sulphur, sulphate oxygen and strontium isotope composition...
TRANSCRIPT
Sulphu
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Abstract
Sulphur (dthenardite) and
Oxygen isotop
have been use
seawater was
seawater Sr a
continental ge
the d18Osulphat
evaporites. As
nonmarine ev
distinguishing
marine and no
concentrations
D 2004 Elsevi
Keywords: Turk
0009-2541/$ - s
doi:10.1016/j.ch
* Correspon
E-mail addr
(M.R. Palmer).
Chemical Geology 209 (2004) 341–356
r, sulphate oxygen and strontium isotope composition of
Cenozoic Turkish evaporites
Martin R. Palmera,*, Cahit Helvacıb, Anthony E. Fallickc
ampton Oceanography Centre, School of Ocean and Earth Sciences, University of Southampton, European Way,
Southampton SO14 3ZH, UK
ndislik-Mimarlik Fakultesi, Dokuz Eylul Universitesi, Jeoloji Muhendisligi, Bolumu, 35100 Bornova-Izmir, TurkeycSUERC, Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride, Glasgow G75 0QF, UK
Received 20 August 2003; accepted 21 June 2004
34S) and strontium isotope (87Sr/86Sr) ratios have been measured in 37 sulphate minerals (gypsum, celestite and
4 sulphide samples (d34S only) from 9 Cenozoic marine and nonmarine evaporites located in Anatolia, Turkey.
e (d18Osulphate) ratios were also measured in 25 gypsum and 1 anhydrite sample from these deposits. These data
d to determine the origin of dissolved sulphate in the brines that precipitated these minerals. They show that
the dominant source of sulphate and Sr in the marine evaporites, but that perturbations from contemporaneous
nd sulphur isotope compositions result from recycling of older evaporites and sulphate reduction. Although
othermal fluids played an important role in supplying the dissolved salts that formed the nonmarine evaporites,
e, d34S and Sr isotope compositions of many of these nonmarine evaporites are indistinguishable from the marine
well as suggesting that recycling of marine evaporites was important for controlling the composition of the
aporites, it also suggests that d18Osulphate, d34S and Sr isotope compositions are not unequivocal tracers in
between these two types of evaporite. For the Turkish evaporites considered here, the major difference between
nmarine evaporites that contain similar d34S–d18Osulphate–87Sr/86Sr relationships is that the latter contain high
of boron that reflect a geothermal contribution to the deposits.
er B.V. All rights reserved.
ey; Evaporites; Strontium; Oxygen; Sulphur isotopes
1. Introduction
A major area of research into evaporites centres on
their potential to record information about palae-
oclimates, ancient tectonic settings and the history of
seawater chemistry. In this regard, there has been
ee front matter D 2004 Elsevier B.V. All rights reserved.
emgeo.2004.06.027
ding author. Fax: +44 2380 593059.
ess: [email protected]
www.elsevier.com/locate/chemgeo
much debate concerning whether individual deposits
were deposited in marine or nonmarine settings (e.g.,
Hardie, 1984; 1991; Ayora et al., 1995; Zimmermann,
2001; Horita et al., 2002). However, it is now widely
accepted that this classification is overly simple, with
many evaporites showing evidence of having formed
from a mixture of open-ocean water (that has under-
gone evaporative concentration) and waters that bear a
continental imprint (e.g., Denison et al., 1998). For
example, a transition is frequently recognised in
which a semi-enclosed marine basin becomes pro-
gressively isolated from the open oceans, such that its
sedimentological and geochemical characteristics
become increasingly influenced by continental inputs
(Ayora et al., 1995; Denison et al., 1998; Flecker and
Ellam, 1999; Taberner et al., 2000). Sr, S and O
isotope studies are particularly useful in monitoring
this process because: (1) their isotope ratios in
seawater are constant at any point in time (within
the limits of analytical precision), (2) these isotope
ratios have varied in time in well-constrained manners
(e.g., Holser, 1977; Claypool et al., 1980; Burke et al.,
1982) and (3) the 87Sr/86Sr and d34S values of
seawater are generally distinct from that of river
water (Grinenko and Krouse, 1992; Palmer and
Edmond, 1989).
Anatolia, Turkey, plays host to a wide variety of
well-characterised marine and nonmarine evaporites
that were deposited at various times during the Tertiary
(Brinkmann, 1976). These deposits lie in an important
location for the potential documentation of tectonic
events, such as the closing of the Tethys seaway, and
climatic events, such as the Messinian salinity crisis.
Hence, they represent a good location in which to
explore the application of Sr, S and O isotope
stratigraphy in more detail.
2. Geological setting
Anatolia, Turkey, hosts a variety of marine and
nonmarine evaporite deposits that range in age from
Palaeocene to Miocene. Schematic stratigraphic sum-
maries of the various areas considered in this study are
presented in Appendix A, with the location of the
deposits illustrated in Fig. 1. Sedimentological, geo-
chemical and palaeontological studies have allowed
the various deposits to be classified as predominantly
marine or nonmarine (AkkusS, 1971; Ergun, 1977;
Ketin, 1983; Bozkaya and Yalcin, 1992; Atabey,
1993; Yagmurlu and Helvacı, 1994; Helvacı and
Yagmurlu, 1995; Ceyhan, 1996; Erdogan et al.,
1996; Helvacı and Ortı, 1998; Ortı et al., 1998; Ciner
et al., 2002). Of the samples considered here, those
from the Sivas, Hekimhan and Darende–Balaban
Basins are all from recognised marine evaporites.
Samples from the Gqrqn, Beypazarı, Cankırı–Corum,
Yerkfy–Yozgat, Emet, Bigadic and Sultancayir evap-
Fig. 1. Map showing distribution of evaporite deposits considered in this study, together with distribution of marine and nonmarine facies in
Turkey during the Miocene (Brinkmann, 1976).
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356342
orites are all unequivocally nonmarine in origin and
are well separated from contemporaneous marine
sediments (Fig. 1). Some of these evaporites are
sufficiently large to be mined for gypsum (e.g.,
Cankırı–Corum), while others contain abundant sul-
phate minerals intercalated with borates and trona that
are themselves of major economic importance.
Samples of gypsum (CaSO4d 2H2O), thenardite
(Na2SO4) and celestite (SrSO4) were collected from the
various deposits and handpicked to obtain mineral
separates for sulphur, oxygen and strontium isotope
analyses. Textural evidence indicates that the gypsum
and thenardite samples are primary precipitates from an
evaporite brine. Celestite formed by interaction of Sr-rich
interstratal brines with gypsum (Helvacı and Firman,
1976). In addition to the sulphate minerals, samples of
realgar (AsS) and orpiment (As2S3) from the Emet borate
deposit were used to examine the isotope composition of
reduced sulphur in these deposits, as these are the only
sulphide minerals of significance in the deposits consid-
ered here. The orpiment and realgar were too intimately
intergrown to allow physical separation. The realgar is
thought to have formed from interaction of As-rich
geothermal springs that flowed into the evaporite basins
with reduced sulphur; orpiment then formed by oxidation
of the realgar on exposure to air (Helvacı and Firman,
1976).
3. Methods and results
Sulphur isotope and sulphate oxygen isotope ratios
were determined at SUERC using standard extraction
and analytical techniques. The d34S results (refer-
enced to CDT) and d18Osulphate (referenced to V-
SMOW) are listed in Table 1. Details of the methods
are listed in Hall et al. (1991). Three analyses of NBS
127 during the course of this study yielded an average
d18Osulphate value of 8.9F0.2x.
The sulphates from marine evaporites have slightly
higher and less variable d34S values (mean 24.8x,
S.D.=2.7, n=16) than those from the nonmarine evapor-
ites (mean 22.4x, S.D.=3.4, n=21), but there is
considerable overlap between the two data sets (Fig. 2).
The reduced sulphur contained within the orpiment
and realgar samples from the Emet deposit has
distinctly lower d34S values of �35.3x to �30.4x(mean �33.7x, S.D.=2.3, n=4).
The d18Osulphate values of the marine evaporites are
lower (mean 13.5x, S.D.=1.8, n=10) than those of
the nonmarine evaporites (mean 16.6x, S.D.=4.2,
n=16), and there is less overlap between the two
populations (Fig. 3).
The Sr isotope compositions were determined at
Southampton using standard analytical techniques.
During the course of the analyses listed in Table 1,
five analyses of NBS 981 yielded an average 87Sr/86Sr
ratio of 0.710247 (S.D.=0.0013%). The samples from
the marine evaporites have a mean 87Sr/86Sr ratio
(0.707271, S.D.=0.000604, n=16) that is slightly low-
er and less variable than the mean 87Sr/86Sr ratio of the
nonmarine evaporites (0.708253, S.D.=0.000813,
n=21), although there is again overlap between the
two data sets (Fig. 4).
4. Discussion
4.1. Marine evaporites
The three deposits considered here are from the
same general area (Fig. 1), and, as noted above, they
have previously been classified as marine evaporites.
The ages of the samples considered here are defined
by the stratigraphy of the deposits and are only precise
to approximately F6 million years. Nevertheless,
comparison between the S and Sr isotope composi-
tions of the marine evaporites with values for
contemporaneous seawater (Paytan et al., 1998;
McArthur et al., 2001) reveals that most of the
sulphate minerals analysed from these deposits were
not simply derived from precipitation of evaporated
seawater (Fig. 5). The history of seawater d18Osulphate
values is less well defined than is the case for sulphur
and Sr isotope ratios. Hence, rather than presenting
the data as an age curve, the d34S–d18Osulphate
relationship defined by our samples is compared with
those measured by Claypool et al. (1980) and Utrilla
et al. (1992) for Cenozoic marine evaporites (Fig. 6).
The Sr isotope compositions of the evaporite
minerals reflect the sources of Sr to the basins,
together with possible interactions between the brines
and rocks within the evaporite basins. The observation
that most of the marine evaporite sulphates considered
here have 87Sr/86Sr ratios that are lower than
contemporaneous seawater suggests that they were
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356 343
precipitated from brines with a significant component
of nonmarine Sr.
Most of the d34S values of the sulphate minerals lie
well above the seawater curve for the past 65 million
years, even after accounting for the 1.6x fractionation
between dissolved sulphate and precipitated sulphate
minerals (Thode and Monster, 1965). Hence, the
sulphate minerals with elevated d34S values must
either arise from the addition of dissolved sulphate to
the basins from a nonmarine source or reflect an isotope
fractionation process within the basins. The only
potential source of sulphur with sufficiently high
d34S values to generate the elevated values observed
in these Turkish sulphate minerals would be from
dissolution of Devonian, Silurian, Ordovician or
Cambrian evaporites (Holser, 1977; Claypool et al.,
1980). There is no evidence of the presence of
evaporites of these ages within any of the drainage
Table 1
Sample mineralogy, location and isotope data
Sample Mineralogy Deposit 87Sr/86Sr d34S d18Osulphate
1 Gypsum Sultancayir 0.708448F17 22.9 21.4
2 Gypsum Sultancayir 0.708700F14 23.8 21.1
3 Gypsum Cankırı–Corum (Sarmasa) 0.707601F8 23.5 14.6
4 Gypsum Cankırı–Corum (Celtek) 0.707626F18 23.0 16.8
21 Gypsum Balibag–Cankırı 0.707616F26 24.0 17.8
23 Gypsum Cankırı–Corum (Dutkfy) 0.707962F21 24.2 17.8
25 Gypsum Cankırı–Corum (Kfprqlq) 0.707392F11 23.5 17.5
27 Gypsum Cankırı–Corum (Kirkfy) 0.707656F18 24.8 16.3
5 Thenardite Beypazari 0.709398F8 22.1
6 Gypsum Beypazari 0.707664F15 24.1 15.9
18 Gypsum Beypazari 0.707660F24 22.2 15.9
19 Gypsum Beypazari 0.707656F16 22.4 15.5
20 Gypsum Beypazari 0.707706F19 22.8 17.0
7 Orpiment Emet (Hisarcik) – �35.1
8 Orpiment Emet (Hisarcik) – �30.4
9 Orpiment Emet (Hisarcik) – �35.3
12 Celestite Emet 0.709410F13 22.8
14 Gypsum Emet (Gfktepe–Hisarcik) 0.709156F7 20.9 17.6
16 Orpiment Emet (Hisarcik) – �34.1
17 Celestite Emet (Hisarcik) 0.709420F20 20.8
10 Celestite Bigadic 0.708047F24 12.7, 12.8
11 Celestite Bigadic 0.708230F23 28.9
13 Gypsum Bigadic (Simav) 0.707960F6 25.3 22.1
S1-1 Celestite Sivas Basin (Kabali) 0.705921F24 31.2
S1 Celestite Sivas Basin (Kabali) 0.706229F18 25.1
S2 Anhydrite Sivas Basin (Kabali) 0.707639F8 23.6 12.1
S3 Gypsum Sivas Basin (Kabali) 0.707760F11 23.2 12.9
S5 Celestite Sivas Basin (Sinekli) 0.707175F27 23.1
S6 Gypsum Sivas Basin (Budakli) 0.707535F8 22.9 12.4
Bud Celestite Sivas Basin (Budakli) 0.707099F24 22.7
S8 Gypsum Sivas Basin (Demirci) 0.707623F13 23.0 12.6
S9 Celestite Sivas Basin (Demirci) 0.706260F27 30.5
S11 Gypsum Sivas Basin (Akcamescit) 0.707680F15 23.2 12.3
S12 Celestite Sivas Basin (Tahtakeme) 0.707743F818 27.0
S13 Gypsum Sivas Basin (Tahtakeme) 0.707428F16 23.1 12.6
S15 Gypsum Sivas Basin (Karayqn) 0.707573F10 24.4 17.3
Se1 Gypsum Yozgat Basin (Yerkfy) 0.707743F6 19.9 14.5
G1 Gypsum Gqrqn Basin 0.710252F9 14.7 3.5
Mh1 Gypsum Hekimhan 0.707827F12 22.6 12.6
D1 Gypsum Darende Basin 0.707607F12 26.8 15.1
D2 Gypsum Darende 0.707243F17 24.9 15.4
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356344
basins considered in this study (Brinkmann, 1976).
Hence, we suggest that the high d34S values of the
sulphate minerals illustrated in Fig. 5 most likely arise
from isotope fractionation during microbially mediated
reduction of SO42� to S2� bearing species. This process
is associated with fractionation of sulphur isotopes (the
light sulphur isotopes being enriched in the reduced
species), such that the d34S difference between the two
species is usually of the order of 30–50x (Hoefs,
1980). If sulphate reduction takes place in a closed
basin setting, the residual dissolved SO42� will have a
higher d34S value than the original seawater. This
process has previously been invoked to account for
elevated d34S values in some Spanish evaporites
(Utrilla et al., 1992).
As noted above, the d18Osulphate–age curve is not well
defined, but the limited data that are available suggest that
the mean oxygen isotope composition of marine evapor-
ite sulphate minerals has varied from ~17x in the
Precambrian to a low of 10x during the Permian. There
was then a steep rise to values of ~16x in the Triassic,
followed by an uneven fall to Cenozoic values of 12–
13x (Claypool et al., 1980). Dissolved sulphate oxygen
isotope compositions can also be affected by bacterial
sulphate reduction, with the residual sulphate being
enriched by between 25% and 50% (i.e., 10–20x) of
the enrichment in d34S (Seal et al., 2000).
The oldest sample (Mh1), from the Palaeocene
Hekimhan deposit, has an 87Sr/86Sr ratio that is
indistinguishable from contemporaneous seawater
and a d18Osulphate value that is within the range of
other Cenozoic marine evaporites. Although its d34S
value is 3.4–5.1x higher than seawater from the time,
the Sr isotope data suggest that these evaporites record
a seawater signature that has only been slightly
perturbed by sulphate reduction, rather than recycling
of older evaporites.
The seven Eocene samples are all from Bozbel
formation of the Sivas deposit and consist of two
gypsum, one anhydrite and four celestite specimens. All
three of the calcium sulphate minerals fall on, or close to,
the contemporaneous seawater Sr and S isotope curves
and have d18Osulphate values of 12.1–12.9x, again
Fig. 2. Histograms showing distribution of d34S values in evaporite
minerals from marine (open squares) and nonmarine (solid squares)
evaporites analysed in this study.
Fig. 3. Histograms showing distribution of d18Osulphate values in
gypsum and anhydrite from marine (open squares) and nonmarine
(solid squares) evaporites analysed in this study.
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356 345
suggesting that this evaporite deposit is dominated by a
marine signature. In contrast, all the celestite samples
have lower 87Sr/86Sr ratios, and the two samples that
show the greatest deviation from the seawater Sr isotope
curve also have distinctly high d34S values. This suggests
that the interstratal brines that reacted with gypsum to
form celestite (Helvacı and Firman, 1976) had undergone
Sr isotope exchange with the volcanoclastic sediments
that are intercalated with the evaporites (Ciner et al.,
2002). Alternatively, the interstratal brines may have
mixed with other circulating fluids that had interacted
with the volcanic material. In either case, the d34S values
indicate that the dissolved sulphur in these brines had
undergone partial reduction to sulphide. Similar processes
were invoked to explain the isotopically heavy d34Svalues in celestite cement from Eocene reefs in NE Spain
(Taberner et al., 2002).
In contrast to the Eocene and Palaeocene data, all the
Oligocene and Miocene gypsum samples have 87Sr/86Sr
ratios that are significantly lower than contemporaneous
seawater, and two (both samples from the Darende Basin)
have d34S values that are N1.6x higher than those of
seawater of the same age. Both the Darende samples and
the uppermost sample from the Sivas deposit also have
d18Osulphate that are higher than previously observed in
Cenozoic marine evaporites. Hence, it is apparent that
Fig. 5. Comparison between d34S values (upper figure) and 87Sr/86Sr
ratios (lower figure) of marine evaporites and contemporaneous seawater.
Squares indicate values for gypsum and anhydrite samples. Triangles
indicate values for celestite. The d34S seawater record is from Paytan et
al. (1998). The 87Sr/86Sr seawater record is from McArthur et al. (2001).Fig. 4. Histograms showing distribution of 87Sr/86Sr ratios in
evaporite minerals from marine (open squares) and nonmarine
(solid squares) evaporites analysed in this study.
Fig. 6. Comparison between d34S–d18Osulphate relationship observed
in this study for Sivas (solid diamonds), Darende (solid triangles)
and Hekimhan (solid square) deposits compared to the relationship
observed in Pliocene (open square), Miocene (open diamond), Upper
Eocene (open triangle) and Middle Eocene (open circle) marine
evaporites. The Pliocene and Miocene data are from Claypool et al.
(1980) and the Eocene data are from Utrilla et al. (1992). The error
bars indicate 1 S.D. of the data presented in these studies.
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356346
there is an additional component of Sr in these samples
and that this component becomes increasingly important
in the younger samples. This conclusion accords with
facies analyses of the deposits that suggest that the
boundary between continental and marine environments
becomes increasingly difficult to recognise in the
Miocene (Ciner et al., 2002). There are several possible
sources of nonmarine Sr in these deposits. Although
volcanoclastic debris is found in the Eocene strata, none
is described for the Oligocene and Miocene. Rather, we
believe that the most likely origin of the low 87Sr/86Sr
ratios in the younger samples is redissolution of the
Eocene and Palaeocene evaporites that were previously
deposited in the same basins. Gypsum from these
deposits has virtually identical 87Sr/86Sr (mean=0.70768,
S.D.=0.00012, n=5) to those measured in the Miocene
and Oligocene samples (mean=0.70753, S.D.=0.00016,
n=6), and the high Sr (and sulphur) concentrations in
gypsum means that their dissolution would have
dominated the Sr (and sulphur) isotope systematics of
local continental waters. Some reduction of dissolved
SO42� would be required to yield the isotopically heaviest
d34S and d18Osulphate values observed in three of the
samples (D1, D2 and S15) even if the SO42� supply to the
basin was derived from dissolution of previously
deposited evaporites. In addition, the fact that both
Miocene celestite samples (S9, S12) have elevated d34S
values suggests that there was active sulphate reduction in
the interstratal brines.
4.2. Nonmarine evaporites
All the nonmarine evaporite deposits considered
here are Miocene in age. The d34S–87Sr/86Sr ratios
and d34S–d18Osulphate relationships of gypsum from
the nonmarine evaporites are illustrated in Fig. 7. It is
evident from this diagram that, in terms of their d34S,
d18Osulphate and Sr isotope compositions, the gypsum
samples from Cankırı–Corum and Beypazarı are
essentially indistinguishable from gypsum from the
marine evaporites considered above.
The eastern and southern parts of Anatolia were
covered by shallow marine seas in the Miocene
(Fig. 1), but the area containing the Cankırı–Corum
and Beypazarı deposits was located well away from
the palaeo-shoreline at the time these nonmarine
evaporites were deposited. Despite the fact that no
large marine evaporite deposits are described in the
immediate vicinity of these deposits, they are
located in areas that were flooded by shallow seas
in the Palaeocene and Middle Eocene, and the
Palaeocene rocks in this vicinity are described as
containing coal and gypsum layers interbedded with
clastic marine sediments (Brinkmann, 1976). Hence,
we suggest that dissolution of previously deposited
marine evaporites constituted a major source of
dissolved salts in the Cankırı–Corum and Beypazarı
deposits.
The nonmarine evaporites from Yerkfy are Miocene
in age, but they are underlain by Eocene marine gypsum
(Ketin, 1983). No samples were analysed from the marine
section, but Eocene seawater had d34S values (17.5–
22.5x) and 87Sr/86Sr ratios (0.70773–0.70786) that
bracket the sulphur and Sr isotope compositions
(19.9x and 0.70774) recorded by the samples (Se1)
from Yerkfy, and the d18Osulphate values are similar to
those measured in Eocene marine evaporites (10.4–
14.1x) (Utrilla et al., 1992). Hence, again, it is
Fig. 7. Relationship between d34S and 87Sr/86Sr (upper diagram)
and d34S and d18Osulphate (lower diagram) of gypsum from
nonmarine evaporites. Closed circle=Bigadic. Open circle=Sultan-
cayır. Closed diamond=Beypazarı. Open diamond=Emet. Closed
square=Cankırı–Corum. Open square=Gqrqn. Closed triangle=
Yerkfy. Grey square=range of d34S, d18Osulphate and 87Sr/86Sr in
gypsum and anhydrite from marine evaporites considered in this
study.
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356 347
reasonable to conclude that the nonmarine evaporites at
this location derived most of their dissolved salts from
dissolution of older marine evaporites.
The remaining nonmarine evaporites considered
here (Bigadic, Sultancayır, Emet and Gqrqn) have
more radiogenic 87Sr/86Sr ratios than the marine
evaporites and trend towards lower d34S and
variable d18Osulphate values. It is possible that
mixing of sulphate and Sr derived from marine
sediments and river waters is also responsible for
the relationship shown in Fig. 7. However, it may
be significant that three of these deposits (Bigadic,
Sultancayır and Emet) also host world-class borate
ore bodies.
The 87Sr/86Sr ratios of gypsum from the
Bigadic, Sultancayır and Emet borate deposits
(0.70796, 0.70845–0.70870 and 0.70916, respec-
tively) fall within the range of 87Sr/86Sr ratios
measured in borate minerals from these deposits
(0.70735–0.70874, 0.70861 and 0.70826–0.70962,
respectively) (Palmer and Helvacı, 1997). This
suggests that the borate and gypsum in these
deposits were derived from fluids that shared a
common source. As the borate minerals formed
from brines that contained a significant component
of geothermal fluids (Helvacı, 1995; Palmer and
Helvacı, 1995, 1997) and gypsum is intimately
associated with the borates in these deposits
(Helvacı, 1995), then the same presumably applied
to the brines that precipitated gypsum in these
deposits. We do not know the Sr isotope compo-
sition of the geothermal fluids that were supplying
these basins at the time of evaporite deposition,
and there are a few Sr isotope data available for
modern Turkish geothermal fluids. The limited data
that are available are for geothermal fluids from
western Anatolia (Vengosh et al., 2002). With the
exception of the carbonate-hosted Pamukkale sys-
tem, the data fall on a mixing line (Fig. 8) that
reflects the interpretation of Vengosh et al. (2002)
that the overall chemistry of these fluids reflects
mixing between leaching of a metamorphic base-
ment (high 87Sr/86Sr, low [Sr]) and Messinian
evaporites (low 87Sr/86Sr, high [Sr]). No sulphur
isotope data are available for the Turkish geo-
thermal fluids, but the fact that the d34S of gypsum
from these three deposits (20.9–25.3x) lies well
within the range of Anatolian marine evaporites
and/or Cenozoic seawater suggests that the contri-
bution of geothermal SO42� to these deposits was
small. This is not surprising as the Turkish
geothermal fluids have relatively low SO42� con-
centrations (mean=275 ppm, n=25) (Vengosh et al.,
2002) compared to saturated brines formed by
dissolution of gypsum. The d18Osulphate values from
the borate deposits range from 17.6x to 22.1xand are significantly higher than those observed in
the marine evaporites. This observation is most
compatible with the sulphate within the borate
deposit being derived from redissolution of the
marine evaporites, with an increase in d18Osulphate
values from partial reduction of the dissolved
sulphate. A similar extent and mode of d18Osulphate
enrichment has been observed in marine sulphate
recycled in Tertiary nonmarine evaporites in Spain
(Utrilla et al., 1992).
The Gqrqn deposit does not host any borate
deposits, but deposition of the sampled gypsum
layer was coincident with andesitic volcanism in the
immediate area (as evidenced by a thick layer of
andesite tuff in the gypsum bearing layer; Atabey,
1993; Onal et al., in press), and collision-related
volcanism and geothermal activity was a feature of
this area of Anatolia throughout the Miocene (Notsu
et al., 1995). Indeed, there continues to be intense
geothermal activity in this and other areas of Turkey
underlain by Neogene and Quaternary volcanic
rocks (Mutlu and Gulec, 1998). There are no
sulphur or Sr isotope data for geothermal fluids or
river waters in this area. However, the d34S value of
the gypsum sample from this deposit (14.7x) is
lower than that of marine evaporites in the area and
is closer to the d34S of dissolved SO42� from
Fig. 8. Relationship between 87Sr/86Sr ratios and Sr concentrations
of Turkish geothermal fluids. Data are from Vengosh et al. (2002).
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356348
geothermal waters from elsewhere in the world
(mean=13.2x, S.D.=8.4x, n=84; Steiner and Raf-
ter, 1966; Robinson and Sheppard, 1986; Truesdell
et al., 1977; McKibben and Eldridge, 1989). The
very low d18Osulphate value (3.5x) is also compat-
ible with sulphate being derived from geothermal
waters (Robinson, 1978). The 87Sr/86Sr ratio of the
gypsum (0.71025) is well above that of Cenozoic
marine evaporites and/or seawater. Hence, it is
likely that geothermal fluids contributed a signifi-
cant proportion of the dissolved salts in the
Miocene section of the Gqrqn deposit, with dis-
solution of underlying Eocene marine gypsum in
the deposit playing a relatively minor role.
Celestite was also analysed from Emet and
Bigadic. At Emet, the 87Sr/86Sr ratios of the
celestite are only slightly higher than that of the
gypsum, and the d34S ratios are also similar (Table
1). This suggests that, as discussed above, this
celestite precipitated from brines formed by dis-
solution of gypsum (possibly by circulating geo-
thermal fluids) followed by partial reduction of the
dissolved sulphate. At Bigadic, the celestite sample
with an elevated d34S value (sample 11, 28.9x) can
again be readily explained as arising from sulphate
reduction. Interpretation of the low d34S sample
(sample 10, 12.7x) is less simple. It does not have
an 87Sr/86Sr value that suggests it precipitated from
brines with a higher component of geothermal fluid.
The observation of minor celestite with very low
d34S values (�21.2x) in the Eocene reefs of NE
Spain was ascribed to local sulphate derived from
reoxidation of sulphide or other reduced species
(Taberner et al., 2002); however, no sulphide
minerals have been identified at Bigadic (Helvacı,
1995). One possible explanation for the low d34S of
sample 10 is that it contains SO42� derived from the
reoxidation of dissolved sulphide formed during
early sulphate reduction of brines that dissolved the
gypsum.
The single sample of thenardite (Na2SO4) from
Beypazarı has an elevated 87Sr/86Sr ratio (0.70940)
relative to gypsum (0.70766–0.70771) and glauber-
ite (Na2SO4d CaSO4) (0.70757–0.70776; Ortı et al.,
2002), but a similar d34S value (22.1x compared
to 22.2–24.1x in gypsum and 20.0–20.6x in
glauberite; Ortı et al., 2002). Thenardite at Beypa-
zarı is considered to have formed from primary
mirabilite (Na2SO4d 10H2O) during early to moder-
ate burial diagenesis (Ortı et al., 2002). The
elevated Sr isotope composition of the thenardite
relative to gypsum and glauberite suggests that this
diagenesis may have involved circulation of brines
that contained a component of geothermal fluid
with elevated 87Sr/86Sr ratios.
The only deposit (marine or nonmarine) that
contains significant amounts of sulphide minerals is
Emet, which contains locally abundant realgar
(AsS) and orpiment (As2S3) formed from As
transported to the basin by geothermal fluids
(Helvacı, 1984, 1986). A d34S value for the fluid
of ~�30x is isotopically lighter than any pub-
lished data for dissolved sulphide in geothermal
fluids that we are aware of. This implies that a
significant proportion of the dissolved sulphide in
the Emet deposit was derived from microbially
mediated sulphate reduction. This conclusion is in
accord with our interpretation of the celestite d34S
data.
4.3. Wider implications
Despite the fact that there are subtle differences
between the 87Sr/86Sr, d34S and d18Osulphate values
of the marine and nonmarine evaporites considered
in this study, it is apparent that there is considerable
overlap between the isotope compositions of these
two types of deposits. It is also apparent that the
fact that 87Sr/86Sr data from individual marine
evaporite deposits and minerals fall on the contem-
poraneous seawater curve is no guarantee that the
sulphur isotope data record seawater d34S or
d18Osulphate values, or vice versa, in agreement with
the observations of Ayora et al. (1995) and Taberner
et al. (2000). This observation emphasises the
comments of Nielsen (1989) that considerable care
has to be taken in using evaporite data to
reconstruct the sulphur isotope composition of the
oceans through geologic time.
Evaporites are thought to play a role in the
genesis of a number of large base metal ore bodies
by the provision of anions for complexing metals in
solution and by providing the sulphur necessary to
precipitate the metals (Kyle, 1991, Warren, 1997).
In many cases, the prime piece of evidence used to
deduce the involvement of evaporites has been the
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356 349
presence of isotopically heavy d34S values in the
sulphide minerals (e.g., Kyle, 1991; Barton and
Johnson, 1996). These evaporites are generally
presumed to be marine in origin on the basis that
this reservoir is the only common source of sulphur
that exhibits high (typically N20x) d34S values.
Designation of the sulphur source as a marine or
nonmarine evaporite may not be of significance if
the objective of the study is simply to assess the
role of sulphur ligands in fixing and transporting
metal ions. However, the observation from this
study that evaporites that are clearly nonmarine in
origin can carry sulphur (and Sr) isotope signatures
that are indistinguishable from their marine counter-
parts suggests that the use of sulphur isotopes alone
to specify the nature of an evaporite involved in ore
deposition is problematic. The potential for error is
compounded if this designation is then used to
specify the tectonic setting of an ore body contain-
ing high d34S values or to deduce further informa-
tion concerning the influence of an evaporite on ore
fluid chemistry. For example, none of the non-
marine evaporites considered here contains signifi-
cant amounts of halite. Hence, although in the
future they might contribute sulphur with a high
d34S value to sulphides in a base metal ore deposit,
these sulphur isotope values could not then be used
to deduce that evaporite-derived chloride ions aided
metal transport.
For the Turkish evaporites considered in this
study, the major distinction between marine and
nonmarine evaporites that contain similar d34S–
d18Osulphate–87Sr/86Sr relationships is that the latter
contain high concentrations of boron that reflect a
geothermal contribution to the deposits. Hence,
studies of ancient ore bodies that also use the
abundance and isotope composition of boron in
tourmaline (e.g., Slack et al., 1989, 1993; Jiang et
al., 1998) in addition to other isotope analyses are
more likely to yield less equivocal evidence con-
cerning the nature of the evaporite involved.
5. Conclusions
Turkey is host to a wide variety of Cenozoic
marine and nonmarine evaporites. Sulphur and Sr
isotope analyses of gypsum, celestite, thenardite and
orpiment-realgar and oxygen isotope analyses of
gypsum and anhydrite from these deposits have been
used to deduce information concerning the source of
the brines that precipitated these minerals.
The three marine evaporites considered here
range from Palaeocene to Miocene in age and are
all from central Anatolia. The 87Sr/86Sr ratios of
gypsum from the older samples lie close to the
contemporaneous seawater Sr isotope curve. How-
ever, the Miocene samples have 87Sr/86Sr ratios that
are most compatible with recycling of older
evaporites in the area. The d34S and d18Osulphate
values of the gypsum and anhydrite vary from
close to seawater values to higher values that are
indicative of sulphate reduction within the evaporite
basins.
The isotope composition of celestite from the
marine evaporites indicates that they precipitated
from brines formed by the dissolution of the
original evaporite. These brines then interacted with
volcanoclastic sediments (or fluids that had inter-
acted with these sediments) in the basins (and
lowered their 87Sr/86Sr ratios) and underwent further
sulphate reduction (raising the d34S of the remain-
ing SO42�).
The d34S, d18Osulphate and Sr isotope composi-
tions of some of the nonmarine evaporite gypsum in
Anatolia are indistinguishable from the marine
evaporites and suggest that dissolution of marine
evaporites and carbonates played a role in defining
the chemistry of the nonmarine evaporites. Gypsum
from the borate-bearing nonmarine evaporites has
elevated 87Sr/86Sr ratios that are most compatible
with a contribution of Sr from the geothermal fluids
that were necessary for the formation of the borate
minerals. However, the d34S and d18Osulphate values
of the gypsum again suggest that recycling of
marine evaporites, accompanied by limited sulphate
reduction, was the dominant source of sulphate in
the brines of these basins.
Sulphur and Sr isotope ratios of celestite and
thenardite form these deposits again indicate that
they formed from dissolution of gypsum in the
deposits, with a contribution from circulating geo-
thermal fluids and sulphate reduction. The impor-
tance of sulphate reduction is emphasised by the
very low d34S values in orpiment-realgar from the
Emet deposit.
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356350
The observation that the d34S, d18Osulphate and
Sr isotope compositions of many of the marine
and nonmarine evaporites are indistinguishable
from one another indicates that there are
problems with using these isotope systems to
distinguish between these two types of evapor-
ites that may have implications for interpreting
the origin of evaporite-related base metal ore
bodies.
Acknowledgments
We are grateful to C. Taberner and A. Makhnach for
their helpful reviews. M.J. Cooper, T. Hayes, A.
McDonald, J.A. Milton and R.N. Taylor are thanked
for technical assistance. Fieldwork for this study was
supported by projects TBAG-685, YDABCAG-155
and YDABCAG-565 of the Turkish National Research
Council. [LW]
Age Formation Lithology Facies Sample
Quaternary alluvium lacustrine
Pliocene
M-U Miocene Karayun sandstone, mudstone, marine
sandy limestone
gypsum marine sabkha S15
conglomerate, sandstone, mudstone fluvial
L-M Miocene Haciali gypsum (+celestite) marine sabkha S13, S12
sandstone, mudstone, limestone marine
gypsum marine sabkha S11
conglomerate, sandstone, mudstone
Oligocene Selimiye gypsum (+celestite) continental sabkha S9, S8
sandstone, mudstone
Eocene Bozbel gypsum (+celestite), shale,
sandstone, limestone
marine S6, S5, S3, S2,
S1, S1-1, Bud
conglomerate, sandstone, mudstone marine
Paleocene Tecer limestone marine
U Cretaceous ophiolite melange
Age Formation Lithology Facies Sample
Pliocene limestone, marl, sandstone lacustrine
Miocene Bayındır halite playa Se1
gypsum
gypsum
marl
Oligocene Incik halite playa
gypsum
marl
sandstone
conglomerate
Eocene Upper volcanics shallow marine
Middle gypsum lagoon
coal
Lower conglomerate, sandstone, mudstone
Paleocene absent
U Cretaceous sandstone, limestone, shale, volcanics volcanic
Appendix A. Schematic stratigraphic logs and sample locations
Sivas Basin
Yerkfy–Yozgat Basin
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356 351
Age Formation Lithology Facies Sample
Quaternary alluvium lacustrine
basalt continental
Pliocene Kangal limestone lacustrine
marl, clay, conglomerate,
mudstone
fluvial
Miocene Gqrqn limestone, andesite,
agglomerates, tuffs
lacustrine
shale, tuffs, conglomerates,
sandstone,
limestone, gypsum bands
lacustrine G1
Gfvdeli Dag sandstone, mudstone, conglomerate alluvial fan
Eocene Demiroluk sandstone, claystone, gypsum upper tidal
clayey limestone, limestone, sandstone,
shale
marine shelf
limestone marine shelf
U Cretaceous Akdere limestone marine shelf
Gqrqn Basin (Sivas)
Age Formation Lithology Facies Sample
Quaternary alluvium lacustrine
Pliocene CaybaYi conglomerate, limestone lacustrine
Kepezdagı basalt, tuffs volcanic
Miocene Tahtalı marl, limestone marine
Oligocene gypsum, sandstone, mudstone marine sabkha D2, D1
U Eocene sandstone, siltstone, marl, gypsum bands lagoonal
Balaban sandstone, marl, conglomerate lagoonal
M Eocene Asartepe marl, limestone marine
Yenice sandstone, marl, limestone shallow marine
Korgan conglomerate marine
L Eoc-Paleo Karakaya basalts, tuffs, agglomerates
U Cretaceous Kırankaya limestone marine
Ulupınar conglomerate, sandstone, shale shallow marine
Tohma reef reef limestone marine reef
L Cretaceous absent
U Jurasic Geniz limestone marine
Darende–Balaban Basin
Hekimhan Basin
Age Formation Lithology Facies Sample
Quaternary alluvium lacustrine
Miocene Yamadag basalt, andesite, tuff volcanic
Oligocene Ugurlu cherty limestone, sandstone, sandy marl shallow marine
Eocene Kızıl Ozq clayey limestone marine
Kızıl Yatak fossilferous limestone marine
Paleocene Yagca dolomite, claystone, marl, gypsum marine sabkha Mh1
U Cretaceous Zorbehan limestone marine
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356352
Age Formation Lithology Facies Sample
Miocene Kirmir alabastrine gypsum lacustrine 20
gypsiferous claystone
alabastrine gypsum 19, 6
gypsiferous claystone
alabastrine gypsum 18
thenardite layer 5
mudstone, gypsum
gypsiferous claystone
claystone
gypsiferous claystone
claystone
gypsiferous claystone
claystone
Sariyer limestone lacustrine
Age Formation Lithology Facies Sample
Miocene Bozkır selenitic gypsum lacustrine
gypsiferous claystone
selenitic gypsum
gypsarenite
selenitic gypsum 3
gypsarenite 27
selenitic gypsum
gypsiferous claystone
selenitic gypsum
gypsarenite
alabastrine gypsum 25, 4
gypsarenite
alabastrine gypsum
thenardite layer
alabastrine gypsum 23
gypsiferous claystone
Kızılırmak sandstone, claystone lacustrine
Bayındır halite–gypsum–claystone lacustrine
Age Formation Lithology Facies Sample
Miocene basalt volcanic
cherty limestone lacustrine
borate-bearing limestone 17, 16, 14, 12, 9, 8, 7
lignite-bearing sandstone
basalts, tuffs
clayey limestone, lignite bands
sandstone
conglomerate
Paleozoic ophiolite, marble, schist basement complex
Beypazari Section
Cankırı–Corum Section
Emet Section
M.R. Palmer et al. / Chemical Geology 209 (2004) 341–356 353
Bigadic Section
Age Formation Lithology Facies Sample
Miocene basalt volcanic
borate-bearing limestone lacustrine 13, 11, 10
tuff volcanic sediments
limestone lacustrine
borate-bearing clayey limestone lacustrine
tuff volcanic sediments
conglomerate lacustrine
limestone lacustrine
basalt volcanic
Paleozoic ophiolite, marble, schist basement complex
Sultancayır Section
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