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AN APPROACH TO GENESIS OF SEPIOLITE AND PALYGORSKITE IN

LACUSTRINE SEDIMENTS OF THE LOWER PLIOCENE SAKARYA AND PORSUK

FORMATIONS IN THE SIVRIHISAR AND YUNUSEMRE-BICER REGIONS

(ESKIS� EHIR), TURKEY

SELAHATTIN KADIR1 ,*, MUHSIN EREN

2, TANER IRKEC3 , HULYA ERKOYUN

1 , TACIT KULAH4, NERGIS ONALGIL

1 ,AND JENNIFER HUGGETT

5

1 Eskis� ehir Osmangazi University, Department of Geological Engineering, TR-26480 Eskis� ehir, Turkey2 Mersin University, Department of Geological Engineering, TR-33343 Mersin, Turkey

3 Anitta Park Sitesi, 2853. Cad. 32, Daire 3/15, TR-06810 Ankara, Turkey4 Dumlupınar University, Department of Geological Engineering, TR-43100 Kutahya, Turkey

5 Natural History Museum, Department of Earth Sciences, London, UK

Abstract—The Lower Pliocene lacustrine sediments of the Sakarya and Porsuk Formations in theSivrihisar and Yunusemre-Bicer regions consist of claystone, argillaceous carbonate, carbonate, andevaporites. No detailed studies of paleoclimatic conditions have been performed previously. The presentstudy aimed to determine the depositional environment and paleoclimatic conditions for the formation ofthese economically important sepiolite/palygorskite/carbonate/evaporite deposits based on detailedmineralogical, geochemical, and isotopic studies. Samples from various lacustrine sediments wereexamined using polarized-light microscopy, X-ray diffraction, scanning electron microscopy, andchemical and isotopic analysis methods. Dolomites are predominantly of micrite, which is partlyrecrystallized to dolomicrosparite/dolosparite close to desiccation fractures. The presence of ostracods anddacycladecean algae in the carbonates reflects a restricted depositional environment. The formation ofsepiolite and palygorskite fibers, either as cement between/enclosing dolomite and/or as calcite crystals,reflects occasional changes in physicochemical conditions provided by fluctuations in the lake-water leveland influx of groundwater in relation to climatic changes during and after dolomite precipitation. Thepositive correlations of SREE with Al2O3, Nb, high-field-strength elements, and transition elements aredue to alteration of feldspar and hornblende in the volcanic units. The high values of Ba and Sr relative toCr, Co, Ni, and V also indicate that felsic rather than ophiolitic rocks were the parent material. Thecrossplot of whole-rock SiO2 vs. Al2O3+K2O+Na2O and V/Cr ratio suggests deposition ofcarbonate�dolomitic sepiolite�sepiolitic dolomite under arid climate and oxic conditions, whereas theNi/Co and V/(V+Ni) ratios of the sediments indicate deposition of organic-bearing sepiolite/palygorskiteunder anoxic-dysoxic conditions. An enrichment in d13C and d18O values of dolomite with respect tocalcite is probably due to differences in mineral fractionations. The d34S and d18O values and 87Sr/86Srisotope ratios for gypsum suggest an intensely evaporitic lacustrine environment fed by an older marineevaporitic source. The Si, Al, Mg, Ca, and enhanced TOT/C required for periodic precipitation of organic-rich brown sepiolite/palygorskite characterize deposition in a swampy environment, while dolomiticsepiolite and sepiolitic dolomite formed in ponds by partial drying of the main alkaline lake.

Key Words—Dolomite, Gypsum, Lower Pliocene, Palygorskite, Sepiolite, Sivrihisar, Yunusemre-Bicer, Turkey.

INTRODUCTION

The widespread Neogene lacustrine claystone layers

that appear as brown, beige, and white colored sediments

in the Eskis� ehir region are either intercalated or overlain

by carbonate, argillaceous carbonate, and to a lesser

extent organic materials such as remnants of plant roots

and stems (Fukushima and Shimosaka, 1987; Irkec, 1988;

Irkec and Unlu, 1993; ITIT, 1993; Irkec and Gencoglu,

1994; Ece and Coban, 1994; Unlu et al., 1995; Karakaya

et al., 2004, Yeniyol, 2014). Changes in physicochemical

conditions are characterized by variations in concentra-

tions of Al+Fe, Mg, Ca, and S; by a pH range of 8 to 9,

which developed due to lithofacies, mineralogy, chemical

composition, and alteration process; and by controlled

periodic precipitation of sepiolite, palygorskite, carbo-

nates, and evaporites in the environment.

The geology, sedimentology, mineralogy, geochemis-

try, stable isotope composition, and 87Sr/86Sr ratios of

carbonate and gypsum in the Sivrihisar area were studied

by Bellanca et al. (1993), Karakas� and Varol (1994),

Altay (2004), Aydogdu (2004), Boyraz (2004), Gungor

(2005), Varol et al. (2005), Karakas� (2006), Altay et al.

(2007), Zeybek (2007), Yes� ilova and Tekin (2007), Kırtıl

(2008), and Altay (2011). Although Kadir et al. (2016)

studied the mineralogy, geochemistry, and genesis of

* E-mail address of corresponding author:

[email protected]

DOI: 10.1346/CCMN.2017.064067

Clays and Clay Minerals, Vol. 65, No. 5, 310–328, 2017.

sepiolite and palygorskite in the Neogene lacustrine basin

of the Eskis� ehir province, no information is available

concerning the general distribution of dolomite, sepiolitic

dolomite, sepiolite, and gypsum in the lake and related

environments. The purpose of the present study was to

investigate the sedimentological, mineralogical, and

geochemical characteristics of the sepiolite and palygors-

kite in lacustrine carbonate sediments of the Sakarya and

Porsuk formations and their relationships with paleocli-

mate and environmental conditions.

GEOLOGICAL SETTING AND DEPOSITIONAL

ENVIRONMENT

In central Anatolia, the Neogene tectonics character-

ized by extensional and strike-slip faulting caused the

development of the Miocene sedimentary basins in

depressional areas (Kahraman, 2010) such as

Yunusemre-Bicer sub-basin and Upper Sakarya basin

separated by a threshold of Paleozoic metamorphic and

Upper Cre taceous ophio l i t i c basement rocks

(Figures 1�3). The basement rocks are overlain uncon-

formably by Upper Miocene volcanics and sediments.

These units comprise continental clastics, volcanics,

volcanoclastics and carbonates, and thick gypsum layers

in the ‘Upper Sakarya Section’ (USS) of the extensive

‘Central Anatolian Neogene Basin’ (CANB) in the south

of Sivrihisar. In the Yunusemre-Bicer sub-basin in the

northern part of the study area, however, the Upper

Miocene sediments comprise continental carbonates and

clastics with discoidal and rosette-like gypsum crystals

(Figure 2). These units are overlain unconformably by

lacustrine sediments of the Lower Pliocene Sakarya

Formation which represents playa-lake environments

(ITIT, 1993; Irkec and Gencoglu, 1994; Figure 2). The

Lower Pliocene sediments in the Yunusemre-Bicer sub-

basin characterize marginal shallow-lake environments

which may be correlated with the Sakarya Formation.

This unit has been described as the Porsuk Formation by

Gozler et al. (1996), Karakas� (2006), and Zeybek (2007).

The Lower Pliocene lacustrine sediments within the

Eskis� ehir province are represented by argillaceous

carbonate, claystone, and gypsum deposited in fluvial

and lacustrine environments (Figures 1, 2). These

sediments have been deposited under alkaline environ-

mental conditions in the USS of the extensive CANB in

the south of Sivrihisar and within the Yunusemre-Bicer

sub-basin in the north (Figure 3).

Figure 1. Geological map of the USS of the CANB in the Sivrihisar and Yunusemre-Bicer regions (adapted from Konak, 2002;

Turhan, 2002). USS: Upper Sakarya Section; CANB: Central Anatolian Neogene Basin.

Vol. 65, No. 5, 2017 Genesis of sepiolite and palygorskite in Turkish lacustrine sediments 311

The organic-rich brown sepiolite occurs in anoxic

swamps in both the marginal zones and central playa lake

zone (ITIT, 1993; Irkec and Gencoglu, 1994; Unlu et al.,

1995; Figure 4a,b). The beige dolomitic sepiolite, with no

organic material, formed in small ponds of the playa lake

(ITIT, 1993; Irkec and Gencoglu, 1994; Unlu et al., 1995;

Figure 4a). Dissolution cavities are filled by beige colored

material in clay, silt, and sand size. The white, massive,

homogeneous, light sepiolitic dolomite generally grades

into brown and beige sepiolites (Figure 4c�f). The

uppermost part of the sequence comprises hard dolomitic

levels (Figure 4f,g). Silica bands and nodules together

with sepiolite lenses are present occasionally. Gypsum

crystals are observed in the lower part of the Sakarya

Formation in the CANB, and thick, massive gypsum

deposits of the Porsuk Formation in the Yunusemre-Bicer

sub-basin (ITIT, 1993). Gypsum/anhydrite occur either as

massive discoidal, swallow-tail, and rosette-shaped crys-

tals (Figure 4h,i) or as discoidal, swallow-tail, and rosette-

shaped crystals in silty claystone and in green smectitic

clays (Figure 4j). All the aforementioned formations are

overlain unconformably by Quaternary alluvium

(Figure 2).

Figure 2. Column sections of the study area showing vertical and lateral distribution of sediments in the USS of the CANB in the

Sivrihisar and Yunusemre-Bicer regions (after Irkec and Gencoglu, 1994; Zeybek, 2007).

312 Kadir et al. Clays and Clay Minerals

MATERIALS AND METHODS

Typical stratigraphic sections were measured to

determine vertical and lateral variations within the

Neogene lacustrine basin of the Eskis� ehir area.

Characteristic fresh and altered samples were collected

(Figures 1, 2, 4) and examined under a polarizing

microscope (Nikon-LV 100Pol). The mineralogical

characteristics of the samples were analyzed by powder

X-ray diffraction (XRD) (Rigaku D / Max � 2200 Ultia

PC, Japan). The XRD analyses were performed with

CuKa radiation at a scanning speed of 1º2y/min.

Samples for clay analysis (<2 mm) were dispersed in

distilled water overnight. These samples were dispersed

further using ultrasonic vibration for 15 min. The fine

silt and coarser materials were separated from the clay

fraction by timed settling. Several oriented mounts of the

<2 mm fractions were prepared from each clay fraction

by dropping a small amount of clay onto a glass slide

and drying in air. One oriented mount was solvated with

ethylene glycol vapor at 60ºC for 2 h to identify

smectite. Further oriented mounts were heated at 300

and at 550ºC for 2 h to detect chlorite. Semi-quantitative

amounts of rock-forming minerals were obtained using

the standard methods of Brindley (1980) and Eren and

Kargı (1995). The relative abundances of clay minerals

were determined using their basal reflections and

mineral-intensity factors (Moore and Reynolds, 1989).

Scanning electron microscopy and energy-dispersive

analyses (SEM-EDX) were performed on selected

samples to determine the micromorphological character-

istics of carbonate, argillaceous carbonate, and evaporite

samples. The analyses were carried out at The Natural

History Museum, London, UK, using an FEI QUANTA

SEM equipped with Bruker Esprit software and an EDX

detector (Berlin, Germany). For SEM-EDX analysis,

representative samples were prepared by adhering the

fresh, broken surface of the sample onto aluminum stubs

with double-sided carbon tape and adding a thin coat

(~350 A) of gold palladium using a Cressington 208 HR

coater (Watford, UK).

Chemical analyses of six carbonate, three argillac-

eous carbonate, and four evaporite whole-rock samples

were performed at Bureau Veritas Mineral Laboratories

(Vancouver, Canada) using inductively coupled plasma–

atomic emission spectroscopy (ICP-AES) (PerkinElmer,

Elan 9000, Waltham, Massachusetts, USA). The Spectro

XLAB-2000 PEDX-ray fluorescence spectrometer was

calibrated using USGS interlaboratory standards. The

Inductively Coupled Plasma Emission Spectroscopy

(ICP-ES) and Inductively Coupled Plasma Mass

Figure 3. Schematic cross-section of the overall depositional environment of USS of the CANB in the Sivrihisar and Yunusemre-

Bicer lacustrine sediments (see Figure 1 for route of the cross-section).


Spectrometry (ICP-MS) analyses were carried out on

lithium metaborate/tetraborate fusions following dilute

nitric acid digestion. Loss on ignition (LOI) was

determined as the weight difference after ignition at

1000ºC. The detection limits for the analyses were

between 0.01 and 0.1 wt.% for major elements, between

0.1 and 5 ppm for trace elements, and between 0.01 and

0.5 ppm for the SREE. The accuracy and analytical

precision of the measurements of major elements, trace

elements, rare-earth elements (REE), and transition

elements (TRE) was measured against standard refer-

ences STD SO-18, STD SO-19, STD GS311-1, STD

GS910-4, STD DS10, and STD OREAS45EA (used by

the Bureau Veritas Mineral Laboratories, Vancouver,

Canada), and duplicate analyses for each samples.

Stable-isotope analyses (d13C and d18O) of ten

dolomite and four calcite samples were performed in the

laboratories of Iso-Analytical Ltd (Crewe, UK). Powdered

samples of 5�10 mg were reacted with 100% phosphoric

acid (H3PO4) at 50ºC. The powdered carbonate samples

were weighed into Exetainer1 vials and placed in an

oven for drying to ensure that no moisture remained in the

samples nor in the containers prior to sealing them and

carrying out the acid conversion to carbon dioxide. The

tubes were then flushed with 99.995% He. After flushing,

0.5 mL of phosphoric acid (H3PO4) was added to digest

carbonate phases (Coplen et al., 1983) by injecting

through the septum caps into the vials. The vials were

left for 24 h at room temperature in order to allow the acid

to react with the samples. After 24 h, the vials were heated

to 60ºC for 2 h to ensure conversion of all available

carbonate to carbon dioxide. The CO2 gas liberated from

the samples was then analyzed by continuous-flow

isotope-ratio mass spectrometry (CF-IRMS) (Europa

Scientific, 20-20 mass spectrometer, Crewe, UK).

Standards IA-R022 (ISO-analytical working standard

calcium carbonate), NBS-18, and NBS-19 were run as

quality-control check samples during analysis of the

samples. All isotopic data are reported in delta (%) vs.

V-PDB standard (Ratio sample/Ratio V-PDB) -1)61000.

The d34S and d18O values were determined on ten

gypsum and anhydrite samples which were selected

carefully by handpicking under a binocular microscope.

Stable-isotope analyses (d34S + d18O) were conducted at

the Department of Geosciences, University of Arizona,

USA, using a MAT 261-8 Mass Spectrometer (Finnigan

MAT, San Jose, California, USA).

d34S was measured on SO2 gas in a continuous-flow

gas-ratio mass spectrometer (ThermoQuest Finnigan

Delta PlusXL, Tucson, Arizona, USA). The samples

were combusted at 1030ºC with O2 and V2O5 using an

elemental analyzer (Costech, Tucson, Arizona, USA)

coupled to the mass spectrometer. Standardization was

based on international standards OGS-1 and NBS123

(Hosono et al., 2014), and several other sulfide and

sulfate materials for sulfur that have been compared

between laboratories. Calibration is linear in the range

�10 to +30%. Precision is estimated to be �0.15% or

better (1d) based on repeated internal standards.

The d18O of sulfate was measured on CO gas in a

continuous-flow gas-ratio mass spectrometer (Thermo

Electron Delta V, Tucson, Arizona, USA). The samples

were combusted with excess C at 1350ºC using a thermal

combustion elemental analyzer (ThermoQuest Finnigan,

Tucson, Arizona, USA) coupled to the mass spectro-

meter. Standardization was based on international

standard OGS-1. Precision was estimated to be �0.4%or better (1d), based on repeated internal standards.

The strontium isotopic analyses (87Sr/86Sr ratios) of

gypsum/anhydrite samples were performed using a Triton

Figure 4 (this and facing page). Field photographs of: (a) thick brown sepiolite overlain by beige and white sepiolites and dolomite in

the Yenidogan pit (Playa lake zone); (b) close-up view of brecciated, soapy, pure brown sepiolite in the Oglakcı pit; (c) close-up view

of brown sepiolite layers overlain by white sepiolite in the Yunusemre pit; (d) thin brown sepiolite band between beige sepiolite

layers in the Oglakcı pit; (e) carbonate-infill along the discontinuity surface between sepiolite and palygorskite layers in the

Yunusemre pit; (f) brown sepiolite band between beige sepiolite and dolomite layers in the Veletler pit; (g) thick, white dolomitic

bed intercalating thin sepiolite layers in the Yenidogan pit; (h) massive gypsum layer in the Mulk gypsum pit; (i) alternation of hard

and friable gypsum layers in the Bicer village; (j) rosette- and swallow-tail-type gypsum in mudstone (claystone) in the Bicer

village.


Multi-Collector Thermal Ionization Mass Spectrometer

(Thermo Fisher Scientific Inc., Waltham, Massachusetts,

USA) with static multi-collection. Analytical uncertainties

were given at the 2m level, and 87Sr/86Sr data were

normalized with 86Sr/88Sr = 0.1194. During the course of

the measurement, the Sr standard, NIST SRM 987, was

measured as 0.710245 � 0.000005 (n = 2).

RESULTS

Petrography

Petrographic determination of the thin sections

indicated that the dolomite and sepiolite-palygorskite-

bearing dolomite samples are micritic in character and

mostly non-fossiliferous (Figure 5a,b). The dolomicrite

was partly converted to dolomicrosparite (Figure 5a) and

dolosparite (Figure 5b) due to recrystallization.

Microbrecciation was observed in some samples.

Dacycladecean algae (Figure 5c) and ostracods

(Figure 5d) are common in some dolomicrite samples.

Gypsum was observed as euhedral to subhedral crystal

forms in some thin sections (Figure 5e,f).

XRD

The XRD data for bulk samples and their clay

fraction confirmed the presence of sepiolite, palygors-

kite, smectite, chlorite, illite/mica, dolomite, calcite,

gypsum, quartz, opal-CT, and feldspar (Table 1;

Figure 6). Dolomite is abundant and associated with

sepiolite, palygorskite, smectite, and chlorite. Dolomite

generally dominates toward the top of the sequence and

is associated with accessory calcite. Dolomite was

identified from sharp peaks at 2.88�2.89 A and calcite

by peaks at 3.87 and 3.04 A (Figure 6). Sepiolite and

palygorskite were identified by peaks at 12.51 and

10.50 A, respectively (figure 5, Kadir et al., 2016).

Gypsum was identified by sharp peaks at 7.66, 4.27, and

2.87 A (Figure 6).

SEM-EDX

The SEM analysis was performed on carbonate,

argillaceous carbonate, claystone, and gypsum samples

(Figure 7). Sepiolite occurs as interwoven and scattered

fibers (Figure 7a,b). Sepiolite and palygorskite either

enclose relicts of dolomite (Figure 7c) or occur as

cement in bridging form between dolomite crystals

(Figure 7d,e). Dolomite and calcite occur as masses of

anhedral to euhedral crystal forms, overlain by traces of

palygorskite (Figure 7f). Gypsum in the Sivrihisar region

occurs in platy, sheet-like, and massive forms

(Figure 7g,h). Gypsum crystals are 1�3 mm in diameter,

and are cemented locally by prismatic and platy fine-

grained gypsum with dimensions of 1 mm60.1 mm.

Chemical analyses

The carbonate and argillaceous carbonate samples are

characterized by high MgO (avg. 13.99% and 20.10% by

weight, respectively), CaO (avg. 20.51% and 31.87% by

weight, respectively), and LOI (avg. 26.63% and 41.5%

by weight, respectively) contents (Table 2; an extended

version of Table 2 has been deposited at http://

www.clays.org/Journal/JournalDeposits.html). Sepiolite

was characterized by the relatively large MgO/

Al2O3+SFe2O3 ratio and SiO2 and decrease in the

MgO/(Al2O3+SFe2O3) ratio in palygorskite.

The Ni+Co contents in the carbonate, argillaceous

carbonate, calcareous claystone, claystone, and evapor-

ite samples showed a positive correlation with both SiO2

(r = 0.781) and Al2O3 (r = 0.664) values increasing with

clay abundance (Figure 8a,b). The Cr/Ni ratio

(<0.68�2.39) reflects the availability of ferromagnesian

phases such as olivine and pyroxene derived from

ophiolitic basement units (Table 2 and the extended

vers ion thereof [ht tp : / /www.clays .org/Journal /

JournalDeposits.html]. The crossplot of Th/Co

(0.3�2.33) vs. La/Sc (0.3�4.46) ratios for carbonate,

argillaceous carbonate, calcareous claystone, and

claystone samples falls in the field of silicic rocks

(Figure 8c). Average Al2O3/TiO2 ratios >14 range

between 15.69 and 20.45 in carbonate, argillaceous

carbonate, calcareous claystone, and claystone samples.

In general, concentrations of Ba (avg. 170.7 ppm) and Sr

(avg. 2213 ppm) are greater than those of Cr (avg.

85.48 ppm), Co (avg. 3.45 ppm), Ni (avg. 76.64 ppm),

and V (avg. 42.01 ppm). Sr values in the carbonate and

argi l laceous carbonate (86.4�3539.1 ppm and

218 .9�5786 .4 ppm, respec t ive ly , excep t for

15967.9 ppm in sample VEL1-1, that is possibly due to

the presence of celestite) are high compared to the Sr

(avg. 423 ppm) in evaporites. Sr shows a negative

correlation with Ca (r = �4.53) (Figure 8d). The SREEshow positive correlations with each of Al2O3 (r =

0.9208), TiO2 (r = 0.8492), Nb (r = 0.877), high-field

strength elements (HFSE) (Hf+Nb+Ta+Th+Ti+Zr) (r =

0.8586), and TRE (Co+Cr+Cu+Ni+V+Sc+Zn) (r =

0.4264) (Figure 8e�i).SiO2 vs. Al2O3+K2O+Na2O data for the carbonate,

argillaceous sediments, and evaporites were plotted on a

paleoclimate discrimination diagram (Figure 9). The Ni/

Co (7.19�100), V/(V+Ni) (0.23�<0.72), and V/Cr

(0.13�<2.20) ratios for carbonate, argillaceous dolo-

mite, calcareous claystone, claystone, and evaporite are

listed in Table 2 (and in the extended version thereof).

Stable-isotope geochemistry

The d13C and d18O values of the dolomite samples

range from �2.98 to +1.73% PDB and from �5.59 to

�0.23% PDB, respectively, whereas those for calcite

range from �7.28 to �1.42% PDB and from �8.80 to

�7.03% PDB, respectively (Table 3; Figure 10).

The sulfur and oxygen isotope compositions of

gypsum and anhydrite range from 15.7 to 22.3% and

from 9.4 to 19.4%, respectively (Table 4; Figure 11).

These compositions are consistent with an evaporitic


lacustrine environment (Onal et al., 2008). These data

also suggest a contribution from pre-Lower Pliocene

evaporite deposits similar to those reported by Garcıa-

Veigas et al. (2011).

87Sr/86Sr isotope geochemistry

The 87Sr/86Sr isotope ratios for gypsum and anhydrite

samples from different parts of the CANB around

Eskis� ehir range from 0.707579 to 0.708203 (avg.

0.70782) (Table 4).

Figure 5. Photomicrographs of: (a,b) dolomicrite showing microbrecciation caused by desiccation fracturing (Fr) and

recrystallization to dolomicrosparite (arrows) and dolosparite (arrow), respectively (crossed polars, YDN-9); (c) Dasycladecean

alga-bearing dolomicrite (crossed polars, YSE-5); (d) ostracod-bearing dolomicrite (crossed polars, IL-11); (e,f) replacement of

algal dolomicrite by gypsum. Arrow showing dasycladecean alga (plane and polarized light, respectively, YSE-5).


Table 1. Mineralogical variations through stratigraphic sections of the lacustrine sediments from the USS of the CANB in theSivrihisar and Yunusemre-Bicer regions.

Sep Plg Sme Chl Ilt/Mca Cal Dol Gp Anh Qz Opl Fsp

Yunusemre - Bicer Subbasin (Marginal sub-basin)YunusemreYSE-3 ++ ++ + acc accYSE-5 acc acc +++++YSE-4 ++ +++ accYSE-14 + ++++YSE-16 +++ ++

BicerBCR-2 +++++BCR-5 +++++

SazılarSZL-2 +++++SZL-6 +++++SZL-8 +++++

OglakcıOGL-6 +++++OGL-9 +++ ++

DemirciDMC-5 +++++

BabadatBBT-1 acc + ++ ++ accBBT-4 acc ++++ acc + acc

MulkMLK-1 + acc +++ + accMLK-5 +++++MLK-6 +++++ accMLK2-3 +++++MLK2-5 +++++

GunyuzuGNU-1 acc acc ++ acc ++++ acc + accGNU-2 acc acc ++++ acc acc

USS of CANB in the south of Sivrihisar (Playa lake basin)VeletlerVEL1-1 ++ +++VEL1-3 ++ +++VEL1-7 + + + acc acc + +VEL1-10 acc acc + acc +++ accVEL2-1 ++ +++ accVEL2-2 ++ +++ accVEL2-6 ++ +++

Kurts� eyh-Insustu TepeKRT-1 + acc acc +++ + accKRT-3 acc acc ++ + + accKRT-5 + ++ + +KI-1 ++ +++KI-6 +++++ acc accKI-11 +++ ++ accKI-12 + ++++KI-20 +++++KI-23 + ++++KI-26 + ++++

AhilerAHL-1 ++ acc +++AHL-2 ++++ acc +AHL-5 acc +++++AHL-7 acc +++++


DISCUSSION

Neogene lacustrine sediments are widespread in the

Eskis� ehir area (part of the CANB) and consist of

alternation of claystone, argillaceous carbonate, and

carbonate beds indicating cyclical climatic conditions.

The sediments show vertical and lateral changes in

lithology and mineralogical and chemical composition.

The increased thickness and spread of carbonates in

swampy playa (dolomitic) lakes indicate formation by

drying of the extensive alkaline permanent lake, result-

ing in thick horizons of brown sepiolite similar to that

reported by ITIT (1993), Irkec and Gencoglu (1994), Ece

and Coban (1994), and Yeniyol (2014) (Figures 2�4).Increase in carbonate-bed thickness upward in the

sequence indicates increasing supersaturation caused

by evaporation, increased Mg/Ca ratio, and consequently

precipitation of dolomite or, where the Si/Mg ratio is

also increased, co-precipitation of dolomite and sepiolite

(Figure 4f,g; Tables 1, 2). The organic-rich brown

sepiolite (Figure 4a�g) in swampy ponds in marginal

zones of the lake formed during the seasonal transgres-

sions and regressions with low-energy conditions and

limited dimensions similar to those reported by Akbulut

and Kadir (2003), Irkec (2011), Celik Karakaya et al.

(2011b), Kadir et al. (2010), and Galan and Pozo (2011).

This interpretation is consistent with the presence of

~2.97 wt.% TOT/C in sample AHL-2 (Kadir et al., 2016)

(locally <7 wt.% TOT/C) in the samples studied. In the

predominant swamp facies, laminated or massive,

brecciated, soapy, pure sepiolites were deposited by an

influx of groundwater and frequent changes in the lake

volume.

Abundant dolomicrite, partly recrystalized into dolo-

microsparite, and locally associated with ostracods and

dacycladecean algae indicates a restricted environment

(Figure 5a�d; Braithwaite, 1979). Micromorphologically,

the occurrence of sepiolite fibers as interwoven aggre-

gates and discrete particles, frequently bridging individual

rhombohedric dolomite crystals, reflects the Si enrich-

ment of the precipitating solution (Figure 7c�f). This may

be derived from supersaturated groundwater, or a change

in the composition of existing pond water, as indicated by

dissolution of dolomite crystal surfaces, giving rise to

neoformed sepiolite and palygorskite fibers. Factors

conducive to sepiolite/palygorskite precipitation are a

pH range of 8�8.5, moderate salinity, and a high

concentration of Mg2+, Al3+, and Si4+; conditions that

are achieved in a semi-arid to arid climate as discussed

previously (Gehring et al., 1995; Jones and Galan, 1988;

Kadir et al., 2002; Akbulut and Kadir, 2003). The

paleoclimatic discrimination diagram plot of SiO2 vs.

Al2O3+K2O+Na2O (Chen et al., 2016; Figure 9) is

consistent with an arid to semi-arid climate during

dolomitization or precipitation of associated argillaceous

sediments in the basin. Development of sepiolite and

palygorskite fibers on dolomite and rarely calcite crystals

in dolomitic sepiolite/palygorskite and sepiolitic dolomite

implies precipitation as a result of decreased Ca/Mg ratio

during dolomitization.

The Ni/Co and V/(V+Ni) ratios of the sediments of

7.19�100 and 0.23�0.72, respectively, suggest anoxic

to suboxic conditions (Table 2 and the extended version

t h e r e o f [ h t t p : / / w w w . c l a y s . o r g / J o u r n a l /

JournalDeposits.html]; Jones and Manning, 1994;

Rimmer, 2004). In addition, V/Cr ratios of 2 in

carbonate, calcareous claystone, and claystone units are

consistent with precipitation in an oxic environment

(Celik Karakaya et al., 2011a,b). The local increase of

Ni up to <512 ppm values and positive correlation

between Ni+Co vs. each of SiO2 and Al2O3 in the

claystone and calcerous claystone suggest an ophiolitic

basement and volcaniclastic sediment source (Jaques et

al., 1983; Sharma et al., 2013; Kulah et al., 2014).

Average Al2O3/TiO2 ratios of >14 for carbonate,

Table 1 (contd.)

Sep Plg Sme Chl Ilt/Mca Cal Dol Gp Anh Qz Opl Fsp

YenidoganYDN1-1 +++++YDN-10 + + +++YDN-11 +++++YDN-12 +++++

Ilyaspas� a +++++IL-1 +++++IL-3 acc + ++++IL-8 +++++IL-12 +++++IL-15 ++++ acc +IL-16 acc acc +++++

Sep: sepiolite, Plg: palygorskite, Sme: smectite, Chl: chlorite, Ilt/Mca: illite/mica, Cal: calcite, Dol: dolomite, Gp: gypsum,Anh: anhydrite, Qz: quartz, Opl: opal-CT, Fsp: feldspar, and acc: accessory, +: relative abundance of mineral (mineral-nameabbreviations after Whitney and Evans, 2010).


argillaceous carbonate, calcareous claystone, and clay-

stone samples, and a crossplot of elemental ratios of Th/

Co vs. La/Sc indicate a felsic origin (Figure 8a; Hu et al.,

2015; Pozo et al., 2016) for the sediment. This

interpretation is consistent with the low concentration

of Cr, Co, Ni, and V values compared to those of high Ba

and Sr (Ahrari Rudi and Afarin, 2016). The positive

correlation of SREE with each of Al2O3, TiO2, Nb, high-

field-strength elements (HFSE), and TRE which are

transported in the terrigenous sediments also indicate

degradation of feldspar and volcanic glass derived from

volcanic materials (Figure 8c�g; McLennan et al., 1980;

Rollinson, 1993; Gonzalez-Alvarez and Kerrich, 2010;

Pozo et al., 2016).

The high Sr values in the carbonate (avg. 1452.1 ppm)

and argillaceous carbonate (avg. 7234.4 ppm) compared

to the evaporates (avg. 423 ppm) may be due to the

leaching of Sr from evaporites which show 87Sr/86Sr

isotope ratios ranging from 0.707579 to 0.708203 and the

association of Sr with carbonates during diagenesis

(Tables 2, 4; Lerouge et al., 2011). The Sr may be

exchangeable as in Callovian-Oxfordian evaporates (cal-

cite, dolomite, siderite, celestite, and detrital minerals) of

the Paris Basin (Lerouge et al., 2011). Degradation of

Figure 6. XRD patterns for: (a) claystone, (b) calcareous claystone, (c) argillaceous carbonate, (d,e) carbonate, and (f) evaporite

samples. Sep: sepiolite, Plg: palygorskite, Cal: calcite, Dol: dolomite, Gp: gypsum, Qz: quartz, and Fsp: feldspar (mineral name

abbreviations after Whitney and Evans, 2010).


Figure 7. SEM images of: (a) sepiolite fibers forming an interwovenmass (OGL-4); (b) close-up view of sepiolite fiber mat (OGL-4);

(c) palygorskite fibers enclosing dolomite relic (BBT-4); (d) dolomite rhomb coated by sepiolite fibers (GNU-1); (e) close-up view

of d; (f) calcite rhombs on dolomite relic (GNU-1); (g) platy form of gypsum crystal (MLK-2); (h) blocky form of gypsum crystal

cemented by anhedral gypsum (DMC-5).


Table 2. Chemical compositions of the selected rock samples in the study area.

Major oxides(wt.%)

CarbonateAvg. (n = 6)

Argillaceous carbonateAvg. (n = 3)

Calcareous claystone+

Avg. (n = 7)Claystone+

Avg. (n = 7)Evaporite

Avg. (n = 4)

SiO2 9.79 17.57 39.66 53.65 1.18Al2O3 1.40 1.28 5.49 6.16 0.24SFe2O3 0.64 0.59 2.92 3.71 0.14MgO 13.99 20.10 15.16 16.04 0.32CaO 31.87 20.51 8.85 1.02 33.08Na2O 0.10 0.12 <0.23 0.16 0.03K2O 0.28 0.14 <1.08 0.99 0.07TiO2 0.07 0.06 <0.35 0.35 0.02P2O5 0.03 0.04 <0.09 <0.06 0.01MnO 0.02 <0.02 <0.06 <0.04 0.01Cr2O3 0.008 <0.006 0.03 <0.08 0.00LOI 41.5 26.63 26.09 17.40 22.18

Total 99.64 98.95 99.76 99.66 57.26TOT/C 11.03 9.14 3.75 0.93 0.70TOT/S <0.03 <0.25 <0.09 <0.10 16.10

Trace elements (ppm)Ba 278 170.1 144 117 30.75Be 1 <1 <2 <2 1.00Co 2.4 1.56 11.87 18.26 0.53Cr 57.02 <38.77 205.26 <543.35 18.82Cs 5.3 10.9 <21.62 32.07 0.40Ga <1.7 6.47 <6.8 26.67 0.50Hf <0.6 0.37 <1.97 1.91 0.13Nb 1.8 1.73 <8.35 10.16 0.45Ni 34 <37.7 238.86 <511.75 20Rb 13.3 11.1 <69.27 64.39 2.43Sc <1.7 <1.7 <8 <9.67 1.00Sn <1.2 <1 <1.33 <1.5 1.00Sr 1452.1 7234.4 567.19 249.91 423.0Ta <0.1 0.3 <0.55 0.66 0.13Th 1.8 2.5 <7.08 5.44 0.35U 7.8 6.1 <2.23 3.04 0.45V 23.5 36.3 <95.33 248.86 9.00W <0.7 <0.5 <1.42 <1.17 0.50Zr 21.8 14.4 64.39 73.13 4.20Y 3.4 2.5 8.9 7.37 0.58La 5.4 5.43 14.77 14.14 1.33Ce 8.7 9.0 29.91 25.20 1.43Pr 1.06 0.89 <3.39 2.72 0.18Nd 3.7 3.0 <12.38 9.99 0.70Sm 0.6 0.54 <2.35 1.89 0.10Eu 0.15 0.13 <0.53 0.38 0.04Gd 0.63 0.55 <2.2 1.56 0.12Tb 0.09 0.07 <0.34 0.23 0.02Dy 0.54 0.41 <1.92 1.38 0.11Ho 0.10 0.08 <0.38 0.25 0.03Er 0.33 0.22 <1.11 0.79 0.06Tm <0.05 0.03 <0.16 0.12 0.02Yb 0.30 0.24 <1.06 0.81 0.07Lu 0.04 <0.04 <0.16 0.12 0.01Mo 0.2 <0.3 <0.35 <0.30 0.15Cu 2.9 5.7 16.47 15.89 0.90Pb 2.0 2.5 6.76 6.19 0.93Zn 6 10 30.43 36 2.00As 7.2 14.3 <7.87 5.91 3.10Cd <0.1 <0.1 <0.2 <0.2 0.10Sb <0.1 <0.4 <0.43 <0.48 0.10Bi <0.1 <0.1 <0.14 <0.2 0.10Ag <0.1 <0.1 <0.5 <0.6 0.10Au (ppb) 1.7 <1.5 7.79 <1.57 0.78


gypsum/anhydrite of the Upper Miocene continental

sediments and crystallization of Lower Pliocene gypsum

in an open hydrologic system may have resulted in the

leaching of Sr and substitution of Sr by Ca in calcite,

dolomite, and Ca-bearing silicate crystal structure, similar

to that reported by Jaworska and Ratajczak (2008).

The d13C and d18O values of dolomite (from �2.98 to

+1.73% PDB and from �5.59 to �0.23% PDB,

respectively) and calcite (from �7.28 to +1.73% PDB

and from �8.80 to �7.03% PDB) show a negative

correlation and suggest an evaporitic, hydrologically

closed system, as well as a meteoric origin of the

solutions and an edaphic source for the carbon. The

oxygen isotope fractionation value of 3 � 1% PDB

between dolomite and calcite (Figure 10) shows that the

d18O and d13C values of coexisting limestone and

dolomite are consistent with that stated by Land

(1980). In such an environment, the formation of

dolomite would correspond to periods of higher eva-

poration rates (Figure 10) similar to that reported by

Lopez-Galindo et al. (1996). The lake water would be

Hg 0.04 <0.02 <0.29 <0.03 0.01Tl <0.1 <0.1 <0.24 0.2 0.10Se <0.5 <0.5 <0.5 <1.6 0.50Ni/Co 33.15 <44.18 79.48 <18.25 70.24Cr/Ni 1.16 0.86 0.86 <1.07 0.94V/V+Ni 0.45 <0.52 <0.39 <0.56 0.31V/Cr 0.99 <1.36 <0.46 <0.46 0.50HFSE 425.58 358.89 2180.04 2189.00 110.13TRE 136.65 131.57 606.22 1387.78 52.24SREE 24.97 <23.11 <84.81 66.95 5.21

HFSE: Hf+Nb+Ta+Th+Ti+Zr; TRE: Co+Cr+Cu+Ni+V+Sc+Zn; n = number of samples; +Kadir et al. (2016).

Table 2 (contd.)

Trace elements(ppm)

CarbonateAvg. (n = 6)

Argillaceous carbonateAvg. (n = 3)

Calcareous claystone+

Avg. (n = 7)Claystone+

Avg. (n = 7)Evaporite

Avg. (n = 4)

Table 3. Stable-isotope compositions of dolomite and calcitefrom carbonates in the study area.

Sample d18O PDB (%) d13C PDB (%)

CalciteBBT-4 �7.03 �7.28MLK-6 �7.82 �5.79KI-20 �8.80 �4.91IL-1 �7.90 �1.42Avg. �7.89 �4.85

DolomiteKI-12 �0.23 �2.80YSE-5 �2.70 �1.94YSE-14 �4.42 +1.73YDN1-1 �4.52 �0.04YDN-11 �5.59 �0.88YDN-12 �4.28 +0.20AHL-5 �3.31 �2.98AHL-7 �3.13 �2.49IL-12 �3.22 �0.82IL-13 �3.09 �0.86Avg. �3.45 �1.09

Table 4. Sulfur-, oxygen-, and 87Sr/86Sr-isotopic composition of gypsum and anhydrite samples from the study area.

Sample Mineralogy d34S V-CDT*(%)

d18Osulfate

V-SMOW* (%)

87Sr/86Sr(�2s in 10�6)

Standard error

SZL-2 Gypsum 20.5 17.6 0.707855 � 0.000050SZL-6 Gypsum 22.2 19.4 0.707706 � 0.000050SZL-8 Gypsum 21.8 17.2 0.707825 � 0.000012MLK2-3 Gypsum 21.0 18.9 0.707579 � 0.000070BCR-2 Gypsum 22.3 17.8 0.708203 � 0.000015MLK2-5 Anhydrite 21.8 9.4 0.707751 � 0.000050BCR-5 Gypsum 15.7 11.3DMC-5 Gypsum 20.3 17.8MLK-5 Gypsum 19.8 14.9IL-8 Gypsum 20.3 16.7

*V-SMOW: Vienna Standard Mean Ocean Water, a standard defining the isotopic composition of fresh water*V-CDT: Vienna Canyon Diablo Troilite, a standard for reporting sulfur isotope ratios


Figure 8. Elemental variation diagrams for major oxides (wt.%) and trace elements (ppm) of the Eskis� ehir samples: (a) Ni+Co vs.

SiO2; (b) Ni+Co vs. Al2O3; (c) Th/Co vs. La/Sc; (d) CaO vs. Sr; (e) SREE vs. Al2O3; (f) SREE vs. TiO2; (g) SREE vs. Nb; (h) SREEvs. HFSE; (i) SREE vs. TRE.


enriched in C and O even under humid conditions

(Talbot, 1990). The concentration of C is related to the

biological processes in the basin (McKenzie, 1985; Kelts

and Talbot, 1989; Talbot, 1990; Talbot and Kelts, 1990).

Carbon isotope systematics in these cases are indepen-

dent of the oxygen isotopic system, however (McKenzie,

1985; Faure, 1986; Kelts and Talbot, 1989; Talbot, 1990;

Talbot and Kelts, 1990). The oxygen and carbon isotope

systems are controlled by the lakewater evaporation rate

(Talbot and Kelts, 1990). The negative C and O values

also support the hypersaline water and bacterial sulfate

reduction which leads to precipitation of carbonates.

The d34S and d18O values for gypsum range from

15.7 to 22.3% and from 9.4 to 19.4%, respectively,

suggesting an evaporitic lacustrine environment

(Table 4). The shift of d18O in anhydrite to lower values

may reflect the effect of evaporation. These isotopic

compositions indicate a lacustrine origin for the

evaporites, implying that they were deposited in playa

or long-lived saline lakes (Onal et al., 2008). This

interpretation is consistent with the occurrence of

gypsum as beds in the Upper Miocene carbonate units.

Further evidence for this interpretation is the develop-

ment of secondary anhedral gypsum crystal cement

between euhedral and subhedral gypsum crystals

(Figure 7h) similar to that reported by Tekin (2001).

The wide range of d34S and d18O values may also reflect

a contribution from hydrothermal fluids and mixing with

meteoric water as reported by Rye (2005). The presence

Figure 9. Paleoclimate discrimination diagram of SiO2 vs.

Al2O3+K2O+Na2O in the USS of the CANB in the Sivrihisar and

Yunusemre-Bicer lacustrine sediment samples (after Suttner

and Dutta, 1986).

Figure 10. A crossplot of d13C vs. d18O compositions of dolomite and calcite from carbonate samples.

Figure 11. A crossplot of d34S vs. d18O compositions of gysum

and anhydrite samples.


of fault-controlled hot springs (Yuce et al., 2015) and

epithermal gold deposits in the vicinity support this

interpretation. Palmer et al. (2004) reported that marine

evaporites were the source of sulfate for non-marine

Miocene evaporite deposits in Turkey. They suggest that

the SO4 and sulfur isotopic compositions of non-marine

Miocene evaporite deposits have similar values to actual

geothermal fluids from western Turkey.

CONCLUSIONS

Dolomite, argillaceous carbonate, and claystone are

widespread in Neogene lacustrine sediments of the

Eskis� ehir province. Dolomites are micritic in character

and partly recrystallized to dolomicrosparite and dolos-

parite. The presence of ostracods and dacycladecean

algae reflects deposition within a restricted environment.

Sepiolite (�palygorskite) and palygorskite occur in many

places in the CANB-USS, and the Yunusemre-Bicer sub-

basin, as scattered fibers, fiber-mats, or bridging relicts

of dolomite crystals in dolomitic units. In swamp and

playa sediments, sepiolite (�palygorskite) and palygors-

kite formed by direct precipitation from saturated

solutions. Textural and morphological features suggest

precipitation from discharging groundwater, rich in Si,

Mg, and Al, during or following dolomitization which

took place at the time of diagenesis.

Contacts between dolomite, argillaceous carbonate,

and claystone may be transitional � especially in the

swampy ponds, or may be sharp and distinct such as in

the ponds of the playa lakes, formed through partial

drying under arid climatic conditions. Sharp contacts

between dolomite, argillaceous carbonate, and claystone

occur due to the precipitation of calcite and further

conversion into dolomite, and the association of these

carbonates with minor sepiolite (�palygorskite) were

controlled by lithology, Mg/Ca ratios, and the concen-

tration of Si and Al under alkaline physicochemical

conditions. The Si, Al, Mg, Ca, and S ions, required for

sepiolite, palygorskite, and associated dolomite, calcite,

and gypsum formation were provided by solution(s) that

percolated through the ophiolitic and volcanoclastic

sedimentary source rocks. Thus, Sr and Ba enrichment

in the carbonate and argillaceous carbonate is a

consequence of degradation of feldspar and hornblende

derived from volcanic units. The presence of Ni+Co in

claystone and calcerous claystone indicates a contribu-

tion by the ophiolitic basement.

The d13C and d18O values of dolomite and calcite are

interpreted as resulting from an increase in evaporation

from the marginal subbasin to the playa-lake environ-

ment, resulting in widespread dolomitization. The d34Sand d18O values for gypsum suggest an evaporitic

lacustrine environment. The low d18O values in anhy-

drite reflect the effect of evaporation. The 87Sr/86Sr

isotope ratios also indicate that Sr originated from a non-

marine source. The aridity and anoxic-dysoxic and oxic

conditions of the precipitation environment in the basin

are demonstrated by the discrimination plot of SiO2 vs.

Al2O3+K2O+Na2O and ratios of each Ni/Co, V/(V+Ni),

and V/Cr.

ACKNOWLEDGMENTS

The present study was supported financially by theScientific Research Projects Fund of Eskis� ehir OsmangaziUniversity under Project No 2014�487. The authors areindebted to the editors and to the anonymous reviewers fortheir extremely careful and constructive reviews whichimproved the quality of the paper significantly. Part of thiswork was presented during the 53rd Annual Meeting ofThe Clay Minerals Society, Georgia State University,Atlanta, Georgia, USA, in June 2016. Jennifer Huggettthanks the staff of the Natural History Museum, London,for assistance with the SEM work.

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(Received 16 May 2017; revised 13 September 2017;

Ms. 1180; AE: W.D. Huff)


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