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Lecture Notes in Earth Sciences Edited by Somdev Bhattacharji, Gerald M. Friedman, Horst J. Neugebauer and Adolf Seilacher
13 Tadeusz M. Peryt (Ed.)
Evaporite Basins
Springer-Verlag Berlin Heidelberg NewYork London Paris Tokyo
Editor Dr. Tadeusz M. Peryt Instytut Geologiczny ul. Rakowiecka 4, PL-00-975 Warszawa, Poland
ISBN 3-540-18679-4 Spnnger-Verlag Berlin Heidelberg New York ISBN 0-387-18679-4 Spnnger-Verlag N e w York Berhn Heidelberg
This work is subject to copyright All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of ~llustratlons, recitation, broadcasting, reproduction on microfilms or In other ways, and storage in data banks DupScat~on of thrs publication or parts thereof is only permitted under the provisions of the German Copyright Law of September 9, 1965, in Its version of June 24, 1985, and a copyrrght fee must arways be paid Violations fall under the prosecution act of the German Copynght Law © Spnnger-Verlag Berhn Heidelberg 1987 Printed In Germany Printing and binding Druckhaus Beltz, Hemsbach/Bergstr 2132/3140-543210
stratigraphic units have been interpreted in very different ways. . . . Evaporite sedimentology is in a considerable state of flux and probably w i l l remain so for some years tocome." A. C. Kendall 1978 'subaqueous evaporites'
Preface Contemporary evaporites are principally to be found in three environments: sabkha, salina, and hypersaline lake, which have also been identified in ancient evaporites; however, for the interpretation of any particular evaporite basin often contrasted sedimentary models are proposed. The concept of evaporite drawdown and deposition of evaporites in great desiccated basins led to a debate on the origin of salt giants, the conclusion to which was that evaporites may form or deposit in a wide spectrum of environments from continental sabkha to deep basin. For a number of reasons, the definite models of evaporite deposition have been not yet formulated, one reason being that in fact only a few evaporite basins have been studied in detail (Miocene Mediterranean basin, the Zechstein basin of Central and NW Europe, and theUpper Silurian basin of Michigan being probably the best-known cases). The second important factor is that evaporites evoluted in the history of the earth and our understanding of the evolution is very imperfect. These two reasons led to the conclusion manifested in the theme o f t h i s volume, that i t would be desirable to summarize our knowledge on some less-known evaporite basins such as those located in China (some of which, like the Tarim Basin discussed in this volume, foreign visitors are not a11owed to enter) or European evaporite basins known from boreholes. Many potential authors, enthusiastic at the beginning of the work on the volume, could not'finish their papers within the promised time, and the delay in publishing occasioned by late chapters would have been - and already was - detrimental to those ~utho~s Who had completed t h e i r papers in time. The unintended bias does not, we hope, affect the main message of this volume. Michal Pawlik and Agnieszka Siara are thanked for technical assistance. Tadeusz Marek Peryt
T~ble of Contents
I ntro duc tion T.M.Peryt .............................. . ..................... I Facie~ models for Aus~r~lian Precambrian evaporites M.D.Muir ..................................................... 5 Characteristic ~nd environments of Sinian evaporite in southern Sic huan, China Xu XiaoSong ................................................. 23 The Lower Carbor~Iferous ~ (Visemn) evaporites in northern France and Belgium: deposltional, diagenetic and deformational guides, to reconstruct a disrupted evaporitic basin J.M.Rouchy, A.L~umondais, E.Groessens ..................... .. 31 Depositlonal models of Lower and Middle Triassic evaporites in the Upper Yangtze area, China Wu Tinglin, Ysm Ya~gJi ....................................... 69 Middle Muschelkalk evaporitic deposits in Eastern Paris Basin D. Geialer-Ous~ey ............................................ 89 Sedimentary models of gypsum-bearing clastic rocks and prospects for associated hydrocarbons west of the Tarim Basin (China) in Miocene Qiu Dongzhou ................................................ 123 Reef-stromatolites-evaporites facies relationships from Middle Miocene examples of the Gulf of Suez and the Red Sea C.L.V.Monty, J.M.Rouchy, A.Maurin, M.C.Bernet-Rollande, J.P. Perthuisot .................................................. 133
Introduction Evaporites may form in a spectrum of environments from continental sabkha (playa) to deep basins (see Kendall 1978 a, b, Schreiber 1978, 1986, Friedman and Krumbein 1985, f o r review). In the last two decades, many ancient evaporite basins have been interpreted using the sabkha model and the deep desiccated basin model, the former not excluding the l a t t e r . However, growing evidence has been gathered indicating that most evaporites are formed in subaqueous environments, so that i t cannot be reasonably expected that one depositional model alone w i l l explain the e n t i r e basin f i l l . The chapters in t h i s volume discuss characteristic examples of evaporite basins, mostly of moderate size. Aspects of a saline giant, the Zechstein basin of Central and NW Europe, have been considered in Volume I0 of "Lecture Notes in Earth Sciences". Muir presents a set of facies models f o r the Precambrian evaporites of Australia, ranging from continental a l k a l i n e playas through continental sabkhas to barred basins. Desiccated deep marine basins have been not recognized in the Precambrian of Aust r a l i a . Xu Xiao Song discusses the Sinian evaporites of southern Sichuan, China which form the top part of the carbonate platform development. Evaporites are related to two models: The Lagoon-salt lake model and the sabkha-salt lake model. During the late stage of evaporite deposition sea level f a l l caused the s a l t lake in the sabkha to evolve into a continental s a l t lake. Rouchy et a l . describe Visean evaporites along ~he F a i l l e du Midi overthrust in northern France through Belgium to the Netherlands. Anhydrites are intercalated in limestones (dolomites are rare), and the faunal record shows a progressive r e s t r i c t i o n from a marine environment and a marine origin of the brines which generated the sulfate interbeds. The evaporitic stage was related to the fall
in sea level. On the evidence of abundant r e l i c s and pseudomomphs of gypsum, i t
is assumed that subaqueous gypsum was an important i n i t i a l
deposit. The predominant
nodular and mosaic structures are interpreted as resulting from burial conversion of gypsum to anhydrite. A d d i t i o n a l l y , primary structures have been destroyed due the Hercynian deformations, and the resulting structures mimic sedimentary structures. This, however, does not imply that even in such tectonized sequences i t is impossible to interpret sedimentary facies. Rouchy et aI. also discuss the origin of the Great Visean Breccia and conclude that i t formed by collapse a f t e r dissolution of anhydrite (and possibly s a l t ) interbeds. In fact~ h a l i t e is not known up to now from these e~apor i t e s , but the presence of recycled h a l i t e in the Rotliegendes of the North Sea and NW Germany might be related to the extensive dissolution of h a l i t e which began w~th the Permian denudation. Lecture Notes in Earth S~ences, Vol. I M. Peryt (Ed.), Ev~onte Basins © Spfn~r-Vefl~ Berlin Heidelbe~ ~87
The evaporites described by Wu Yinglin et a l . are included into two depositional mode~s. The f i r s t one,the platform sabkha model, bears analogies with the recent sabkhas of the Persian Gulf although the topography of the platform has been, as is sopposed, more d i v e r s i f i e d than the recent topography in Abu Dhabi. There existed some d i s t i n c t depressfons in the mamgin of the platform, forming coastal lakes, and in the inner parts of the platform. Accordingly, sabkha and saline environments pass l a t e r a l l y , or transform, one into another. I t was possible to distinguish three stages in the evolution of platform sabkha: the coastal s a l t lake ( s a l t pan) stage when mainly h a l i t e has been deposited, the sabkha stage (when gypsum, h a l i t e , and p o l y h a l i t e have been deposited), and the playa lake stage (when deposition of an: hydrite and p o l y h a l i t e dominated). The~seoond model, the desiccation-lagoon model refers to the s a l t lake separated from the lagoon in the platform by a rapid regression. Geisler-Cussey discusses the effects of continental influences on evaporitic sedimentation in a part of the Middle Muschelkalk s a l t basin. This b a s i n e x e m p l i f i e s a quite common geological situation when the intracontinental basin had marine characteristics but a continental context, a tendency more accentuated in the Keuper basin. The sedimentary record in the Middle Muschelkalk indicates a c y c l i c evolution of s a l i n i t y which was related both to the nature of the connection with the Tethyan water supply through the Silesian S i l l ,
that allowed considerable brine concentration
before reaching the Paris Basin, and to the freshwater supply from the continental. The basin was not very deep and the brines were not commonly s t r a t i f i e d . Except f o r the centre of the basin, the salts have been affected by d i s s o l u t i o n - - r e p r e c i p i t a t i o n processes, and the s a l t has been recycled both by freshwater and unsaturated seawater, the l a t t e r probably being of major significance. Qiu Dongzhou characterizes the depos i t i o n in a continental lake basin which has been occasionally invaded by the sea, and hence possesses lake features with a few marine characters; such a complex origin is r a r e l y considered in the f o s s i l record. Monty et a l . discuss a much disputed problem of reef-evaporite relations: the answer is of greatggeofogfcal end economical significance. They demonstrate that the o r i g i n of reef complexes in the RedSea Miocene predated the deposition of massive evaporites. Most evaporites formed subaqueously during lowstands in sea level~ although t h i s does not implicate overall desiccation of the basin. Sea level fluctuations resulted in alternated phases of exposure and flooding of reefs, and hence, t h e i r complex diagenesis and the p r o l i f i c development of stromatolites. The chapter is a standard f o r studies of evaporite-related stromatolftes as w e l l . The volume shows that evaporitic basins have been dynamic systems, and that sea level changes have been of important significance f o r evaporite deposition: h i t h e r t o ,
their importance has been recognized for the pre-evaporitic phase (e.g. Peryt 1984 for the Zechstein basin). Tadeusz Marek Peryt
References Friedman G M, Krumbein W E (Eds) (1985) Hypersaline ecosystems - The Gavish Sabkha. Ecological Studies, Springer-verlag Berlin Heidelberg New York, 53:484 pp Kendall A C (1978 a) Facies models 11. Continental and supratidal sabkha evaporites. Geosci Canada, 5, pp 66-78 Kedall A C (1978i~b) Facies models 12. Subaqueous evaporites. Geosci Canada, 5, pp 124-139 Peryt T M (1984) Sedymentacja i wczesna diageneza utwor6w wapienia cechsztyflskiego w Polsce zachodnLej. Prace Inst Geol 109:80 pp Schreiber B C (1978) Environments of subaqueous gypsum deposition. SEPMShort Course, 4, pp 43-73 Schreiber B C (1986) Arid shorelines and evaporites. In: Reading, H.G. (ed.), Sedimentary environments and facies, pp 189-228. B1ackwe11, Oxford
FACIES
MODELS
FOR
AUSTRALIAN
CRA
Exploration
M.D.
EVAPORITES
Muir
P.O. FyshwIcK,
PRECAHBRIAN
Pty,
Box
ACT,
Ltd.
655 Australia
SGO9
INTRODUCTION
There of
are
the
have
records
Australian been
evidence
remains
evaporlte
at
Subcontinent.
The
by to
occurrences
For
for
the
evaporitlc
Archean
the
North The
stratlgraphically has
been
age
for
barite are
dated
also
Pole in
a
slllclfied,
Pole,
Groves
&
deposits rocks
3.45
Gyr,
galena
to an
the
of
but
in
better
these
Australia
the
Early
have I).
Known, by
highly
dealt
With
evaporlt~s,
(Donne~ly,
volcanic Is
in
from
Dunlop
&
Differ
Fletcher
and
Warrawoona
considered
&
by
BlocKley,
and
to
Formation,
corroborated
arenlte
over-
Archean
are
of
are
models (Figure
the
AUSTRALIA
(Richards,
which
of
1979).
which
chert,
will
Known
deposit
the
evaporltic Few
facies
sequences
crystals
sufficient
Precambrlan.
only
WESTERN
the
age
developments
oldest
BuicK,
Proterozoic
evaporlte but
and
Western
occur to
sequence and
paper,
BARITE,
equivalent at
North occurs
discussed,
POLE
Pole host
this
by
the
and
minerals,
evaporltic
of
North
Dunlop,
of
other
studied,
the
with
Archean
Australian
fully
of
the
majority of
the
been
number
in
extensive
in
beginning
NORTH
The
times
will
order, of
variety
indicate
purposes
1978;
Group.
a
have
a
sequences
stratlgraphlc the
evaporltes
different
developed
Groves,
abundant
replaced
conditions
been
of
a
which 5.4 G y r
1981). T h e
conglomerate
underlain
be
by
which slightly
Lecture Notes in Earth Sciences, VoL 13 T M. Peryt (Ed.), Evaporite Basins © Springer-Veflag Berlin Heidelberg 1987
metamorphised slliclfied rather &
ma~ic
and
stromatolltes
controversial
Walter,
described
ultramafic
1983; by
(Walter,
mlcroTosslls
Buick,
1984). T h e
Dunlop
volcanics. Buick
&
(DUnlop
et
rocks
of
Within
the
Dunlop, al. the
sequence
1980),
1978;
are
AwramlK,
North
Pole
are some
Schopf
were
first
(1976).
PINE CREEK GEOBYNCLINE MoARTHUR BASIN ~ N.W. OUEENSLAND
]~ENORTH POLE .,. BITTER 8PRINGSqF FORMATION
]I~RINGWOOD D O M E ~ ,
OFFICER BASIN
I)|CALLANNA GROUP
,
Figure this
I. Localities paper.
The
barite
exploited. cm
in
length
which The
The
top
of
the
non-deformed
twinned
of
pseudomorphs
in
after
of
crystals twins, barite
crystals cubic
and
and
with fills
places
have
the
have may
been
been
crystals
laminated
space
between
eroded,
in
commercially
contain
overlying the
discussed
chert
crystals.
and
conglomerates,
5-a0
clasts
of
indicating
crystals.
are and
%
evaporites
and
intraformatlonal
gypsum,not
gypsum
beddin@,
tops,
in
formation the
extensive,
across
crystals
swallow-tail
typical
are
Precambrian
bottom-nucleated
crystal
occur
Although
were
are
over
synsedimentary
sln@le
deposits beds
barite
observed
Australian
radiating
drapes
bedded
of
i
now on
crystals, barite. are crystals
barite,
measuring concluded Silica
Lambert tl%e
that
the
pseudomorphs
also
present,
as
which
may
been
have
et
al.
interracial
crystal after
well
(1978)
angles
faces
single as
halite.
of
or
silica Studies
of
sul~ur
isotopes
also
volcanogenic,
and
sulfur
from
exhalatlve
oxygen
was
implied
formed
supplied
as
that
a
sulfur
of
surflcial
result
sources. by
the
The
the
authors
action
of
was
evaporitic,and
oxidation
suggest
that
blue-green
of
reduced
the
al~ae
non-
required
or
sulfur
bacteria. The barite
evidence is
sequence and
for
clear. consist
of
cross-bedding,
features
such
contalns
partially
voids.
The
environment
The
is
in
subsequently
the
the
possible
emergent
by
by
reduced
sulfur.
Dunlop
basin
et
added
evaporitlc
Buick,
(barred)
Lambert
to
al.
the
~ypsum
(1978) consists
the
Bedded
&
basin,
followed
sulfate
Groves
environment
deposlts
This
the
were
model
(1981) (Figure for
of by
was
a),
who
deposition
of
sulfates.
--=-_-~----
!
-
--
CLOSED
-__~--/
: : ::::::::: ~ :::.:.:.:.~.~.:.............................;.:~ : :~: : : : :i: :~: "k~'~¢~;J"~;~'~'6"~h'~'~'"?;,~i~:~:i:i::':'"
BASIN
OPEN
a. S c h e m a t i c m o d e l for t h e e v o l u t i o n of t h e Pole (after Buick, Dunlop & Groves, 198i).
PINE
rocks
CREEK
of
event
at
1.8 G y r
dated
at
2.47
Gyr
occurs
Territory
(Figure
found
Needham,
in
chert
rhomblc
depositlonal
for
environments.
----INTERTIDAL---MUD--FLA'[- FACIES-- ~
Geosyncllne
graded
The
and
carbonate origin
Pole rock
desiccation
mud-cracks.
BASIN
The
as
and
rllombs,
evaporltlc
North host
such
marks,
dolomite
being
water
iiiii!ii::iiiiii!i!iiiiiiiii!::..-
Figure North
the
cherty
features
ripple
to
for
the
crystals.
envisa@ed
of
closed
evaporitic
an
in
and
water
exhalations
shallow
precursor
emergent
carbonate,
with
barite
re~ined a
to
intraclasts,
intraclasts,
consistent
oxidation
formed
water
shallow
model
gypsum
structures
replaced
the
~acles
postulated
shallow
curved
sulfurous
microbial then
as
of
evaporltic
scouring,
postulated
precursors
juvenile
an
Sedimentary
the and
GEOSYNCLINE,
Pine
(Page, to
Creek
overlie
the
I), a n d Crick
Geosyncline
granitic
Compston south a &
NORTHERN
and
summary
&
and
oT
Stuart-Smith
of the
unit,
TERRITORY
underwent
gnelssic
Needham, east
chert-barlte
1980). Darwin, regional
(1980).
a
metamorphic
basement The in
complexes Pine
the
geology
Coarsely
Creek
Northern may
be
crystalline
magnesite
and
dolomite
Rivers
Uranium
Jungle,
and
There
the
>
300
pelites
and
which
is
limits
are
in
The 1979,
Fields
in
are
with
rocks in
of
reaching
a
and
weathered which
have
a
surface.
will
be
stromatolltlc small
and
The
The water
shallow
developed
(which
are
to in
neccessarily
blade-shaped
or
swallow-tail
twins
are
some
beds
as
crystals.
However,
expected
in
suggested
that
which
if
the
crystalllsed
identical (Muir,
crystal
1979),
a
cubic below
forms
&
some
in
Muir, of
all
there on
crystal
the casts
with
ripple
non-
marks, and
these
are
the
Conical
appearance
to
and small
structures
interpreted
as
environments
do
described
has
never
abundant
Cruciform shapes
casts.
not
The
lamellae
been
the
could
Bone
forms
the
have
for
of
be
(1983)
magneslte
respectively. from
also
rocks
occur.
were
and
are
origin
twin
shapes o 150 C
above
which
long.
then
these
been
contain
metamorphic
case,
and
cm
cubic
a
the
and
i
they
Orthorhombic
discoidal
have
formation
up
abundant
were
and
(Crick
sub-aqueous
because
implying
carbonates,
the
age
too).
contain
this
or
the
diameter.
by
unit
2.2 Gyr.
structures
indicated
uncommon.
marbles,
interbedded
interbedded
stromatolltes
littoral
crystals,
not
as
abundant
are
Rum
region.
arenite
common,
pipe"
teepee
coarse-grained
discoidal
described
Tlle
shallow
are
old
cross-beddlng,
as
supralittoral,
places
developed
contain
environment
emergent.
carbonates
and
well
at
Rivers
basal
similar
they
contain
as
depositional
having
present,
which
as
"organ
but
in a
are
a
well
stromatolites
Dolomites
stromatolitic
and
are
shortly,
structures,
is
m,
Alligator
basement.Although be
stromatolites
1.5
characteristic
carbonates
Intraclasts.
been
of
discussed
scour
The
domal
height
the
abundantly
("Conophyton")
stromatolites formations,
are
are
Jungle,
could
and
Alligator
which
with
carbonates
rocks
the
Rum
Jungle
Coomalie
in
at
Rum
and
carbonates,
contact
broad,the
carbonate
the
Celia
overlie,
unconformable
very
in
Formation
these
which
1980). S t r a t i f o r m
domes
the
Cahill
m
occur
However,
Amelia
subjected
Dolomite
to
elevated o
temperature
and
Amelia
Dolomite
(cuBic)
and
Further
can
be
length-slow The event,
strain
evaporite
in
they
must the
Anhydrlte
is
1975), a n d
the
(discoidal), evidence
have
to
original
and
certainly
not
interpreted
as
the the
the
Rum
must
the unlike
gypsum
of
the
of
C.
after
crystals
the
primary
a
The halite
are
sulfate
grade Pine
L8
also at
so
Rum
variety
Gyr
form.
since
non-evaporitic
in
Being
luteclte,
survived
their
high
io0
of
anhydrite.
metamorphism
survive
above
presence
presence
have
retained
Jungle
former
pseudomorpl%s
minerals
crystals,
are
for
from
which
post-date
Known
conditions,
shapes
adduced
quartz
since
carbonate
crystal
gypsum
interpreted. Jungle
pressure
there
Replacement are
carbonates metamorphism
Creek
rocks
metamorphic
no in
by
signs the
of
area.
(SerduchenKo, would
l%ave
been
converted A (1980)
to
anl~ydrite
~acies
model
(Figure
durln~
burlal
these
deposits
~or
diagenesls was
(West,
developed
196g).
by
Crick
&
Muir
3). t, PRIMARY CARBONATES
~
5. BURIAL AND METAMORPHISM ANHYDRITE
u
2. DIAGENETIC GYPSUM
6. POST- METAMORPHIC DIAPIRISM
3. LATE DIAGENETIC MASSIVE GYPSUM
7. MgCO3 CONVERSION
4. COMPACTION AND FIRST DIAPIRISM
8.WEATHERING = KARSTING
F i g u r e 3. Stages in t h e d e v e l o p m e n t of Alligator R i v e r s a n d R u m Jungle Uranium (after C r i c k & Muir, 1980). The they
crystals
grew
conditions &
Mulr
(Figures the
(from
hlghly
the
3.1 a n d
and
have
concentrated
both
the
carbonate
sedimentary
~.a).
their
of
in
(1980) i n t e r p r e t
carbonates
dlaplrs
habits
displasively
thls
gypsum
muds
behaved relationship evaporltic
in
structures
environment
Geological
the uranium Fields, P i n e
to
evidence diapirlcally to
brines
in
and
halite
shallow already
been area the
have
been
an
arld
Crick sabKha
indicates
geometry suggest a
that
to e m e r g e n t
described).
the and
indicate
water
have
mlneralisatlon may
deposits in t h e C r e e k Geosyncline
that
of
the
that
the
source
for
the
10
metals
in
the
deposits
in
uranium
the
deposits,
and
The
rocks
arenlte
as
metamorphic of
the
identified
metasomatic
the
a
one,
This
led
were
The as
a
host
turbidity
beds
shows
However,
if the
denser
of
only
this,
the
Eocene
shortlte this
mineral
water. waters.
It Thus
of
a
ran of
across
producing
there
are
quartz
the
in
of
is
of
very
preclpi%ate only
Wyoming
as
pPeclpitate
presence
of
a
from
shortite
deposits. resulting
of
of
the
denser settle
graded
as
soft
would
sediment.
water
body,
thl~ough
the
pseudomorphs
environment. anhydrite,
appear
sodium
to
and
lake
of
evaporation
shortlte
of casts)
which
such
impossible of
alkaline is
a
in the
presence
it
the
is
also
Calcium
deposits
1980). T h e
In
have
because
evaporation (or
and
probably
(Eugster,
result
such
structures
sabKha
alkaline
significant,
structures,
bed.
casts of
which
callche
replacing
crystal
with
a
of
currents,
a
and
in
carbonate
association
Forma%lon
occur nodules
the
double
graded
discoidal
would
of would
crystals
(198£) as
surface
surface
was
scapolite.
diagenesls.
None
traction
particles
are
al.
lake,
the
perfectly
casts as
the
the a
or
across
fossil
et
there
most
slump
of
Connor
stratified
ran
flow,
such
sedimentary
but
serlcite,
"scapolite"
early
many
mineral,
so-called
in
of
recent
addition,
minerals,
marks,
presence by
that
the
have
that
caPbonate,
the
sediment
structures
flows
a
can
to
casts
However,
In by
evaporite
ripple
the
bottom
shortlte,
to
shale,
products
showed
contain
that
abundant
density
most
Green
in
been
black
the
196a)
minerals.
primary
by
However,
pseudomorphs
1985)
have
crystal
as
quartz,
conclude
contain
in
not
displayed
original
the
crystal
precipitated
Page,
of
the
Of
Muir,
did
clay
of
&
including
interpreted
gypsum
of
metal
metamorphosed
Davidson,1970).
habits
in
flows
column the
sequence.
morphology is
slgn
discoidal
support the
variety
cessation
of
&
(198a) to
turbidity
such
water
Some after
al.
flows
if
then
at
crystal
were
any
expected
base
which
been
regarded
Johnson
crystals
indicated
beds
casts
sequences
most
and
graded-beddlng,
breaks
graded
grade,
others
sediments
from
be
of
et
cross-beddlng,
The
have
(Connor,
displaclvely
erosional
in
undeterminable
Connor
grown
occur which
"scapolite"
many
replacing
had
They
(Ramsay
work
and but
(1.74-1.5g Gyr,
crystal
rocks
"scapollte"
variety
microcline, not
smaller
some
grade.
fluids
so-called
Formation
abundant
metamorphic
as
sedlmentological of
in
QUEENSLAHD
Corella
contain
carbonate
Because
hosted
the
scapollte.
and
greenschlst
been
of
@ueensland
identified
as
area.
NORTHWEST
northwest
well
as of for sea
lake
proitive
11
indication In
of
the
detailed suggested,
non-marine Corella
facies on
structures,
Formation
models
the
that
subaqueous,
depositional
basis the
with
in
have of
northwest
been
the
deposltlonal
mar~inai
environments. @ueensland,
proposed,
evaporite
casts
environment
carbonate
although
Connor
et
and
of
sabkhas,
the
the
al.
sedimentary
hlacl¢
and
no (1982)
shale
was
fluvio-lacustrine
arenltes,
HALLAPUNYAH
The
Mallapunyah
McArthur
Basin
they
in
lle
Muir,1979), of
FORMATION
carbonates
Formation
(Figure
the
and
lower
consist and
AND
and
I) in
the
part
of
of
an
interbedded
AMELIA
DOLOMITE,
Amelia
Northern the
McArthUr sequence with
m
BASIN
occur
in
the
Statigraphically,
Group
(Figure
overlain
subordinate
by
a
@:
from
sequence
arenltes,
0
Looking Glass _~ Formation O Stretton Sst D Yalco Formation~~ ~9 .~ Lynott Formation
Dolomite
Territory.
arenite shale
HCARTHUR
1kin
~LDPC T
L Lensed gypsum costs
Reward Dolomite
LDNP
Formation
~ Emmerugga Dolomite
N Acicu/ar gypsum casts
P P,/smafic gypsum casts Batr2o[da/ quartz nodules C after anhydride
Barney Creek ~ Teena Dolomite
D D,L¢ca;dal gypsum casts
LDNP LDNPH
H Ba M T
Halite casts Barite Massive replacement by gypsum Teepee structures Signlf/cant evaporde body
O1 T°°ganinie< Formation ~ / Tatoota Sst Amelia Dolomil
JFMo:l:a, iP-~nyah
LDHM
LOPHM LDCHM Ba
LDCHM 8a T
F l g u r e @. S c h e m a t i c stratigraphlc section t h r o u g h the McArthur GrOUp showing the Mallapunyah Formation, Amelia Dolomite, Barney Creek Formation, and Yalco Formation, all of which contain evaporite deposits.
12
was
The
presence
first
noted
Amelia A
Dolomite
precise
than
the
for
i.68
GyP
surfaces
casts,
of
that
grew &
by
flakes
of
of
dolomite
habits
are
the
arld
sabhKa
the
is
than
original or
with
Abu
and
deposition by
replacement of
halite form,
sulfate
magnesite,
reinforced
a
the
the
of
Dhabi
in are in
Lagoon
Algalmat,
~'aters
primary gyp. arag. calc.
5abkha ;urface 3 L2
tl LO ~OLOCENE
on
of
in
(1979). older
is
1981). HcArthur
underlying the
bottom
of
halite
waters.
Other
halite
cubes
early
the
Primary Subtidal to intertidal
Algal mat, gyp. Supratidal mbkha cement. Qtz. sand Arag./caL muds gypsum mush on surface, gy. cemt. Algal mat + gyp cemt. anh. nodls.
are
dlagenesls
them,
but
variably a
sabKha
Gulf
after
discoids.
now
the
ferroan.
All
crystals
The
crystal
environment.
This
occurrence
anhydrite
Arabian
pseudomorphs
dlsplaclve
abundant
nodular
in
casts,
some
of
which (Muir,
is
botryoidal typical
of
1979).
Environment
Diagenetic Lithology
the
surface
mud
Environment
Height tn ¢ection (m)
and
replacements
Hulr
the
occur
the
it
(Page,
of
dissolution
of s a l i n e
carbonate
crystalline
consistent
nodules,
fine
casts
after
carbonate
in
far
showing
interpretation
formed
by but
Group for
1967).
consist
quartz
Dolomite
halite
evaporation
model
Deposit
formations
Amelia
the
McArthur
proposed
H.Y.C
all
the
sabKha
determined,
the
in
the
or
in a
was
been
for
of
and
chert
abundant some
in
of
Interstltlally
HoPe
not
common
so
result
are
Emery,
gypsum, have
a
Formation has
Many
evaporites (i977), a n d
determined very
arenltes as
however,
(Neev
age are
Formation.
preclpltated
al.
deposit
partlcularly
Hallapunyah
relic
et
Hallapunyah the
casts
and
abundant WalKer
and
age
Halite Group,
of by
Lithology
(early)
Primary
Dlageaetic (early)
Vadose and late diagenetic
Intertidal
Inner flood recharge zone Intermed. flood recharge zone
Stratiform stromatolites Beach/splash travertine
Supratidal to high supratidaL
Dol./chert small Dol. re~ryst/ gyp pseudorecemented
morphs
Outer flood recharge zone AMELIADOLOMITE
9 8 7 6 5 4 3
Uncunsofidated, [rerrestrial uncemented aeolianltes. Large anh. nodls. 3 x 1 m. Gyp. interstitial cemt. Halite, sylvite, polyhalite, and deU'ital clay in lenses and beds
High suprafidal zone
Dol. shale/silt Terrestrial/ ?eolian shallow Cauliflower chert, cubic casts, K-feldspar beds
Gyp./anh. halite, anh. andls. ?polyhalite, ?sylvite, ~Jgh suprafidal Dol./chert
Dol. recryst/ recemented High K in claystones gives K-feldspar'anh. nodls. sitlcifled
2 1 MALLAPUNYAEFORMATION
~I.EISTOCZ~
Table i. compared
Stratigraphy of t h e Abu wlth that of tlqe A m e l i a
Dhabl sabKha (after Butler, 1969), Dolomite and Hallapunyah Formation.
13
A and
comparison
lowermost
Arabian Table
Gulf i).
and
comparlsion a
new
was,
i969)
fossil
water,
to
marginal
the
a
conclusion
that
the
may
have
that
but
the
but
could
Amelia
to
altered
and
Abu of
Thus does
just
as
%o
Since
this made
sabKha.
sulfate
studies
of
is
a
that of
the
Thus water
shallow
a
indicate
represent
shallow
encompass
the
proved
itself
readily
In
for
identification
environment.
Dolomite
197i;
interpreted
Dhabl
not,
the
(i981) h a v e
the
the
of
(Muir,
the
same.
hydrological
lacustrine
basal be
the
Formation
Holocene
Klnsman
source
sabKlqa
supralittoral
and
the
&
of
the
new
Dhabl
Mallapunyah
similarities
are
groundwater.
Abu
the
similar,
hydrology
conditions,
of
1979)
the
are
Patterson
assumed
continental
sediments
(Muir,
of
of
Pleistocene
striking
both
published,
was
sea
fact,
analogue
marine
shows
environments
first
it
was
the
dlagenetlc
was
in
part
wlth
for
studies,
anhydrlte
uppermost
llthologles
interpretation
earlier
it
the
Dolomite
(Butler,
The
primary
of
Amelia
the
marine
water
lake
environment.
H.Y.C.
An the
account
McArthur
deposit
has
information Williams
The
Early
was
features
of
the
water,
bUt
llthlfled
Formation The
intraclast
the by
by
Muir,
those
For
is r e f e r r e d
discussed
further
to
(196i).
papers
Williams
the
flne-grained
beccla
of
of
the
the
Cooley
reported to
their
lead-zinc
were
by
indicate
the
deposition llthlfied
conglomerates;
(a)
carbonate
pisoids.
that
The
presence
under
shallow teepee
pseudomorphs combination
Intraclast
conglomerates
Borch
Lock
(1979) f r o m
ephemeral
&
der
Australia, Broch
pseudomorphs from
in the
and
(1980) (see the
from also
Barney
Mallapunyah
of
crusts,
and
South
the
& Logan
deposltlonal
on
(I)
(3) p e d o g e n i c
Shale
Member.
Williams
emergent
arguments
sulfide
Pyritic
Dolomite
environment
results water
described
by and
depositional
H.Y.C
are
&von
of
(1978). T h e
structures
anhydrlte
with
196i).
Williams
slltstone
together
region,
Lock
deposit
BlnneKamp
detail.
features
and
vonder
Coorong
nodular
identical
teepee
reader &
depositlonal
taken
&
(Page,
extremely
the
H.Y.C, lead-zinc
Logan
have
some
based
The
giant
the
shallow
anhydrite;
crusts,
described of
a
authors
that
and
nodular
of
talus
conditions.
structures,
in
BASIN
Gyr
Rye
dolomitlc
fault
These
1.68
(i98S)
consists
deep
the
Walker,
and
deposit
neccessitate
lacustrine
are
b),
carbonaceous with
of
in at
Muir
the
MCARTHUR
mlnerallsation,
and
environment. certain
given
and
interpretations
(i981)
been
the a
deposit
by
sequence
lakes
dated
of
Interbedded
after
been
(i96i)
hosted
geology
is
on
environment
the
Basin
(1978
Logan
of
DEPOSIT,
alkaline
the thls
Creek
of has
Yalco paper).
Formation
Formation,
and
14
are
the
products
replaced the
anhydrite
sediment
earliest
deposition nodules
surface
concentrated
of
tl~e
&
capillary
fringe
A
5.
indicate
It
of
arid
the
humid
environment,
quite
subtle
The
Yalco
by
Thus
higher
than
carbonates
the
as
no
nodules
&
the
facies
evaporlte
an
the
sediment from
in the
described
model
the
in
in
by the
shown
anhydrlte CrUStS,
evaporltic
facies
if%at
drawn
deposition
lithlfled
indicate
that
and
pisoids
of
pile.
because
to
as
nodules
by
but
appears
HCARTHUR
of
the
McArthur
Yon
tier
Borch
Creek
analogy seasonally
be
recording
,
of
Basin
laterally-linked
laminae
and
been
lles
and
marks,
casts
has
(1980). It
sedimentary
ripple
evaporlte
BASIH
Formation,
variety
and
distinct
or
d981)
but
FORHATION,
great
domal
are
be
pedogenic
interest
lakes
Barney a
through can
sediment
Logan's
the
conglomerates
stratlform, There
Lock
with
intraclast
&
indicates
atmosphere,
carbonate
the
presence
variations.
Formation
Muir,
of
conditions,
climatic
The
The
Formation
the
moving
from
particular
YALCO
detail
crusts.
ephemeral
Creek
conclusion
emergence
sabKha
environment.
to
were
formed
Williams'
of
Coorong
exposed
llthlfied
after
sabKha
Barney
the
same
(1981)
is
a
brines
The
Logan
cartoon
Figure
in
groundwater
Williams
in
was
dlagenesis,
occurrence
with
of
consists
features,
of
the
stromatolites
sequence.
tend
in
include
mud
cracks,
and The
to
be
cherty
These
crossbeddlng, stromatolites,
in
described
stratigraphlcally
oncolltes.
chert
occurs
preferentially
slliclfied. The
Yalco
dolomite Lagoon,
South
sedimentary are
and
Coorong
lake of
in
epllemeral the
lakes
lakes,
sequence
in
dry the
the
more
summer wet
Coorong evaporite
months,
winter
mineral
the
Proterozoic
and
is
an
The
the
lakes
are
(halite),
out
genuine the
of sites
but
for
seasonally
their
it
a
slow
positions in
the in
the
salts
varies
to
halite.
is
redlssolved
Thus
deposition humid
for
precipitating
of
system.
the
sequentially
precipitate
salts
aragonite
drawn wlth
out
by
Coorong of
sequences
be
system
salts
the
the
Holocene
composition and
precipitates,
flushed
basis
controlled
soluble
The
dolomite,
the
cropping
soluble
more
lakes.
halite
and
is
Holocene
of
can
evaporitic
least
the
end
conclusions
groundwate'r
composition
distal
months,
ephemeral
On
system
through
wlth
southern
al., 1980).
progressively
hydromagneslte,
compared
the
e%
alkaline
regime.
with
at
hydrological
whose
groundwater
proximal
from
alone,
similar
is
lakes
(Muir
migration
in
sequence
ephemeral
structures
The
oceanward
in
Australia
identical
both.
Formation
forming
In
although of
a
climatic
the in the
typical regime
15
ensures
tl%at
however,
With
preserved, Yalco
no
preservable
their"
and
i%
deposits
particularly
is
these
of
halite
distinctive
structur'es
that
remain.
The
sedimentary are
so
carbonates,
structures
characteristic
are
of
the
Fo~,n~+ i~n
WES TERN FA UL T BLOCK
C(
EVAP( Western Fault
Salt Lake
Figure (after
5. S e d l m e n t a t i o n model Logan, Williams &
The HcArthur 6) in
Yalco
Formatlon
Group
and
developed the
for
Sub-group
Formatio[l, the
upper
the
Yalco
or
can
the
range
through parts
lake
be
whole
of
the
to
CALLANNA
The
sediments
Australia,
are
Proterozoic 1.4-0.8 younger Hurrell
GyP, age
of
the
although may
(1978)
be and
the
dated, are
recent more
are
Stretton
SOUTH
but
of
are
The
Sub-group facies
of
model
1980).
The
the
(Figure
formations
subaqueous
in
and
environments
sabkha ephemeral
the
lake
succeeded
the
by
Willouran
usually
Lynott in
cycles
the
of
fluvial
as
Hurrell
a
Ranges,
included
accepted results
Group &
al.
Deposit
AUSTRALIA
unpublished
Rutland
et
H.Y,C.
Sandstone.
generally
accurate.
Prelss,
overall
The
Group
facies,
Batten
themselves
GROUP,
Adelaldean.They
an
(MUir
Formation.
Callanna
imprecisely
to
lacustrine,
and of
the
suprallttoral
Lynott
arenlte
nodular
of
related
from
Tollow,
flne
part
Sub-grOUp
littoral
Formation
playa
is
for the 1981).
as
suggest whole
(1981).
in
being
the
South later
between that
is d e s c r i b e d
the by
16
Cauliflower cherts Pseudomorphs
after gypsum
Stromatolites Groundwater movemel Evaporation
base l~vel
:-_--:L~-Z-
-
.
.
.
.
.
.
.
-Z---Z-Z----
.
Figure 5. Model f o r r e g r e s s i v e development of t h e Yalco a n d c o n t i g u o u s f o r m a t i o n s o~ t h e M c A r t h u r Group; note p r o p o s e d reflux p l u m e ( h a c h u r e d ) WhiCh invades the upper Lynott Formation, causing leaching wlth & consequent sillcification and dolomltizatlon (after Muir, Lock Yon der Botch, 1980),
The been Tl%e
sequence
described crystal
forms
up
stumpy have
to
I0
and
calcium
that
mineral
beds,
by
0.5
casts, well
occurs
cm
wide.
now
at
as is
to
after
to
gaylussite Magadi
gypsum,
rosettes
but
and
as
be
now
(1980).
in
addition,
short
These
all
pseudomorphs of
In
wltll
(Na 2 C O 3 ~ of
Borch
matchstick-llKe
and
an
CaC03
of
sodium
alkaline
authlgenlc
casts
have
of
carbonate
crystals
Crystal
which
microcllne.
(1980)
double
casts der
are
by
dlsplacive
LaMe
yon
There
Delleved
be
&
al.
the
crystal
consist
replaced
environment.
alkaline
as
Jarvls
described
shortlte,
mlcrocline
the
numerous
Rowlands
of
suggested in
as
and
evaporltlc
are
found
have
crystals
forms
The
an
Discoidal some
long
by
Blight,
they
typically
systems,
morphology
cm
identified
crystal
in
Rowlands, that
irregular
been
formed
characterlsed
by
forms
various
lake
is
and playa
having
arrow ~
head
5 H 2 O),
a
Kenya. mlcrocllne,
cauliflower
also
chert
occur
nodules
in
after
anhydri%e.
the
Rowlands
et
Callanna
Group
sabKhas, graben which
in
a
%hat
continental
system as
ai.(1980) p r e s e n t
stated
is
graben
confirmed before
a
envisages
cannot
by
facies
model
for
development
of
system. the
The
from
evaporltes
playa
continental
presence
precipitate
the
of
lakes
nature
shortlte
sea
water
of
of and the
relics, during
17
evaporation. modern is
They
East
compare
ATrlcan
common
in
The
Bitter part
(Stewart,1979) volcanlcs. Springs rocks
in
(1979) on
still
the
these
all
as
gypsum,
moved
Basin
at
and
shale
wlth
in
and
so
far The
brecciated gypsum
and
in
Bitter
equivalent
diaplrically
(Browne,
Woolnough,
exception facies
system
breccia,
of
dolomite massive
a
reef.The
Land
described,
of
the
models
van
de
work
have
of
yet
bipartlte
been
is
::".':'."":":'..':.:;..:.~~~_~
a
The
upper
and
this
secondary
lower
dolomite,
Reef
anhydrite,
is
.
'
~
by
Stewart
anhydrlte.
Open Sea
Stromutolite$
"
the
overlain
Reef brecco
Carbonatesand
,
,
""
of
which
after
127
which
part
limestone,
Barrier
Gypsum
evaporltes
crystalline
breccia,
stromatolitic gypsum
with
bituminous
coarsely
gypsum
Ringwood
the
dololutite.
Lagoon Elituminoul dolom te
is
pyritic
chlorltic
and
~
~
J
I
7. Dlagrammatlc representation of hypothetical barred showlng major rock-types of Rlngwood evapoplte in lagoon stromatolitlc r e e f in B i t t e r S p r l n g s area (after Stewart,1979).
Stewart Ringwood
(1979)
evaporlte
basin
from
precipitating
first then
reef
evaporltes
transgressed
develops (Figure
marine
barrier the
rare
the
&
no
breccia
reef
the
0.9 G y p
(Jackson
Dome,
consists
Figure basin, behind
in
about
occur
1965)
volcanism
comparison.
Amadeus dated
the
Australia
Ringwood
limestone
as
Ranford,
the
evaporlte
(1979) i n t e r p r e t s
is
halite
Western
with
gypsum.
by
dolomite
satin-spar
the
It
chert,
and
However,
deposits
preserved
contains
TERRITORY
in
wlth
alkaline
NORTHERN
car]~onate,
have
that
the
occurs
&
out
systems
deposits.
the
characterlsed
point
rift
strengthening
gypsum
Basin,
they
dlaplrs).
Unlil~e
of of
Officer
Group
Territory.
(Wells, F u r m a n
the
for
Formation
Northern
consists
1981) w h e r e
Stewart
and
Group,
FORHATIOH,
volumes
Formation
developed
m
the
and
Madley
are
Springs
Lar~e
in
Graaff, and
SPRINGS
of
Callanna
system
Callanna
BITTER
southern
Rlft
the
the
a 7).
waters
from
across
and
carbonates migrated
the
barred The the
and
across
being lagoon.
trapped
then the
dissolved The
basin
facies
stromatolite sea
sulfates, evaporlte when
primary
model
reef
Cut
water
then
mainly
normal
a
and marine
was
the back
evaporated
gypsum.
lagoon
gypsum
for
off
The
prevented waters
converted
to
18
anhydrite,
which
tectonic
was
later
reconverted
to
gypsum
as
a
result
of
post-
erosion.
SUMMARY
The from
facies
models
continental
The
classic
Sea,
of
presented
alkaline
Phanerozolc
the
Messinian
desiccation
of
Australian
the
Not
the
evaporltes
represent
original
basins
Precambrlan.
may potash
styles
tlqe
the
not
any
place
of
environments
barred of
appear
basins.
the
to
records
in
of
with the
North
represent
recognised
associated
resting
of
Permian
been
there
often
range
which
have
are
microcllne
a
sabKhas,to
of
Mediterranean
marine
salts,although
represent
playas,contlnental
evaporlte of
deep
here
the
potash
Proterozolc
potassium
from
minerals,
ACKNOWLEGDEMENTS
I
acknowledge
Pty.
wlth
Ltd.;
thanks
and
am
organisations
for
CricK,
Dunlop,
J.S.R.
Stewart,
N.
Commission,
permission
grateful
permission
to
R.G,
International
Economic
Paleontologists
Australia,
and
Bureau
D.
Logan,
and
CRA
von
International of
Exploration
individuals
diagrams: C.C.
R.
BuicK,
IoH.
Borch,
A.J.
Atomic
Geological
Resources,
Geology
and
der
Sedlmentologlsts,
Mineralogists,
Mineral
from
following
LocK,
Association
of
publish
the
reproduce
D.I. G r o v e s ,
Williams,
to
to
and
Agency
Society
of
Society
of
Geophysics,
Canberra.
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der
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Borch
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20
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P.G., i980
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i-22.
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Isa
of
ages
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of
the
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R,W,,
Inlier,
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R.J.
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22~-2~5,
Proterozoic
Northern
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Territory,
Uranium Atomic
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precise
growth
-
Hydrologic
Bulletin
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The
rocks
framework
American
of
origin Mary
Mineralogy
I.R.
isotopic
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i98i
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to
Fletcher
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Proterozoic
Geochronology
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Australia.
the
39-68.
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Field,
the
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galenas:
of
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Uranium
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Research,
R,S,,
Archaean
&
C.R.
volcanism
Precambrian
Needham
along
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Richards
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i980,
sabKh
superposed
Proceedings
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Vienna,
Ramsay
W.
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of
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evolution the
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i98i
oldest
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the
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Petrology, J.G.,
in
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Deposita,
16,
7-S0. Rye
D.M. at
&
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McArthur
isotope
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Geology, D.P.,
evolved Stewart
from
Walker
River.
of
base
Territory,
the
H.Y.C.,
metal
Australia,
Ridge,
and
Precambrian
deposits
III. T h e Cooley
stable
Deposits.
Lithos,
8,
the
scapolite-bearing
Amadeus
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I-7.
marine
evaporite
Basin,
in
the
Central
Upper
Australia.
33-62. &
Lock
D.,
1979
Geological
28,
Sedimentology,
R.G.
and
BinneKamp
J.G., 1978
the
H.Y.C.
associated
Geological
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Society
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of
8i3-82z~.
concerning N.T.. J o u r n a l
sulfide
1-26.
barred-basin
25,
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Some
A
C.C.
R.N., L o g a n advances
76,
of
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Sedimentology, der
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Northern
1975
A.J., 1979
Proterozolc
yon
1981
geochemistry
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SerduchenKo
N.,
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Australia,
24,
geological HcArthur ~65-380.
21
WalKer
R.N.,
1977.
Mulr
Proterozolc 255, Walter
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W.L.,
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Of
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N., the
Nature,
526-529.
M.R., B U I C K
3.500
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from
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the
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L.C~, 1965
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Resources
Basin,
Geology
-
Stromatolltes
Western
-
The
Nature,
geology
Northern
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the
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85. West
I.M., 196~ Dorest.
-
Evaporite
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oT
the
In
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330. Williams
N., 1978a
Rlver,
Northern
Deposits. Williams
Studies
organic-C
Williams
N.
strati~orm Society 198L
of
of
Economic
Logan Pb-Zn
"Sediments
metal
of
the
Geology,
5th
through
I.
-
The
sulfide
at
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II.
concordant 73,
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The
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I005-I0~5.
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R.G,, 1981
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of
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5,
Geological 8.
t i l e H.Y.C. Geologlcal
Convention,
Perth,
CHARACTERISTIC
AND ENVIRONMENTS IN
SOUTHERN
Xi Chengdu
EVAPORITE
CHINA
XiaoSong Institute
and
OF SIMIAN
SICHUAN,
Mineral
Chengdu,
of
Geology
Resources Slchuan
China
INTRODUCTION
During
prospection
province
in
the
interbedded was
1970",
with
Proterozoic
in
Sinlan
salt
This
rock
dolomite,
the
southern
up
dolostone
and
in
The
of
Asia. the
to
thickness
a
to
of
(of
provided
information
part
intraclastic
discovery
evaporltes
an
hydrocarbons
algal
discovered.
present
Top
alto
new
example
tllls
geologists
Sichuan 200
for
the
communication
interested
m),
anhydrlte
in
late is
to
evaporites
elsewhere.
GEOLOGIC-TECTONIC
The
Sinian
Slchuan
is
orogenic
cycle
the
continental the
Doushtuo clastic consists overlain
is
South-West
first at
the
clastlc
underlying
granite
in
land
of
and
of
Yangtze
of
due
late
to
Sinian
Dengying carbonate
Cambrian
Early
deposits.
composed
early
the
with
southern
Platform
Proterozolc.
glacial
core
marine by
including
Upper late
phosphorlte,
shallow
conformably
in of
China
unconformable
Formation and
end
rocks
old
angularly
rocks
cover
BACKGROUND
Its
after
basal
is
consists contact
rocks, hyollths
in and
of part
of
With
rocks
orogenic
composed
Formation
of
Yangtzeian
Slnian
eplmetamorphic Jinning
part
and
movement.
of latest
littoral Slnlan
evaporltes,
trllobits.
Lecture Notes in Earth Sciences, Vol. 13 T.M. Peryt (Ed.), Evaporite Basins © Springer-Verlag Berlin Heidelberg 1987
24
After China
Jlnning
formed
was
the
the
Songpan
to
the
north-west was
the
strikes
the
rhomb in
its
about
the
Sinlan
of
the
filled m
The
basal on
platform
north
of
the
Nlushoushan
land
the was
in of
situated
To which
South-West
which
to
Yunnan
land.
elevation
core
north
Central
old
submarine
with
facies
the
the
The
two in
i).
formation
groups
the
area
Changnlng
dolostone,
(Figure
and
were
east-west
islands. and
thick
paleotectonlc
there
and
subsidence
centre
the
Platform,
the
old
the
there east
land,
east
was
of and
of
the
neighboured
shelf.
late
margin
io00
sedimentary by
the
north-east
fault
the
Jiangnan
open-sea
of
to
of
the
movement,
Yangtze
Trough.
islands,
During
along
Upper
Kunlun-@inlin
platform with
orogenic
the
of
old of
faults
basin
the
saline
faults the
cross
was
anhydrite
Therefore the
side
the
saline
nodular
of
of
west
formed
right and
with
platform, a
located
rock
salt
distribution
of
basin
was
controlled
frameworK,
Flgure i. S e d i m e n t a r y facies in t h e Dengylng Formation of t h e late Slnlan in s o u t h e r n Sichuan, I open sea limestone facies, II intertldal-subtldal dolomite facies, III intertidal dolomite facies, IV intertidal algal dolomite facies, V supratldal sabKha algal dolomlte-anhydrlte facies, VI sabKha-salt lake evaporite facies,
25
ROCKS
Dengylng into
three
thick.
Formation
to
The
second
top
algal
of
evaporltes
200
m
of
called
The
There
(the
is
rock
be
is
of
453-606
m
thick
algal-detrltal that
in
was
metres
dolostone,
I00-500
salt
divided
member)
dozens
layer
dolostone,
can
third
some
stpomatolitlc
member
2), i n c l u d i n g
rocks
m
thick
in
part
and
is
dolostone
Changnlng
is
46-
Algal
-
four
subtypes
stroma~olltl¢
algal
intertidal mainly
ROCKS
are
dolostone,
the
and
second
and
are
of
dolos~one.
There
dolostone
oncoids
and in
dolostone
algal
with
terplgenous intertldai
ooids second
and
supratldal
zone
or
lower
energy
it
the
two
Minds
consists
intraclast fragments,
pelletold
It
nodular, It
limestone
In
lligll-energy
algal
in
suDtldal
the
first
blrd's-eye
laminated
anhydrlte
occurs
the
in
black
environment
first
occur
of
the
dolostone,
and
Micritic
dolostone
dolostone
wlth
zone
and
formation. bambooformed
in
formed
in
member.
dolomltlc
and
shoals (b)
lower-energy
member
includes
and
occurring
of
and
deposited
are
algal
Formation;
occur
the
of
on
were
These
platform,
Dengying
intraclasts
subtldal
over
of
sabKha.
Dolomltic
Others.
algal-lamlnated
Formation.
mainly -
origin,
dolostone.
formed
mainly
and
includes
which
dolog~one.
dolostone
are
and
member
different
sands-they zone,
Supra~Idal
leaves
Sparry
the
It
Dengylng
(a)
structure
grape-algal
distributed
member
dolostone.
occurs
composition,
dolos~one.
dolostone,
sediments
in
by
In~f'aclas~
the
of
rich-algal
and
SECTIOH
thick,
CARBONATE
the
types
residue
the
first
SALIHE
formation
a
limestone,
(Figure
THE
two
the
dolostone
dolomltlc
and
of
leaving
member
of
OF
conslstlng
The
evaporites.
composed
SE@UEHCE
paleoeroslon,
consists
possibly
THE
members.
subjected
and
AND
argilllte
in
the
first
member
of
formation. EVA FORITES Drlllholes
Hali~e.
Halite
is
stratified
pure
halite,
NaCI
is
of
Ningl
93
×, KCl
stage
of
that a
Z,
Nlng2
or
halite a
are
considered
are
5-7
crystals and
Br
-
was
glauberlte 0.0088
coefficient
the
lagoon
its
halite
0.I
bromine-chlorlne
indicating
and
anllydrite
and
cm
(Br~i000/Cl)
salt
lake.
iS in
the The
an
size,
example. There
Average
Z(O.0OZ~zf-O.OOi
precipitated
continental
in
halite.
as
content
×); t h e
halite
of
varlatlon
O.i-0.15(hlghest: early
are
O.2)
deposltlonal crystals
are
26
large
and
intense
few
primary
sedimentary
recrystalllzatlon
and
secondary
Ebian
Emei
structures
are
preserved
because
of
enlargement.
Changning
Ya.gch~
I/I J'-A .o %
c
kJ,,v O
d
a
f'------I 1o ~, 3
0.-7
I.~,.1 1t z I j12
,",'--4
"4- 8
r~
13
m
Figure a, L l t h o f a c l e s correlation and t y p e s of s e q u e n c e of e v a p o r i t e in Dengylng Formation. i glauberlte, 2 - anhydrlte, 3 - oncolite, 4 - algal stromatolite, 5 - algal laminated limestone, 6 - grapestone lump, 7 - bird's-eye, 8 - hallte, 9 dolomite, I0 - q u a r t z sandstone, II sand gravel, 12 limestone, i~ siliceous rocK, a sandy algal dolomite, b - algal dolomite, c - edgewise dolomite, d - nodular" anhydrlte.
Anhydrite.
It
accompaniment. nodular,
in
extended
as
anhydrite
metres
appearance or
the
water
in
lower
stripe
shows in
top that the
rainwater
the
~ormed
in
halite
continental playa at
that
was
halitlc of
the
supratidal in
unit.
It
~resh
water by
causing
as and
The
cycles
is
The
its lumpy
spotted sometimes
occurrence
of
sabKha/lagoon.
the
leached
time,
layers
layer,
stratification.
concentrated
the
halitlc
cunular-sphaerollc, in
layer
to
is
the
cycles
hali%ic
i%
of
in
spotted,
of
parallel
suggests
the
is
series
Glauberite
halite and
a
the
a
Glauberl~e. of
occurs
Anhydrlte
forming
anhydrlte
the
mainly
is
interval spotted
flowed
into
penetrating the
increase
some
and
the
Its
salt
surface of
dozens
lumpy.
lake fresh
calcium
ion
27
and to
the form
interaction the
glauberlte.
transition
from
salt-~orming first
between The
marine
processes,
member
of
(a)
Asymmetrical
and
(b)
the
wlth
section
of
be
of
first
quartz
sands;
having
basal
potted
mlddle-algal-pelletal surface
dozens
the
regressive
(sabKha)
from
the
Formation
algal-lamlnated
covering
and
oncolitic
intertidal
shoal,
ANALYSIS
in
the
There
first
of
member
three
types
---
Stripped Lump
anhydritic
-~-
deposi~ional
the
first
There
are
(4)
two
Pure
The
five
saline
took
place
the
upthrow
types
halite
(5) Halite
the
member
wlth
in
the side
model
anhydrlte constitution
Slat/salt
second is
flat
member
of
composed
of
algal the
grape
high-energy
sequence.
taken
NODEL
lower
as
(from
a
salt
typical
bottom
to
cumular-sphaerolic
---
pure
---
layers example,
top): anhydrltic
halite.
cumular-sphaerollc
of
sab1~ha-sal~
formation
lathe.The
the
of
evaporite
sequence:
---
stripped
glauberi%ic
---
evaporlte
mentioned carbonate Of
formed
sands,
halite.
of
of
tidal The
can with
anhydrltic
halite
anhydrlte
types
strata
halite halite
pure
The in
---
anhydrltlc
nodular
of
and
and
upper-algal
tripartite
lake.The
are
of
The
west
quartz the
platform
sequence
halite
potted
anhydritic
halite
formation
evaporite
the
with
DEPOSITIONAL
lagoon-salt
lake.
strata
dolostone,
Which
EVAPORITE
the of
the
the
dolostone
cracks; and
transgressive
of
anhydritlc
halite (a)
THE
model
Lump
(S)
OF
depositional
are
(1)
the
to
saline
anhydrlte
The
all
in types
representing
salt
laln
evolution
dolostone
showing
the
the
algal-oolltlc
the
dolostone-anhydrlte-
environment.
stably
dolostone,
dolostone,
of
carbonate
two
the
to
dolostone-anhydrlte-
dolostone
cycles.
sequence
subtldal
wlth
dolostone
of
section
into
fop
of
desiccation
bamboo-leaves
some
mark
brine
of
and
dolostone,
and
sallne
formation
the
erosion
suggests
The
the
a
According
anhydrlte,
flat
matched
lower-slllceous
of
Dengylng
is
is
divided
wlth
tidal
of
area
the
be
composed
the
dolostone,
consisting
member
Changnlng
tripartite:
of
glauberlte-dolostone the
intercrystalline
glauberite
consisting
cycle
of
and
deposition.
can
cycle
sequence
the
south-west
the
constitution Formation
Symmetrical
evolutional
water
continental
the
Dengylng
cycles:
fresh
formation
to
halite,
halite-halite
the
the
potted
taken
platform faults
show with
as
sequence
that dry
formed
upper a
salt
typical
layers example.
halite,
glauberitlc
depositional
above
old
are
the
and
two
evaporlte
climate.
the
halite.
salt
The flat
types
of
deposition
upwarping (sabKha).
of The
28
subsidence
of
"the
and
playa The
side late
the
Slnlan,
of
late
between
drop
type the
of
in
and
But
halite or
playa
direction
as
the
in
characteristics
strike
sequence
of
part
Sichuan
of
around
evaporlte
which
and
was
have
of
of
leveled
second
member
are
seldom
and
most
Of
the
east
and
time,
both sea
During
shelf,
the
Jlangnan
period
marginal
shoals
enter.
an
the
from
anhydrlte.
In
Which
block
deposition, to
the
the salt
the
thickness
the
marginal regression,
lame
in
the
algal
llallte
shoal
of
of
the
which
flat
with was
stopped
the
sabKha
of
The
and
the
seawater
to
which
in
a
of
became
evolved
Of
salt
lake
syndeposltlonal the
the
evaporlte
highland
supplying, into
the
nodular
shallow
of
the
because
causing
lot
the
seawater
has
the side.
exposed.
prevented
because
lake
west
flat.
stage
salt
that
structures
originated late
sands
At
platform
climate,
there
first
wlth
the
was
dry
islands
the
dolostone
algal
growing
southern
tides.
possibility
other
oT
was
the
facies
the
joined
platform
the the
supratidal
bull~s -
terrigenous by
were
evaporite
During
the
from
a
the
wlth
platform
and
depression
of
a
tlle
tear-
north-eastward
deposition
that
east
with
to
relatively
subsidence,
short
salt
dolomite
in of
shows
that
supplied
supratidal
Later,
is
sedimentary
influenced
restricted
evaporation
the
huge
fault
of
the
tl%e
the
dolostone
place.
intensive
%o
platform
algal
took
transition
in
the
of
being
the
suggest
so
was
regression,
environment
dolomltlzatlon of
the
the The
sabKha
platform,
during
sides
elevation
of
structure
Formation,
water
with
gypsum
flat
the
east.
the
zoning
from
in
faults.
strata,
carbonate
platform
west
sea
of
Abundant
indicate
the
seawater
of
ENVIRONMENT
down
Dengylng
the
submarine
rock
by
extends
old
opposite
toward
gypsum
the
saline
shallow
been
and
open
the
a
of
the
by
stage
beginning
the
i), w h i c h
the
depositing
platform
tlqe
PALEOGEOGRAPHICAL
The
of
whole
(Figure
on
gypsum
migration
The
deposited
lake
followed
Doushantuo
Intruded
was
formation
Luzhou.
the
transgression
gypsum
the
was
There
The
the
lagoon,
deposited
During
Platform
Jinyang.
formed
mainly
county,
make
resulted
salt
same
Yangtze
Yanjln
faults
lake.
direction.
Yanyuan
would
pattern.
eye
the
salt
platform
the
and
stage
of
supply
Upper of
regression
part
in
Ningnan
Dengylng
in
the
area
continental
seawater
south-west
part
cross
the
evaporlte
of
the
the
the
so
due tllat
continental
lake. The
occurrence
of
salt
deposition
ended
glauberlte
formed
continental
fresll
by water,
the
glauberlte in
the but
the
also
proves
continental
intermixing the
potted
of and
tl%at
lake.
tlqe evolution The
residual
lump
of
thln-banded brines
glauberlte
was
with formed
29
by
replacing
the
water
penetrated
stage
after
dolostone halite all
in
salt of
basin
area
high.
Dengying
small,
evaporite
of
in
brine
The
layer,
in
between
during
occurrence
the
the
halite
the
halite
the
short,
resulted
stage,
platform
halite
interaction
ratio
content
of of
Changning
the of
the
early
algal
area
between
in
was
diagenetic
interbedded
thickness bromine
fresh
the
the
halite
precipitated
seawater.
was
thickness
the
halite.
(24:i), a n d
depositing
was
These
of
the
the
under
intercrystalline
lower
that
from
evaporation
that
the
the
anhydrite
indicate
The
and
deposition
and
directly
dolostone
in
halite
is
brine
deposition.
than
supply
was
and
the
that
the
layers
transgression
which
less
algal
forty not
concentration deposition varies was
dolostone
of
thousand
sufficient, of
the
halite
considerably.
expanded was
sq. kin. T h e
and
the
brine was
not
unstable
During
seawater
deposited,
process
was
ending
the covered thus
so and
late all the
THE LOWER CARBONIFEROUS (VISEAN) EVAPORITE5 IN NORTHERN FRANCE AND BELGIUH: DEPOSITIONAL, DIAGENETIC AND DEFORHATIONAL GUIDES TO RECONSTRUCT A DISRUPTED EVAPORITIC BASIN
JM, Rouchy*, A. Laumondals** and E Groessens***
*U.A. 1209, Laboratoire de Geologie, Museum National d'Histolre NaturelIe,43, rue Buffon, 75005 Paris, France. ** TOTAL C.F,P.,B.P. 47, 92069 Paris la Defense, France. *** Geological Survey of Belgium, 13, rue Jenner, 1040 Brussels, Belgium.
I NTRODUCTION
In the Franco-Belgian part of Hercynian orogene, presently isolated thick Dlnantian
anhydritic formations were discovered in two wells (Fig. i) : Saint-Ghislatn in Belgium and Epinoy I in northern France (Dejonghe eta/, 1976; Delmer, 1977; Groessens et al, 1979; Rouchy et al, 1984alb;
Laumondais eta/' i984; Rouchy, 1986) ; widespread
extended breccia, the "Grande Breche de Dinant et de Namur", and numerous pseudomorphs of gypsum or anhydrite have been observed in their stratigraphic equivalents in boreholes (W6pion, Douvraln, Heugem) and in outcrops (Bless eta/' 1980; 1981; Swennen et al, 198 I; Swennen and Viaene, 1985; Hance et Hennebert, 1980; Hennebert and Hance, 1980; Conil et Groessens, 1986; Groessens eta/, 1979; Rouchy, 1986; Rouchy eta/' 1984 a/b; i986 a/b). In order to reconstruct the original character of these formations and to understand their tectonic impact, a detailed sedimentological and geochemical isotopic study was carried on the three groups of sediments : thick anhydritic formations, scattered pseudomorphs and breccias (Pierre eta/, t984 ; Pierre, 1986;
Lecture Notes in Earth Sciences, Vol. 13 T M. Peryt (Ed.), Evaporite Basins © Springer-Veflag Berlin Heidelberg 1987
32 Pierre and Rouchy, 1986; Rouchy, 1986; Rouchy et al, 1984, 1986b). This study reveals that the present distribution of evaporites is controlled (with local variations) by post-depositional parameters such as tectonism and dissolution, dissecting a regionally wldespread unit. whlch extended In all the structural umt of thls part of the Hercyman orogene
STRUCTURAL AND STRATIGRAPHIC SETTING OF EVAPORITES
The Variscan area in Belgium and northern France may be broadly divided into three major structural units (Fig. I) : 1) the Brabant Massif, which is a fragment of the Caledonian orogen ; 2) surrounding this first unit, the autochthonous Variscan area Is formed by the Namur Basin in the South and the Campine Basin in the North [in this part, the Devono-Dinantian ends by a thick coal formation (Borinage ~ Campine)] ; 3) in the South, the Dinant Nappe known from the Ruhr to the Ireland is carried , in the South-North direction, over the Synclinorium of Namur by a major overthrust, the "Faille du Midi". This naPPe may be traced over 125 km to its roots in the northern part of the Paris Basin (Aubouin, 1985; Cazes eta/, t 985). The regional structural pattern, already well-known through petroleum exploration (C.F.P.(M), CO.PE.SEP.,R.A.P., S.N.P.A., 1965) can be treated as thin-skinned tectonics (Laumondais etal, 1984; Becq-Giraudon, 1983; Cazes et al, I985), The structure results from potyphased tectonic activity in which the major thrusting phase (Asturian phase) is late-Stephanian (Colbeaux et al, 1977 ; BecQ-Giraudon, 1983). Below the main overthrust and in front of it, a multiple-system of thrust slices is observed in paraautochthonous and autochthonous series, particularly in the coal formation. In the studied area, a broad DeMod of denudation occurs duMng the Permian and partly the Triassic. The Mesozoic Paris Basin overlies the southeastern part of the Hercynian area and a small Cretaceous basin is developed in the central Part of the Synctinorium of Namur (Mons Basin) including the type section of the Montian stage of the lower Coenozoic. In the studied area, the evaporites occur at several stratigraphic levels within the
33 Devono-Dinantian column but the tl~ickest anhydritic formations are found in the Givetian of three wells (Tournai, Vieux-Leuze and Annapes 1) in the northern edge of the Svnclinorium of Namur (Coen-Aubert etal, 1980; Rouchy, t986) and in the Dinantian of Saint-Ghislain and Epinoy 1 wells where respectively 765 m and 904 m of limestone and anhydrite deposits were encountered (Fig. 2). Elsewhere, pseudomorphs of gypsum and anhydrite or very thin evaooritic deposits occur in the Givetian (Preat and RouchY, 1986), the Frasnian and the Famennian (Graulich 1963; Groessens eta/, 1979; Goemaere eta/, 1985; etc) and in the above-mentioned Dinantian occurrences. The pseudomoroh-rich sediments as well as the main Visean breccia offer a good stratigraphic correlation with the anhydritic levels of 5aint-Ghislain; the Middle Visean (V2b-V3a interval) contains the main anhydritic intercalations, the Great Breccia (Grande Breche de Dinant et de Namur) and numerous evaporite pseudomorphs (Bless et a/, 1980; Groessens eta/' 1979; Conil and Groessens, 1986; Rouchy, 1986).
.~-~ ....
~-~
IBruxels
,,,,, ,---- ,,
~ ' A n n a p e s , . Tournai LEGEND Lille , ,_....'1" 0 Thick a ~ f o r m o t i o n a {Soint.Ghisloin and Epinoyf ~eholes ) ( ~ Pseudomorphs after sulfote~ in boreholes. (~,j3ombrai-" ( ~ Pseudomorphs oftersu/fofe~ and breccioe in outcrops. _ [] "11" Devonian evaporites. .ooz,,u.u,t I Other wells toi) ~k n Fod• le du - * Midi" ~over thru=.
o
Douvrain ,.
~ ¢~.~
v
(~
~L,~;~ ~,~'
Yves ~ADinont
(~)
~c
.'"; N ~
~
50kin
(R~
i...
~..
N
~"
Fig. l - Location of wells and localities mentioned in the text
Until recently, the distribution and the significance of these evaporites, particularly the Dinantian evaporites, were underestimated and Poorly understood because of limited data in spite of the paper of A. Delmer (1972) who insisted on
34 iml~ortance of evaporites for the understanding of the regional geology. The limestone and anhydrlte Visean deposits of Saint-Ghistain located in an area of Devono-Dinantian thlckening, was first considered as deposited in a narrow subsiding trough (the "Sillon Borain °) in front of the Hercynian overthrust. A sedimentological study (Rouchy et a/~ 1984 a/b) concluded that the Saint-Ghislain formation constitutes a residual fragment of a widespread formation extending southward ; this hypothesis was confirmed by the discovery of an another thick anhydritic formation in the Epinoy 1 well below the "Faille du Midi" overthrust, where this formation is situated in inverted position and in a complex slice thrust system (Laumondais eta/, 1984) ; the evaporitic sedimentation could then have begin in Tournaisian and continued into Visean (Fig. 2). General sedimentological research carried out in Belgium and the Netherlands have revealed the presence of numerous evaooritic pseudomorphs in all the structural units shown in Fig. 1 : autochthonous in the south and the east of
the Brabant, Boulonnais, Dinant nappe ;
evaporites of the same age are known in Great Britain (Giffard, 1922-23; Georges, 1963; Llewetyn and Stabbins, 1968; Llewetyn eta/, 1968; West eta/, 1968).
INTERCALATED LIMESTONES PALEOENVIRONMENTAL SIGNIFICANCE
The Visean limestone in which the anhydrite beds are intercalated is a relatively homogeneous formation characterized by the scarcity or even the lack of the terrigenous components (Fig. 2). Dolomite
is surprisingly rare compared to other ancient
carbonate/evaporite sequences,
at least in the thickest evaporite series of Saint-
Ghistain and Epinoy. An important phase of dolomitization is related to the fracturing of limestone has been observed in association with a breccia in the Wepion borehole. Although the faunal association is poorly diversified, Groessens et a/(1979) indicate the presence of fossils (radiolarians. foraminifers,
in all parts of the Saint-Ghislain formation
ostracods, serpuIids, br!/ozoans, crinoids, brachiopods,
gasteropods, corals, even goniatites and algaes) and, at a few levels, the fauna appears to be rich. In contrast, some organisms (ostracods and brachiopods) are scarce in the cores of the Epinoy I well.
35
[EPINOY 1~ FRASNIAN STRUNI.~ ~
1900
1905m 2612m
'~"
2000
2200
. 2300 :
I,,~i ~ ,-= ~, , " i
2400
m
2500
Z
2600
>~ .~ . , ~
I
breccios
~ = ' °°~
2670m
I I
I- 2700
]~l'l' T-'I'll
VISE Anhydrlte
3516m
~.= co~bonotes , I
i I
I,I.,I
, I
-
2900
E-~'~'3 Sheles
~_L~L~
T-II'~'
~--'-~--~-~- .3000
Fig. 2.- Schematic stratigraphic columns of the Saint-Ghislain and Epinoy I boreholes; note the presence of a deep karst at Saint-Ghislain and the reversed position of the Epinoy 1 series in which we can observe an intensely deformed interval corresponding to the intersection of the thrust stices (between 3,300 and 3,400 m).
Planar or undulating laminated limestones of possible cryptalgal nature are common (Fig. 3, A,B,C). Columnar stromatolites (10 cm in height) have been only observed in one level at Saint- Ghislaln (Fig. 3,B). In outcrop, Mamet et ai(1986) observe the frequent occurrences of the SDongiostromata facies. By the study of the faunal changes in some Visean outcrops, Hance and Hennebert (1980) showed
sequences
of
progressive
36
Fig. 3.- Facies of the intercalated carbonates. A.- Planar cryptalgal laminites; the intraformational brecciation could be related to desiccation. Saint-Ghistain borehole; 1,848 m; scale bar is 2 cm. B.- Columnar stromatolites. Saint-Ghislain borehole; 2,265.20 m; scale bar is 2 cm. C.- Dark, finely laminated limestone probably of algal origin. Some diagenetic anhydrite nodules may be pseudomorphs after gypsum. Saint-Ghislain borehole; 1,959.90 m; scale bar is 2 cm. D.- Sequence beginning by a goniatites-rich (arrows) sediments grading upward into dark laminated sediments (I) prior to the evaporite deposition. Saint-Ghislain borehole, 1,946.60-1,946.80 m; scale bar is 2 cm. E.Oncolitic limestone. Saint-Ghislain borehole; 2065.40 m; scale bar is 2 cm. F.- Thin section photomicrograph of peloidal limestone (pelsparite). Epinoy I borehole; 3,133.60 m; scale bar is 100 tim.
37 increase in restriction from a normal marine environment (foraminifers and ostracods) to evaporitic conditions (algal sediments with pseudomorphs after sulfates). This observation argues for a marine origin of the brines which have generated the evaporitic interbeds. Similar changes in depositional conditions could explain in the Saint-Ghislain borehole
(1945,15m),
the rapid transition
between the
sediments
containing
goniatites,the cryptalgal taminites (Fig. 3D) and the nodular sulfates (Rouchy eta/, 1984a) ; in other cases, evaporites and carbonates are associated without apparent sequential transition. Oo'ids and oncolites are present in thin layers (Fig. 3,E) while beds of peloidal limestones are well developed in Epinoy 1 cores (fig. 3, F). Algal facies are widely represented. Alternating more or less restricted marine and evaporitic conditions are evidenced by the sedimentary and faunistic changes. As is the case in all evaporitic subaqueous environments, the development of the microbial accretions (stromatolites)
following
the faunal diversity impoverishment, indicates the strongest restriction stage before the salt saturation (Guelorget et Perthuisot, 1983). In the Visean, there is no evidence of halite (or more soluble salts) with the exception of perhaps a carbonate-sulfate breccia in Saint-Ghislain borehole. The assumed deioositional model shows relationships between carbonates and sulfates in a restricted to repeatedly open lagoonal setting; the evaporitic stage, related to strong reduction of the marine influx or barred conditions, is generally characterized by the lowering of
the water
level;
this produces, in weakly-differentiated
pateogeography, the emersion of large areas and the perslstance of evaPoritic conditions in lows or subsiding areas.
HEANING OF THE PRII'IARY AND EARLY DIAGENETIC ANHYDRITE FEATURES
Gypsum, the common expression of the calcium sulfate in the surface conditions, becomes unstable at depth as the consequence of temperature increase and is changed into anhydrite; the transformation produces a textural homogeneization with obliteration
38 of the gypsum crystall.ine structures and the development of nodular and mosaic anhydrite (RoucbY, 1976;
Loucks and Longman, 1982). The range of depth depends on
various parameters, principally geothermal gradient, tectonism, seismicity and salinity of the connate waters, but it is commonly estimated to the range of 700 - I000 meters (Murray, 1964), Gypsum can be also altered into anhydrite In surface syndeposltlonal conditions, and therefore confusing interpretation may arise; Rouchy et ai(1976), Rouchy ( 1980), Loucks and Longman ( i982) and Shearman (1985) discussed this problem with regard to the Miocene and Cretaceous evaporites. As in all the deeply buried evaporitic formations, anhydrite is the sulfate main component with a nodular morphgology fashion used here In a broad sense including cm to dm-slzed isolated nodules, coalescent nodules forming a mosaic structures (Fig. 4,A), contorted nodular or enterolithic features ; in some cases, the host-sediment appears deformed around the nodules as a consequence of early diagenetic growth or perhaps diagenetic evolution. Numerous pseudomorohs of gypsum indicate its former presence; traces of gypsum were identified at depth (3900 m) in Epinoy 1 well (Bouquillon, 1984; Coullloud and Moine, in Rouchy et al, 1984b). Pseudomorphs of gypsum crystals (Fig. 4,B,C) exhibit two types of habit : isolated lenticular or lozenge-shaped crystals (ram to cm In size) and vertically standing gypsum crystals beds (cm in height) of selenite type (single or twinned crystals); the first characterizes an early diagenetic growth in carbonate mud or in algal lamlnltes (Salnt-Ghislain, 1932 m) and the second results from primary subaqueous crystallization on the floor of the depositional basin, Some samples show the transitional stage between a well preserved crystalline habit and rough pseudomorphs or even nodular fabrics. Many nodules with angular forms evidently had gypsum precursors. The original shape of the crystals is best preserved when the crystals are isolated within a carbonate matrix or when they are replaced by calcite or silica, suggesting the destruction of the sedimentary structure is broadly post-depositional and probably burlal-related. As it is evidencied by some samples of Saint Ghislaln, the disappearance of the crystal shape and the development of the nodular aspect could indicate that the original gypsum bed was thick and massive.
39 Considering all data previously discussed, we can demonstrate that the gypsum could has been an important component
in the depositional sulfate phase despite the
predominant nodular Pattern of the anhydrite, These data do not exclude the early diagenetlc growth of nodular anhydrite in temporarily emerged carbonate blanket, but this mechanism cannot explain the formation of the whole anhydrite. We shall see the tectonic deformation greatly contributes to destroy the primary structures.
Fig. 4.- Facies and petrography of the sulfates, A.- Typical nodular to mosaic ("chicken-wire") anhydrlte. Salnt-Ghislain borehole, 2,219.13 m. B.- Anhydritic pseudomorphs after crystalline gypsum (I); note the transformation of gypsum aggregates erase the primary structure of the gypsum and lead to a "pseudo-nodular" (2) or "Dseudo-mosalc" structure. Saint-Ghlslain borehole; 2,108 m C.- Sparry calcite replacement after lenticular gypsum aggregates which have resulted from early diagenetic growth into black laminated sediments., the voids (I) and perhaps the fracturatlon (2) probably resulted from gypsum to calcite volume reduction. Saint-Ghlslaln borehole; 1,932.86 m; scale bar in all photos is 2 cm.
ANHYDRITE TECTONIC DEFORHATION
In the Jower part of the Saint-Ghislain formation and in the whole Epinoy I series a great variety of deformational structures like stretching, lamination, isoclinal microfolding, augen-like
and mylonitic structures (Rouchy et al, 1984alb ; Rouchy,
4o
1986)-are generated by compressive tectonic stresses. The similaritles between tectonic-generated
structures
and
sedimentary
(lamination)
or
diagenetlc
(pseudo-nodules) features could lead to incorrect interpretations. Similar structures were also observed in Permian Bellerophon formation of the Italian Alps (Helman and Schreiber, 1985) as in Tuscany (Ciarapica and Passeri 1976 ; Schreiber and Fitzgerald, oral. comm.) and also in relation with salt migration in many diapiric structures (Wall ez a/, i961 ; Schwerdtner, 1966 ,,Martlnez, 1974 ...). The Saint-Ghislain anhydrltic formation shows a progressive downward deformation, in which changes are interpretated as the result of the increasing tectonic stresses. Textural change begins with the rotational deformation of the nodules which become oblique (I 5-25 degrees) with respect to the layering of the undeformed carbonates (Flg. 5, A,B,C); the layers composed of elongated nodules may be separated one from the other by glide planes showing fold offset. The increase of the deformatlon leads to the tectonic lamination which can be very regular when any carbonate fragment disturbs it (Fig. 5,D)I a confusion
with simllar sedimentary
lamination could lead to a
misinterpretation, The microscopic observation (Fig. 6, A,B,C,D) reveals the crystal
Fig. 5. - Tectonic and halokinetic deformation of the anhydrlte. A. - Stretchlng and oblioue reorientation of the anhydrite layers, intercalated between weakly deformed limestone laminae. Saint-Ghislain borehole; 2,192.40m. B. - Stretched and deformed mosaic structure. Salnt-Ghislaln borehole; 2,169 m, C. - Stretched mosaic structures between two carbonate beds showing white calcite filled fractures, Saint-Gh~slain ; 2,i68.46 m. D. - Tectonic lamination the dark laminae are composed of reoriented carbonate fragments (mylonitlc structure~ I) resulting of the boudinage of former layers ; note the mlcrofolding (2) of some laminae and the presence of isolated Isocllnal hlnge (3). Epinoy I borehole~ 2,939.i0 m, E. - Augen-like structure resulting from the rotation of dolomitlc fragments during the anhydritic flow ~ note the drag fold in the anhydrlte, Epinoy 1 borehole; 2,939.40 m, F. - Large fractured limestone fragments dragged in the laminated anhydrite ; the penetration of the anhydrite in the open fractures (I) is followed by the boudinage of the thin limestone beds (2). Saint-Ghlslain borehole~ 2,308.96 m, G. - Fragmentation and microfoldlng of the calcareous layers. Epinoy i borehole~ 2,928.80 m. H. - Laminated and microfolded anhydrite. The lamination is deformed by asymetrical chevron folds with slight inclined axis, A dolomitic layer is involved in a isoclinal microfold with axial plane parallel to the lamination. Epinoy 1 borehole~ 2,930.70m to 2,931.37 m. Scale bar in all photos is 2 cm.
41
42
reorientation parallel to the lamination and sometimes, their fragmentation in minute fragments during intragranular gliding and dislocation. Schwerdtner (1974) noted the lineation of the anhydrite rocks in evaporite domes has the same kinematic significance as schistosity in metamorphic tectonites. As this deformational stage, the calcareous interbeds have undergone brittle deformation ; the style and the importance are depending of their relative thickness. The thin layers are stretched and disrupted ("boudinage") or microfolded (Fig. 5,D) ; augen structures (Fig. 5,E) result from the dissemination along the foliation of numerous fractured and rotated fragments of carbonate or of isolated bends of isoclinal microfolds with the axial plane lying parallel to the lamination ; the rotation of some fragments can disturb the regularity of the lamination inducing drag folds in the anhydrite (Fig. 5,E) particularly well developed around competent bodies such as quartz or silicified aggregates, even showing sigmoidal tails of the recrystallized calcite (i.e. pressure shadows). A great number of drawn out hard crystals or fragments produce a disorder in the lamination. Thick carbonates layers are generally brocken and large fractured blocks are enclosed within the flowed anhydrite (Fig. 5,F,G). These blocks present a dense network of fractures (sometimes "en echelons") filled by recrystallized calcite and anhydrite;
in Epinoy 1 cores, native
sulphur is present in the calcitic infilt (Fig. 8,E). Pseudo-nodules of anhydrite seem to result from the injection of flowing anhydrite into open fractures (Fig. 5,F). In more deformed intervals of Epinoy 1, the peloids display oblique stretching. A more confusing fabric which mimics a sedimentary sequence results along the horizontal axis of isoclinat folding in the anhydrite ; indeed, a typical mosaic structure develops in the thickened hinge of the fold and an horizontal and regular lamination characterize the stretched limbs. Large chevron folds with gently inclined axial planes deforms both the lamination and the isoclinal microfotds near the depth of 2,930 m in Epinoy 1 (Fig. 5, H). The strongest deformation appears in the lowermost core of Saint-Ghislain in which a very irregular mylonitic-like structure composed of brecciated carbonate fragments associated with flowed and injected anhydrite is seen (Fig. 5,G).
43
Fig. 6. - Microscopic deformations. A. - Irregularly microfolded anhydrite. Saint-Ghislain borehole ; 2,046,66 m ~ plain light. B. - Microfolded anhydrite including a rotated fragment.'Epinoy 1 borehole ; 2,928,75 m ; plain light. C. - Regularly laminated anhydrite showing reoriented crystals and stretched (boudinage) limestone laminae. Saint -Ghislain borehole ; 2,048,46 m ; plain light. D. - Laminated anhydrite. Saint-Ghistain
borehole ~ 2,928,75 m ; crossed nichols ~scale bar in all photos is 500 l~m. The significance of the above mentioned deformation must be discussed with regard to both the structures and to the mechanisms. Firstly, in an inhomogeneous formation composed of an alternation of ductile (anhydrite) and brittle (limestone, accessory dolomite) layers, both the style and the intensity of the deformation vary considerably with respect to the relative thickness of each component.; deformation increases with the thickening of the ductile layers. Secondly, the ubiquitous deformational fabrics of the anhydrite cannot allow one to distinguish between regional tectonic compressive
44
stresses and geostatic movements associated or not wlth former saline beds whlch produce very similar fabrics (Wall et al, 1961
;
Schwerdtner, 1974)
;
in their study of
the mechanical behaviour of the anhydrite, MOller et ai(1981) suggest that the deformation of the anhydrite might be yielded by a steady-state flow at relatively low temperature and low stress. We can admit that the tangential tectonism release flow processes as in halokinesis. Looking the Saint-Ghislain borehole, the downward increase of the deformation to a maximum near the base of the formation suggests it corresponds to a mechanical discontinuity underlined by a deep karst and collapse-solutlon breccia. In the two boreholes, the regularity of the style of the deformation also with the gentle inclined lamination, except of a part of the Epinoy 1 well seem to be due to transverse differential displacements in relation with tangential tectonic stress (i.e.shear). It is possible therefore, that the structures result from a combination of the Hercynian comPressional forces and of the subsequent flow of the evaporite ; the combination of the two mechanisms and the concentration of the forces through the mobility of the evaporites can easely explain the presently observed discontinuity of the evaporitic bodies. The extreme deformational features in the Epinoy i formation reflects the.more complex structural setting of the formation associated with a multiple-system of slice thrusts below the main overthrust of the "Faille du midi" (Fig. 7). The location of the borehole at the intersection of this main thrust with a SW-NE transverse direction induced by a resistant spur of the Caledonian massif of Brabant (Becq-Giraudon et al, 1981 ; Laumondais et al, 1984) can have increased the tectonic deformation. Considering all the data, it can be assumed the evaporites played an active role in the buckling of the regional Hercynian structure of thin-skinned Qattern as detachment or gliding layers and more specially in the genesis of duplex structures. Producing mechanical thickening of evaporites in some area and stretching and breaking in others, the associated flow induces the observed discontinuity of the formation (Fig. 7) : in agreement with Delmer's hypothesis (1977), the irregular morphology of domes and troughs of the Paleozoic roof in the Hainaut (basin of Namur) could be due to haloklneticltectonic flow combined with the subsequent dissolution of the evaporites
45
(Fig. 7) ' the presence of thick evapOrites (Fig. 7) in Saint-Ghislain borehole, situated on the dome edge and of dissolution breccias in Douvrain well recorded in a trough (Leclercq, 1980) confirms this interpretation.
£~er 3IIIF-J£E
DINANT NAPPE ,/~,
f
---J_LU ~u-Of
,
NAMUR SYNCLINOR UM ",
BRABANT MASSIF' ~
I.--
I I
i I
I t
[ ~
...... ? :x'" i~
,
s#
gy;'//•
;
:::: i::: :::
v
SILESIAN
EVAPOR/TES
v
v
DINANTIAN
v
v
v
UPPER DEVONIAN
I vvv Anhydrffe ~ Pseudomorphs (}fief sulfo~es
MIDDLE rTO LOWER DEVONIAN ~/TRHUST
SILURIAN
PRE. SILURIAN ROCKS
FAULTS
~'~'e Oissolulionbrecci(~s
Fig. 7. - !nterpretative cross-section showing the possible structural situation of the visean evaporitic bodies.
The example of the Visean anhydMte emphasizes the great importance of the recognition of the anhydrite deformational fabrics as they are similar to sedimentary features and therefore misinterpretations can result.
46 DIA6ENETIC EVOLUTION
Important diagenetic changes observed in Visean evaporitic beds in boreholes as well as in outcrops are influenced by multiple controls during the complex depositional evolution of the series ; among them, we can note: depositionat pore-fluid composition, pressure and temperature changes during burial, tectonic deformation, and finally the rote of groudwater with the exhumation of the series This chapter describes the sequence of crystal authigenesis and diagenetic replacements in order to elucidate the impact of each parameter and to recognize them in the residual series after the tectonic deformation and the dissolution. We have previously discussed the problem of early diagenesis of the calcium sulfate and of the burial-controled gypsum-anhydrite conversion. A more complex set of diagenetic processes leads to the authigenesis of celestite, fluorite and albite, and to the silica and sulfate replacements.
I -
The accessory mineral authigenesis : c e l e s t i t e , fluorine, a l b i t e C e l e s t l t e has a wide stratigraphic distribution occurring in Givetian, Tournaisian
and Visean in which it is usually present as scattered mm to cm-sized crystals or flabellate crystalline aggregates (Fig. 8,A). The celestite is more abundant in carbonates interbeds than in evaporites
where it is nevertheless present in small amounts; in
Epinoy 1 cores it forms rare massive centimetric layers of blocky or chert-like microcrystalline aggregates. The inclusion by the prismatic crystals of numerous carbonate relics and even peloids or shell fragments indicates a diagenetic growth in a host-sediment. The celestite crystals can be broken and the layers microfolded during the deformation of the anhydrite. Among the three kinds of mechanisms generally infered to explain the early diagenetic growth of the celestite: (I) the release of Sr ++ during aragonite-calcite conversion (Kinsman, 1969) or (2) during gypsum-anhydrite alteration and (3) the direct precipitation, the first and second ones easily explain the diagenetic character of the
47 Visean celestites.
Fluorite is the next authigenic mineral, specifically associated with Visean strata In the well cores (Saint-Ohlslaln, Epinoy i) or in the outcrops (Walhorn. BomeI, etc.). The euhedral to subhedral crystals (70 LLm to 400 Lira, rarely 1 ram) appear scattered in limestones or in deformed anhydMte (Fig. 8, B), especially in Eplnoy 1 core. The corroded boundaries of the crystals in limestones suggest an early diagenetic growth, In deformed anhydrite, the crystals could have been pulled away from fragmented carbonates or could represent relics of a gypsum phase as in some samples of Saint-Ghislain (1848 m) where the fluorite is included in calcitic pseudomorphs after gypsum. Considering that there is no evidence of hydrotherma] activity nor noticeable volcanic contribution in the studied Visean stratas as in some present alkaline lakes with waters of high fluorine content, the genesis of fluorite is classically attributed to two processes : precipitation from saline waters (Sabouraud-Rosset, 1970 ; Sonnenfeld, 1984) or organic pre-concentration (Lowenstam, 1981). The occurrences of fluorite in gypsum crystals or in anhydrite suggest an early dlagenetic precipitation with gypsum but we cannot exclude yet another origin,
Alblte appears as small euhedral crystals (less than 200 l~m in length) displaying a single prismatic habit or a twinned (polysynthetic or "en sabIier") form ; generally, the crystals seem to grow nearly or at the contact of the stylolites ( Fig. 8, C) and, in Epinoy 1 cores, their number increases with the depth : the crystals include small carbonate rel ics. The growth of the alblte apparently took place during the compaction from pore waters enriched by dissolutlon processes and the crystallization was probably favoured by thermal effect as it is suggested by Kastner ( 1971 ).
2. 5ilici[Icatlon
Several varieties of authigenic quartz and chalcedony have been observed replacing
48
gypsum crystals, anhydrite and sometimes
skeletal limestones. They are: single
idiomorphic quartz (up to I cm) i coarse quartz mosaic ; radiating fibrous quartz crystals fibrous minerals as quartzine and lutecite ; interlocking aggregates of idiomorphic and petaloid quartz associated with spherules or crusts of fibrous varieties. In the anhydritic nodules, the quartz encloses various quantities of anhydrite relics, sometimes so numerous that the crystal boundaries are difficult to distinguish. In tectonic laminated anhydrite with elongated and parallel arranged crystals, the authigenic quartz encloses anhydritic relics which display an irregular or
a felted
texture typical of early diagenetic anhydrite (Fig. 8, D). In some Epinoy 1 samples (3135m), the silicified gypsum crystals are well preserved whereas the primary morphologies are elsewhere destroyed by the burial anhydritization and the tectonic deformation ; quartz-chalcedonic aggregates are desintegrated during the tectonic flow of the anhydrite and their fragments destroy the lamination ; sometimes (Saint Ghislain, 2,171 m) a "tail" of recrystatlized calcite (pressure shadow) is developed at the border of a rotated authigenic quartz. All the observations lead to the assumption that the main part of the siliceous replacement predates the tectonic deformation. In the outcrops, replaced sulphate noduIes show a brecciated texture with broken silicified
fragments
cemented by sparry calcite or dolomite. Similar examples of silicified evaporites are known from formations ranging in age from Precambrian to Miocene (Munier-Chalmas, 1890 ; Siedlecka, 1972 ; Chowns and Elkins, 1974 ; Milliken 1979...) and even are considered as a memory of vanished evaporites (Folk and Pittman, 1971 ; Siedlecka 1976 ; Schreiber 1974). Silicification is a process which can take place during any time during the post-depositional history but very early growth of authigenic quartz has been reported from present day lagoonat environments (Giresse, 1968).
Fig. 8. - Accessory minerals. A. - Thin section photomicrograph of radial aggregates of lenticular crystals of celestite which are partly replaced by caltite. Saint-Ghislain borehole ; 1,787.50 m; plain light; scale bar is 200 pm. B.- Thin section microphotograph showing fluorite crystals (arrows) around a small anhydritic nodule, Epinoy 1 borehole 3,1501.62 m ; plain light; scale bar is 500 I1m. C,- Albite crystals along stylolite (thin
49
section mlcrograph). Epinoy I borehole ; 3,137.50 m ; crossed nicols ; scale bar is 20 I~m. D. - Authigenic quartz crystals (arrows) into laminated anhydrite ; in quartz (I), the minute anhydritic inclusions develop a felted structure fairly different of the reoriented fabric of the anhydritic host-sediment (thin section photomicrograph). Saint-Ghislain borehole ; 2,046.60 m, scale bar is 500 pm. E. - General vlew of calcite pseudomorphs after lenticular crystals of gypsum ; this transformation related to reduction of sulfates is followed by a volume reduction (arrows show voids) and in some cases by the formation of native sulphur illustrated in F, Saint-Ghlslain borehole, 1,932.80 m ; scale bar Is 2 cm. F. - Large native sulphur pockets (S) included in the secondary calcite infilling the fractures in a black limestone fragment. This fragment appears isolatedinto the tectonic laminated anhydrite. Epinoy I borehole ; 2,937.35 m ; scale bar is 5 cm.
50 tn our examples, an early diagenetic replacement must be considered. The silicification does not involve the external contribution of silica the origin of which can be the concentrated brines or fluids enriched by solution of siliceous organisms accumulated during the pre- or the interevaporitic sedimentation; destruction of clays minerals in relation with pH changes during diagenesis in evaporites may contribute to provide silica (B.C. Schreiber, oral comm.).
3. The carbonate r e p l a c e m e n t of s u l f a t e s and the n a t i v e sulfur.
The calcite and dolomite ubiquitously replace the sulfates (gypsum, anhydrite and celestite) in various kinds of processes ; this replacement is sporadically observed at various
depths in
subsurface
whereas
the
carbonate
or
carbonate-siliceous
pseudomorphs after scattered sulfates nodules or crystals occur commonly at specific stratigraphic levels in Visean outcrops (Hennebert and Hance, t980 ; Poels and Preat, 1983 ; Swennen eta/, 1981 ; Swennen et Viaene, 1986 ; Rouchy, 1986).
- Reduction of the s u l f a t e s and the n a t i v e s u l f u r f o r m a t i o n . - A typical
example shows centimeter-sized lenticular gypsum disseminated in black laminated limestones probably algal in origin (see above) (Saint-Ghistain, 1932 m; Fig, 8, E). The crystals are replaced by a mosaic of clear sparry calcite. Many replaced gypsum crystals have a central cavity delineated by the projecting heads of the calcite crystals. The origin of the replacement by bacterial reduction of the sulfate in organic-rich sediments is both supported by the petrographic data and by the isotopic composition of the carbon ( C=-8,5 %, Pierre. 1986). Generally, the reaction involves : 1) a volume decrease (20 % for anhydrite-calcite, 50 % for gypsum-calcite) which can explain the holds observed in the former gypsum crystals (secondary porosity) and the diagenetic fracture of the host-sediment ; 2) the release of H2S which can be, if it is in contact with dissolved oxygen, reoxydized into native sulfur in situ or in adjacent layers ; 3) production of
$1 energy. These processes are well illustrated in the Permian Castile Formation of the Texas (Kirkland and Evans, t976 ; Shearman, 1971), in Miocene of Sicily (Dessau et al. 1962) and of Egypt (Rouchy eta/, 1985). Native sulfur nodules (cm to din) are frequently observed in Saint-Ghislain cores and are common in Epinoy 1 where they are located within the intensely fractured (tectonic) carbonates and anhydrite (Fig. 8, F) : the nodules are associated with the sparry calcite infilling of the fractures. In the strongly tectonized section of Epinoy 1 the native sulfur formation could be produced by reduction processes related to the hydrocarbon migration in a fractured formation ; we cannot exclude however the desulfuratlon of sulfurous hydrocarbons.
- O t h e r m o d a l i t i e s of c a r b o n a t e r e p l a c e m e n t after sulfate. -
Except the
above described mechanism, this replacement is usually the result of the sulfate dissolution by bicarbonate waters followed by recrystallization of calcite or dolomite, Different varieties of sulfate appear to be replaced in Saint-Ghislain borehole and in Visean outcrops: lenticular gypsum, nodular or mosalc anhydrite, single or aggregated crystals of celestite. The replacement carbonates are schematically of two distinct types : 1) aggregates of closely intergrown (30-100 ~m) or mosaic of subhedral large crystals (up to 500~m) either containing more or less numerous inclusions of opaque materials and small anhydritic relics, rarely (Yves Gomezee wells) calcite crystals display an elongate and rectangular shape and a fetted fabric which suggest an isomorphic replacement of anhydrite, the relics of which can be observed. In SaintGhislain well (4,161.10 m) a group of celestite crystals is replaced by an admixture of calcite, quartz and albite suggesting a relation with burial conditions. When any sulfate is preserved within the carbonate, the authigenic quartz, rich in anhydrite relics, authentifies their former sulfate nature (outcrops of Walhorn in the synclinorium of Dinant and Napoleon in the Boulonnais for instance). 2) Mosaic of large and limpid sparry calcite or dolomite (up to 1 cm); the replacement appears often in the outcrops and in the near-surface well samples (Yves
52
Gomez~e for instance); when the two kinds of fabric are represented, the first forms an irregular outer part or floating aggregates within the second. It is assumed that the first type results from a subconcomitant dissolution-recrystallization process occurring at various stages of diagenesis of uncertain timing (early diagenesis, burial, weathering in surface conditions...), the second one is a void filling after complete dissolution of a carbonate siliceous replacement of residual sulfate. Swennen et ai(1981) described / sulfate nodules in which the quartz is the first replacement phase and the dolomite formed later after the dissolution of the residual sulfate inducing an internal brecciation, The isotopic composition of the calcite ( 13C and
180) of the sulfate
samples studied by Pierre (1986) shows two distinct groups which could be related to the surface conditions or to the fresh water phreatic zone (early or later diagenesis) and to the burial diagenesis.
3) The replacement and void-filling anhydrite. Replacement and void-filling anhydrite are common
diagenetic features in
carbonates associated with evaporlte layers of different ages (Dunham, 1948 ; Kendall and Waiters, 1978 ; Jacka and Franco, 1974). A recent and well documented description and discussion have been presented with regard to Purbeckian beds of Aquitaine in France Clark and Shearman, 1980). The Givetian and Visean subsurface formations of Northern France and Belgium exhibit a wide variety of replacement anhydrite the study of which brings new views on the chronology of the diagenetic changes (Rouchy et al, 1984 alb ; Rouchy, 1986). There are four fundamentally different types of replacement anhydrite : I. - The porphyroblasts (Fig. 9,A,B) are euhedral to subhedral; equant prismatic crystals (I00 lira to I cm) generally displaying a square, triangular or rectangular section with sometimes, curved or "corroded" faces ; characteristic brown color results from the inclusion of very abundant, small relics of the host-limestone and probably of organic matter (Fuller, 1956, in Clark and $hearman, 1980) ; the square sections may possibly be confused with halite pseudomorphs. A narrow inclusion-free rim outlines the edges of the crystals allowing, in some cases, one to distinguish the inclusion-rich
53 crystalline body from its matrix (in thin section.) Crystals occur singly, in association of a few individuals or in polycrystalline aggregates in which the crystals loose their euhedral morphology. It is very important to note that porphyroblasts (and the veinlets) grow preferentially in the fine-grained limestones. 2, - The porphyroblasts are frequently associated with anhydritic veinlets accordlng to two principal fashions (Fig. 9C): first, the porphyroblasts are arranged on both sides of the veinlet which is filled with clear anhydrite, suggesting the replacement progresses into the carbonates from the veinlets which can be little fractures or other discontinuities (bioturbation); second, some veinlets are composed of clear anhydrite in a narrow axial zone,outlined by an inclusion-rich rim. When clear anhydrite-f111ed veinlets cut across the porphyroblasts, the common optical characters suggest that the porphyroblasts and the veinlet form a single crystal and have the same orlgin ; this observation is in agreement with Clark and Shearman's interpretation assuming the veinlets were the expression of the volume increase (25 %) generated by the replacement itself. 3. - The large monocrystals, termed domino-llke or stairsteP (Dunham, 1948; Jacka, 1977), differ from the preceding by an irregular outline with rectangular-shaped projections and re-entrants. (Fig. 9D). Contrary to the porphyroblasts, this kind of replacement of anhydrite is preferentially developed in any matrix such as oolitic, peloidal or skeletal limestones. This difference in behaviour is not well understood. The structure of the host-limestone components (oolits, pellets, shells) may be cut linearly by the boundary of the crystal and is faithfully revealed within the anhydrite by numerous relics. Large anhedral anhydrite crystals form a pseudo-cement filling the interoolite porosity and partially replacing the components; these crystals differ from the preceding by the lack of rectilinear boundaries, probably due to a competitive growth of the adjacent crystals. Several thin sections of peloidal limestone of Epinoy 1 show features as the simultaneous replacement of several peloids and of some part of the cement by the same crystal of anhydrite (Fig. 9,E). 4. - Some rounded or oblong bodies composed of radiating or interlocked aggregate of large bladed crystals (up to 2 cm) seem to have filled cavities of organic or of
54
dissolution origin in the limestone ; similar aggregates form the cement of breccia (Fig. 9, F). Nevertheless, the conservation of carbonate relics floating into the anhydrite crystals seems to indicate that if the void-filling is the principal control, a concomitant replacement must be considered. The relationships between the replacement anhydrite and the structure of the host-sediment reveal the substitution post-dates compaction and the interlocking of the oolds. More significant are the relations with
tectonic deformation. At times the
porphyroblast aggregates are developed in bends of microfolds in the limestones but they are not themselves deformed by the folding. The growth of the replacive porphyrobtasts appears to be initiated along the block joins which constitute glide planes. Besides, the associated veinlets cut the axial phase of the microfold obliquely. Other examples from Saint-Ghislain core show large porphyroblasts growing from stylolites ~similar features are also observed in Triassic of the Jura (France, Pisu and Rouchy, unpublished report). All the observations, taken together, allow the dating of the replacement as later than limestone diagenesis and in many examples, synchronously or later than the tectonic deformation ; another example of late diagenetic control is illustrated by Kendall and Waiters (1978) in the Mississipian limestones in which the anhydrite substitution appears post-Triassic in age. Nevertheless, it is evident this dating cannot be applied to the anhydrite replacement in all formations. Clark and Shearman (1980) have observed, for instance in Purbeckian and In Devonian beds, replacements formed before the first phase of limestone diagenesis. Fig. 9. - Microscopic view of diagenetic replacements. A. - Anhydrite porphyroblasts in the hinge of a microfold; each porphyroblasts contains numerous micritic impurities of the host sediment and a narrow clear border. Note also the anhydritic veinlets which cut obliquely the microfold axis; Saint-Ghislain borehote; 2,036.90 m; plain light; scale bar is 500 lim. B. - Porphyroblasts surrounding nodular reoriented anhydrite indicating their growth post-dates the deformation. Saint-Ghislain borehole; 2,041.78 m; plain light ; scale bar is 500 tim. C. - Large replacement anhydrite veinlets similar to the porphyroblasts in having inclusions-rich body, narrow clear border and limpide anhydrite in the middle part ; these veinlets are frequent in the more deformed part of the Epinoy 1 formation. Epinoy 1 borehole; 3,148.02 m; plain light; scale bar is 1 ram. D. Domino-like replacement anhydrite (clear) in a peloidal limestone (dark). Saint-Ghislain.
55
borehole', 2,054.30 m; plain light', scale bar is I00 I~m. E. - Monocrystalllne anhydrite (clear) replacing the cement (I) as well as the peloids (2) in a peloidal limestone. Epinoy I borehole; 3,135.30 m; plain light; scale bar is 200 pm. F. - Prismatic anhydrite cementing a carbonate breccia. Saint Ghlsla~n borehole; 2,057.53 m; crossed nicols ; scale bar is 500 ~m.
58 Probably, the anhydritic substitution implies a nearly concomitant dissolution of the limestone and precipitation of anhydrite, processes which can be controlled by the migration of fluids along the diagenetic or tectonic discontinuities (stylolites, small gliding planes, bends of microfolds, anhydrite-limestone boundary...) and by structural opening of porosity. Even if the replacive anhydrite in the limestone does not imply that the limestones were deposited in evaporitic environments, as pointed out by Clark and Shearman (1980), their presence provides the evidence that these limestones are or have been interbedded with anhydritic layers. Their recognition can be very important for reconstruction of vanished evaporitic formation (Rouchy eta/, 1986b).
THE BRECCIA$
One of the more difficult geological problems in Belgium concerns the genesis of the Visean great breccias, particularly the "Grande Br~che de Namur et de Dinant", which end the Visean sequence throughout the greater part of the Dinant and Namur structural units. The
interpretations that have
been alternatively proposed
are tectonic
fragmentation, sedimentary transport or gravity flow (olistostroms), favoured by the presence of evaporites as postulated by Pirlet and Bouckaert, 1976). The various facies of the brecciated horizons have been documented by Bourguignon (1950-1951) in his synthetic work. West (1969) was the first who indicate, in an unpublished report, the presence of gypsum pseudomorphs in the cement of the "Grande Br~che". Since the discovery of Saint-Ghislain evaporitic formation, many of the studies focused on Vlsean Limestone outcrops showed the numerous occurrences of pseudomorphosed sulfates, Fig. I0. - Dissolution breccias and pseudomorphs after sulfates. A. - Sample showing a calcite pseudomorph after mosaic anhydrite; Salet road near Dinant, Dinant nappe. Scale bar is 2 cm. B. - Thin section microphotograph showing sparry calclte pseudomorphs after sulfates probably crystalline aggregates of gypsum. Yves Gomez~e borehole, $2 ; 26.50 m; plain light; scale bar is i mm. C. - Thin section photomicrograph showing domino-like anhydrite (white) replaced by sparry calcite. Note the characteristic outline
57
anhydrite with square pattern, re-entrants and projections ; we can recognize pellets (arrow) replaced into former anhydrite. Yves Gomez6e boreholes, 58; 12.70 m ; scale bar is 500~m. D. - Breccia probably related to the sulfates dissolution. Quarry of Landelies, Dlnant nappe. Scale bar is I0 cm. E. - Mechanical breccia with anhydrltic cement. Epinoy I boreholel 3,144.10 ml scale bar is 2 cm. F. - Solution-breccia in the deep karst of Saint-Ghlslaln. Saint-Ghlslain borehole; 2,529.45 m; scale bar is 2 cm.
58 particularly in association with brecOated horizons (Fig. I0, A, B, C).
These
observations lead to the conclusion the breccia have been originated from collapse after the evaporite solution (Swennen et al, 1981; Swennen and Viaene, 1986; Mamet et al, 1986; Rouchy et al, 1986alb). The breccia beds can be encountered in subsurface (Douvrain, Ghlin, W~plon, Saint Ghlslain) but the extensive formations appear in the surface outcrops or at shallow depth as, for instance, in the Yves Gomez~e wells near Philippeville (Rouchy et al, 1986b). Many authors (Bless et al, 1980; Groessens et al, 1979; Rouchy et al, 1986a;
Conil and
Groessens 1985) have pointed out that the brecciated intervals may be correlated with bands of anhydrite in the Saint-Ghislain borehole; the V2b-V3a interval (Middle Visean) contains both the upper massive anhydrite of Saint Ghislain and the great breccia of Namur and Dinant. Thus, in the Douvrain borehole which is situated about 4 kilometers of Saint-Ghlslain, the upper part of the evaporite section is represented by a breccia associated with silicified sulfates (Leclercq, 1980). The cores of the Yves Gomez~e wells and the quarry of Landelies in the Dinant nappe offered an excellent opportunity to study the great breccia of the V2b-V3a (Rouchy etal, 1986b ) and to elucidate thetimlng of the dissolution. The fragments are highly angular and irregular as well in shape as in size and the fabric is often chaotic (Fig. IOt D) ; almost continuous layers of limestones are floating within the breccia. The matrix type varies irregularly : white recrystallized calcite, silt, very fine calcite, etc. Similar features have been observed in karstified evaporites of Messinl-an age or in Triassic "Calcare cavernoso ° from Tuscany (B.C.Schrelber, oral comm.). The fragments as well as the unbrecciated carbonates, contain nodular sulfates replaced by white calcite ; some of them may be former anhydrltic nodules whereas others which have rectilinear and angular boundarles are probably pseudomorphosed gypsum aggregates (Fig. I0, B). The mlcrofabric of carbonates (see above) and the preservation of minute anhydrite relics in the calcite and in the scattered authigenic quartz make obvious the replacement; pseudomorphs after lenticular gypsum are often
59 observed. The recognition of the pseudomorphs after replacement anhydrite in the form of domino-like monocrystals (Fig. IO,B), porphyroblasts and veinlets, corroborates the former presence of evaporlte interbeds indicating that the brecciation post-dates the burial diagenesis and even probably one stage of tectonic deformation. In the cores of Yves Gomezee wells and in Landelies outcrops, the fragments present a network of fractures truncated at the fragment boundaries (Fig. IO,D). This observation confirms that in this example, the brecciation clearly seems to have taken place after a tectonic fragmentation (Fig. IO,E). It is probable that the extensive solution of the evaporites begins with the Permian denudation and continues over the long period until recently, as is postulated by Delmer et ai(1982) and de Magnee et ai(1986). It is assumed here that a mechanical pre-brecciation and the solution processes favour the Increase of water circulation. Thus, the presence of a saline water aquifer in the deep cave solution with breccia (Fig. IO,F) at the base of the anhydritic formation on the Saint Ghislain well (Delmer et al, 1982) is very demonstrative ; this cave coincides probably with a minor tectonic glide plane (Rouchy etal, 1984 a/b). It is not suggested however that all the Visean breccias are necessarily formed in this way, other breccias could have a different timing. In the breccia of Namur (Grands Halades), Mamet
et al (i986) provide criteria of early polyphased brecciation.
On the basis of sedimentological and stratigraphical data, the formation of the Great Visean breccia is most logically explained by collapse after dissolution of anhydrite (eventually salt) interbeds of significant thickness; thus, the extensive distribution of the breccia and of the pseudomorphs which cover a large part of the synclinorium of Namur and of the nappe of Dinant, provides the evidence of southward extension of the evaporites; their original distribution appears to have been independant of the present organization in the structural units.
CONCLUSION
The complicated distribution of the Visean evaporites in north-western Europe
60
(Northern France and Belgium) is inherited from a complicated paleogeographic, tectonic and post-tectonic history which have strongly modified their former facies, thickness and limits. The stratigraphical and sedimentologlcal studies of the thick anhydritic deposits, as well as the pseudomorphs and breccias in the outcrops, allow to the reconstruction of the depositional modalities, the successive diagenetic changes, the deformational features and the post-tectonic events. Diversified environments of deposition resulting from repeatedly restricted open lagoonal conditions led to the deposition of subaqueous sulfates (gypsum) and sporadic subaerial anhydrite diagenesis; in the thickest formations, the predominant nodular and mosaic structures is interpreted as resulting of burial conversion of gypsum to anhydrite which stresses the primary depositional features rather than a generalized early diagenesis in sabkha-like conditions. The chronology of the mineralogical and textural post-sedimentary changes was established based on the early diagenesis (celestite and fluorite authigenesis, siliclfications, limited gypsumlanhydrite conversion), the burial conditions (complete gypsum-anhydrite conversion, albite authlgenesis, sulfate calcitization...), and the tectonic deformation (carbonates replaced by anhydrite during or Immediately after the deformation). The deformational fabrics of the anhydrite in relation with Hercynian tangential stresses and subsequenf flow mechanisms, leads to the destruction of the primary structures and to the development metamorphic
of structures sometimes
similar to some
rocks (stretching, boudinage, mlcrofolding, tectonic lamination
schistosity, augen-like, mylonitic). Some
of the tectonic features may
or
mimic
sedimentary structures. The recognition of the deformational features allows us to envisage the important role of the evaporites in the Hercynian deformations. The evaporites supplied detachment and gliding planes and favoured formation of minor slice thrusts; this is suggested for the base of anhydrite formation of Saint-Ghislain and demonstrated by the implication of Epinoy i evaporites in reverse position and in a multi-system of slices below the major overthrust of the Midi. The formation of the greatest part of the extensive Visean breccia CGrande Br~che
81
de Namur et de Dinant") may be most logically explained by solution-collapse as suggested by the presence of pseudomorphs of evaporites, fabrics of the breccia, stratigraphic correlation between breccias and thick anhydritic formation... It is assumed the dissolution occurred after the Hercynian deformation and in some cases, until a recent period (cf. breccia of Saint-Ghislain) ; this observations lead to the conclusion that widespread evaporitic body of Visean age (Middle Vlsean, V2b-V3a at least) extended into the Dinant and Namur structural units. Although the area in which evaporation and precipitation took place cannot be exactly delineated in geographic extent, all the data provide the evidence that the isolated thick anhydritlc deposits (Saint-Ghislain and Eplnoy I) represent the relics of more widespread evaporitic formation extending more or less throughout the different structural units: autochthonous in the Namur basin, para-autochtonous, allochtonous in the Dinant nappe. Its present discontinuity is due to structurally and halokinetically controlled thickening in some areas and, in contrast, the thinning or the disappearance in others; this latter results from the combination of mechanical lamination and breaking and/or of dissolution. The important role of the evapoMtes in the genesis of the Hercynian regional setting which displays an Appalachian thin-skinned type of deformation appears well documented both by the deformational fabrics of the anhydrite and by the structural framework of Salnt-Ghislain and Epinoy I formations.
ACKNOWLEGMENTS. - We are grateful to C. Pierre for her active participation to this work studying the isotopic composition of the Vlsean sulfates and carbonates described in this paper and for the stimulating discussions, B. Moine and D. Couilloud so have provided many petrographical and geochemical indications. The authors thank B.C. Schrelber for reading the manuscript and offering valuable suggestions for its improvement. Subsurface cores and logs have been provided by the Geological Survey of Belgium and the Compagnie Fran~aise des P~troles TOTAL. Research was conducted on a grants from the Compagnie Francaise des Petroles TOTAL and from the National Programme "G6ologie Profonde de la France". Gratitude is also extended to Mrs A. Cambreleng, N. Day, R. Deletoille,M. Destarac, G. Tortel, Mr L. Ganon for the quality of their assistance in manuscript drafting, reading, typing, photography and thin section making.
62
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06
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Poels J.P. & Preat A., 1983. - Mise en ~vidence d'une serie evaporitique darts le Viseen inferieur de Vedrin (Province de Namur). Bull. Soc. beige G6oI., 92, 4, p. 337-350. Preat A. & Rouchy J.M., 1986. - Facies pre@vaporitiques dans le Givetien des bassins de Dinant et de Namur. Bull. Soc. beige G~oI., 95, 2-3, p. 177-190.
06
Rouchy J.M., 1976. - Sur la genese des deux principaux types de gypse (finement lit~ et en chevrons) du Miocene terminal de Sicile et d'Espagne m~rldlonale. Rev. G~ogr. phys. G~ol. dyn., (2), XVIII, p. 347-364. Rouchv J.M., 1986. S~dimentologie des formations anhydritlques giv~tiennes et dinantlennes du segment varisque franco-belge. Bull. Soc. belge G~ol., 95, 2-3, p. 11 I-128. Rouchy J.M., Maurln A.F. & Bernet- Rollande M.C., 1980, - M6thodes de description (terrain, subsurface, laboratoire) destinee a une meiIleure compr~henslon de la sedimentation des ~vaporites. In M~thode d'~tude des ~vaporites, Ed. Technlp., p. 11-28. Rouchy J.M., Groessens E. & Laumondais A., i984a. - S~dimentologle de la formation anhydrltique vls~enne du sondage de Saint-Ghlslain (Halnaut, Belgique). Implications paleog~ographiques et structurales. Bull. Soc. belge G~ol., 93, I-2, p. 105-145. Rouchy J.M., Pierre C., Moine B., Couilloud D., Laumondals A. & Groessens E., 1984b, - S~dimentatlon, diagen~se et d~formatlons tectoniques des ~vaporltes paleozoiques; inter~t pour l'Interpr~tation pal~ogeographique et structurale. Programme Geologle profonde de la France, lere phase d'investlgations 1983-1984; rapports g~n6raux et communications. Th~me I: Chevauchements nordvarisques. Doc. B.R.G.M., 81-I, p. 71-82. Rouchy J.M., Monty C., Pierre C., Bernet-Rollande M.C., Maurin A. & Perthuisot J.P., 1985. - Gen~se de corps carbonates diag~n~tlques par r~duction de sulfates dans le Miocene ~vaporitique du Golfe de Suez et delaMerRouge. C.R. Acad. Sci. Paris, 301, 16, p. 1193-1198. Rouchy J.M., Pierre C., Groessens E., Monty C., Laumondals A. & Molne B., i986a. Les ~vaporites pr~-permiennes du segment varisque franco-belge, aspects pal~ogeographiques et structuraux. Bull. Soc. belge Geot., 95, 2-3, p. t39-150. Rouchy J.M., Groessens E. & Conil R., 1986b. Signification des pseudomorphoses d'~vaporites associees aux br~ches vis~ennes dans les sondages de Yves Gomez~e (Synclinorium de Dinant, Belgique). Bull. Soc. belge G~ol., 95, 2-3, 167-176. Rouchy J.M., Bernet-Rollande M.C. & Maurin A.F., 1986c. - Petrographie descriptive des ~vaporites, Applications sur te terrain, en subsurface et au taboratoire. In, Les series a ~vaporites en exploration p~troli~re, Tome 1 : M6thodes g~ologiques. Ed. Technip., p. 73-122. Sabouraud-Rosset C., 1970. Sur les compagnons de cristallisation du gypse. C.R. Acad. Sci., Paris, 270, D, p. 1-2. Schreiber B.C., 1974. - Vanished evaporites : revisited. Sedimentology, 2t, p. 329-33 I. Schwerdtner W.M., 1966. - tntragranular gtiding in domal salt. Tectonophysics, 5, 5, p. 353-380. Schwerdtner W.M., 1974. Schistosity in Deformed Anhydrite A reinterpretation. Fourth Intern. Syrup. on Salt, North. Ohio Geol.. Soc., I, p.
67 235-240. Shearman D.J., 197i. - Marine evaporltes. The calcium sulphate facies. Unpubl. notebook. The Univ. of Calgary, A,A.P.G. Seminar, 65 p. Shearman D.J., 1985. - Syndeposltional and Late Diagenetic Alteration of Primary Gypsum and Anhydrite. Sixth Internat. Symp. on Salt, Salt Inst., I, p. 41-50. Siedlecka A., 1972. Length-slow chalcedony and relicts of sulfates Evidences of evaporitic environments in the Upper Carboniferous and Permian beds of Bear Island, Svalbard. J. Sedim. Petrol., 42, 4, p. 812-816. Siedlecka A., 1976. - Silicified Precambrian evaporite nodules form Northern Norway : a preliminary report. Sedim. Geol., 16, p. 161-175. Sonnenfeld P., 1984. - Brines and Evaporites. Academic Press, 613 p. Swennen R., Viaene W., Jacobs L. & Van Orsmael J., 1981. - Occurrence of calcite pseudomorphs after gypsum in the Lower carboniferous of the Vesderregion (Belgium), Bull. Soc. belge GEol,, 90, 3, p. 231-247. Swennen R. & Viaene W., 1986. Occurrence of pseudomorphosed anhydrite nodules in the Lower Visean (Lower Molinacian of the Verviers Synclinorium, E. Belgium). Bull. Soc. belge G~ol., 95, 2-3, p. 88-99, Wall R.W,, Murray G.E. & Diaz T.G., 1961. - Geological occurrence of intrusive gypsum and its effect on structural forms in Cohahuila marginal folded province of Northern Mexico. Am. Assoc. Petrol, Geol. Bull., 45, 9, p. 1504-1522. West I.M., 1969. Examination of the Grande Br~che of Belgium, a project supported by a grant from the Bernard Hobson Fund. Rep. of the British Assoc. for the Advanc. of Sci., Unpubl. Rep., IOp. West I.M., Brandon /~ & Smith M., 1968. - A tidal flat evaporitic facies in the Visean of Ireland.J. Sedim. Petrol., 38, 4, p. I079-I093.
DEPOSITIOHAL
MODELS
EVAPORITES
IN
WU
OF
THE
LOWER
UPPER
Ylnglln
Chengdu
AHD
and
Institute Mineral
MIDDLE
YANGTZE
CHINA
YangJl
Yan
of
TRIASSIC
AREA,
Geology
and
Resources
Chengdu,
Slchuan
China
REGIONAL
The
Upper
between
Yangtze the
iiO ° east.
Its
orogenic is the
equator
Lower the old of
basement
was
formed
(i.5 b.y.). T h e
m
and
land the
and
which
formed
shelf,
in
alluvial sandstone,
a
east, a
(Figure
oolite
layer
the
a
barrier
the
outside
and
aa).
braided
conglomerate,
were
Figure (1)
leaving stream sandy
Jinning
to
Permian)
The
Of
the At
was
which
can
mainly
which
was
flat
and
2a
land, the
sediments mudstone,
of
m
shallow
sabKha
in
the
of thick;
most sand
inside
of
water the
following to
exposed;
consisting
then
in
oolite
middle
basalt
0-350
the
of
Kangdian
traced
shelf,
show
with
sea,
the
the
the
there
beginnig
open
be
the
Table I.
platform
of
near
of
in
the
an
margin
Figure old
shown
of
in
was
correlation
are
the
tidal
and
the
the
(Slnian
strike.
shoal
i)
i02 ° a n d
during
progradatlon
the i
in
(Figure
considered
regions
basically
first
with
there
area
margin
area
area
elements:
-
west
forming
topography, plain
of
east
north-south
Yangtze
sheet
lagoon
addition,
the
the
the
Cl%ina
longitudes
cover
Paleotethys,
and
developed
Yangtze
paleogeographical mountain
Upper
formed
in
with
barrier
toward
bacRshoal
the
of
middle
Triassic,
and
Precambrlan
east
the
Upper
barrier
in
located
west,
south-west
sedimentary Triassic
the
sand
the
SETTING
33 ° n o r t h
During
mountains
Triassic oolite
in
thick.
Lower
coastal
located 26 ° a n d
between
During
is of
2,000
Triassic
were
area
PALEOENVIRONMENTAL
latitudes
movement
about
AND
(2)
high the
purple-red (5)
the
Lecture Notes in Earth Scien~s, VoL 13 T.M. Peryt (Ed.), Evaporite Basins © Springer-VeflagBerlin Heidelberg 1987
70
tidal
flat
mudstone red
sediments with
-
algal-mat
interbedded
top
(5)
the
oolite
more
than
thick)
wlth
I00 are
sand m
mainly
Facies Se¢'t i~m
thln
I.
thick;
m
the
tl%ick;
mlcritic
shelf
limestone
map
the t~aasgr~ssiv~ l e ~ t ~,~ r e s r t s ~ , w
~.~,:,'~,o.
of
stage
Felxlanguan
-
oolite
limestone, m
thick;
limestone,
sediments
contalnlng
Drown-
sabkha
200-300
-
and
containing
the
bloclastic
T
Paleogeographlc
lagoon
(5)
bioclastic
water
siltlte
limestone
anhydrlte,
massive
bedded
(4)
oolitic,
and
shallow
banded
bioclastic
wltll
-
(7) t h e
f g ; $~'d g~g~s b~ ow ~he ll.~ o
Figure
m
300-600
dolostone
barrier
thick;
brown-red
with
interbedded
sabkha
of
300-400
gastropods,
limestone
the
m
bedding,
marls and
in
composed
flaser
mudstone,
pelecypods
are
(300-~00 ammonolds,
71
WEST
AND
CENTER
EAST
¢9
Member Tzt
,...1 T~
T~I 4
~
T2/3
T~
Member
Leikoupo
T21 e Te
Formation
Tianjingshan
.~
c::a
Formation
Tel l T~j s
Tlj s
Ttj 4
9
"~
Ttj z
O
TI/
T~
T~j l
Jialingjiang
TIj:
Ttf ~
©
..N
Daye
,.....,
T~
Tif 1
Tlt ,
T~d
[
Table I, Stratigraphic correlation the Upper Yangtze area. During
the
continued
to
Nanjlng to
(during
west
series the
being
of
TIJ5
sabkha Lower
the
tidal
of
flat
and
generally
was
the
area,
llme
a
plain
sabKha -
the
map
There
are
T I j I
in
The as
lagoon
(playa, shoal the late
mainly
but
(from
stage
-
the
sabKha, deep of
the
to
alluvial coastal shallow
Lower
which
tldal
flat
regression, .and
the
of
late
elements land
by
T I j4 a n d
the
flat
water late
cycles
tidal
a
formed
T Ij3 _ in
to east
area
was
the
the
and
Yangtze
three
in
platform
from
during
the
geomorphology)
and
Upper
paleogeographlcal
follows
slope the
in
the T I j2)
deposits
deposited
shoal;
Triassic
distance
T I j 2 ,
_
was
in
T I jl _
its
the
sahKha
mud
platform
of
In
formed d),
sabKha
mud
the
Middle
(during
shoaling,
i.e.
in
are
platform-margin
paleogeographical
llme
evaporites 2b,c
the
and
the
Wuhan
Kllometres.
calcarenite
(Figure
(it
to
regression.
the
Lower
Triassic,
to
transgression, and
Triassic
-
1,600
and
and
land
plain
due
consisting
in
During lagoon,
dolostone
the
over
cycles
correlated
and
Lower eastward
TI iS)
transgression
are
old
late
expand
of
the
sea): t h e
plaln/eluvlal salt
lake)
water
shelf;
-
shelf see
Triassic
the for
a
72
typical
example
(Figure
the
o~
At emerged was
end
above
formed
layer
of
and
salt p l a y a
its
evaporlte
ash
up
the
the
open
desiccation The
i m
of
thick
sea
but
The
the
occurs
8
in
new
was In
so
old
that
land
the
in
platform
called
activity
deposited some
the
it
Jiangnan
occurred,
the
whole
continental
a
Upper
depressions,
this
the
of
following
Welyuan,
~
-
Xuanhan,
9
-
shows
platform
the
the
the
platform
and
and
of
and
T 2 11 -
deposition
the
platform,
developing
Figure
Middle
limestone
(i.e.
type of
immersed 2f
between of
basin
movement
was
(Figure
by
cycles
the
~).
and
Late
ended
Triassic
the
marine
area.
5. A n h y d r l t e
-
characterized
evaporlte
dropping
emerged
orogeny
is
mud
mainly and
uplifting
distribution
Figure
rose,
volcanic
Triassic
lime
it
when
when
Indosinian
in
of
DISTRIBUTION
in
a
areas.
Middle
uplifting
basin
in
deposition
crust
addition,
nelghbourlng
T214),
by
resulted
to
the
meanwhile
In
consisting
TglSand
forming
level,
east.
deposition
affected
Triassic,
formed.
The
T212,
sea
the
volcanic
Yangtze
and
the in
S).
Lower
OF
evaporltes covers
an
thirteen
Chengdu, Wangcang,
5 10
-
in area
EVAPORITES
the of
regions:
Upper
Yangtze
500,000 i
-
sq.Km
area but
Nanchong,
Jlangyou,
6
-
Daxian,
Qljiang,
II
-
Wanxlan,
a
7
-
Ia
is
shown
halite
only
Zigong,
DianJlang, -
Jlannan,
iS - Zlqongxian.
Figure a. Facles section showing deposltlonal environments and m o d e l s Of E a r l y a n d M i d d l e T r i a s s i c in t h e U p p e r Y a n g t z e area, I - a l l u v i a l plain, II - s h o r e s l d e plain, III - t i d a l flat, IV - s a b K h a and salt lake: IV I - tidal flat, sabKha (dolostone dominated); IV~ sabkha salt b a n k (gypsum dominated); IV, - t e m p o r a r y d e s i c c a t i o n lagoon (argillaceous dolostone dominated); IV43 salt lake (IV41 coastal salt lake, IV42- playa). V - l a g o o n and bay (V1 - c o n t a i n i n g red ]3ed, V2 - lower energy, V 3 - high energy), VI - barrier islands, VII shallow-water shelf, VIII platform marginal bank, i micrltic limestone, a bioclastlc, oolitic limestone, S calcarenite, dolostone and nodular anhydrite, 5 algal-mat limestone, 6 bioclastlc limestone, 7 wormy limestone, 8 pelletal limestone, 9 sucroslc, banded anhydrlte, iO halite, iI laminated anhydrlte, la polyhalite, iS - a r g i l l a c e o u s dolostone, 14 shaly limestone, 15 red sandstone, 16 red mudstone, 17 diagenetlc dissolution.
?3
Hanzhong 0
j.~'% ,~.~,.,r
I-%.%
o
~
t, %,.,.,.~.,
Ch
n gdu,-~
8oohn
iC
y
probably
stratified.
Formation
generated
primary
dlagenesls algal
processes
thin
suggest
a
algal
growth
is
by have coast
probably
but
laminated
They
The
influxes,
before
sediments,
of
mats.
basin.
is
at
sea
Mediterranean depth
in
the
fresh of
actually
detrital
water
caused
The
after
commonly
sulfate
fine
hand, German
located
the
of
is
Therefore
precipitation.
salt
than
and
not
ape
early
a
preservation.
influx
that
settlement
Interruped
solar
of
of
of
through
brines
were
the
cl%ange,
is
brine
evaporated
from
procesess.
brines
Ca-sulfate
rather
in
and
normal
recycling
dlssolutlon-repreclpltat!on
to
brine
other
in
deposit. at
edges
periods
halite
demonstrate
the
eustatlc
increasing
halite
saturated
connection
On
pseudomorphs
during
mostly
supplies
considerable
growth
an
preventing
salt but
water
allows
subsidence
the
show
are
connected
a
salt
allowing
forming
from
Tethyan
maximum)
the
dlagenetic
exposure
(Gall, D u r a n d be
means
Basin.
(its
Towards
cUbeS
The
the
conditions
Basin Could
transgression
to
main
deeper,
sallnlty. with
area.
cycle
of
from
the
of
area
generated
indicates
edges
the
with
significant
corresponds
mud.
evolution
a
Lorraine
preservation.
argillaceous
dissolve
to
German
Paris
the
levels
place.
salinity
general
from
iS .p r o b a b l y
salt
eastern
salinity
and
marine
This
of
highest
normal
the
of
the
decrease
1975); t h a t
the
the
the
Formation
therefore
an
in
of
distance.
period
to
top
Ca-sulfate
salinity
takes
HuschelKalk,
great
probably
middle
Beds
Triassic
reaching
dilution
to
evolution
Middle
a
this
resulting
progressive
Grey
at
of
return
sill (Kozur,
before
end
domain,
Of
a
the
two
correponds marks
transgression
wlth
Silesian
concentration at
before
towards
contains
which
cyclic
beginning the
occurrences
Formation
Muschelkall~
1977), t h e
the
through
level
Beds
correlations
Muller,
gypsum Formation
dolomite,
Upper
From &
salt
White of
the
by
Beds
middle
apperance when
shown
carbonate been of low,
or
observed southern but
the
1t8
deposits
display
sediment
of
transformed
The clear of
Spain
into
beds,
molluscs,
in
which
episodes
of
pedogenetic
Magnesium
mainly
the
White
formed,
into
shows
shown
by
of
a
of
in
a
sl%ells
dolomites,
basin.
shallowing desiccation
such
shows
presence
the
is
problem.
Formation
The
the solar
gypsum
of
Interlayered
water
of
correlation
Beds
whole
present
something
salfnites.
sea
as
such
the
as
of
Paris
Basin
zones
of
the
normal
is
carbonate
ape
The
water
With
some
brecclas
to
and
layers
The in
bPlnes
Formation.
and
at
causes
This
the
top
and
Such
early
an
Upper
of
the
magnesium
magneslan-rlch
the
an
enrichment
develops
generated.
suddenly
diagenesis
character
MuschelKal}~
of
With
limestones.
diagenesls
related
dissolution
Beds
structures.
marine
late
interstitial
White
dolomltlzatlon
coPrensite,
disappears
present
the
the
where
sedimentary
sedimentation deposition
in in
to
sequences,
clays,
The
Beds
diagenesls
restricted
deposltional rich
of
in
burial,
lateral
remains
Mlllolldeae
enrichment
early
preserves
good
the
preservation
described
al., 198~), A f t e r
lower
normal
exposure,
Further
processes.
important is
been
very
to
and of
White
aerial
et
dlagenesis,
water
inflow
the
has
environment
the
exposure.
wlth/without
it
The
by
ostracods
of
as
anhydrite.
periodic
aerial
(Ortl-Cabo
deposltlonal
supports
just
generated
evolution
of
gypsification
structures,
WorKs
sulfate
evidence
undergoes
sedimentary salt
no
the
in
the
entry
fissure
Middle
of
Muscl%elKalK
meteoPlc
filling
with
of
waters.
satinspar
eastern
It
develops
gypsum.
COHCLUSIOHS
Middle the
large
the
effects
fresh
sea
The
of
the
introducing
carbonates,
controlling evolution
a
becomes
the
on
is
an
causes
a
us
%o
of
study
sedimentation:
dissolution.
basin
extension
It allows
evaporltlc
salt
layered
and
sequences the
More
cyclic
or
which
or
less
evolution
The
halite.
general
prove
the
water
the
basin.
and
Pate
In
WorKing
scale
in
milllmetric
environment:
fresh
evaporation
aye
shows
which
filling
depositional
sequential
dominant.
the
particles,
Ca-sulfate
larger
of
increasing
sedimentation at
Into
deposltlonal
dilution,
and
Basin
itself.
series.
generally
detrltal
Paris by
influences
the
in
unit
supplies,
oPganizatlon
changes
caPPing
eastern
an
flowing
is
primary
internal
supplies
factors
water
deposit
elementary
of
detrltal
throughout
centimetPic
the
than
continental
and
salinity
of
Basin
of
water
evaporated of
MuschelKalR German
causing
fact, at
depends
the
thls upon
evolution
sea
complexity
They
reflect
fresh
water
water
inflow
precipitation main
factors
fine
scale
which
one
results
to
£n
and of
a
the these
typical
119
sedimentary The
cycle. structural
distribution may
also
Algal
and
preserve
mat-liKe
middle
of
tlle
Middle
of
a
or
sedimentary
large
of
evaporltlc
of
the
by
eastern
sedimentary
controls
deposits.
Dlagenesls
sedimentary
structures.
Ca-sulfate
toward
layer
basement
the
primary
and
develop
of
study
Hercynlan
extensive
cycle
corrensltes
the
the
destory
undergo
MuschelKalK
for
of
preservation
totally
deposits
magnesium-rich
example
behavior
sometimes
diagenesls
Its
top,
in
the
dolomites
and
layer.
Paris
Basin
Processes
is
a
involoved
very
good
the
edges
for
many
on
basin.
ACKROWLEDGEMEHTS
The
author
helpful
would
like
suggestions
to
and
than}~
Dr.
Drs.
T.HIIIy
B.C.Schrelber
and
for
G.Busson
critical
reviewing
the
manuscript.
REFERENCES
Adloff
M.-C., D o u b l n g e r
et
J.
sedimentologlque
stratlgraphlques, la
Terre,
Braltsch
O,
XXV, &
in
Cosmochlmlca Dellwlg
R.L. over
&
Land
J,,
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Vertellung
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le
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an
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in
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Point
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Saline
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du
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304,
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der
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in
the
Third
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on
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67-77. petrographiques moyen
de
nouvelles
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les
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Geol.
31-39,
Structures de
Tell
lamination
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und
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1970
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evaporlte
5,
salants
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UNESCO, 1975
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Haget
a68
germanlschen
Roux
de
de
Sedlmentology
Evaporltes:
G.
Frelberger
Le
la
sedlmentologlque
Marais
Sedlmentology,
germanischen
Fr,,
Approche
extraordinarily
Paris
Laugier
de
geochimlques.
medlteraneen
-
Wardlaw
rocks:
Kunasz
superflclels
193-240.
Canada;
der
moyen
contlnental-saDh}~a
W,T,,
Kozur
-
48,
1982
L.A,, 1964 £84,
facies
(Sud
et
generateures
fosslles.
California,
HolseP
les
Salln-de-Giraud
Messlnlen
C,R.,
Holocene
sel:
71-90.
D.,
actuelles
de
au
MuschelKal1
,the the
In
the Eocene
Mississippian
Michigan
many
1986),
cases
bioconstructed
of
(ME$OSELLA however, carbonates
et the
of t h e p y r e n e a n
the
Artlc
left corner).
in t h i s study.
on
and Gebel
each
side~
Esh Mellaha
rough - Abu
135
m .i ul- i-
(n 14. u.i w
z uJ U 0 uJ ! (,9 ..~
=
o
I11
w
U 0
Iw
! uJ z
~;
0 _
:Ew
B
rr
~W >-m n-
;:~.-,~--~.x.
~
quaternary sands stromatolites associated iF~-~ with gypsum [ ~ gypsum
andlng°°nalchalkssands
F i g u r e 2. C o m p o s i t e s e c t i o n s of three t r a n s e c t s t h r o u s h the Abu Shaar el Q i b l i - E s h el M e l l a h a c a r b o n a t e complexes. L o c a t i o n of s e c t i o n s is s h o w n by e m p t y a r r o w s on the s i m p l i f i e d map of Plate i.
146
lagoonal
deposits,
erosional the
phases,
seaward
debris
of
and
the
coral
complex.
The
i; Figure
Excellent
complex
thick
1983)
and
as well
the
Sedimentary
extension
tip
the
components,
Eeh el of
dips
appear
lie
of
the
Mellaha, carbonate
may
be
over
on top or edges
on
the
Esh
6).
These cap
authors
influxes
el
and
have
Abu
Shaar
Mellaha
coral
facietal
el
Range
