Sulphur, sulphate oxygen and strontium isotope composition ...kisi.deu.edu.tr/cahit.helvaci/Sulphur.pdf · Sulphur, sulphate oxygen and strontium isotope composition of Cenozoic Turkish

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




7 Orpiment Emet (Hisarcik) – �35.1



12 Celestite Emet 0.709410F13 22.8

14 Gypsum Emet (Gfktepe–Hisarcik) 0.709156F7 20.9 17.6


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


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.


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.


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.


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).


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


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.


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


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




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)



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



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



Miocene Kirmir alabastrine gypsum lacustrine 20

gypsiferous claystone

alabastrine gypsum 19, 6


alabastrine gypsum 18

thenardite layer 5

mudstone, gypsum


claystone


claystone


claystone

Sariyer limestone lacustrine


Miocene Bozkır selenitic gypsum lacustrine


selenitic gypsum

gypsarenite

selenitic gypsum 3

gypsarenite 27

selenitic gypsum


selenitic gypsum

gypsarenite

alabastrine gypsum 25, 4

gypsarenite

alabastrine gypsum

thenardite layer

alabastrine gypsum 23


Kızılırmak sandstone, claystone lacustrine

Bayındır halite–gypsum–claystone lacustrine


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


Bigadic Section


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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