,

the

greatest concentration o f these minerals occurred i n Spanish T e r t i ary basins under special environmental conditions. THE S P A N I S H TERTIARY BASINS The m o s t i m p o r t a n t T e r t i a r y b a s i n s a r e a l o n g t h e T a j o , and G u a d a l q u i v i r r i v e r s ( F i g .

Duero,

Ebro

1).

The b a s i n o f t h e T a j o c a n be d i v i d e d i n t o t h r e e s e c t i o n s o r sub-basins:

the eastern,

the central,

and t h e western.

The A l t o m i -

r a S i e r r a separates t h e e a s t e r n and t h e c e n t r a l , and t h e t h r e s h o l d o f Talavera de l a Reina, central

(Fig.

2).

Toledo,

separates t h e western from t h e

89

EXPLANATION A

ALMAZAN - - W I N

4E

A L W X T E BPSN

R

:ROUPAR

M

M.B

cra S

so 8 8

BdDpJoZ W N

8.C

WREM u)RRxxI(

CR

UUOIV) Rowu) WB-BASIN

C 1 6 . CALATAW-TERLU W I N

S.P0 T

V VA

z

F i g . 1.

-

T e r t i a r y basins i n the I b e r i a n Peninsula

Toward t h e south, and s e p a r a t e d b y t h e e a s t e r n spurs o f t h e Toledo Mountains, t h e T a j o b a s i n connects w i t h t h e Ciudad Real basin).

Toward t h e south-east,

-

D a i m i e l b a s i n ( t h e Manchegan

i t continues along t h e Albacete basin.

The Duero b a s i n has t h r e e d i f f e r e n t s e d i m e n t o l o g i c a l areas. The l a r g e s t , t h e V a l l a d o l i d sub-basin, o c c u p i e s t h e c e n t r a l zone. Toward t h e west, t h e Ciudad Rodrigo s u b - b a s i n i s f o u n d and toward t h e e a s t t h e Almazan ( F i g . 1 ) . The Duero b a s i n connects on t h e n o r t h - w e s t w i t h t h e Ebro b a s i n through t h e Bureba c o r r i d o r , The Ebro b a s i n c u t s a c r o s s t h e n o r t h - e a s t c o r n e r o f t h e I b e r i a n P e n i n s u l a i n a NW-SE d i r e c t i o n w h i c h s e p a r a t e s t h e I b e r i a n Range a t t h e s o u t h f r o m t h e Pyrenees a t t h e n o r t h , and t h e C a t a l a n Mountains a t t h e n o r t h - e a s t ( F i g . 1 ) . To t h e s o u t h o f t h e Ebro b a s i n and t o t h e e a s t o f t h e Almazan b a s i n l i e s t h e Calatayud-Teruel b a s i n , an i n t r a m o u n t a i n o u s b a s i n o f t h e I b e r i a n Range.

90

N

MI MADRID T: TOLEDO G = GUADALAJARA W i THE WESTERN SIB-BeSIN C :THE CENTRAL SUB-BASH(THE MALMilD BESIN1 E: THE EASTERN SUB-BbSW H = HUETE T : TABLADILCO P.M- PUEBLA DE MCUTALBAN S Y P i S I N W I N E€ PUSA T R = TALAVER4 DE L A REINA

F i g . 2.

-

0 a0 U l c____

The T a j o b a s i n

The T e r t i a r y b a s i n o f t h e G u a d a l q u i v i r i s l o c a t e d i t s e p a r a t e s t h e I b e r i a n M a s s i f f r o m t h e B e t i c Range

s m a l l T e r t i a r y b a s i n s : t h e Granada, t h e Guadix-Eaza,

n s o u t h e r n Spain; I n t h i s b a s i n appear

he Gorafe-Huelago,

etc.

I n G a l i c i a and A s t u r i a s , i n n o r t h w e s t e r n Spain, e x i s t s m a l l b a s i n s o f T e r t i a r y m a t e r i a l s d i r e c t l y l y i n g on t h e P a l e o z o i c basement. A s e r i e s o f s m a l l b a s i n s w i t h t h e same c h a r a c t e r i s t i c s : t h e T o r r e j o n , t h e Coria, t h e M o r a l e j a , and t h e Castelo-Branco can b e f o u n d i n t h e western p a r t o f t h e P e n i n s u l a (Spanish-Portugese b a s i n s ) .

A l s o i n t h e south, b u t w i t h

d i f f e r e n t s e d i m e n t o l o g i c a l c h a r a c t e r i s t i c s i s t h e Eadajoz b a s i n , wh ch c o i n c i d e s w i t h t h e h y d r o g r a p h i c b a s i n o f t h e Guadiana r i v e r . F i n a l l y , i n Levante ( e a s t e r n Spain) e x i ' s t s a g r e a t number o f sma 1 b a s i n s p a r t i a l l y interconnected, from Almeria t o Valencia. Most o f these b a s i n s were a f f e c t e d by c o n t i n e n t a l c o n d i t i o n s

91

a t l e a s t d u r i n g some stages o f t h e i r e v o l u t i o n .

The occurrence o f s e p i o l i t e -

p a l y g o r s k i t e m i n e r a l s i n Spain i s a s s o c i a t e d w i t h t h e s e c o n t i n e n t a l episodes, o r w i t h p e r i o d s o f a l i m i t e d c i r c u l a t i o n t o t h e sea.

THE TAJO BASIN Geological s e t t i n g The T a j o b a s i n i s l o c a t e d i n t h e c e n t r a l p a r t o f t h e P e n i n s u l a ( F i g . l ) , and i s bordered b y t h e Guadarrama and Gredos S i e r r a s on t h e n o r t h and n o r t h west, t h e Toledo Mountains on t h e south, and t h e I b e r i a n Range on t h e e a s t (Fig. 2 ) . T h i s b a s i n was formed b y f r a g m e n t a t i o n o f t h e s h i e l d ( t h e I b e r i a n N a s s i f ) d u r i n g t h e A l p i n e o r o g e n e s i s and was f i l l e d by a c o n t i n e n t a l s e d i m e n t a t i o n during the T e r t i a r y .

The basement o f t h e t r o u g h i s covered by Cretaceous

and Paleogene sediments, above which a r e found Neogene m a t e r i a l s a f f e c t e d o n l y by subsequent movements t h a t gave r i s e t o f o l d i n g ( A l i a and Capote, 1971). During t h e P l i o c e n e t i m e s t h e b a s i n t i l t e d t o w a r d t h e south-west. The c o n t i n e n t a l s e d i m e n t a t i o n o f t h i s b a s i n extends f r o m t h e Paleogene t o the Q u a t e r n a r y , t h e m a t e r i a l s d e r i v i n g f r o m t h e s u r r o u n d i n g mountains.

The

thickness o f t h e T e r t i a r y sediments r e a c h more t h a n 1600 meters (Carames e t a l . 1973) and p r o b a b l y as much as 3000 m e t e r s i n some areas (Megias e t a l . 1982). L i tho1 ogy The s e d i m e n t a t i o n o f t h e w e s t e r n s u b - b a s i n i s e s s e n t i a l l y d e t r i t a l ( g r a v e l s , sands and sandy c l a y s ) .

The c l a y s a r e m a i n l y composed of i l l i t e

and smecti t e s . The e a s t e r n sub-basin i s m a r l y - c a l c a r e o u s and g y p s i f e r o u s , w i t h d e t r i t a l intercalations.

I t s s e d i m e n t a t i o n has been c l e a r l y i n f l u e n c e d by t h e

I b e r i a n Range e s s e n t i a l l y composed o f Mesozoic l i m e s t o n e s , c l a y s and sands. The u p l i f t o f t h e A l t o m i r a S i e r r a o c c u r r e d a f t e r t h e e v a p o r i t i c s e d i m e n t a t i o n and d i d n o t s e r v e as a s o u r c e area f o r t h i s sub-basin. The c e n t r a l sub-basin i s t h e most i n t e r e s t i n g i n terms o f s e p i o l i t e and palygorskite.

A d e t r i t a l facies ( a l l u v i a l deposits) related t o the

surrounding mountains, b o r d e r s t h e c e n t r a l sub-basin, and i s known a c c o r d i n g t o i t s g e o g r a p h i c a l l o c a t i o n s , as t h e M a d r i d

92 facies,

Toledo facies,

(Benayas e t a l .

1960).

evaporitic facies (Fig.

A l c a r r i a f a c i e s and G u a d a l a j a r a f a c i e s It i n t e r f i n q e r s toward t h e c e n t e r w i t h an 3).

N

PEDlmNT _____

FUNTIAN LIMESTONES MARLY W0FKlES T W I T I O H FACIES DETRITAL SUEFACIES

a ____

DETRITAL F K I E S

[a$16 EVAFWfITIC

FAUES

-

SEPlOLlTE BED

Fig.

3.-

The C e n t r a l s u b - h a s i n o f t h e T a j o b a s i n S e c t i o n t y p e of

t h e T a j o b a s i n and g e n e r a l c r o s s s e c t i o n

NW-SE

11 = M a d r i d , T = = T o l e d o ,

G==Guadalajara

93

Between t h e M a d r i d f a c i e s and t h e e v a p o r i t i c f a c i e s i s a rnarlyclayey transition facies, cal characteristics.

l o c a l l y showing p l a y a - l a k e

t h e s e f a c i e s c a n be seen i n F i g .

of

sedimentologi-

The r e l a t i v e p o s i t i o n s and r e l a t i o n s h i p s o f The f o l l o w i n g i s a d e s c r i p t i o n

3.

their characteristics:

Detrital facies.

- C o n s i s t s o f conglomerates and f e l d s p a t i c sand

w i t h ssme i n t e r l a y e r i n g o f g r a v e l s a n d s a n d y c l a y s o f a r e d - y e l l o w ish color.

:

-

Transitions facies.

a) Detrital, subfacies: Located i n t h e lower p a r t , zone.

occupying p r i m a r i l y the eastern

I t i s made u p o f t w o b e d s .

The l o w e r i s c l a y e y ( d a r k

c l a y w i t h i l l i t e a n d l o w - c r y s t a l l i n e s m e c t i t e s ) w i t h some lens-shaped l e v e l s o f dolomitic

rocks.

A discontinuous

l a y e r o f s e p i o l i t e appears a t t h e t o p o f t h e l o w e r bed r e l a t e d t o t h e d o l o m i t i c l a y e r s . The t h i c k n e s s i s i r r e g u l a r (max.

2 m.).

The u p p e r b e d i s d e t r i t a l ,

c o n s i s t i n g of

fine

micaceous sands ( m o s t l y b i o t i t e s ) o f a d a r k green c o l o r . I n t h e upper middle p a r t there i s another l a y e r o f pinkish sepiolite,

o f wrinkled texture,

and t h i c k e r and more c o n t -

inuous than p r e v i o u s . A s s o c i a t e d w i t h c h e r t and c a l c i t e , i t continues t o the d e t r i t a l

facies (Madrid facies).

The

thickness o f t h i s l e v e l reaches 4 meters. b) Marly subfacies: T h i s s u b f a c i e s i s s m a l l e r i n s u r f i c i a l e x t e n s i o n and i s l o c a t e d t o t h e e a s t o f t h e p r e v i o u s l y d i s c u s s e d one.

It

c o n s i s t s o f l i m e s t o n e s , m a r l y limestones and s m e c t i t i c clays o f a saponitic nature. base a r e l a y e r s o f sand.

Toward t h e west and i n t h e

T h e t o p o f t h i s s u b f a c i e s i s made

up o f a brown l a y e r o f c h e r t and massive s e p i o l i t e ,

which

o c c a s i o n a l l y c o n t a i n p a l y g o r s k i t e as a m a j o r component. The l a y e r i s c o n t i n u o u s b u t o f v a r y i n g c o m p o s i t i o n . Fig.

4 i s a c o r r e l a t i o n diagram o f various sections

i n t h e Tajo basin.

Two l a y e r s o f s e p i o l i t e a r e c l e a r l y i n

5 s h o w s some X r a y d i f f r a c t i o n patterns corresponding t o c h a r a c t e r i s t i c

evidence i n t h e central sub-basin. materials o f t h i s facies.

Fig.

94 EXF'LANATITIW

SYECTITE-SEPIOLITE CLAY

c-l

YPlalTE ILLITE-SIECTITE

CLAY

LIMESTONE AND SEROClE-SIECTITE M A Y

0 OETRITAL FACIES E V I p w l T l C FACIE'

F i g . 4.

-

L i t h o s t r a t i g r a p h i c c o r r e l a t i o n diagram i n t h e T a j o b a s i n . S e c t i o n s o f : 1 ) T a l a v e r a d e l a Reina, 2 ) Maqueda, 3) V i c a l v a r o ,

'

4) Brihuega, 5) Y u n c l i l l o s - M a g d n , Chinchdn, 7 ) Pastrana, and 8) T a b l a d i l l o - P a r e j a areas

Evaporitic facies:

T h i s f a c i e s i s c h a r a c t e r i z e d by a l a r g e f o r m a t i o n o f

chemical sediments w h i c h can b e d i f f e r e n t i a t e d i n t o two s u b f a c i e s :

a ) a sub-

f a c i e s o f r e d g y p s i f e r o u s c l a y s , l i m e s t o n e s and sodium s a l t s ; and b ) a m a r l y calcareous subfacies which, toward t h e n o r t h - e a s t becomes t o t a l l y c a l c a r e o u s . I n b o t h l a y e r s , t h e r e a r e t r a c e s o f p a l y g o r s k i t e t o g e t h e r w i t h i l l i t e , and sometimes k a o l in i t e and smecti t e s

.

On t o p o f t h e s e m a t e r i a l s appears a bed made up o f m i c r i t i c c a l c a r e n i t e s and l i m e s t o n e d a t e d as P o n t i a n , which c r e a t e a r e g i o n a l l y t y p i c a l r e l i e f c a l l e d "mesas". A t t h e base of t h e l i m e s t o n e s '"mountain l e a t h e r " ( s e p i o l i t e ) has been found,

f o r example a t Jadraque i n G u a d a l a j a r a .

The youngest m a t e r i a l s a r e a P l i o - Q u a t e r n a r y bed o f r e d c l a y s and sandstones t h a t covers most of t h e T a j o sub-basin. On t h e b a s i s o f i n f o r m a t i o n f r o m s e i s m i c r e f l e c t i o n , c o n s i s t s o f f i v e t e c t o r e d i m e n t a r y u n i t s (TSU) (Megfas

t h e Madrid basin

95

m-a-sp 336

2.118

3b

Fig. 5.

-

L

L

Ib

ib

h

*

29

X-ray powder diffraction patterns of characteristic clay materials o f the Tajo basin. ( C u K radiation) 1.- I l l i t e - s m e c t i t e clay ( d e t r i t a l subfacies) , 2.- Vicalvaro s e p i o l i t e ( d e t r i t a l subfacies, lower l e v e l ) , 3 . - Low-crystalline Mg-smectite, 4.- Yunclillos s e p i o l i t e ( d e t r i t a l subfacies, lower l e v e l ) , 5.- Sepiolite (marly subfacies) , 6.- Palygorskite (marly subfacies). Sp = Sepiolite,

Pa = Palygorskite, Sin = Smectite, I = I l l i t e , Q = Quartz, F = Feldspars, Ca = Calcite, Do = Dolomite.

96 e t a l . 1982b).

According t o t h i s i n t e r p r e t a t i o n t h e p r e v i o u s l y described

l a y e r s o f s e p i o l i t e a r e l o c a t e d i n t h e f o l l o w i n g way: t h e upper l e v e l o f t h e d e t r i t a l s u b f a c i e s i n a r k o s i c t e c t o s e d i m e n t a r y u n i t (TSU 8 ) ; t h e l o w e r l e v e l o f t h e same s u b f a c i e s i n t h e upper p a r t o f TSU 6 ( u n i t made up o f d e t r i t a l and chemical subfacies, which, a t t h e edges, change t o f l u v i a l d e t r i t a l f a c i e s ) ; and f i n a l l y , t h e s e p i o l i t e l a y e r o r t h e m a r l y s u b f a c i e s i n t h e l o w e s t p a r t of TSU 7 ( d o l o m i t i z e d c a r b o n a t i c m a t e r i a l w i t h f i b r o u s c l a y minerals present). (Fig. 6).

9---

F i g . 6.

-

Tectosedimentary u n i t s i n t h e T a j o B a s i n a c c o r d i n g t o Megias e t a l . (1982b).

S e p i o l i t e l o c a t i o n a c c o r d i n g t o t h i s paper ( w i t h o u t s c a l e )

1.-Basement, 4.-Salts,

2.-Granite,

3a.-Mesozoic,

gypsum, magnesite, e t c .

3b.-Eocene-Oligocene,

(TSU 4 ) , 5 , - 6 . - D e t r i t a l

gypsum,

sand, d o l o m i t e , e t c . (TSU 5 and 6 ) , 7 . - D o l o m i t i z e d c a r b o n a t i c m a t e r i a l s w i t h f i b r o u s c l a y m i n e r a l s , and P o n t i a n l i m e s t o n e s (TSU 7 ) , 8 . - A r k o s i c u n i t (TSU 8 ) , 9.-Unconformity The c o r r e l a t i o n between t h e f a c i e s h e r e d e s c r i b e d and t h e i n v o l v e d TSU’s are indicated i n the adjoining table: TABLE I C o r r e l a t i o n between t h e f a c i e s d e s c r i b e d i n t h i s paper and t h e t e c t o s e d i m e n t a r y u n i t s (TSU) c i t e d by Megtas e t a1 (1982b) Pontian limestones

,

Detrital T r a n s i t i o n f a c i e s 1Mar,y Evaporitic facies

, .

Marly-Calcareous Gypsum

--

--

/

TSU 7b TSU 8 TSU 7a TSU 4,5,6

97 The V a l l e c a s - V i c a l v a r o s e p i o l i t e d e p o s i t ( p r o v i n c e o f M a d r i d ) T h i s d e p o s i t i s s i t u a t e d t o t h e n o r t h - e a s t o f t h e c i t y o f Madrid, and occupies a p p r o x i m a t e l y 6.6 Kin 2

.

I t i s a p a r t of t h e d e t r i t a l s u b f a c i e s i n t h e t r a n s i t i o n f a c i e s o f t h e T a j o b a s i n . F i g . 7 shows a l o g a t t h i s d e p o s i t .

C N R T AND SLICECUS LIMESTONE SYCTITE-SEPIOLITE

20m

CLAY

SEPIOLITE ILLITE-SMECTITE CLAY 25 m

&O&;IE

cyfySMECTITE-

W A Y LIMESTONE

F i g . 7.- Log a t V i c a l v a r o , M a d r i d Two e x p l o i t a b l e l a y e r s o f s e p i o l i t e a r e p r e s e n t .

The upper l a y e r changes

l a t e r a l l y t o dark c h e r t , and t h e l o w e r changes l a t e r a l l y t o s m e c t i t e s ( e s s e n t i a l l y o f t h e s t e v e n s i t e t y p e ) a t t h e n o r t h - w e s t (Galan e t a l . 1981). Toward t h e south-east,

t h e l o w e r s m e c t i t e c l a y s change t o s a p o n i t i c b e n t o n i t e s

o f i r r e g u l a r d i s t r i b u t i o n and q u a l i t y . The s e p i o l i t e i s f a i r l y p u r e (between 65% and more than 95%), b e i n g accompanied by q u a r t z , i l l i t e , f e l d s p a r s and carbonates. The l o w e r l e v e l c o n t a i n s s t e v e n s i t e , o r o t h e r p o o r l y - c r y s t a l l i z e d s m e c t i t e s ( F i g . 5, samples I n T a b l e I1 a r e chemical a n a l y s e s o f t h e s e s e p i o l i t e s . F i g . 8 i s an e l e c t r o n m i c r o g r a p h o f t h e s e p i o l i t e . O t h e r d a t a o f i n t e r e s t can be found

2 and 3 ) .

i n T a b l e 111. T h i s i s t h e w o r l d ' s most i m p o r t a n t known d e p o s i t o f s e p i o l i t e . 90% o f t h e w o r l d ' s known r e s e r v e s a r e f o u n d i n t h i s area. has been p u r i f i e d and processed, most o f i t i s e x p o r t e d . than 50 i n d u s t r i a l .uses.

More t h a n

Once t h i s s e p i o l i t e S e p i o l i t e has more

98

TABLE I 1 CHEMICAL ANALYSES O F S E P I O L I T E

1

2

3

4

63.10

60.60

60.10

59.18

1.08

1.73

3.74

1.85

0.27

0.62

0.85

0.65

23.80

22.45

20.60

23.40

0.49

0.40

0.44

0.52

0.09

0.16

0.71

0.25

0.21

0.58

1.40

0.58

10.88

13.22

11.95

12.60

99.92

99.21

99.83

99.03 ~

1,2,3;

Vallecas sepiolite,

d i f f e r e n t grades; 4:

Yunclillos

TABLE I 1 1 S E P I O L I T E DEPOSIT OF VALLECAS: Mineralogy

PROPERTIES A N D U S E S

Properties

Uses

Sepiol i t e

P o r o s i t y = 17%

Decoloring agents;

(up t o 95%)

Particle size:

absorbent granules;

Smec t it e s

8000 x 250 x 40A3

c a t 1i t t e r ; c a r r i e r s

I l l i t e

S p e c i f i c g r a v i t y :2 . 2

f o r i n s e c t i c i d e s and

Palygorskite

Shell Index:2.7

Calcite

2.7

Do1 o m i t e

Water a b s o r p t i o n

Kg/cm3

Kg/cm3

herbicides; dispersants;

saline d r i l l -

i n g muds;

rubber and

Quartz

(FORD) = 1 1 0 - 1 3 0 %

plastic industries;

Cristobal i t e

Specific surface:

asbestos substitute;

Feldspars

350 m2/g

cosmetic;

C.E.C.

= 26 meq/g.

ture.

agricul-

99

F i g . 8.- T r a n s m i s s i o n e l e c t r o n m i c r o g r a p h o f t h e V a l l e c a s - V i c b l v a r o s e p i o l i t e The Y u n c l i l l o s s e p i o l i t e d e p o s i t ( p r o v i n c e o f Toledo) S i t u a t e d 15 Km n o r t h o f t h e c i t y o f Toledo, i t s e x t e n t i s a p p r o x i m a t e l y

3 Km2.

I t a l s o forms p a r t o f t h e d e t r i t a l s u b f a c i e s i n t h e t r a n s i t i o n f a c i e s

o f t h e T a j o b a s i n , and i t s l o g i s shown i n F i g . 9.

One observes, as i n The upper i s o f

V a l l e c a s , t h e e x i s t e n c e o f two s e p i o l i t e - c o n t a i n i n g l a y e r s .

v a r y i n g c o m p o s i t i o n , c o n t a i n i n g n o t a b l e i m p u r i t i e s o f Mg-smectites,

and l a r g e

nodules o f c h e r t , i r r e g u l a r l y d i s t r i b u t e d , and occupying an i n t e r m e d i a t e p o s i t i o n i n t h e s e p i o l i t e bed.

The l o w e r l e v e l i s f a i r l y c o n t i n u o u s and pure

( F i g . 5, sample 4 and T a b l e 1 1 )

om 2m SEPDUTE-SMECTITE CLAY WITH CHERT

F i g . 9.- Log a t

0

SAND AND CLAYEY SAND

Yuncl i110 s , To1 edo

SEFIOLITE 12m Ism

20 m

ILUTE-SMECTITE &NO SEPlOLlTE

CLAY

ILLITE-SMECTITE CLAY

100 Other occurrences o f s e p i o l i t e and p a l y g o r s k i t e Magan T h e l i t h o s t r a t i g r a p h i c s e r i e s i n Magan ( p r o v i n c e o f T o l e d o ) i s f o r m e d by an a l t e r n a t i o n o f f i n e m i c a c e o u s sands and b e n t o n i t e c l a y s o f a saponite n a t u r e (see column 5,

Fig. 4).

Between t h e s e

c l a y s a r e t h i n l a y e r s o f s e p i o l i t e (maximum 5 0 c m ) .

The p u r i t y of

t h e s e p i o l i t e i s o n l y 50-70%, p r i m a r i l y because o f t h e presence of saponites.

These c l a y s a l s o b e l o n g t o t h e d e t r i t a l s u b f a c i e s o f

the Tajo basin t r a n s i t i o n facies.'They

can be s t r a t i g r a p h i c a l l y

correlated with the lower sepiolite exploited i n Yunclillos. San M a r t i n d e P u s a

-

Toledo

Microconglomerates o f q u a r t z and q u a r t z i t e s w i t h a cement formed o f p a l y g o r s k i t e and s m e c t i t e s w i t h c r i s t o b a l i t e o r carbona t e s have been d e s c r i b e d by Ordonez e t a l .

(1977a).

These a r e i n

t h e western sub-basin o f t h e T a j o ( T a l a v e r a de l a Reina) ( F i g .

2)

and a l s o n e x t t o t h e s o u t h e r n b o r d e r of

at

t h e c e n t r a l sub-basin,

t h e n o r t h o f t h e Toledo Mountains (San M a r t i n de Pusa, Puebla de Montalban, ces).

s o u t h of

i n t h e area surrounding Toledo and other pla-

These m a t e r i a l s have been d a t e d as d i f f e r e n t l y as Upper Cre-

taceous,

Paleocene,

Oligocene and Miocene,

according t o the loca-

tion. The e a s t e r n s u b - b a s i n o f t h e T a j o The c l a y m i n e r a l o g y o f T e r t i a r y m a t e r i a l s f r o m t h e e a s t e r n sub-basin outcrops between t h e A l t o m i r a S i e r r a and t h e I b e r i a n Range ( F i g .

2 ) have been s t u d i e d b y G a r c i a P a l a c i o s ( 1 9 7 7 ) .

ward t h e c e n t e r o f t h e sub-basin, dominate,

To-

Mg-smectites and s e p i o l i t e pre-

b u t t h e y do n o t a p p e a r t o g e t h e r . A l - s m e c t i t e s

and

p a l y g o r s k i t e appear more f r e q u e n t l y t h a n s e p i o l i t e on t h e b o r d e r s . Vertical mineralogical cycles occur i n t h i s sub-basin: c y c l e b e g i n s w i t h A1-Mg

(palygorskite, Al-smectite,

the

Al-Mg-smec-

t i t e ) a n d e n d s r i c h i n Mg ( M g - s m e c t i t e o r s e p i o l i t e ) . To t h e n o r t h o f t h i s s u b - b a s i n ,

close t o Tabladillo (province

o f Guadalajara) and between t h e g y p s i f e r o u s m a r l s o f t h e e v a p o r i t i c facies,

two l a y e r s o f p a l y g o r s k i t e have been d i s c o v e r e d

( M a r t i n Pozas e t a l .

1981).

Found i n t h e t o p o f t h e s e r i e s ,

they

101 a r e 0.4

a n d 2m t h i c k .

by s e p i o l i t e ( 1 0

-

The p a l y g o r s k i t e ( 6 6

20%), mica, quartz,

-

70%) i s accompanied

calcite,

d o l o m i t e and opal.

THE D U E R O B A S I N Lithology This vast basin l i e s i n the north central ian Peninsula (Fig.

region o f the Iber-

1) and c o i n c i d e s l a r g e l y w i t h t h e hydrographic The m a t e r i a l s t h a t f i l l t h e b a s i n a r e be-

basin o f t h e Duero r i v e r .

l i e v e d t o be o f t h e M i o c e n e age.

Three u n i t s a r e i n v o l v e d . They are,

from o l d e s t t o youngest: The Lower U n i t .

T h i s u n i t c o n s i s t s o f sandstones,

conglomerates

a n d s a n d s , w i t h some c l a y i n t e r l a y e r s , w h i c h b e c o m e m o r e a b u n d a n t f a r t h e r away f r o m t h e b o r d e r s o f t h e b a s i n . T h i s i s t h e u n i t w i t h the largest superficial

extension.

Toward t h e n o r t h - e a s t ,

t h i c k n e s s d e c r e a s e s t o a m i n i m u m o f 10 m e t e r s .

its

I n some p a r t s ,

un-

d e r n e a r t h t h i s d e t r i t a l l o w e r u n i t a p p e a r m a r l y m a t e r i a l s composed of white marls,

w i t h a n d w i t h o u t gypsum,

The M i d d l e U n i t . i s evaporitic,

and c l a y .

T h i s u n i t c a n b e d i v i d e d i n t o t w o b e d s . The l o w e r

f o r m e d o f l a y e r s o f gypsum ( w i t h l a r g e a r r o w h e a d -

shaped t w i n s ) and g y p s i f e r o u s m a r l s w i t h d o l o m i t e and s e p i o l i t e . The u p p e r ,

m a r l y bed i s composed o f an a l t e r n a t i o n o f l i m e s t o n e s ,

marls and calcareous c l a y s . A t t h e top,

a n a p p r o x i m a t e l y 1 cm

t h i c k "mountain l e a t h e r " p a l y g o r s k i t e c l a y l a y e r i s found,

w i t h an

irregular distribution. The U p p e r U n i t c o n s i s t s o f P o n t i a n l i m e s t o n e s Fig.

-

"Paramo l i m e s t o n e s " .

10 shows a s c h e m a t i c d i a g r a m o f t h i s b a s i n a n d v a r i o u s c o l u m -

nar sections which c o r r e l a t e t h e described materials. Sepiolite-palygorski t e occurrences

So f a r ,

no s e p i o l i t e - p a l y g o r s k i t e d e p o s i t s o f commercial

t e r e s t have been'found.

However,

minerals i n t h e Middle U n i t

-

a l s o c a l l e d "cuesta facies"

t o Aranda d e l Duero and T o r r e s a n d i n o ( P r o v i n c e o f Burgos), outskirts o f Valladolid,

in-

a series o f ' i n d i c a t i o n o f these

-

close i n the

i n Sacramenia ( p r o v i n c e o f Segovia),

have

been d e s c r i b e d ( G a r c i a d e l C u r a a n d L o p e z Aguayo 1974; O r d o n e z e t al.,

1977b;

Pozo a n d Carames,

1983; M a r t i n Pozas e t a l .

1983).

102 P a l y g o r s k i t e i s more abundant t h a n s e p i o l i t e and sometimes c o n s t i t u t e s a s much a s 9 0 % o f

the marly-clayey material.

The d o m i n a n t

carbonate i s dolomite. Lequey e t a l .

( t h i s volume) have r e p o r t e d t o t h e south-west

o f Segovia conglomerates w i t h D a l y g o r s k i t e cement w i t h c h a r a c t e r i s t i c s d i f f e r e n t from those o f the "cuesta facies"

and v e r y s i m i -

l a r t o t h e San M a r t i n d e P u s a m i c r o c o n g l o m e r a t e s . N

EXPLANATION UPPER UNIT L I M E S T M S . MARLS. CLAYS, GYPSUM, WRLS, U I T E

o

LOWER UNIT

l-

M,DDLE sp-po)

wRLr AND GYPSIFERRLS MATERIALS PALEOZOIC AND MESOZOIC ROCKS

F i g . 10.-

General diagram o f t h e Duero b a s i n and l i t h o s t r a t i g r a phic correlation

T H E EBRO B A S I N The s e d i m e n t o l o q i c a l c h a r a c t e r i s t i c s a r e s i m i l a r t o t h o s e o f the Tajo basin,

b u t i n t h e Ebro b a s i n t h e r e e x i s t s a d i s t i n c t

s t a q e o f m a r i n e s e d i m e n t a t i o n d u r i n g t h e Eocene epoch.

103 P a l y g o r s k i t e - s e p i o l i t e o c c u r r e n c e s have been d e s c r i b e d by P i n i l l a (1966), Alonso and Galvan (1961), (1974),

Alonso (1970),

Huertas e t a l .

and Gonzalez and Galan ( i n p r e s s ) b u t t h e m a t e r i a l s ana-

l y z e d do n o t h a v e t h e c h a r a c t e r i s t i c s r e q u i r e d t o b e m i n e d . Two f u n d a m e n t a l evaporitic facies

t y p e s o f m a t e r i a l s can be d i s t i n g u i s h e d : t h e

(gypsum,

anhydrite,

the marly-calcareous facies. stant.

halite,

etc.),

and above i t ,

Both a r e m i n e r a l o g i c a l l y very con-

I l l i t e p r e d o m i n a t e s among t h e c l a y m i n e r a l s . O c c a s i o n a l l y ,

s e p i o l i t e appears i n t h i n l a y e r s , contrast w i t h the Tajo basin,

b u t these a r e n o t continuous.

In

t h e Ebro b a s i n has no d e f i n e d t r a n s -

i t i o n facies. Generally speaking, investigation.

t h i s b a s i n has n o t undergone a d e t a i l e d

Only the Ablitas-Tarazona-Borja

area (province o f

Zaragoza) has been s t u d i e d r e c e n t l y ( G o n z a l e z and Galan, aration).

i n prep-

R e l a t i v e l y i m p o r t a n t l a y e r s composed o f s e p i o l i t e a n d

t r i o c t a h e d r a l smectites w i t h carbonates and d e t r i t a l i l l i t e ,

have

been i d e n t i f i e d i n t h i s a r e a .

T H E GUADALQUIVIR B A S I N The Neogene c l a y d e p o s i t s o f t h i s b a s i n a r e e s s e n t i a l l y o f m a r i n e o r i g i n . Only v e r y r a r e l y do f i b r o u s c l a y m i n e r a l s a p p e a r . However,

near t h e Guadalquivir o u t l e t (Fig.

1 1 ) t h e r e i s an impor-

t a n t p a l y g o r s k i t e m a r l d e p o s i t i n l a c u s t r i n e P l i o c e n e which has been s t u d i e d b y G o n z a l e z G a r c i a a n d P e i r o ( 1 9 5 8 ) .

Huertas e t a l .

(19741, and Galan and F e r r e r o ( 1 9 8 2 ) . The L e b r i j a p a l y g o r s k i t e - s e p i o l i t e d e p o s i t The U p p e r P l i o c e n e s e d i m e n t s n e a r L e b r i j a ( p r o v i n c e o f Sev i l l a ) c o n t a i n commer'cial

d e p o s i t s o f p a l y g o r s k i t e and s e p i o l i t e .

Two u n i t s c a n b e d i s t i n g u i s h e d i n t h e c o n t i n e n t a l P l i o c e n e : a " m a r l y - c a l c a r e o u s bed" a n d an u p p e r " p a l y g o r s k i t e bed".

The b a s e

o f the lower u n i t i s usually a s i l i c i f i e d limestone o r a limestone with chert (white o r gray),

b u t i n c e r t a i n places,

d i a t o m i t e forms

t h e base o f t h e P l i o c e n e . The " m a r l y - c a l c a r e o u s limestone,

bed" i s 25-30 m t h i c k and c o n s i s t s o f

m a r l y and sandy l i m e s t o n e , marl and c l a y e y marl,

i n t e r b e d d e d t h i n beds ( u p t o 1 m t h i c k ) o f d a r k brown,

with

l i g h t brown

or p i n k i s h w h i t e m a r l y c l a y named " T i e r r a d e l V i n o " ( w i n e e a r t h ) , b e c a u s e t h e m a t e r i a l f o r m e r l y was u s e d t o c l a r i f y a r l d p u r i f y w i n e . The u p p e r u n i t (

1 5 m t h i c k ) i s named t h e " p a l y g o r s k i t e b e d "

104 because o f i t s h i g h content o f p a l y g o r s k i t e . range from 30 cm t o 3 m i n thickness.

The p a l y g o r s k i t e l a y e r s Limestone layers a r e interbedded i n

this unit.

A g r e a t abundance o f microfauna was noted i'n these calcareous m a t e r i a l s , which a r e c h a r a c t e r i s t i c o f brackish f a c i e s o r swamp o f t h e Upper Pliocene o r Quaternary.

Pa

WLYMRSKITE

Sp

SEPiULlTE

I

ILLITE

Sm

SYECTITE

EXPLANATION MIL N W A M LIIIE8TOfIF WLYGORSIIITE C L m

WINE PL-

-

W L M R S K I T E MARL

ALLOCHTHONOUS YATERIAIs

0

cmss

@ SANDY

SECTO IN

CLAYEY S4NC LIHSTONE

h?kY&g:zy

@ LIMESTONE TIERRA CEL VlNO

Fig. 11.-

Location o f the L e b r i j a p a l y g o r s k i t e - s e p i o l i t e deposit, crosss e c t i o n SW-NE across t h e Mesa del Cuervo and Laguna de 10s T o l l o s , and the s t r a t i g r a p h i c column ( a f t e r Galan and Ferrero, 1982).

105 The " T i e r r a d e l V i n o " a r e t y p i c a l l y 5 0 % c a l c i t e a n d 50% s e p i o l i t e , with minor smectite,

p a l y g o r s k i t e and q u a r t z .

neral suites e x i s t i n the lower u n i t :

Three clay-mi-

sepiolite + palygorskite i n

the bottom; s e p i o l i t e + palygorskite f i l l i t e i n t h e center,

and

palygorskite + i l l i t e f s e p i o l i t e f smectite i n t h e upper part. I n t h e p a l y g o r s k i t e bed, skite + i l l i t e (Fig.

t h e main clay-mineral

s u i t e i s palygor-

P a l y g o r s k i t e v a r i e s from'35 t o 75% i n

11).

t h e c l a y and m a r l l a y e r s . THE TORREJON B A S I N The T o r r e j o n e l R u b i o b a s i n ( p r o v i n c e o f C a c e r e s ) s t a n d s o u t among t h e S p a n i s h - P o r t u g e s e T e r t i a r y b a s i n s w i t h f i b r o u s c l a y m i n e r a l s because o f i t s g r e a t abundance o f p a l y g o r s k i t e . t a n t d e p o s i t was d i s c o v e r e d i n t h e e a r l y 1 9 6 0 ' s ,

This impor-

b u t these marly

p a l y g o r s k i t e s have been used l o c a l l y as whitewash s i n c e a n c i e n t times.

T h e e x i s t e n c e o f t h e d e p o s i t was p o i n t e d o u t b y A l v a r e z

E s t r a d a a n d Sanchez Conde ( 1 9 6 7 ) . al.

I t has been s t u d i e d b y Galan e t

(1975) and reviewed by Galan e t a l .

(1982).

Geologic S e t t i n g The T e r t i a r y b a s i n o f T o r r e j o n e l Rubio ( F i g . a p p r o x i m a t e l y 250 Km2, imum l e n g t h o f 3 7 Km.

12) occupies

and g e n e r a l l y extends east-west,

w i t h a max-

The base c o n s i s t s o f Cambrian s l a t e s o f t h e

I b e r i a n M a s s i f . To t h e n o r t h a n d n o r t h - e a s t

o f t h e b a s i n i s an i m -

p o r t a n t q u a r t z i t e r e l i e f ( t h e Corchuelas, M i r a v e t e and t h e Extranj e r a S i e r r a s ) w h i c h now s e p a r a t e s t h e b a s i n f r o m t h e T a j o b a s i n . To t h e s o u t h a n d s o u t h - e a s t

a r e two e x t e n s i v e outcrops o f Hercynian

granites surrounded by aureoles o f cornubianites. The basement i s a f f e c t e d by two systems o f H e r c y n i a n f r a c t u r e s running north-eas

-

south-west and south-east

- northwest.

The

f o r m a t i o n o f t h i s t e c t o n i c t r o u g h appears r e l a t e d t o t h e second s e t o f fractures,

due t o r e a c t i v a t i o n s d u r i n g t h e Miocene which c o n t i n -

ued d u r i n g t h e f i l i n g o f t h e basin. Lithology From b o t t o m t o t o p , basement,

t h r e e u n i t s can be d i s t i n g u i s h e d : a ) t h e

b ) t h e d e t r i t a l - c l a , y e y bed, and c ) t h e "rana".

Rana i s a

S p a n i s h t e r m f o r a c o n s o l i d a t e d mudf1o.w d e p o s i t c o n t a i n i n g a n g u l a r blocks o f rock o f a l l sizes,

e.g.

a fanglomerate.

OUARZITE SLbTE (BASEMENT!

ST-3LISrLOG NUMBER

?

MINE

319: ELEVATION IN M

Fig.12.-

Flap s h o w i n q l i t h o l o i i c u n i t s o f T o r r e j 6 n b a s i n a n d r e v r e s e n t a t i v e 1 0 7 s . P a = P a l y g o r

.

I=Illite

107 The b a s e m e n t c o n s i s t s o f b r o w n i s h - p i n k i s h c l a y e y s l a t e s w i t h d i s s e m i n a t e d p y r i t e a n d s m a l l d i k e s o f m i l k y q u a r t z . An a l t e r a t i o n o f t h e s l a t e s t o w h i t i s h and g r e e n i s h c l a y s can be observed i n t h e

upper p a r t o f t h i s basement.

T h i s a l t e r a t i o n d o e s n o t a p p e a r when

r e s t s d i r e c t l y on t h e basement.

the "rana"

The c l a y e y - d e t r i t a l and g r a v e l s ,

b e d i s made u p o f a n a l t e r n a t i o n o f s a n d

w i t h c l a y s more o r l e s s r i c h i n q u a r t z and c a r b o n a t e s .

The l e v e l s a r e l e n s - s h a p e d a n d o f r e l a t i v e l y c o n s t a n t t h i c k n e s s , v a r y i n g a r o u n d 0.7m. 3 m thick,

alteration, zone). zone.

I n t h e base one o b s e r v e s a c l a y e y bed,

0.3

-

which contains r e l i c t i c s l a t e w i t h d i f f e r e n t grades o f more abundant t o w a r d t h e w a l l

( t h e basement a l t e r a t i o n

T h e maximum t h i c k n e s s c o i n c i d e s w i t h t h e l o w e s t t o p o g r a p h i c A t t h e t o p one f i n d s a c o n t i n u o u s sandy l a y e r o f v a r y i n g

thickness (0.15

-

1.5 m).

The t o t a l t h i c k n e s s o f t h i s b e d v a r i e s

between 6 a n d 5 0 m. The t h i r d b e d ,

the "rana"

( L a t e Miocene - Pliocene) i s a red-

dish fanglomerate o f q u a r t z i t e pebbles which occupies the topographically higher levels o f the basin.

It occurs w i t h greater f r e -

quency i n t h e s o u t h e r n a n d s o u t h - w e s t e r n "

borders and c r e a t e s a

me s a "

Mineralogy The s l a t e s a r e composed o f q u a r t z , ites of the sheridanite-clinochlore tites,

f e l d s p a r s , micas and c h l o r -

type,

w i t h k a o l i n i t e , smec-

g o e t h i t e and p y r o p h i l l i t e o c c a s i o n a l l y present.

I n the al-

t e r e d s l a t e s t h e m i n e r a l o g i c a l a s s e m b l a g e i s t h e same a s i n t h e previous,

together with palygorskite,

i n t e r s t r a t i f i e d clay minerals

and dolomite. The c l a y e y - d e t r i t a l or palygorskitic,

bed has two zones.

The l o w e r ( 0 . 5

has t h e f o l l o w i n g assemblage:

i l l i t e f s m e c t i t e k c h l o r i t e f s e p i o l i t e (Pa + I b e i n g Pa

>

I; w h i l e t h e u p p e r , o r i l l i t i c ,

same a s s e m b l a g e , smectites.

but with I

>>

-

4 m),

Palygorskite +

*

Sm

*

Ch

_+

Sp),

i s c h a r a c t e r i z e d by t h e

Pa, a n d t h e c o n s t a n t p r e s e n c e o f

The o t h e r components a r e q u a r t z ,

The s m e c t i t e s a r e o f s a p o n i t e t y p e .

f e l d s p a r s and dolomite.

P a l y g o r s k i t e c o n t e n t can

r e a c h 70%. T a b l e I V d e s c r i b e s t h e m i n e r a l o g i c a l c o m p o s i t i o n s .

Table

V i n c l u d e s r e p r e s e n t a t i v e a n a l y s e s o f t h e basement and t h e a l t e r a t i o n zone as w e l l a s t h e p a l y g o r s k i t e and i l l i t e zones.

I n t h e pa-

l y g o r s k i t e z o n e a g r a n u l o m e t r i c d i f f e r e n t i a t i o n c a n b e made b e t w e e n the t o p and bottom.

'TABLE I V

2

0

W

MINERALOGICAL COMPOSITION OF TORREJ9N MATERIALS

Illitic zone

Palygorski te zone

Values

Q

Range

15-35

1nd.-30

25-55

Ind. -20

Norm

20-25

15-2.0

35-40

10

Range

10-45

35-70

1nd.-15

0-15

Norm

30-40

45-50

10

5-45

25-45

25-5

Pa

I1

Sm

Ch-K

Ind. - 1 0

F

Do

0-10

0-15 very little

5

1nd.-5

0

0-5

0-5

0-60

Ind.

Ind.

0-20

5-20

1nd.-5

little

Range

5

10-Ind.

0-40 little

A1 teration zone

Ca-Cb-Sp

Norm

25-30

30-40

10-15

Range

15-40

-

25-35

Norm

25-30

-

25-30

Slate

5-10

Ind.

Ind-5

10-50

5-1 5

Ind

30-35

10

5

Q = Quartz; Pa = Palygorskite; I1 = Illite; Sm = Smectite; Ct, = Chlorite; K = Kaolinte; F = Feldspars; Do = Dolomite; Ca = Calcite, Cb = Cristobalite; Sp = Sepiolite; Ind = Traces.

0

109 TABLE

V

REPRESENTATIVE CHEMICAL ANALYSES OF TORREJON MATERIALS AFTER HEATING AT 1000°C Slate

A1 t e r a t i o n zone

Pa zone

I 1 zone

Bottom -Top Si02

72.98

73.23

75.86

-

73.77

62.19

A1203

14.49

13.70

10.12

-

12.18

19.94

Fe203

4.14

'4.74

3.78

-

4.43

7.88

MgO

4.14

4.36

7.78

-

7.0

4.18

CaO

0.52

0.46

1.0

-

0.9

0.96

Na20

1.56

1.52

0.33 -

0.33

0.43

K20

2.28

1.98

1.11 -

1.38

4.39

H20t

3

5

9.5

9

7

(average)

TABLE

VI

THE TORREJON PALYGORSKITE DEPOSIT Mineralogy P a l y g o r s k i t e (up t o 85%) Quartz Feldspars

Chemistry ( X ) Si02:51 .5 A1 203: 10.03 Fe203: 2.36

Do1 omi t e Calcite

C r i stobal it e Saponi t e Illite Sepiol i t e Kaol i n i t e Chlorite Org. Mat.

FeO: 0.52 Mg0:12.28 H20+:14.43 -

H20-: 7.36

Properties o f Palygorskite

Uses

P a r t i c l e size: 0 . 5 - 4 . 5 ~ long 150-300 8 t h i c k

F l o o r absorbents Carriers for insecticides

C.E.C*=26.5 meq/g S p e c i f i c surface:

D r i l l i n g i n saline waters.

146 m2/g

110

The f o l l o w i n g p o i n t s a r e i m p o r t a n t f o r u n d e r s t a n d i n g t h e s e a n a l y s e s : a ) Si02 c o n t e n t remains c o n s t a n t f r o m t h e s l a t e t o t h e t o p o f t h e p a l y g o r s k i t e zone, w h i l e i t d i m i n i s h e s i n t h e i l l i t i c ; b ) w i t h r e s p e c t t o t h e e n t i r e c l a y e y - d e t r i t a l bed, A1203 d i m i n i s h e s i n t h e p a l y g o r s k i t e zone and i n c r e a s e s c l e a r l y i n t h e i l l i t i c ; c ) t h e MgO remains c o n s t a n t , except i n t h e p a l y g o r s k i t e zone, where i t i n c r e a s e s ; d ) Na20 and K20 decrease a l o n g t h e a l t e r a t i o n and t h e p a l y g o r s k i t e zones, i n c r e a s i n g a g a i n i n t h e i l l i t i c , e s p e c i a l l y K20; and e ) Fe203 a l s o i n c r e a s e s i n t h e i l l i t i c zone. F i g . 13 shows d i f f r a c t o g r a m s o f t h e d i f f e r e n t t y p i c a l m i n e r a l o g i c a l a s s o c i a t i o n o f t h e d e s c r i b e d beds.

T a b l e V I c i t e s some o f t h e c h a r a c t e r i s t i c s

o f t h e e x p l o i t e d p a l y g o r s k i t e (Galan e t a l . 1975; Galan, 1979).

0

2

F i g . 13.

-

X-ray powder d i f f r a c t i o n p a t t e r n s o f c h a r a c t e r i s t i c m a t e r i a l s of t h e T o r r e j o n b a s i n . 1.- S l a t e (basement), 2.- A l t e r a t i o n zone on s l a t e , 3.- P a l y g o r s k i t e zone, 4.-

I l l i t e zone.

Pa=Palygorskite,

I = I 1 1 it e , K=Kaol i n i t e , M=Mica, C l = C h l o r i t e , Q = Q u a r t z , F=Feldspars , Do=Dolomite, Cu K r a d i a t i o n .

111 MISCELLANEOUS I n G a l i c i a a n d A s t u r i a s t h e r e a r e a number o f s m a l l T e r t i a r y t e c t o n i c b a s i n s commonly f i l l e d w i t h c o n t i n e n t a l s e d i m e n t s o f e s s e n t i a l l y k a o l i n i t i L nature. (Roupar,

However,

i n three o f these basins

Puentes de Garcia Rodriguez and S a r r i a ) ,

s l a t e basement,

w h i c h r e s t on a

p a l y g o r s k i t e m a r l s w i t h s e p i o l i t e and i l l i t e have

been d e s c r i b e d ( i u c a s e t a l .

1963, B r e l l ,

1972; B r e l l and Doval,

1974). I n t h e d e p r e s s i a n s o f Granada,

Gorafe-Huelago,

and Guadix-Baa,

p a l y g o r s k i t e h a s b e e n f o u n d o n l y i n some s t a g e s o f l a c u s t r i n e f a cies, mixed w i t h smectite, (Huertas e t a l .

1974;

i l l i t e , and o t h e r d e t r i t a l m i n e r a l s

Sebastian e t a l .

To t h e n o r t h - e a s t o f Granada,

1975,

1979).

i n the Middle Subbetic,

bento-

n i t e s have been found t o c o n s t i t u t e a p a r t o f t h e Fardes Formation (Early Cretaceous),

formed by t h e weathering o f volcanic rocks.

S i g n i f i c a n t q u a n t i t i e s o f palygorskite are found together w i t h the smectites.

The g e n e s i s o f b o t h m i n e r a l s f r o m t h e s e v o l c a n i c r o c k s

has been s t u d i e d b y S e b a s t i a n e t a l .

(1982).

I n t h e T e r t i a r y b a s i n o f t h e Mancha, nce o f Ciudad Real),

close t o Daimiel

M a r t i n Pozas a n d M a r t i n V i v a l d i

(provi-

(1981) have

found t r a c e s of p a l y g o r s k i t e a s s o c i a t e d w i t h s m e c t i t e ,

i l l i t e and

kaol i n i t e .

So f a r ,

no i n d i c a t i o n s o f t h e s e m i n e r a l s have been found i n

the T e r t i a r y basin o f Badajor o r Levante. I n t h e T e r t i a r y o f t h e Cuevas o f A l m a n z o r a and Vera

o f Almeria),

(province

p e r i m a r i n e p a l y g o r s k i t e m a r l s have been found ( u p t o

20% p a l y g o r s k i t e ) w i t h i n d i c a t i o n s o f s e p i o l i t e , smectites and i l l i t e (Galan e t a l .

i n

together with

preparation).

I n other areas

o f t h e Almeria T e r t i a r y (between Sorbas, Tabernas and Garucha), palygorskite i s frequently found i n the marly materials. Finally,

i n the T e r t i a r y basin o f Calatayud-Teruel,

c i t y o f Teruel,

near the

t h e e x i s t e n c e o f p a l y g o r s k i t e has been n o t e d i n t h e

smectitic marls.

As a m i n e r a l o g i c a l c u r i o s i t y , o n e n o t e s t h a t M a r t i n V i v a l d i and L i n a r e s ( 1 9 6 2 ) m e n t i o n e d " a random i n t e r g r o w t h o f s e p i o l i t e a t t a p u l g i t e " i n t h e b e n t o n i t e d e p o s i t s o f t h e vo c a n i c r e g i o n o f Cab0 de G a t a ( p r o . v i n c e o f A l m e r i a ) .

D I S C U S S I O N A N D CONCLUSIONS The d e s c r i b e d T e r t i a r y d e p o s i t s w i t h s e p i o l t e o r p a l y g o r s k t e

112 are c l e a r l y o f a continental character.

These m i n e r a l s do n o t ap-

pear i n connectio-n w i t h any v o l c a n i c a c t i v i t y , t h e r m a l phenomena.

n o r w i t h any hydro-

The a c c u m u l a t i o n o f t h e s e m i n e r a l s i s n o t con-

t r o l l e d by tectonics.

On t h e c o n t r a r y ,

t h e i r s t r a t i f o r m morphology

and t h e i r p o s i t i o n w i t h r e l a t i o n t o o t h e r sedimentary m a t e r i a l s suggests an o r i g i n i n c l o s e d c o n t i n e n t a l sedimentary basins ( l a c u s t r i n e environment),

o r a n o r i g i n w i t h r e s t r i c t e d sea w a t e r c i r -

c u l a t i o n (perimarine environment;

lagoons,

swamps,

t i d a l zones,

etc.). The d e p o s i t s i n S p a i n c a n b e d i v i d e d i n t o f o u r g r o u p s b a s e d on t h e i r g e o l o g i c a l s e t t i n g and m i n e r a l o g y :

2) Torrejon type, b r ij a type.

1) Tajo basin type,

3 ) B e n f i c a - S a n M a r t i n d e Pusa t y p e ,

and 4) Le-

The c h a r a c t e r i s t i c s o f each t y p e a r e d e s c r i b e d b e l o w .

1 ) T a j o b a s i n t y p e (sepiolite-palygorskite-Mg-smectite d e p o s i t s ) . The s e d i m e n t a t i o n b a s i n i s a t e c t o n i c d e p r e s s i o n o f v a r y i n g dimensions,

s i t u a t e d i n a c r a t o n i c area.

The s u r r o u n d i n g a r e a s a r e

made u p o f a c i d i c r o c k s ( p l u t o n i c a n d / o r m e t a m o r p h i c ) a n d c a l c a r eous r o c k s .

They u n d e r w e n t w e a t h e r i n g a f t e r a l i g h t u p l i f t ( o r

progressive sinking o f t h e basin). This process supplied the basin w i t h d e t r i t a l materials and ions i n solution, ning waters. areas,

transported by run-

The c o a s e r d e t r i t a l s were d e p o s i t e d i n t h e m a r g i n a l

while f i n e d e t r i t a l sediments ( d e t r i t a l

t r a n s i t i o n subfa-

c i e s ) were i n t h e d i s t a l zones o f t h e a l l u v i a l f a n s .

In the typi-

c a l l y l a c u s t r i n e zones an e v a p o r i t i c s e d i m e n t a t i o n w i t h v e r y f i n e grained materials,

such as c l a y s ( m a r l y t r a n s i t i o n s u b f a c i e s and

m a r l y e v a p o r i t i c f a c i e s ) was p r o d u c e d . T h e p r e c i p i t a t i o n o f a u t h i genic c l a y minerals mainly r e s u l t e d i n a playa-lake environment during a period o f t e c t o n i c calm (Fig.

14).

The m i n e r a l o g y o f t h e s e s e d i m e n t s i s composed o f i n h e r i t e d minerals (quartz, feldspars,

micas,

kaolinite, chlorite,

diocta-

hedral smectites) and authigenic minerals ( c a l c i t e , dolomite, sum,

palygorskite,

sepiolite,

saponite,

stevensite).

i n t e r m e d i a t e phases ( t r a n s f o r m e d m i n e r a l s ) appear (e.g.

r illite-smectite,

gyp-

Some a l t e r e d mixed-

or illite-chlorite).

The i n h e r i t e d m i n e r a l s d o m i n a t e t h e d e t r i t a l f a c i e s ,

while

a u t h i g e n i c ones a r e more f r e q u e n t i n t h e more d i s t a l zone o f lake-shore area.

Nevertheless,

with the clastic material authi-

c m i n e r a l s can a l s o be p r e c i p i t a t e d . The p r e c i p i t a t i o n o f c a l c i t e o r d o l o m i t e

-

unlike that of

113 sepiolite tors,

-

depends on t h e p a r t i a l Dressure of

such as t h e e n v i r o n m e n t a l temperature,

organic catalysts, man,

C02, a n d o t h e r f a c -

evaporation,

salts,

and t h e nresence o f s u l n h a t e s and c h e r t ( L i p D -

1779; V e n i a l e e t a l .

1982; Baker and K a s t n e r ,

1381).

.ITE

MUD

A L L U V I A L FAN

Fin.

1p.-

FLAT

Slock d i a n r a i showinn t h e sedimentary environment i n t h e Tajo basin during s e p i o l i t e formation

The i n h e r i t e d c l a y m i n e r a l s a r e m o s t l y i l l i t e a n d d i o c t a h e d r a l s m e c t i t e s . The a u t h i q e n i c m i n e r a l s a r e M q - r i c h s i l i c a t e s , d i c a t e s t h a t t h e y w e r e f o r m e d i n S i 0 2 a n d '1'19-rich

which

it+

environment w i t h

l e s s e r n u a n t i t i e s o f A l . A c c o r d i n g t o t h e d a t a on t h e s y n t h e s i s and s t a b i l i t y o f s e p i o l i t e , 1962; W o l l a s t e t a l .

~ a l y q o r s k i t ea n d s t e v e n s i t e ( S i f f e r t ,

1368; S i n g e r and N o r r i s h ,

1977 a n d 1 9 7 8 ; IKhoury e t a l .

1782; e t c . ) ,

should o s c i l l a t e between 8 and 9. o f s e n i o l i t e i s favored,

on t h e a v a i l a b l e e d w h e r e t h e nH

quantity

I n pH 8

1 7 7 4 ; La I g l e s i a ,

t h e pH o f t h e s e s o l u t i o n s

-

8.5,

the precipitation

as w e l l as t h a t o f p a l y q o r s k i t e , depending o f ,Al.

Smectite precinitation i s favor-

3. The l a t e r a l c h a n g e s i n t h e r a t i o s o f t h e s e m i -

n e r a l s d e D e n d p r i m a r i l y o n t h e l o c a l pH a n d t h e a v a i l a b l e A l . excess s i l i c a of

precipitates

m a s s i v e l y a s c h e r t (C-T

The

o p a l ) when a l l

t h e l o c a l Vq h a s b e e n c o n s u m e d .

A t l e a s t two s e p i o l i t e - r i c h aDoear i n t h e T a j o b a s i n .

enisodes (an upner and a l o w e r )

They a r e a s s o c i a t e d w i t h t h e d e t r i t a l

f a c i e s o f t h e d i s t a l zones o f a l l u v i a l f a n s ( d e t r i t a l s u b f a c i e s ) . I n the Vallecas-Vicilvaro

deposit,

the sepiol i t e o f the lower level

i s p o o r l y c r y t a l l i z e d and i s c o n t a m i n a t e d b y Mq-smectites. associated w i t h d o l o m i t i c l e v e l s and c h e r t .

I n contrast,

It i s

the sepio-

l i t e o f t h e u p p e r l e v e l a p p e a r s w e l l - o r d e r e d a n d w i t h l e s s Mg-smect i t e contamination.

I n this level,

calcite andlor chert,

the s e p i o l i t e i s associated with

These s i g n i f i c a n t m i n e r a l o g i c a l and c r y s t a l -

114 l o g r a p h i c d i f f e r e n c e s can be e x p l a i n e d by geochemical changes d u r i n g s e d i mentation.

D u r i n g t h e s e d i m e n t a t i o n process o f t h e l o w e r l e v e l t h e average

pH must have been 9, w i t h an excess o f Mg w i t h r e s p e c t t o s e p i o l i t e s a t u r a t i o n . I n t h e second case i t appears c l e a r t h a t Mg was l e s s abundant and t h a t t h e pH was l o w e r , 8.5, w i t h c o n d i t i o n s i d e a l f o r t h e s l o w c r y s t a l l i z a t i o n o f o r d e r e d s e p i o l it e . I n the marly subfacies, the authigenic minerals a r e g e n e r a l l y o f g r e a t e r c r y s t a l l i n i t y than those o f the d e t r i t a l subfacies.

I n a d d i t i o n , aluminium i s

more abundant ( p a l y g o r s k i t e i s more f r e q u e n t ) which, c o n s i d e r e d i n c o n j u n c t i o n w i t h t h e g r e a t e r abundance o f carbonates makes one t h i n k t h a t t h e s e m a t e r i a l s were produced s l o w l y , and w i t h physico-chemical c o n d i t i o n s i d e a l f o r growth (La I g l e s i a , 1977, 1978). 2)

Torrejon type ( p a l y g o r s k i t e deposits) During the Alpine orogenesis i n the I b e r i a n peneplain, north-west

-

s o u t h - e a s t H e r c y n i a n f r a c t u r e s were r e a c t i v a t e d , a l l o w i n g t h e c r e a t i o n o f s m a l l depressions i n t h e s l a t e basement. i n t e r m i t t e n t lakes.

Running w a t e r f i l l e d t h e s e b a s i n s , c r e a t i n g

O x i d a t i o n o f t h e abundant p y r i t e a p p e a r i n g i n t h e s l a t e

caused t h e a c i d i t y o f t h e s t a n d i n g w a t e r t o i n c r e a s e .

These s l i g h t l y a c i d i c

waters s u p e r f i c i a l l y d i s s o l v e d t h e s l a t e s , r e l e a s i n g a l k a l i n e and ferro-magn e s i a n elements, e s p e c i a l l y f r o m micas and c h l o r i t e s , and a l k a l i n i z i n g t h e environment. Under t h e s e c o n d i t i o n s , degraded micas ( K - d e f i c i e n t ) and c h l o r i t e s p r o b a b l y w i t h t h e b r u c i t i c l a y e r s i m p a i r e d and t h e o c t a h e d r a l l a y e r s p a r t i a l l y d e f e c t i v e , tended t o e q u i l i b r a t e , f i x i n g magnesium and r e c r y s t a l l i z i n g as p a l y g o r s k i t e o r s m e c t i t e s , a c c o r d i n g t o t h e pH and t h e a v a i l a b i l i t y o f Mg. S i n c e t h e o v e r a l l chemical c o m p o s i t i o n o f t h e a l t e r a t i o n zone i s s i m i l a r t o t h a t o f t h e s l a t e s w h i c h c o n t a i n s i g n i f i c a n t q u a n t i t i e s o f c h l o r i t e (“20%), i t i s n o t necessary t o suppose any o u t s i d e s u p p l i e s d u r i n g t h e a p p a r e n t

t r a n s f o r m a t i o n (by f i e l d c r i t e r i a ) , and one can assume t h a t t h e t r a n s f o r m a t i o n occurred i n a

c l o s e d system.

Only t h e decreases o f Na and K i m p l y an

a l t e r a t i o n o f f e l d s p a r s and muscovites and an a b s o l u t e l o s s i n t h e s e elements. The 2 : l u n i t s o f c h l o r i t e c o u l d a c c e p t Mg.

However, s i n c e t h e p a l y g o r s k i t e

a t t h e b o t t o m o f t h e p a l y g o r s k i t e zone has a magnesium-aluminium r a t i o s i m i l a r t o t h a t o f the c h l o r i t e i n the s l a t e o f

115 t h e basement, a g e n e t i c a l

r e l a t i o n s h i p between t h e s e two m i n e r a l

t y p e s c o u l d b e c o n j e c t u r e d b y m e a n s o f a n i n t r o d u c t i o n o f Mg i n 2:l

(di-trioctahedral)

A mechanism i s

incomplete c h l o r i t e units.

proposed whereby p a r t o f t h e t e t r a h e d r a l l a y e r would i n v e r t p e r i o dically,

so as t o a d a p t t o an i n c o m p l e t e o c t a h e d r a l l a y e r , g i v i n g

a palygorskite rather than a saponite structure. o f Mg a t h i g h e r pH w o u l d p r o d u c e s a p o n i t e .

A local increase

Interstratified chlorite

s m e c t i t e and i l l i t e - s m e c t i t e have been observed as i n t e r m e d i a t e stages. The f o r m a t i o n o f p a l y g o r s k i t e b y means o f t r a n s f o r m a t i o n o f s m e c t i t e s h a s b e e n s u g g e s t e d b y Weaver a n d Beck ( 1 9 7 7 ) a n d b y T r a u t h (1974). They d e s c r i b e a s i m i l a r mechanism, b u t w i t h o u t g i v i n g s u f f i c i e n t evidence.

Galan and F e r r e r o (1982) have described t h e

f o r m a t i o n o f p a l y g o r s k i t e b y means o f t h e t r a n s f o r m a t i o n o f i l l i t e i n a s i m i l a r manner.

I n a l l explanations,

t h e Mg i s i n t r o d u c e d f r o m

outside t h e system. Recent s t u d i e s (Galan,

i n preparation)

have demonstrated

t h a t t h e s l a t e basement o f t h e T o r r e j o n b a s i n can a l t e r i n t o s e p i o l i t e and s a p o n i t e .

T h e e x p e r i m e n t was c o n d u c t e d b y a t t a c k i n g t h e

s l a t e w i t h an a c i d i c s o l u t i o n (pH=3.1, teen days, week.

a d j u s t e d w i t h HC1) f o r f o u r -

a n d t h e n a l k a l i n i z i n g w i t h Mg(OH)2 ( p H = 9 . 5 )

f o r one

T h e f i l t r a t e c o n t a i n e d t h e same q u a n t i t y o f q u a r t z a n d f e l d -

spars as t h e s l a t e ;

c h l o r i t e d e c r e a s e d f r o m 30% t o 15%; m i c a s d e -

c r e a s e d f r o m 25% t o 20%; a n d s e p i o l i t e a n d s m e c t i t e appear, approximate c o n c e n t r a t i o n o f 10% and 15%, r e s p e c t i v e l y . p e c t e d t h a t new e x p e r i m e n t s w i t h l o w e r - p H

(e.g.

8.5)

a t an

It i s ex-

and lower pro-

p o r t i o n s o f Mg w i l l a l s o demonstrate t h e p o s s i b i l i t y o f p a l y g o r s k i t e genesis, (Galan e t a l .

a s has been proposed h e r e f o r t h e T o r r e j o n b a s i n 1982).

I n t h e s p e c i f i c case o f t h i s b a s i n and i n o t h e r s o f t h e western area o f t h e I b e r i a n peninsula,

one assumes t h a t t h e g r a d u a l

growth o f t h e b a s i n and f o r m a t i o n o f t h e t r o u g h a l l o w e d t h e t r a n s portation and accumulation o f d e t r i t a l materials i n various states o f degradation and o f i o n s i n s o l u t i o n , lines.

such as S i ,

Mg a n d a l k a -

By m e a n s o f t h e s e e l e m e n t s a n d t h e d e t r i t a l p h y l l o s i l i c a t e s

i n d i s e q u i l i b r i u m w i t h t h e medium p a l y g o r s k t t e c o u l d be formed. A u t h i g e n i c p a l y g o r s k i t e c o u l d a l s o have been p r e c i p i t a t e d f r o m t h e f r e e A1 a n d w i t h t h e e x c e s s S i a n d Mg o f t h e m e d i u m ( G a l a n e t a l . 1 9 7 5 ) . Mg a n d S i c a n o c c a s i o n a l l y f o r m p a r t o f d o l o m i t e a n d c r i s t o b a l it e ,

r e s p e c t i v e 1y .

P a l y g o r s k i t e formed by t r a n s f o r m a t i o n i n t h e blocks a d j a c e n t

116 t o t h e l o w e s t zone o f t h e b a s i n c o u l d have been removed d u r i n g t h e p r o g r e s s i v e s i n k i n g o f t h e -basin and sedimented w i t h o t h e r d e t r i t a l m a t e r i a l s . The b a s i n was capped by an i l l i t i c bed, o r i g i n a t e d f r o m m a t e r i a l s r i c h i n m u s c o v i t e and low i n c h l o r i t e and p a l y g o r s k i t e f r o m areas c l o s e t o t h e b a s i n which underwent an a c i d i c a1 t e r a t i o n b u t n o t a t r a n s f o r m a t i o n t o p a l y g o r s k i t e . T h i s happened d u r i n g t h e l a s t phase o f t e c t o n i c a c t i v i t y ( a t t h e l o c a l s c a l e ) , d u r i n g which s e d i m e n t a t i o n r e f l e c t s c o n d i t i o n s o f g r e a t e r calm.

The v e l o c i t y

of s e d i m e n t a t i o n must have been g r e a t e r t h a n t h a t o f t h e s i n k i n g o f t h e basement

.

A f t e r t h e " r a n a " , w h i c h was a r e g i o n a l episode, and t h r o u g h t h e a c t i o n o f p e r c o l a t i n g w a t e r r i c h i n i r o n , a p a r t i a l f e r r i t i z a t i o n o f t h e i l l i t i c bed and s m e c t i z a t i o n o f t h e m u s c o v i t e and t h e p a l y g o r s k i t e were produced. I n T o r r e j o n , t h e e s t a b l i s h m e n t o f t h e f l u v i a l network c r e a t e d t h e p r e s e n t morphology of t h e b a s i n w i t h t h e a l m o s t complete disappearance o f t h e n o r t h f l a n k , t h r o u g h w h i c h t h e T a j o now f l o w s .

F i g . 15 shows t h e f i v e phases o f

t h e e v o l u t i o n and s e d i m e n t a t i o n o f t h e m a t e r i a l s t h a t f i l l e d t h e T o r r e j o n basin.

The f e r r i t i z a t i o n and s m e c t i z a t i o n produced d u r i n g phase 4 a r e f a c u -

l t a t i v e and do n o t o c c u r i n a l l b a s i n s o f t h i s t y p e .

Phase 5 i s s p e c i f i c t o

the Torrejon basin.

3) B e n f i c a ( P o r t u g a l ) and San M a r t i n de Pusa Spain t y p e ( p a l y g o r s k i t e cement) P a l y g o r s k i t e appears as t h e p r i n c i p a l c l a y m i n e r a l i n t h e cement o f conglomerates and sandstones be1 i e v e d t o have been formed between t h e Upper Cretaceous and t h e Oligocene.

They appear i n t h e B e n f i c a Complex ( G a l o p i n de

Carvalho, 1968), i n t h e w e s t e r n s u b - b a s i n o f t h e T a j o b a s i n ( T a l a v e r a de l a Reina), t o t h e n o r t h o f t h e Mountains o f Toledo (San M a r t i n de Pusa, Puebla de Mantalban) (Ordonez e t a l . 1977a), and i n t h e e a s t e r n sub-basin. t o these a r e those d e s c r i b e d by Leguey e t

Similar

a l . (1983, t h i s p u b l i c a t i o n ) on

t h e s o u t h - e a s t b o r d e r o f t h e Duero b a s i n ( p r o v i n c e o f S e g o v i a ) . The cement i s made up o f p a l y g o r s k i t e t s m e c t i t e + c a l c i t e f dolomite

t

silica.

Ordonez e t a l .

(1977a) proposed a d i a g e n e t i c

o r i g i n f o r t h e p a l y g o r s k i t e by means o f t h e t r a n s f o r m a t i o n of i l l i t e through smectite.

Leguey e t a l .

(1983), on t h e o t h e r hand, i n

117 t e r p r e t t h e f o r m a t i o n o f t h e p a l y g o r s k i t e b y n e o f o r m a t i o n a t pH

8.5,

i n r e l a t i o n with the high porosity o f the rock,

of d o l o m i t e o r M g - c a l c i t e and s i l i c a ,

t h e presence

and a f t e r an orogenic a c t i -

vity. EXPLANATON

_ _ _ WATER

-FACE

R A ~ A

A

S

-

ILLlTlC CLAY

SAND AND PALVXftSKITE

ALTERATION ZONE SLATE

S

Fig.

15.-

P a l y g o r s k i t e f o r m a t i o n a t T o r r e j d n and e v o l u t i o n o f t h e b a s i n . ( F o r e x p l a n a t i o n , see t e x t )

T h i s d i a g e n e t i c p a l y g o r s k i t i z a t i o n c o i n c i d e s i n time w i t h an important "palygorskite event"

i n the e a r t h ' s sedimentary h i s t o r y

118 (Callen,

1 9 7 8 a n d 1 9 8 3 ) . T h i s was o f m a r i n e c h a r a c t e r ,

between t h e C r e t a c e o u s a n d t h e Eocene,

occurring

a n d was p r o b a b l y r e s t r i c t e d

t o t h e warm w a t e r s b e t w e e n 2 0 " a n d 40"N a n d S l a t i t u d e . T h e w a t e r s , b e i n g a d j a c e n t t o l i r n d rnbsses u n d e r g o i n g i n t e n s i v e w e a t h e i n g ,

pro-

v i d e d t h e s e a w i t h a s u i t a b l e g e o c h e m i c a l e n v i r o n m e n t f o r pa 1 y g o r s k i t e diagenesis.

A s i m i l a r o r i g i n can be i n f e r r e d here. ble,

o f varia-

Source areas,

b u t m a i n l y c a r b o n a t i c l i t h o l o g i e s , w e r e e r o d e d u n d e r semi - a r i d

o the

o r s e a s o n a b l y a r i d c o n d i t i o n s . Mg a n d S i w e r e b r o u g h t i n marginal

zones t o g e t h e r w i t h d e t r i t a l m a t e r i a l s .

The d i a g e n e t i c

f o r m a t i o n o f p a l y g o r s k i t e and s m e c t i t e s c o u l d have t a k e n p l a c e as Leguey e t a l .

(1983) i n d i c a t e .

4) L e b r i j a type (palygorskite-sepiol i t e marl s) S e d i m e n t a t i o n was p r o d u c e d i n a b r a c k i s h l a c u s t r i n e e n v i r o n ment o r p e r i m a r i n e . The s u r r o u n d i n g landmasses s l o w l y s u p p l i e d S i a n d Mg ( d o l e r i t e s ,

d o l o m i t i c r o c k s ) . On t h e o t h e r h a n d ,

dissolu-

t i o n s o f diatom c o l o n i e s ( e x t e r m i n a t e d b y an environmental

change

f r o m m a r i n e t o c o n t i n e n t a l ) a l s o c o u l d have i n t r o d u c e d s i l i c a t o t h e medium.

U n d e r t h e s e c o n d i t i o n s , w i t h t e c t o n i c s t a b i l i t y a n d an

a r i d climate,

s e p i o l i t e f o r m a t i o n was f a v o r e d a t a b o u t pH 8 .

Later, a f t e r s i g n i f i c a n t weathering o f t h e source area,

(be-

cause o f a s l i g h t subsidence o f t h e b a s i n and a m o i s t e r c l i m a t e ) g r e a t amounts o f magnesium,

iron, silica,

and d e t r i t a l m i n e r a l s ( q u a r t z , the basin.

Under t h e s e c o n d i t i o n s ,

than s e p i o l i t e .

etc.,

as i o n s o r g e l s ,

mica, c h l o r i t e ) were suppl i e d t o p a l y g o r s k i t e was f o r m e d r a t h e r

In a d d i t i o n , d e t r i t a l m i n e r a l s ( e s p e c i a l l y micas)

transformed t o p a l y g o r s k i t e i n the brackish environment,

as a r e -

s u l t o f an e q u i l i b r i u m between t h e u n s t a b l e p h y l l o s i l i c a t e s and t h e s o l u t i o n (Galan and F e r r e r o ,

I n the L e b r i j a deposite, and p a l y g o r s k i t e ,

1982).

t h e c l o s e r e l a t i o n s h i p between i l l i t e

as w e l l as t h e p o s s i b l e random i n t e r s t r a t i f i c a -

t i o n o f i l l i t e a n d p a l y g o r s k i t e i d e n t i f i e d , seem t o s u p p o r t t h e hypothesis o f the i l l i t e - p a l y g o r s k i t e

transformation.

The s m e c t i t e s i n t h e s e c l a y e y s e d i m e n t s c a n be d e t r i t a l o r c a n be formed by t r a n s f o r m a t i o n o f c h l o r i t e , by neoformation.

Occasionally,

i l l i t e or palygorskite,

or

c l i m a t i c o r t e c t o n i c changes p r o d u -

ced abundant d e t r i t a l m a t e r i a l s t h a t i n t e r f i n g e r i n t o t h e c l a y series. The a l t e r n a t i o n o f v a r l y a n d c l a y e y l a y e r s i n t h e s e r i e s c o u l d

119 p o s s i b l y h a v e been a r e s u l t o f p e r i o d i c c l i m a t i c c h a n g e s . Wet p e r i o d s f a v o r e d t h e f o r m a t i o n o f o a l y g o r s k i t e , and duri'ng d r i e r p e r i ods, e v a p o r i t i c s e d i m e n t a t i o n took p l a c e , w i t h l i t t l e s e p i o l i t e

or s m e c t i t e f o r m a t i o n . I n summary: The Spanish continental denosits of s e p i o l i t e and palygorskite can be grouped under four models whose principal f e a t u r e s a r e a s follows: Type 1: Tajo Basin Environment and f a c i e s

Deposits

a ) Detrital f a c i e s of

Vallecas-Vicilvaro Yunclillos Maga'n

d i s t a l zones o f alluvial-fans. Playa-1 ake b ) Marly f a c i e s of

1 acus t r i ne zones

c ) Evapori t i c f a c i e s (marly and/or gypsi ferous )

Principal Authigenic minerals (decreasing order)

SJ,

a, Sap,

Ca-Do, Ch,

Se, C h

Sap, S P

occurrences in Tajo S.1, basin( e.g .Esqui v i a s , Cerro de 10s Angeles, Pinto, e t c . )

pa.

C h , Ca

occurrences in Tajo Ca, Do, Y , Pa, S p basin(e.g .Tabladil l o ) ; Duero basin (e.g.Sacramenia); Ebro basin (e.g.Tarazona-Borja); Calatayud-Teruel basin; and Galician basins?

Type 2: TorrejBn Environment

Depos i t s

Tectonic basin on s l a t y basement. Palygorskite formation from a1 tered c h l o r i t e , and by a u t h i genesis

Torre j B n Coria La Ploraleja Cas telo-Branco Galician basins?

Principal transformed o r authigenic minerals (decreasing order)

pa, I , Cb

Sap, S o , Mo, Do, Ca,

120 Type 3: Benfica-San M a r t i n de Pusa Environment

Deposits

Principal authigenic minerals

Diagenetic formation (authigenesis ) i n d e t r i t a l sediments, i n s l i g h t l y a l k a l i n e pH f r o m Mg s o l u t i o n s . M a t e r i a l comes t o b a s i n a f t e r orogenic a c t i v i t y and p a l y g o r s k i t e forms under s e m i - a r i d o r seasonably a r i d c o n d i t i o n s

San M a r t i n de Pusa d e Pusa ( T o l e d o ) B e n f i c a Fm ( P o r t u g a l ) Valdegrados (Segovia)

Pa, Mg, Sm, Ca, Do, Ch

Environment

Depos it s

P r i n c i p a l transformed o r authigenic minerals

B r a c k i s h 1acus t r i n e e n v i ronmen t o f perimarine o r i g i n P a l y g o r s k i t e by transformation o r authigenesis

L e b r ij a Eastern basins (Almeria, Murcia)

Pa, Sp, Ch, Sm (Carbonates sometimes v e r y i m p o r t a n t )

Type 4: L e b r i j a

Minerals underlined correspond t o present ( o r p o t e n t i a l ) mine deposits C a = c a l c i t e ; Do=dolomite; Ch=chert; Y=gypsum; P a = p a l y g o r s k i t e ; Sap=saponite; Sp=sepiol it e ; S t v = s t e v e n s i t e ; I = i 11 it e ; Mo=montmori 11o n i t e ; C b = C r i s t o b a l it e

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125

SEPIOLITE IN THE AMBOSELI BASIN OF KENYA: A NEW INTERPRETATION

RICHARD L. HAY AND RONALD K. STOESSELL Department o f Geology and Geophysics, University o f C a l i f o r n i a , Berkeley, Cali f o r n i a 94720 (U.S.A.) and Department o f Earth Sciences, University o f New Orleans, New Orleans, Louisiana 70148 (U.S.A.)

ABSTRACT The Sinya Beds of Kenya (lower? P l e i s t o c e n e ) a r e s p r i n g - r e l a t e d d e p o s i t s o f t h e Amboseli Lake Basin.

They c o n t a i n both bedded waxy s e p i o l i t e and meer-

schaum, a massive l i g h t w e i g h t porous s e p i o l i t e .

The meerschaum d e p o s i t s a r e

l a r g e l y r e s t r i c t e d t o t h e c r e s t a l a r e a o f t h e Sinya Dome, which is about 760 x 215 m i n a r e a l e x t e n t .

-

Here t h e Sinya Beds c o n s i s t of 1.5

5 m o f dolomitic

c a l i c h e b r e c c i a , mostly i n t h e form o f dome- and mound- shaped masses, overl a i n by 1-3 m o f i n t e n s e l y folded and f r a c t u r e d waxy bedded s e p i o l i t e . Meerschaum occurs a s i r r e g u l a r pockets and small v e i n s , most o f which a r e i n t h e caliche breccias. The meerschaum-bearing p a r t o f t h e Sinya Beds o r i g i n a t e d a s follows. F i r s t , s e p i o l i t e and carbonate were p r e c i p i t a t e d along t h e s o u t h e a s t margin o f t h e l a k e b a s i n , which was f e d by s p r i n g s from Kilimanjaro.

This

s e p i o l i t e is o f

t h e bedded, waxy v a r i e t y . S l i g h t u p l i f t o f t h e Sinya Dome r a i s e d t h e c r e s t a l d e p o s i t s above t h e water t a b l e .

The c a l i c h e b r e c c i a s were formed within t h e

s e p i o l i t i c c l a y s by evaporation o f ground water i n t h e vadose zone.

Precipi-

t a t i o n o f carbonate was l o c a l i z e d over permeable zones ( f r a c t u r e s ? ) , r e s u l t i n g i n caliche-breccia

mounds and domes, t h e growth of which folded and f r a c t u r e d

t h e overlying clays.

Meerschaum was p r e c i p i t a t e d from ground water i n t h e

c a l i c h e b r e c c i a s and o v e r l y i n g c l a y s , very l i k e l y following a rise i n t h e water t a b l e . INTRODUCTION Scope and Purpose The o l d e s t P l e i s t o c e n e d e p o s i t s o f t h e Amboseli Basin c o n t a i n two v a r i e t i e s of s e p i o l i t e .

That o f economic importance is meerschaum,

lightweight form used f o r t h e manufacture o f high-quality

a massive, pure,

pipes.

More comnon

is a d e n s e r , waxy bedded s e p i o l i t e t h a t h a s not been u t i l i z e d economically. Dolomite is t h e h o s t rock f o r most of t h e meerschaum.

The Kenya d e p o s i t s have

been s t u d i e d by g e o l o g i s t s o f t h e Kenya Geological Survey (Williams, 1972) and by R.

K.

Stoessell (Stoessell,

1977; S t o e s s e l l and Hay,

1978). The s e n i o r

author v i s i t e d t h e s e d e p o s i t s only b r i e f l y i n 1975 with S t o e s s e l l .

Stoessell

discovered k e r o l i t e , a hydrated disordered v a r i e t y of t a l c , and proposed a geochemical and hydrologic e x p l a n a t i o n f o r t h e o r i g i n of t h e s e p i o l i t e ,

126

k e r o l i t e , and dolomite. New i n s i g h t on t h e o r i g i n of t h e Amboseli d e p o s i t s a r o s e i n t h e course o f s t u d i e s on Mg-silicate c l a y s and carbonates i n t h e Amargosa Desert of Nevada and C a l i f o r n i a (Hay e t a l . , 1980; Teague, 1981). The present paper is essent i a l l y a r e i n t e r p r e t a t i o n of t h e f i e l d d a t a already e s t a b l i s h e d by Williams (1972) and S t o e s s e l l and Hay (1978). Geologic S e t t i n g The Amboseli Basin is semiarid and covers an a r e a of about 400 km2 on t h e Kenya-Tanzania border. The western h a l f is dominated by a playa, Lake Amboseli, which bears water only during t h e r a i n y season. The basin (Fig. 1)

is bordered on t h e north by h i l l s of Precambrian metamorphic rock and on t h e south by M t . Kilimanjaro, which c o n s i s t s l a r g e l y of a l k a l i n e l a v a s , princip a l l y o l i v i n e b a s a l t s . M t . Kilimanjaro is a major source of water, which flows i n t o t h e basin a s streams and ground water.

'1'40'9

0

5

10

I S lam

Fig. 1. Map of t h e Amboseli Basin i n Kenya, a f t e r Williams (1972) and S t o e s s e l l (1977). Arrows i n d i c a t e r e g i o n a l flow p a t t e r n of s u r f a c e and subs u r f a c e water.

127

Lake sediments of P l ei s t o cen e Age comprise t h r e e s t r a t i g r a p h i c u n i t s (Willi a m s, 1972). The lowest is t h e Sinya Beds, which a r e exposed p r i n c i p a l l y on t h e c r e s t o f an a n t i c l i n e named t h e Sinya Dome, near t h e southern edge o f t h e basin. The maximum known t h i ck n es s of t h ese beds, pe ne tra te d by d r i l l i n g , is

18 m.

The Amboseli Clays unconformably o v e r l i e t h e Sinya Beds i n t h e v i c i n i t y A

of t h e Sinya Dome and u n d e r l i e t h e p r es ent l a k e ba sin a t shallow depth.

maximum t h i c k n e s s of about 60 m was estimated by Williams (1972). These a r e s e p i o l i t i c c l a y s with au t h i g en i c c a l c i t e , dolomite, g a y l u s s i t e , and Kfeldspar. I l J i t i c c l a y is widespread and may be d e t r i t a l , authigenic, or both. The 01 Tukai Beds a r e t h e youngest Ple istoc e ne u n i t . These comprised silts, c l a y s , c l ay - cl as t aggregates and c a l i c h e s . The formation is found i n t h e southern p a r t of t h e b as i n and h as a maximum thic kne ss of about 8 m. Authigenic m i n e r al s i n cl u d e s e p i o l i t e , analcime, o p a l , and calcite. THE SINYA BEDS The Sinya Beds a r e found i n both Kenya and Tanzania, but only t h e Kenya d e p o s i t s are considered i n t h i s paper. They are exposed p r i n c i p a l l y i n excav a t i o n s on t h e crest of t h e Sinya Dome, which is about 760 m long and 215 m 5 m of wide (Williams, 1972). Here t h e exposed beds c o n s i s t of about 1.5

-

nodular and b r ecci at ed dolomite, mostly i n t h e form o f e longa te mounds or domes, o v e r l a i n by 1-3 m o f s t a t i f i e d waxy s e p i o l i t e t h a t is inte nse ly folded and f r a c t u r e d . Dolomite b r ecci a c h a r a c t e r i s t i c a l l y forms t h e cores of a n t i c l i n e s (Fig. 2) and may occur a s i r r e g u l a r masses within deformed s e p i o l i t e . Dolomite masses a r e i n p l aces t h r u s t over crumpled beds o f s e p i o l i t e . The p a t t e r n of f o l d i n g is h i g h l y v a r i a b l e , but Williams (1972) noted some evidence t h a t minor f l e x u r e s r a d i a t e o u t from t h e core of t h e Sinya Dome. Meerschaum occurs a s i r r e g u l a r masses and small v e i n s , most comonly f i l l i n g t h e space between nodules and b l o ck s of dolomite. It forms l e n t i c l e s and v e i n s along f r a c t u r e s i n t h e waxy s e p i o l i t e . The meerschaum is ge ne ra lly undeformed, although Williams (1972) noted f r a c t u r e - f i l l i n g meerschaum with lin e a t e d s u r f a c e s s u g g es t i n g movement a f t e r de position. The amount o f meerschaum is small r e l a t i v e t o t h e dolomite and waxy s e p i o l i t e , and J. Walsh ( i n Williams, 1972) h as estimated 7.3 kg of meerschaum per c ubic m of host rock. Ke r o l i t e l o c a l l y o ccu r s around t h e s e p i o l i t e , s e p a r a t i n g it from t h e dolomite ( S t o e s s e l l and Hay, 1978). The waxy, bedded s e p i o l i t e is green or gre e nish gra y, l o c a l l y rootmarked, and c o n t a i n s t h i n v ei n s of dolomite and c a l c i t e .

The s e p i o l i t e is i n pla c e s

surrounded by t h i n s h e e t s o f waxy k e r o l i t e , which is p a l e grey t o p a s t e l green.

The c o n t act may be g r a d a t i o n a l over a d i s t a n c e o f 1 or 2 cm, and t h e

k e r o l i t e may w e l l be an a l t e r a t i o n product of t h e s e p i o l i t e ( S t o e s s e l l , 1977;

128

Fig. 2. Exposure of t h e Sinya Beds i n an excavation on t h e crest of t h e Sinya Dome. In cen t er o f photograph is a c a l i c h e bre c c ia dome forming t h e c o r e o f an a n t i c l i n e and flanked by i n t e n s e l y deformed c la ys. A t t o p a l a y e r o f rubble o v e r l i e s t h e Sinya Beds. T h i s exposure of t h e Sinya Beds is about 3 m high. S t o e s s e l l and Hay, 1978). The meerschaum, waxy green s e p i o l i t e , and k e r o l i t e a r e r e l a t i v e l y pure Mgs i l i c a t e c l a y s (Table 1 ) . Bulk samples of meerschaum have 0.2 t o 1.8 percent A1203 and 0.5 t o 1.0 percent FeO + Fe203 (Williams, 1972; S t o e s s e l l and Hay,

1978). A sample of waxy green s e p i o l i t e h as 1.8 percent Al2o3 atid 0.1 t o 0.7 percent FeO + Fe203. The amount of K20 ranges from 0.2 t o 1.0 percent and roughly c o r r e l a t e s with t h e amounts of aluminum and i r o n . This r e l a t i o n sugg e s t s t h e presence of a small amount o f c l a y mica, possibly phe ngitic i l l i t e . The d o l o m i t i c b r e c c i a s

consist

of

angular

blocks

and

irregular

to

subrounded nodules a s much a s 30 cm i n average diameter. Their s u r f a c e s commonly have a reticulate p a t t e r n of s u r f a c e c ra c ks, which may be f i l l e d by meerschaum ( S t o e s s e l l arld Hay, 1978). Adjacent blocks and nodules ge ne ra lly f i t t o g e t h e r , i n d i c a t i n g only s l i g h t displacement. Shearing is widespread and widely p a r a l l e l s t h e margins o f t h e b r e c c i a domes giving t h e appearance o f

129

TABLE 1. Chemical Composition of Sediments of the Sinya Bedsb s.d.a Si02 Ti02

0.09

A1203

0.04

Fe203 FeO

0.02

0.01

MnO

1

2

3

4

53.17

54.51

3.66

0.12 1.15

0.17 1.76

0.03 0.49

0.01 0.18

0.64 0.02

0.99 0.04

0.10

0.09

0.00

0.01

0.00

0.00

0.000

0.000 24.70

0.000 28.01

0.0005 20.11

0.23

0.52

31.48

0.85 0.26

0.06

53.70

NiO MgO CaO Na20

0.05 0.02

23.31 0.03

0.02

0.67

0.45

K20

0.03

0.61 0.02

0.97 0.04

0.03

0.06

9.83 9-76

8.29 8.79

7.97 7.18

44.78 0.38

99.86

99.61

99.95

100.83

2 '5 ' .H 0 '

2 H20-

+ C02

~~~

Total

0.01

~

a. Standard deviations were computed from duplicate analyses of major oxides on all samples. b. R. Stoessell did the analyses using a modified procedure of Shapiro and Brannock (1962). Totals of H20+ and C02 were computed using ignition loss with a correction for FeO. Sample 1 is fracture-filling massive white sepiolite (meerschaum); 2 , massive green sepiolite of the bedded clays; 3, gray kerolite; 4, dolomite. Samples 1 and 3 represent the purest specimens collected of sepiolite and kerolite, respectively. The computed formula for the white sepiolite (no. 11, based on 8 oxygens to balance all cations except H+, is (Mg 1,gONaO.07K0.04) (si2.94A10. 08Fe0.03) q . 5 ( O H ) .3.07H20* Similarly, the computed formula for the kerolite (no. 31, based on 11 oxygens, is 12K0.03Ca0-04) (Mg2. 9) (si3 .9 l M 0 .04Fe0. 01 'lo( OH) 2*2*62H20* Fe in the formulas refers to FeZ. anticlinal folding. Some of the blocks and nodules of dolomite contain rounded, sharp-margined masses of waxy sepiolite as much as a cm in diameter. The dolomite also contains finely disseminated Mg-silicate clay. The one sample studied in detail contains 10 percent of a trioctahedral smectite. This smectite is very likely stevensite (Mg smectite) in view of the very small amounts of A1 and Fe in the analyzed dolomite Table 1 , no. 4).

130 AS shown by d r i l l cores, t h e Sinya Beds on t h e f l a n k s and away from t h e dome c o n s i s t principall-y o f c l a y and mudstone, much o f which c o n t a i n s car-

bonate (dolomite?), and a t l e a s t some o f which is s e p i o l i t i c (Williams, 1972). Meerschaum was found i n a s i n g l e d r i l l hole away from t h e crest of t h e dome. The dolomitic b r e c c i a s a r e apparently r e s t r i c t e d t o t h e c r e s t of t h e dome. GEOCHEMISTRY A t temperatures and pressures corresponding t o near earth-surface condit i o n s , t h e i n i t i a l formation of magnesium s i l i c a t e s is determined by r e a c t i o n k i n e t i c s r a t h e r than chemical s t a b i l i t i e s . Preliminary s t a b i l i t y r e l a t i o n s between Amboseli c r y p t o c r y s t a l l i n e s e p i o l i t e and k e r o l i t e were reported by S t o e s s e l l (1977) from 25OC and 1 bar. These hydrolysis experiments l a s t e d 13 months for s e p i o l i t e and 6 months f o r k e r o l i t e . For each mineral, experiments were run i n 5 s o l u t i o n s with s t a r t i n g compositions ranging from a c i d i c t o basic. The r e s u l t s implied e q u i l i b r a t i o n with k e r o l i t e i n s o l u t i o n s having a f i n a l pH less than 8 and e q u i l i b r a t i o n with s e p i o l i t e i n more b a s i c s o l u t i o n s . The thermodynamic l o g K values for s e p i o l i t e (Mg2Si34.5(0H).3H20) and kerol-

i t e (Mg3Si4Olo(0H),.nH20) were 15.50 2 0.21 and 23.54 f o r t h e following r e x t i o n s :

0.19,

respectively,

s e p i o l i t e + 4H+ = 2Mg2+ + 3Si02 + 5.5H20 k e r o l i t e + 6H+ =

3N2++

4Si02 + (4tn)H20

The value f o r s e p i o l i t e is thermodynamically c o n s i s t e n t with t h e 1 bar solub i l i t y data a t 51' and 90°C reported by C h r i s t , H o s t e t l e r , and S i e b e r t (1973).

W e know of no o t h e r experimental d a t a for k e r o l i t e . These r e s u l t s a r e t e n t a t i v e , and f i n a l experimental d a t a (8 year e q u i l i b r a t i o n s ) w i l l be reported later by t h e j u n i o r author. The K values imply s e p i o l i t e i s metastable with r e s p e c t t o k e r o l i t e , and both a r e metastable with r e s p e c t t o talc. S e p i o l i t e is s t a b l e with regard t o s e r p e n t i n e a t aqueous s i l i c a a c t i v i t i e s g r e a t e r than quartz s a t u r a t i o n . Only a t very high s i l i c a a c t i v i t i e s ( g r e a t e r than amorphous s i l i c a s a t u r a t i o n ) does s e p i o l i t e become more s t a b l e than k e r o l i t e and talc. The r a t h e r c o m n low temperature formation of s e p i o l i t e must then be due t o k i n e t i c i n h i b i t i o n s i n t h e formation of o t h e r magnesium silicates. Water chemistry d a t a f o r 23 samples taken within Amboseli Basin were reported by Stoessell and Hay (1978). The water samples range i n s o l u t e s from 60 t o 7,000 p a r t s p e r million (ppm). These data show a general i n c r e a s e i n 2 a 2+/(a and a ~ i 0 2in water moving towards t h e l a k e bed. Mg H+

Two p a r a l l e l

131

trends were observed, one for s u r f a c e water and one for ground water. Twelve of t h e samples were supersaturated with respect t o both s e p i o l i t e and keroli t e . S i g n i f i c a n t formation o f Mg s i l i c a t e s appeared t o occur a t pH values g r e a t e r than 7.9 a s shown by r e v e r s a l s i n a c t i v i t y trends. This supports t h e experimental observatioh by S i f f e r t (1962) t h a t a pH of a t l e a s t 8 is necessary t o nucleate s e p i o l i t e . Field r e l a t i o n s a t Amboseli imply k e r o l i t e formed l a t e r than waxy s e p i o l i t e and sometimes a s a s e p i o l i t e a l t e r a t i o n product. The present-day ground water compositions i n t h e Sinya Beds have high concentrations of Mg ( > 10 ppm) and

sio2

60 ppm), pH between 7.9 and 8.3, and t o t a l dissolved s o l i d contents below 1000 ppm. The experimental d a t a of Stoessel (1977) a r e c o n s i s t e n t with k e r o l i t e nucleation below a pH of 8. For these reasons, we would hypothesize k e r o l i t e forming in, contact with s l i g h t l y basic waters of low s a l i n i t y . These waters contain Mg and Si02 derived from leaching t h e o l i v i n e b a s a l t s of M t . (>

Kilimanjaro. The l a c k of A 1 i n d e t r i t a l m a t e r i a l within t h e predominantly carbonate Sinya Beds prevents t h e formation of saponites or palygorskite, r e s u l t i n g i n r e l a t i v e l y pure magnesium s i l i c a t e s . W e want t o emphasize t h a t t h e formation of Mg s i l i c a t e s a t Amboseli is a problem of r e a c t i o n k i n e t i c s , not chemical s t a b i l i t y . Waters i n t h e basin become supersaturated a s a r e s u l t of normal weathering processes. Because k e r o l i t e is more s t a b l e than s e p i o l i t e , i n c r e a s e s i n ang2+, aSiO2, and pH w i l l increase t h e thermodynamic p o t e n t i a l t o transform s e p i o l i t e i n t o k e r o l i t e . However, thermodynamics tell us only t h e r e a c t i o n d i r e c t i o n , not t h e r e a c t i o n kinetics. W e do know t h a t t o p r e c i p i t a t e k e r o l i t e d i r e c t l y r e q u i r e s very high supersaturation (Jones, 1982). This is probably not t h e case f o r transformat i o n from a precursor such a s s e p i o l i t e or s t e v e n s i t e .

The nature of t h e pre-

cursor w i l l have an important effect on t h e r e a c t i o n k i n e t i c s . The k i n e t i c importance of pH i n t h e formation of Mg s i l i c a t e s is not y e t understood. The effect of pH on k e r o l i t e formation may have t o do with t h e k i n e t i c s of transformation of t h e precursor. I n t h e hydrolysis experiments of S t o e s s e l l (19771, t h e r e a c t i o n k i n e t i c s decreased s i g n i f i c a n t l y with increases i n pH. Our conclusion t h a t a high pH is n o t necessary t o form s i g n i f i c a n t amounts of k e r o l i t e is based on preliminary experimental results, t h e p r e s e n t d a y ground water chemistry within t h e Sinya Beds, and t h e assunption t h a t k e r o l i t e is p r e s e n t l y forming i n t h e s e beds.

Other researchers might

disagree. Khoury, Eberl, and Jones (1982) b e l i e v e k e r o l i t e formed i n t h e Amargosa Desert d e p o s i t s i n waters of higher pH and s a l i n i t y than those presently found i n t h e Sinya Beds a t Amboseli. Those conclusions a r e based on the experimental observation by S i f f e r t ( 1962) that t a l c can be p r e c i p i t a t e d with a t r i o c t a h e d r a l smectite a t a pH above 9 , together with an observed

132

a ss o c i a t i o n of small amounts o f h a l i t e with k e r o l i t e and s t e v e n s i t e i n t h e Amargosa Desert deposits, Jones 1982) p o i n t s out t h a t k e r o l i t e i s o f t e n t h e

result o f a r e a ct i o n between Mg i n t e r l a y e r s in a p r e e x i s t i n g smectite with aqueous Si02. K er o l i t e i n t h e margosa Desert d e p o s i t s is i n t e r s t r a t i f i e d with s t e v e n s i t e and may r ep r es en t an a l t e r a t i o n of a p r e e x i s t i n g s m e c t i t e ; whereas, a t Amboseli, k e r o l i t e appears t o have o f t e n had a s e p i o l i t e precurs o r . These d i f f e r e n c e s i n p r ecu r s o r s should n e c e s s i t a t e d i f f e r e n t s o l u t i o n compositions t o overcome d i f f e r e n t k i n e t i c c o n t r a i n t s . O R I G I N OF SINYA BEDS

Previous i n t e r p r e t a t i o n The o r i g i n o f t h e Sinya Beds i s i n f er r ed by S t o e s s e l l and Hay (1978) a s f 01lows

.

1.

S e p i o l i t e was p r e c i p i t a t e d along t h e southe rn, spring-fed margin of t h e

lake.

Water l e v e l f l u c t u a t e d , and a t times of low level t h e s e p i o l i t e dehy-

d r a t e d , producing d e s i c c a t i o n cr ack s , and developing a b r e c c i a t e d , nodular texture. 2.

The waxy bedded s e p i o l i t e which now o v e r l i e s t h e dolomite was pre c ipi-

t a t e d i n t h e l a k e following a rise i n l e v e l .

3.

The lower, f r act u r ed s e p i o l i t e was dolomitized during a drop i n l a k e l e v e l . I t was suggested t h a t t h i s ground water was low i n s i l i c a and derived from recharge a r e a s i n Precambrian carbonate

rocks t o t h e north.

The Mg and

Si02 r e l e a se d i n t o s o l u t i o n by d o l o mi t i zat i on were p r e c i p i t a t e d a s s e p i o l i t e in open s p a c e s around t h e carbonate blocks. The small, rounded masses of waxy s e p i o l i t e i n some o f t h e dolomite were considered unreplaced relicts o f t h e primary s e p i o l i t e . The s h ar p co n t act between t h e dolomite and ove rlying bedded s e p i o l i t e was believed t o r ep r es en t t h e water t a b l e a t t h e time of dolomitization. 4.

Doming and i n t e n s e , smaller-scale deformation were a t t r i b u t e d t o t e c -

t o n i c a c t i v i t y following d ep o s i t i o n o f t h e Sinya Beds.

5.

Kerolite was formed from s e p i o l i t e by a lowering o f pH, e s s e n t i a l l y a s a weathering product. Revised I n t e r p r e t a t i o n T h i s new i n t e r p r e t a t i o n

o f t h e meerschaum-bearing p a r t o f t h e Sinya Beds

d i f f e r s from t h e e a r l i e r one i n t h e o r i g i n of t h e dolomitic bre c c ia and meers c h a m , m d i n t h e cause and timing o f t h e i n t e n s e f o l d i n g of t h e c l a y s above t h e dolomitic b r ecci as .

The i n t e r p r e t a t i o n is a s follows.

133

1.

S e p i o l i t e and carbonate (dolomite?) were p r e c i p i t a t e d along t h e south-

e r n , spring-fed margin o f t h e l ak e.

Th i s s e p i o l i t e inc lude s t h e waxy s e p i o l -

i t e forming t h e upper p a r t o f t h e Sinya Beds. 2. S l i g h t doming r a i s e d t h e c r e s t a l d e p o s i t s of t h e Sinya Dome above t h e water t a b l e . Ground water from Kilimanjaro seeped upward through permeable zones, probably f r a c t u r e s , i n t h e c r e s t a l area. Nodules of carbonate with disseminated s t e v e n s i t e were formed i n evaporation of ground water a t o r above th e water t a b l e and within t h e p r e- ex i s t i n g s e p i o l i t e c l a y s (Fig. 3).

Contin-

ued evaporation r e s u l t e d i n t h e growth o f new nodules below those already formed, pushing them upward and deforming t h e ove rlying c l a y s .

Fra c ture s i n

t h e deformed c l a y s would have aided evaporation and l o c a l i z e d nodule growth, u l t i m a t e l y r e s u l t i n g i n t h e dome-shaped masses of c a l i c h e b r e c c i a t h a t form c o r e s of a n t i c l i n e s . Mann and Horwitz (1979) have c a l l e d upon t h i s mechanism f o r t h e growth of steep-sided c a l c r e t e ( = c a l i c h e ) domes i n western A ustra lia . These domes, l i k e some of t h e Amboseli domes, have s t r u c t u r e s engendered by shear and c o n c en t r i c f o l d i n g due t o upward growth pre ssure .

Inte nse , upward

small-scale deformation of t h e bedded c l a y s is a t t r i b u t e d t o growth of t h e domes and i r r e g u l a r masses of c a l i c h e b r ecc ia . The small rounded masses of waxy s e p i o l i t e i n some o f t h e dolomite nodules and bloc ks a r e considered c l a s t s of matrix c l a y incorporated d u r i n g growth of t h e carbonate. A s y e t unresolved is whether t h e c a l i c h e b r e c c i a s were formed d i r e c t l y a s dolomite or by dolomitization of calcium carbonate.

3.

Meerschaum f i l l i n g space between dolomite bloc ks and f r a c t u r e s in

folded c l a y s was deposited a f t e r growth of t h e a dja c e nt blocks and f o l d i n g of the clays.

Indeed, most or n e a r l y a l l of t h e meerschaum may have been depo-

s i t e d a f t e r growth and u p l i f t o f t h e c a l i c h e b r e c c i a s and deformation of t h e clays.

The change i n

p r e c i p i t a t i o n from carbonate

(plus stevensite)

to

s e p i o l i t e may have been caused by a rise i n t h e water t a b l e , with t h e meerschaum deposited from ground water less evaporated t h a t t h e vadose water f r o m which t h e c a l i c h e b r e c c i a s were p r e c i p i t a t e d . Some, a t l e a s t , o f t h e meerschaum was probably deposited b ef o r e growth of t h e c a l i c h e b r e c c i a s had been completed, i n view o f t h e l i n e a t e d ( s l i ck en side d? ) f r a c t u r e - f i l l i n g meerschaum noted by Williams. Meerschaum could have been deposited during growth of t h e c a l i c h e b r e c c i a s a s a r e s u l t of a s l i g h t , temporary rise i n t h e water t a b l e , followed by a lowering d u r i n g which more c a l i c h e bre c c ia was formed. 4. Doming continued following d ep o s i t i o n of t h e Sinya Beds, and they were eroded i n t h e a r e a p r i o r t o d ep o s i t i o n of t h e Amboseli c l a y s . s e p i o l i t e i n t h e lower p a r t o f

Seams of white

t h e Amboseli c l a y s i n t h e c r e s t a l a r e a

( S t o e ss e l and Hay, 1978) were probably p r e c i p i t a t e d from ground water seeping along f r a c t u r e s , s i m i l a r t o p r e c i p i t a t i o n of meerschaum i n t h e Sinya Beds.

134

W

a

I.-I

lake levelL ~-

-_sepiolite &

1 c I _ _ _

carbonates

,water

groundwater

E

It

20m

table

discharge

Fig. 3. Schematic east-west cross-section showing t h e development o f t h e Sinya Dome and c a l i c h e b r ecci a masses i n t h e Sinya Beds. Se c tion ( a ) shows t h e Sinya Beds p r i o r t o folding. Section ( b ) r e p r e s e n t s t h e e a r l y s t a g e s of doming, and Section (c) is of t h e dome a f t e r f o l d i n g and shows c a l i c h e b r e c c i a mounds, which were formed a t or above t h e water t a b l e following and possibly during doming. Bedded s e p i o l i t e and carbonates above t h e bre c c ia mounds were deformed by t h e i r growth. COMPARISON WITH AMARGOSA DEPOSITS

Deformation of beds by growth of c a l i c h e (= c a l c r e t e ) from below have been reported by Price (1925), Jennings and Sweeting (19611, and Reeves (1976, p. 60-64). Reeves (1976, Fig. 3-14) and Horwitz and Mann ( 1979) f i g u r e c a lic he b r e c c i a domes g e n er al l y s i m i l a r i n t e x t u r e and s t r u c t u r e t o those of t h e Sinya These domes a r e , however, smaller than those of t h e Sinya Beds, and a s s o c i a t e d Mg-silicate c l a y s were not reported.

Beds.

Some o f t h e Pliocene and lower? P l ei s t o cene d e p o s i t s i n t h e Amargosa Desert o f southwestern Nevada and s o u t h eas t er n C a l i f o r n i a a r e s t r i k i n g l y s i m i l a r i n

most r e s p e c t s t o t h e Sinya Beds on the crest of t h e Sinya Dome. The Amargosa Desert was a l a k e b as i n i n t h e Pliocene and probably e a r l y Pleistocene. Springs supplied l a r g e a m u n t s of water t o t h e ba sin, r e s u l t i n g i n l a r g e quant i t i e s o f carbonates and Mg-silicate c l a y s - p r i n c i p a l l y s e p i o l i t e and stevens i t e with i n t e r l a y e r e d k e r o l i t e (Khoury, 1978). Most of t h e c l a y s were

135

deposited i n playa and marshland environments. Caliche-breccia masses comparable i n s i z e t o those of t h e Sinya Beds. are widespread a t two p l aces i n t h e d e s e r t (Teague, 1981). I n t h e e a ste rn p a r t they form a narrow zone about 1 km long t h a t appears t o be loc a liz e d along a p r e - e x i st i n g f a u l t . Near t h e southwestern margin the y unde rlie most o f an a r e a about 3 h long and 600 m wide. A s seen i n cross-section, t h e sm a lle r, better-exposed c a l i c h e b r ecci a masses form domes and mounds 2-3 m high and 4-6

m wide.

The o v er l y i n g and ad j acen t c l a y s a r e deformed, comnonly i n t o a n t i -

c l i n e s w i t h c a l i c h e b r e c c i a co r es . Some of t h e c a l i c h e b r e c c i a s form piercement s t r u c t u r e s .

The l a r g e s t masses, only incompletely exposed in excava-

t i o n s , have eroded t o p s and a r e a t l e a s t 7 m t h i c k . l a r g e r masses and some o f t h e s mal l er ones.

Shearing is comnon in t h e

The b r e c c i a s c o n s i s t of angular fragments and nodules many of which have r e t i c u l a t e s u r f a c e c r a c k s a s i n dolomite o f t h e Sinya Beds. The carbonate i n t h e Amargosa b r ecci a can be dolomite, c a l c i t e o r both. suggest t h a t t h e dolomite has replaced c a l c i t e .

Field relationships

The carbonate rocks contain

an average about 10 p er cen t o f disseminated Mg-silicate c l a y , p r i n c i p a l l y kerolite-stevensite. I n t e r s t i t i a l c l a y is p r i n c i p a l l y ke rolite -ste ve nsite b u t can be s e p i o l i t e .

With few exceptions t h e i n t e r s t i t i a l c l a y is deformed i n

folded and sheared zones, showing that most o f it had been deposited before growth and displacement of t h e c a l i c h e b r e c c i a s had been completed. The Amargosa and Amboseli c a l i c h e b r e c c i a s d i f f e r p r i n c i p a l l y i n t h e amount and mineral composition of t h e i n t e r s t i t i a l Mg-silicate c la y. This may l a r g e l y r e f l e c t a d i f f e r e n c e i n t h e water composition, with t h a t of t h e Amargosa d e p o s i t s derived l a r g e l y from recharge a r e a s in carbonate rocks whereas that of Amboseli is from v o l can i c rocks.

Hydrologic and c l i m a t i c d i f f e r e n c e s

may have been a d d i t i o n a l f a c t o r s , which cannot pre se ntly be evaluated. ACKNOWLEDGEMENTS The work o f Williams (1972) and S t o e s s e l l (1977) provided most of t h e f a c t s upon which t h i s a n a l y s i s was made. F i n an ci a l support for t h e Amboseli f i e l d work was and provided by National Science Foundation Grant DES 72-021523 and DES 74-12782.

Work i n t h e Amargosa Desert was supported by National Science

W e a r e indebted t o t h e Republic of Kenya f o r permission t o study t h e Amboseli d e p o s i t s and t o I n d u s t r i a l Minerals Ventures, Inc., and t o Jack Mayhew, t h e i r g e o l o g i s t , f o r t h e opportunity t o study t h e Foundation Grant EAR 78-01776.

Amargosa d e p o s i t s .

136 REFERENCES C h r i s t , C. L., Hostetler, P. B., and S i e b e r t , R. M. (1973) Studie s i n t h e s y s t e m Mg0-Si02-C02-H 0 111: The act i v i t y-produc t c onsta nt o f s e p i o l i t e . Am. J. S c i . , 273: 65-83. Hay, R. L., Wiggins, B., and Teague, T. T. '(1980) Spring-related c a rbona te s and Mg-silicate c l a y s i n t h e Amargosa Basin o f Nevada and C a l i f o r n i a ( a b s . ) . Geol. Soc. Am. Ab s t r act s with Programs 12: 443-444. Jennings, J. W., and Sweeting, M. M. (1961) Caliche pseudo-anticlines i n t h e F i t z r o y Basin, western Au s t r al i a. Am. J . Sci., 259: 635-9. Jones, B. F. (1982) Clay mineral d i ag en es is i n l a c u s t r i n e sediments. U.S. Geological Survey Prof. Paper ( i n p r e s s ) . Khoury, H. N. (1978) Mineralogy and chemistry of some unusual c l a y d e p o s i t s i n t h e Amargosa Desert, southern Nevada. Unpublished Ph.D. t h e s i s , Univers i t y of I l l i n o i s , Urbana, 171 pp. Khoury, H. M., E b e r l , D. D., and Jones, B. F. (1982) Origin of magnesium c l a y s from t h e Amargosa Desert, Nevada. Clays and Clay Minerals, 30: 327-336. Mann, A. W., and Horwitz, R. C. (1979) Groundwater c a l c r e t e d e p o s i t s i n Aust r a l i a . J. G e o l . Soc. Aust., 26: 293-303. Price, A. W. (1925) Caliche and pseudo-anticlines. Bull. Am. Assoc. Pe trol. G e o l . , 9: 1009-1017. Reeves, C. C. (1976) Caliche; o r i g i n , c l a s s i f i c a t i o n , morphology, and uses. Estacado Books, Lubbock, Texas, 233 pp. S i f f e r t , B. (1962) Some r e a c t i o n s o f s i l i c a i n s o l u t i o n : formation of c l a y . Reports G e o l . Map S er v i ce Alsace-Lorraine, 21: 100 pp. S t o e s s e l , R . K. (1977) Geochemical s t u d i e s of two magnesium s i l i c a t e s , s e p i o l ite and k e r o l i t e . Ph.D. Th es i s , University of C a l i f o r n i a , Berkeley, CA, 122 pp. S t o e s s e l , R . K., and Hay, R. L. (1978) The geochemical o r i g i n of s e p i o l i t e and k e r o l i t e a t Amboseli, Kenya. Contrib. Miner. Pe trol., 65: 255-267. Teague, T. T. (1981) Authigenic s i l i c a t e s and carbonates i n playa and r e l a t e d d e p o s i t s from t h e Amargosa Desert, Nevada. M.S. Thesis, University of C a l i f o r n i a , Berkeley, CA, 78 pp. W i l l i a m s , L. A . J . (1972) Geology o f t h e Amboseli area. Geol. Surv. Kenya, 90: 86 pp.

137

SEPIOLITE I N PLEISTOCENE LAKE TECOPA, I N Y O COUNTY, CALIFORNIA HARRY C. STARKEY AND PAUL D. BLACKMON U.S. GEOLOGICAL SURVEY, DENVER, COLORADO, U.S.A.

A b s t r a c t - - P l e i s t o c e n e Lake Tecbpa, i n s o u t h e a s t e r n I n y o County, C a l i f o r n i a , was formed i n a c l o s e d b a s i n when t h e Amargosa R i v e r was b l o c k e d a t t h e s o u t h e r n end o f t h e v a l l e y .

The l a k e - b o t t o m sediments c o n s i s t o f mudstones i n t e r b e d d e d

w i t h t u f f s formed from i n t e r m i t t e n t v o l c a n i c ash f a l l s . S e p i o l i t e i s found n e a r t h e m a r g i n s of t h e l a k e b a s i n , s t r a t i g r a p h i c a l l y w i t h i n about 2 m e t e r s o f t h e uppermost t u f f s .

The s e p i o l i t e was p r o b a b l y

p r e c i p i t a t e d when s i l i c a t a k e n i n t o s o l u t i o n f r o m t h e v o l c a n i c ash became a v a i l a b l e t o t h e magnesium-bearing,

high-pH (9.0)

l a k e waters.

Z e o l i t e s were

formed w i t h i n t h e ash beds and t h e s e p i o l i t e s were formed o u t s i d e t h e ash beds.

A p p a r e n t l y s e p i o l i t e was n o t produced w i t h i n t h e ash beds because o f t h e

presence o f r e a c t i v e a1 umina. INTRODUCTION S e p i o l i t e was r e c o g n i z e d by Sheppard and Gude (1968) i n t h e f i n e r - t h a n - 2 - u m f r a c t i o n o f some mudstones i n P l e i s t o c e n e Lake Tecopa.

They presumed i t t o be

a u t h i g e n i c and t h e o t h e r c l a y s t o be d e t r i t a l , and t h e y suggested f u r t h e r sampling t o d e f i n e t h e d i s t r i b u t i o n o f t h e s e p i o l i t e and i t s r e l a t i o n t o t h e other c l a y minerals. O f 158 samples c o l l e c t e d by t h e p r e s e n t a u t h o r s f o r c l a y s t u d i e s o f t h e Lake

Tecopa beds, o n l y 43 c o n t a i n e d s e p i o l i t e .

Only t h o s e samples t h a t c o n t a i n e d

s e p i o l i t e , regardless o f q u a n t i t y , are included i n t h i s report.

Results o f t h e

s t u d i e s o f a l l t h e samples c o l l e c t e d have been p u b l i s h e d elsewhere ( S t a r k e y and B1 ackmon, 1979). P l e i s t o c e n e Lake Tecopa, about 23 km l o n g and 18 km wide, i s l o c a t e d i n t h e W a v e D e s e r t about 32 km e a s t o f Death V a l l e y N a t i o n a l Monument i n southeastern I n y o County, C a l i f o r n i a , w i t h i n Tps. 20, 21, and 22 N and Rs. 6 and 7 E.

Las Vegas, Nevada, t h e n e a r e s t l a r g e c i t y , i s a b o u t 97 km t o t h e e a s t

(Fig. 1). GEOLOGY OF THE BASIN The Amargosa R i v e r , t h e c h i e f s u r f a c e d r a i n a g e o f t h e area, o r i g i n a t e s i n Pahute Mesa, a b o u t 175 km n o r t h w e s t o f Las Vegas, Nev.

I n t h e area under s t u d y

t h e r i v e r i s d r y e x c e p t w h e r e , w a t e r i s s u p p l i e d by s p r i n g s n e a r Tecopa and

138 117O

116O

115O

36

-

0 35

0 Baker

50 Km

Fig. 1. Index map showing l o c a t i o n o f Lake Tecopa. Shoshone, C a l i f o r n i a , and by i n f r e q u e n t heavy r a i n s .

During Pleistocene time

t h e r i v e r was b l o c k e d s o u t h o f t h e p r e s e n t town o f Tecopa, and t h e muds and v o l c a n i c ashes were d e p o s i t e d i n t h e r e s u l t i n g l a k e water.

E v e n t u a l l y , as t h e

sediments f i l l e d t h e b a s i n t h e w a t e r o v e r f l o w e d , c u t t i n g t h r o u g h t h e b a r r i e r and d r a i n i n g t h e l a k e . The mudstones and t u f f s have a s l i g h t b u t d e f i n i t e d i p toward t h e c e n t e r o f t h e b a s i n which p r o b a b l y was produced by t h e o r i g i n a l s l o p e o f t h e b a s i n and by p o s t d e p o s i t i o n a l compaction.

They a r e d i s s e c t e d by s t e e p s i d e d washes, which

make t r a v e r s e d i f f i c u l t b u t p r o v i d e e x c e l l e n t exposures o f t h e beds f o r study, a l t h o u g h t h e l o w e s t beds a r e n o t exposed. The t u f f s t h a t a r e a s s o c i a t e d w i t h t h e s e p i o l i t e d e p o s i t s range i n t h i c k n e s s f r o m s e v e r a l c e n t i m e t e r s t o about 4 m ( F i g . 2).

Three o f t h e t h i c k e r t u f f s

were l a b e l e d A, B, and C i n descending o r d e r by Sheppard and Gude (1968). t u f f s m a i n l y c o n s i s t o f z e o l i t e s , g l a s s , m o n t m o r i l l o n i t e , and i l l i t e .

The

The

z e o l i t e s p r e s e n t a r e p h i l l i p s i t e , c l i n o p t i l o l i t e , and a few m i n o r occurrences o f e r i o n i t e and c h a b a z i t e .

I t appears p o s s i b l e t h a t a t h i n ash bed may have

e x i s t e d about 7.6 t o 9.1 m above t u f f A, b u t we found n o t r a c e o f it.

However,

139

I

---A

.... . .. ...... ....... ,.::.: :,.. .,.;.

Sandstone

xxxxxx

3

Tuff

Tuff

2 20

METERS

A:::L-

xxxxxxxx

---x x x x x x

Fig. 2. G e n e r a l i z e d s t r a t i g r a p h i c s e c t i o n o f P l e i s t o c e n e Lake Tecopa d e p o s i t s showing s t r a t i g r a p h i c l o c a t i o n o f s e p i o l i t e - b e a r i n g samples ( m o d i f i e d f r o m Sheppard and Gude, 1968). Numerals i n d i c a t e t h e number o f samples t a k e n a t a given s t r a t i g r a p h i c l e v e l .

140

o t h e r n o n s e p i o l i t e - b e a r i n g samples c o l l e c t e d a t t h a t e l e v a t i o n d i d c o n t a i n c l i n o p t i l o l i t e and m o n t m o r i l l o n i t e , b o t h p r o d u c t s o f a s h d e v i t r i f i c a t i o n t h a t d o n o t n o r m a l l y o c c u r i n t h e mudstones o f Lake Tecopa. DESCRIPTION OF THE SEPIOLITE E l e c t r o n m i c r o g r a p h s show t h a t most o f t h e s e p i o l i t e f i b e r s a r e l e s s t h a n

1 wn l o n g , a l t h o u g h one sample d i d c o n t a i n f i b e r s more t h a n 2 um l o n g . T r a n s m i s s i o n e l e c t r o n m i c r o g r a p h s o f s u r f a c e r e p l i c a s , and s c a n n i n g e l e c t r o n m i c r o g r a p h s show t h a t a t l e a s t some o f t h e s e p i o l i t e f i b e r s o c c u r i n s m a l l , randomly o r i e n t e d bundles. The s e p i o l i t e i s , i n a l l samples, a d m i x e d w i t h o t h e r m i n e r a l s , t h e l a r g e s t amount b e i n g a b o u t 50%.

An a t t e m p t t o p u r i f y t h e s e p i o l i t e i n one sample b y

p h y s i c a l means was n o t s u c c e s s f u l . fraction,

The p u r e s t f r a c t i o n ,

t h e less-than-O.2-um

c o n t a i n e d s e p i o l i t e , s a p o n i t e , i l l i t e , and p o s s i b l y p o t a s s i u m T h i s f r a c t i o n was t r e a t e d w i t h a 1:3 a c e t i c a c i d : w a t e r s o l u t i o n f o r

feldspar.

t e n d a y s t o d e s t r o y t h e s a p o n i t e (MacEwan and W i l s o n , 1980; S t a r k e y and o t h e r s , The r e s u l t i n g sample appeared, b y X - r a y powder d i f f r a c t i o n , t o b e

1977).

s e p i o l i t e c o n t a i n i n g some i l l i t e and p o s s i b l y K - f e l d s p a r .

I

I

I

The X-ray powder

I

I - - I llite impurities may contribute to the intensities of these peaks

P--Potash feldspar impurities may contribute to the intensities of these peaks

60

DEGREES F i g . 3. X-ray d i f f r a c t i o n p a t t e r n (CuKa r a d i a t i o n , 40Kv, 30mA) o f t h e l e s s than-0.2-wn f r a c t i o n a f t e r t r e a t m e n t f o r t e n d a y s w i t h a s o l u t i o n o f 1:3 a c e t i c a c i d : w a t e r , compared w i t h a p a t t e r n o f a s e p i o l i t e sample f r o m E s k i C h e h i r , Turkey

.

141 d i f f r a c t i o n d a t a , w i t h t h e i l l i t e and f e l d s p a r r e f l e c t i o n s d e l e t e d , a r e compared i n T a b l e 1 w i t h p r e v i o u s l y p u b l i s h e d d a t a . The c o a l e s c i n g o f peaks and t h e b r o a d c h a r a c t e r i s t i c s o f most o f t h e peaks can be seen i n F i g p r e 3. TABLE 1 Comparison o f X - r a y powder d i f f r a c t i o n d a t a f o r s e p i o l i t e f r o m P l e i s t o c e n e Lake Tecopa w i t h t h o s e f r o m t w o p r e v i o u s l y r e p o r t e d o c c u r r e n c e s . [ B r a c k e t s i n d i c a t e peaks w h i c h c o a l e s c e . B, b r o a d ; NR, n o t r e s o l v e d ; _ _ _ _ _ , n o t found o r n o t reported] Lake Tecopa, Calif. d

d

I

12.3 7.5 6.6 5.0 4.49 4.25

ion

-_---

Eski Chehir Asia Minor1

4 6 7 33 15

Kenya

I

12.3 7.6

_____ 4.9 4.5 4.3

-----

_----

__--_

11 9 26 22 6

3.746 3.49 3.34

208 5

3.76 3.45 3.32 3.23 3.00

1

12.1 7.7 6.7 5.0 4.47 4.31

100 5B 5B 5B 18 25

4.17 3.738

---_-

20NR ,B 2.98

_____ 2.67 2.56

d

(40NR,B)

3.339 3.187 3.048 2.79? 2.675 2.59 2.56

5 20

----35 12 5 4 8NR 40NR

2.49 2.421

17B

2.26 2.12 2.06

11B 7B 4B

2.01 1.97 1.924 1.720 1.668

4 4 4 6 78

1.589

_--_-

68

-----

1.513

1. B r i n d l e y , 1959

19

2.43 2.36 2.24

_____ 2.08

1.58 1.551 1.517

7

in 14

2.44 2.39 2.259 2.117 2.071

15NR

_____

__-_-

188 5B 78

1.722 1.692

5 8

1.583 1.548 1.517

9B 10 15

142 A chemical a n a l y s i s o f t h e t r e a t e d f r a c t i o n was o b t a i n e d ( T a b l e 2) t o further characterize the sepiolite.

The r e s u l t s o b t a i n e d f r o m t h e sample,

which was impure, may be h e l p f u l i n u n d e r s t a n d i n g t h e f o r m a t i o n o f t h e sepiolite. TABLE 2 A n a l y s i s o f t h e less-than-n.2-pm f r a c t i o n o f a s e p i o l i t e - b e a r i n g sample ( i n p e r c e n t ) a f t e r a c e t i c a c i d l e a c h i n g f o r t e n days compared w i t h a n a l y t i c a l d a t a from Two Crows, Nevada, s e p i o l i t e ( P o s t , 1978). [Analysts: J. W. Baker, A. J. B a r t e l , and J. S. Wahlberg. ----- , n o t reported] Oxide

Lake Tecopa

Two Crows

58.9 4.67 3.09

53.98 0.20

Fe0 Mg0 CaO Na o K% T,ib Mn p2?5 . . Loss on 1 n i t i o n

Cf

-----

12.9 0.12 0.16 2.71 0.18 0.04