approximately 200 km", This Neogene basin is bordered by granite and ... Facies associations characterizing a playa complexcrop out in this Neogene basin.
SEDIMENTOLOGY AND EVAPORITE GENESIS OF NEOGENE CONTINENTAL SABKHA PLAYA COMPLEX, KARAKE(;ILI BASIN, CENTRAL ANATOLIA, TURKEY
'lbrahim TORKMEN and 2Mehmet OZKUL 'Firat Oniv. Mah. Fakultesi, Jeoloji MM. Ba!amil. E/azil. Turkey 2Pamukka/e Oniv. Mah. Fakidtesi, Jeoloji MM. Balama, Denizli, Turkey ABSTRACT: The Karakecili basin is an intermontane basin located about 60 km SE of Ankara in central Turkey and covers an area of approximately 200 km", This Neogene basin is bordered by granite and gabbro of the KiI§ehir massif to the north-northeast and east, and massive gypsum of the Mezgit Formation(Oligocene)to the west and southwest. Facies associations characterizinga playa complexcrop out in thisNeogene basin. These facies associations include, from the basin margin to the center, I-Red massive conglomerateandpebblymudstone (alluvialfan),2-Organicallyrich mudstone,bearing sparsegypsum crystals (marsh), 3-Cross-laminated-bedded gypsarenite (eolian), 4-Brown-gray mudstone bearing gypsum-roses and discoidal and radial gypsum crystals (saline mudflat), and 5-Bedded-laminated gypsum (ephemeral salt lake). Evaporites occur commonly as discoidal crystals, sigmoidal crystals, rosettes, and nodular forms. These were formed displacively within mudstone from calcium sulphate - rich groundwaterduring the arid conditions. Stratified gypsum represented by macrocrystallineaspects is generally restricted laterally and is precipitatedby the evaporationof brine sheets on mudflats. The source of evaporites in the Karakecili basin is the gypsum of the OligoceneMezgit Formation.
INTRODUCTION
The study area is located in the Karakecili district, approximately 60 Ian southeastof Ankara in central Turkey (Fig. 1). Neogene basins are widespread in central Turkey. Thesebasinsweretypically filledwithalluvial fan,river.Iake, and occasional playa deposits. Many Pre-Quaternary continental sabkhas have been recorded in the geological literature (Wolfbauer 1973; Eugster and Hardie 1975; Surdam and Wollbauer 1975; Sagri et al. 1989; Inci 1991; Gierlowski-Kordesch and Rust 1994; Rosen 1994; Yalmurlu and Helvaci 1994; Karadenizli 1995; Tiirkmen and Kerey 1996; BIanc-Valleron and Schuler 1997; Curialand Moretto 1997; Dromart and Dumas 1997; Orti 1997a,b; Orti and Salvany1997; EI-Tabakhet al. 1997; Rouchy 1997; Salvany 1997; Veigas 1997). Although nonmarine evaporites are common in modem arid closed basins, most of the Phanerozoic evaporites have been interpreted as marine deposit (Smootand Lowenstein 1991; Geisler-Cussey 1997; Orti 1997; Oru and Rosell 1997; Rosell and Pueyo 1997). Recent continental playas documented in the literature include Salina Valley, Deep Spring Valley (Hardie et al. 1978), Bristol Dry Lake,California (Handford 1982) and Tuz Galii(Ergun 1988). In thisstudy,a Neogene continental playa complex has been investigated from the viewpoint of facies characteristics, depositional process and origin, and was correlated with its recent counterparts.
Kirsehir Massif, which is the oldestrock unitat thebottomof the basin, is made up of granite and gabbro. The Kartal Formation consists of red conglomerates, sandstones, and siltstone. Thesesediments characterize alluvialfansandriver facies deposited from Maestrichtian to the Eocene (Rigo de Righi and Cortesini 1959; Gorur 1981). Generally, the greenish-gray coloredKirkkavak Formation consistsof shale with pelagic (G/obigerina sp. and Globorotalia sp.) and benthic (Rota/ia sp and Mi/iolid) foraminifera. These sediments were interpreted as deep-water and slope facies and, arc Danian-Monician in age (Unalan et al. 1976; Gorur 1981). The MezgitFormation occurs as massive gypsum at the basementof the Karakecili basin. The age of the Mezgit Formation is considered to be Oligocene based on its stratigraphic position (Oktay and Dellaloglu 1987; Gonir 1981). The Neogene playa complexin the basin consists of alternations of pebbly red mudstone with granular gypsum and gypsiferous mudstone in the central part of the basin, interlayered red massive conglomerate and red mudstone at the marginal parts of the basin. The basin center facies pass into the basin margin facies both in vertical and lateral directions. The complex is not greatlyaffectedby tectonism and is still horizontal. The playa complex that covers the Oligocene gypsum above an angular unconformity and is considered to be Mio-Pliocene in age. DESCRIPTION AND DISTRIBUTION OF THE MAJOR FACIES
GEOLOGICAL SETTING
The Neogene Karakecili basin is located in an intermontane area and coversan area of 200 krn', The basinis surrounded by Upper Cretaceous-Tertiary sediments of the Kartal and Eskipolatli Formations totheNNW,Oligocene gypsum to the SSW, and Kir§ehir Massif to the E and NE (Fig. 1). The Carbonates and Evaporites, v. 14, no. I, 1999, p. 21-31.
Six facies were identified through detailed sedimentological analysis of six measured sections (Figs. 2 and 3) around Karakecili, Thesefacies are interpreted as alluvial to playain nature. Facies associations and their interpretation are discussed as follows.
SEDIMENTOLOGY OF CONTINENTAL SABKHAPLAYA COMPLEX, TURKEY
N
f
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EXPLANATION Alluvium
I:::; :::cl NeoClene deposits Congl~meratP. mudstone-, gypsum 1--".,-,\ Mezgit Form. (Oligoc~n~) MaSSive gYP~um r=-=1 Klrkkavak Frn. (Low~r-Upp~r PQI~ocl L.=.-J Sandstone. mUdstone
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(Ma~.trichtian -Eoc~ne)
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Figure 1. Geologic mapof the study area.
Facies 1. Massive Conglomerate These conglomerates are red colored, matrix supported, poorly- sorted and internally disorganized (Fig. 2a). The thickness of individual beds of the facies is about 1-2 m. Pebbles arc usually angular and, in some places, show an imbricate structure. The lithological composition of the grains varies from one locality to another. In the Keklicek section (Fig. 2a) magmatic and calcareous pebbles are common. The pebblesize ranges up lO 1 m. The facies are 22
massive, normally and/or inversely graded and widely distributed. It grades into red mudstones in both vertical and lateral directions.
Interpretation.--llris facies corresponds to the Gms lithofacies of MiaJ] (1977). The features, such as lack of bedding, poor sorting, matrix support, and normal and/or inverse grading all indicate that these sediments were transported and deposited as debris flows (Hooke 1967; Schultz 1984).
TORKMEN AND OZKUL
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cecr s. uD..ard
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Gypsum rose Siqmoidal 9tpsum Radial gypsum
Discoidal gyp sum
Figure 2. Measured stratigraphic sections: a. Keklicek measured section, b. Kaldirim measured section, c. ArmutlubClji measured section.
Facies 2. Planar Cross-Bedded Gypsiferous Sandstone
lower parts andstratified gypsum (Facies 6) in its upper parts.
This facies has been observed at the Kaldirim section, on the
Interpretation.-Planar and trough cross bedding may develop by the migration of ripples or dunes under aeolian transport Similar facies developed viathemigration of small barchan dunes onsandflats at theperiphery of theBristol Dry Lake Playa (Handford 1982). In the Gemerek basin (east central Turkey), similar structures had been observed in the gypsiferous units oftheMiocene andhavebeen interpreted as aeolian deposits (Turkmen and Kerey 1996).
western partof the basin (Fig. 2b). It is characterized by low angle planar cross-bedding (Fig. 4), and rare trough crossbedding in fine-to medium-grained sandstones. Mostof the grains are gypsum in composition and are cemented by gypsum. In otherwords, thissandstone is a gypsarenite. The set thickness ranges upto 1m,andthecoset upto4 m. Facies 2 is associated with organic-rich mudstone (Facies 4) in its 23
SEDIMENlOLOGY OF CONTINENTAL SABKHA PLAYA COMPLEX, TURKEY
@ Marsh Playa
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~ Bedded gypsum
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Figure 3. Measured stratigraphic sections: a.Kocalar Yokusu measured section. b.Sarpinba,i measured section, c. Gokariau; Hill measured section.
Facies 3, Red Pebbly Mudstone
This facies is characterized by red colored mudstone and is observed at Kaldirim, Annutlubasi Hill, Sarpinbasi and Keklicek sections (Figs. 2a,b,c and3b). Pebbly mudstones are widespread and alternate with the massive conglomerates of facies 1 in theKeklicek section. In thissection, blocks areup to 1 m in size and are found in the mudstone thatconstitutes thebaseof the sequence (Fig. 2a). In the mudstone occurring 24
at the upper level of the section, the maximum pebble size is about3 em. Caliche witha thickness of 1-5m is present as paleosol horizons in somelevels of thisfacies. The facies has been observed at the base of other measured sections. It contains coarse quartz granules which werederived from the granitic mass, laying along theeastandnortheast of thestudy area. Facies 3 grades in itsupperpartintomudstones thatare rich in organic matter (Facies 4), or into gypsiferous mudstones (Facies 5).
TURKMEN AND 0ZKuL
Figure 4. Planar cross-bedded gypsiferous sandstone (Facies 2).
Interpretation-s- Red pebbly mudstones intercalated with paleosoland coarseclastsindicate a continental environment (Nilsen 1982). Alternation of the facies with the massive conglomerates (Facies I), which was produced by a debris flow,indicates deposition as part of an alluvial fan. A section dominated by mudstone with coarse quartz grains tends to occurin thecentralpartof thebasinand ischaracterized by the distal alluvlliI plain apron of the fan. Facies 4. Organlc-Rich Mudstone
Facies 5. Gypsiferous Mudstone
The facies is represented by red-gray mudstones bearing discoidal and radialgypsum crystals and gypsum roses. The gypsiferous mudstone is typically overlain by the stratified gypsum (Facies 6). The mudstones are up to 5 m thick. Gypsum veins have developed within the desiccation cracks andfractures. Coarsegrainedgypsum rosettesup to 2-3 em in diameter were developed as a result of concentric growth of sandsizedanddiscoidal gypsum crystals. Someclusters reach up to 30 em in length (Fig.7). These crystals can be clearly seen in outcrops of the red mudstone which overlie the stratified-gypsum (Facies 6). Some of the crystals are discoidal and othersare sigmoidal (Fig.7). Theyhaveperfect (010) cleavage planesandshowgoodstackingcharacteristics. These crystals occur typically as normal and oblique to the bedding.
This facies is represented by the gray-black organic rich mudstone. The facies tends to occur in the middle to upper part of the sequence in most of the measured sections, and is dominant in the Armutlubasi and Kaldirim sections in the western part of the basin (Fig. 2b,c). It passes vertically and laterally intothebeddedgypsum in thecentralpart of thebasin and into gypsiferous mudstone or bedded gypsum (with a lenticular geometry) in the periphery of thebasin (Figs. 5 and 6). In somehorizons, the facies areassociated witha few thin 2-5 em thickcoal bands.
Nodulargypsum scarcely occursin gray mudstone separated fromeach other by a thin mud film. Nodules rangefrom 2-8 cm in size.
Interpretation.-The gray color usually interpreted as a reflecting reducing condition at or just below the sedimentation surface. Such conditions likelyoccurbeneath thick saline water masses in a lake or back-swamp environment (Collinson 1978). Such organically rich sediments may be deposited in an environment having little detrital input such as a flood plain or swamp on a coastal setting(BeslyandCollinson 1991). Because thisfacies grades vertically and laterally into gypsiferous horizons, it may be interpreted as beinga depositof a swamps adjacenttoa saline playa.
Interpretation.-Gypsiferous mudstone facies are commonly foundwithin salinemudflats at theperiphery of recentplayas (Hardie et al. 1978; Handford 1982). Shearman (1963) and Kinsman (1966) assert that discoidal gypsum crystals on the AbuDabi coastalsabkhas were formed by displacive growth in carbonate deposits which are formed by capillary evaporation in the early stage of diagenesis. Ergiin (1988) noted that calcareous mudstone having similar discoidal gypsum crystals were verycommonin Tuz Galti (saltlake in central Turkey). These clusters grew within mudstone as a result of changes in the hydrochemical regimes of the basin
25
SEDIMEN1OLOGY OF CONTINENTAL SABKHA PLAYA COMPLEX, TURKEY
Figure 5. Organic rich mudstone (Facies 4) - gypsiferous mudstone (Facies 5) - stratified gypsum (Facies 6) interbeds (Sarpinbali measured section).
Figure 6. Organic richmudstone (A) andstratified gypsum (B).
(El-Tabakh et al. 1997). In the investigated area, the desiccation cracksindicate dry mudflat facies that developed at drying period. The lateral and vertical transition of this facies to lenticular bedded stratified gypsums shows thatthis facies hasbeendeposited on thedrymudflat around theplaya. Facies 6. Stratified Gypsum
Thefacies is characterized by thin to laminar bedding (Fig. 6). The individual bed thickness is 2-5 em, The facies is composed of interbeds of stratified gypsum bearing aligned 26
macrocrystals and gray-green clay laminae. Gypsum veins werealsodeveloped incracksparallel totheclaylaminae. On somelevels, wavy bedding is common. Thestratified gypsum is generally transitional in relation to the organic rich mudstone facies at lower levels (Fig. 6),andwithgypsiferous mudstone facies (Facies 5) at upper levels. The facies has a wide lateral continuity in the middle part of sequences and forms lenticular bodies at lower and upper levels of the sequences. Thewidth of the stratified gypsums are up to 5060 m. Tepee structures havebeendeveloped in the stratified gypsums neartheedgeof the basin (Fig. 8).
TORKMEN ANDOZKUL STRATIGRAPlllC CORRELATION AND PALEOGEOGRAPlllC EVOLUTION
Figure 7. Sigmoidal gypsum in gypsiferous mudstone (Facies 5).
Figure 8. Tepee structures in bedded gypsums (Kaldirim measured section).
Interpretation.-Due to the presence of the aligned macrocrystalline, primary gypsum crystals, the stratified gypsum units are interpreted as beingformed in very shallow waters (Schreiber 1978; Aigner and Bachmann 1989). The restricted lateral extension of the unit indicates that the interstratified gypsum-mudstone units were precipitated by the evaporation of a thin saline water layer (brine-sheets) occasionally covering the mudflats (Schreiber et al. 1976; Aigner and Bachman 1989; Orti 1997a,b; Orti and Salvany 1997; Salvany 1997).
The Neogene Karakeeili basin is located in an intermontane depression and has notbeenaffected by tectonic events. That makes facies correlation quite easy. Regularand continuous facies changes havebeenobserved fromtheedgetothecentral part of the basin(Fig.9). At the north-northeastern margin of the basin in the lower part of the Go~ Hill section (Fig. 3c),the mudflat facies which consists of an alternation of red andgray-green mudstone, passesupwardintoa playa-mudflat facies whichconsists of gypsum and gypsiferous mudstones. Thissequence, comprised mainly bythemudflat facies, passes into the playafacies of theplaya-mudflats environment to the southwest toward the centerof the basin (Fig.9). Sarpinbasi and Kocalar Yokufu sections showsimilarfeatures (Fig.3ab). These sections are dominated by playa-salty mudflat facies thatconsists of interbedded stratified gypsum (Facies 6) and gypsiferous mudflats (Facies 5). Alongthe south- southwest part of the basin, in the Armutlubasi and Kaldirirn sections, the salty mudflat and swamp facies are dominant (Fig.2ab). Cross-bedded gypsarenite found in some horizons of the Kaldirirn section were probably developed on dunes at the edgeof the basin. Alluvial fan deposits, formed by subaerial debris flows, are common at the north - northwest part of the basin. Paleocurrent analysis done on these fan deposits have pointed the currentdirection towards south-southeast Most of the coarse clasts were derived from Pre-Miocene terrains that border the basin along north and northwest (Fig. 1). Another fan complex had developed along south-southeast margin and at the central part of the basin. The fan deposits aremonogenic in character andwerecompletely derived from nearby granites. Four different depositional environments have been determined in the Karakecili basin. These are: 1- Alluvial fans that spread out from north-northwest and southsouthwest margins of thebasintowards thecentral part of the basin; 2- Dunes, which have limited distribution at the southwest part of the basin; 3- Swamp and salty mudflats alongthe southwest andnortheast margin of the basin; and4The ephemeral lake, which forms the basin center and occasionally is changed to a dry mudflat (Fig. 10). In conclusion, the sediments in the Karakecili basin can be classified as a typical playa complex developed in an The occurrence of regular intennontanous setting. alternations of dry mudflats and playa facies in the centerof the basin indicates a periodic desiccation which happened during the filling of the basin. Thelenticular gypsum bodies arecommonat the upperpart of the measured section in all sitesof the basin. This pointsout that a large numberof small salinelakes were developed on the mudflats.
27
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.
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3 km
-
