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The East Anatolian fault system (EAFS) is the 80-km-wide, 700-km-long, NE-trending sinistral strike-slip fault system forming a seismically very active intracontinental transfom fault boundary. It is located between Karlıova County in the northeast and Karataş-Samandağ counties in the southwest, and forms the southeastern boundary of the Anatolian platelet.
Turkish Journal of Earth Sciences (Turkish J Earth Sci.), Vol 21, 2012,ET pp.AL 547570 Copyright âTĩBTAK S ầOLAK doi:10.3906/yer-1002-14 First published online 16 August 2011 The Palu-Uluova Strike-Slip Basin in the East Anatolian Fault System, Turkey: Its Transition from the Palaeotectonic to Neotectonic Stage SERAP ÇOLAK1, ERCAN AKSOY1, ALİ KOÇYİĞİT2 & MURAT İNCEÖZ1 Fırat University, Deparment of Geological Engineering, TR–23119 Elazığ, Turkey (E-mail: eaksoy@firat.edu.tr) Middle East Technical University, Department of Geological Engineering, Active Tectonics and Earthquake Research Laboratory, Üniversiteler Mahallesi, Dumplupınar Bulvarı, TR–06800Ankara, Turkey Received 16 February 2010; revised typescripts received 19 June 2010, 17 January 2011 & 16 June 2011; accepted 08 July 2011 Abstract: The East Anatolian fault system (EAFS) is the 80-km-wide, 700-km-long, NE-trending sinistral strike-slip fault system forming a seismically very active intracontinental transfom fault boundary It is located between Karlıova County in the northeast and Karataş-Samandağ counties in the southwest, and forms the southeastern boundary of the Anatolian platelet The Palu-Uluova basin is one of several strike-slip basins located along the EAFS It is surrounded by several push-ups such as the Karaömerdağı, Mastardağı and Askerdağı push-ups caused by the complexities peculiar to strike-slip faulting The Palu-Uluova basin consists of three sub-sections: two are NE-trending strike-slip sub-basins, the Uluova and the Palu-Kumyazı sub-basins, while the third is a ramp basin, the E–W-trending Yolüstü basin which links the earlier two sub-basins The Palu-Uluova basin is characterized and shaped by a 130-m-thick neotectonic basin infill (Palu Formation) and a series of bounding strike-slip fault zones such as the Sivrice, Adıyaman, Uluova, Elazığ, Pertek and Yolüstü fault zones The Palu Formation is an undeformed fluvio-lacustrine sedimentary sequence The youngest palaeotectonic rock-stratigraphic unit is the Upper Miocene–Lower Pliocene Çaybağı Formation, deposited in a ramp type of intermontane basin bounded and controlled by the reverse faults The Çaybağı Formation is intensely deformed (steeply tilted, folded and thrust to reverse-faulted) on a regional (mappable) scale The compressional deformation pattern of the Çaybağı Formation is truncated, sealed and overlain with angular unconformity by the nearly horizontal undeformed Plio–Quaternary Palu Formation This regional angular unconformity reflects: (a) a series of pre-Late Pliocene regional tectonic inversions (e.g., type of the tectonic regime, style of deformation and nature of magmatic activity), and (b) the timing of the major transition from the folding and thrust to reverse faulting-dominated palaeotectonic period into the strike-slip faulting-dominated neotectonic period is Late Pliocene Key Words: East Anatolian fault system, Palu-Uluova strike-slip basin, intermontane basin, Turkey Doğu Anadolu Fay Sistemi Üzerindeki Palu-Uluova Doğrultu Atımlı Fay Havzası, Türkiye: Paleotektonik Dönemden Neotektonik Dửneme Geỗi ệzet: Dou Anadolu Fay Sistemi (DAFS) 80 km genilikte, 700 km uzunlukta, KD-gidili, sismik bakmdan ỗok etkin, sol yanal dorultu atml ve kta iỗi dửnỹỹm tỹrỹ fay niteliinde bir plaka snrdr DAFS kuzeydouda Karlova ile gỹneybatda Karata-Samanda ilỗeleri arasında yeralır ve Anadolu plakacığının güneydoğu sınırını oluşturur DAFS üzerinde çok sayıda doğrultu atımlı havza yer alır Bunlardan biri Palu-Uluova doğrultu atımlı fay havzasıdır PaluUluova havzası, doğrultu atımlı faylanmalara özgü karmaşıklıklardan kaynaklanmış Karaömerdağı, Mastardağı ve Askerdağı gibi bazı bindirme (ters faylanma) yỹkselimleriyle ỗevrelenir Palu-Uluova havzas ỹỗ alt bửlỹmden oluur Bunlardan ikisi KD-gidili dorultu atml alt havza, ỹỗỹncỹsỹ ise, DB gidili bir dağarası havza olup ilk iki alt havzayı birbirine bağlar Bunlar sırayla KD-gidişli Uluova, Palu-Kumyazı ve Yolüstü alt havzalarıdır Palu-Uluova havzası 130 m kalınlıkta neotektonik bir havza dolgusu (Palu Formasyonu) ve bir seri kenar fay zonu ile karakterize edilir ve şekillenir Önemli kenar fay zonları Adıyaman, Sivrice, Uluova, Elazığ, Pertek ve Yolüstü fay zonlarıdır Neotektonik havza dolgusu Palu Formasyonu ile temsil edilir Palu Formasyonu deformasyon geỗirmemi (yatay konumlu) bir gửl-akarsu sedimanter istifinden oluur En genỗ paleotektonik birim Geỗ MiyosenErken Pliyosen yaşlı Çaybağı Formasyonu’dur Çaybağı Formasyonu ters faylarla sınırlanıp denetlenmiş bir daaras havzada ỗửkelmitir ầayba Formasyonu bửlgesel ửlỗekte (haritalanabilir) ve yeince deformasyon geỗirmitir (dikỗe eimlenmi, kvrmlanm ve ters faylanmtr) ầayba Formasyonunun skmaya bal deformasyon biỗimi, PliyoKuvaterner yal ve deformasyon geỗirmemi 547 PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM olan Palu Formasyonu tarafndan yer yer ỹstten andrlarak kesilmi ve aỗl bir uyumsuzlukla ửrtỹlmỹtỹr ki formasyon arasndaki bửlgesel ửlỗekli bu aỗl uyumsuzluk, aadaki sonuỗlar yanstmaktadr: (a) Geỗ Pliyosen ửncesi gerỗeklemi bir seri tektonik dửnỹỹmỹ ( ửrnein: tektonik rejimin tỹrỹ, deformasyon biỗimi ve magmatik etkinliğin karakterindeki değişme gibi), (b) kıvrımlanma ve bindirme faylarıyla karakterize edilen paleotektonik dönemden, doğrultu atımlı faylanma ile karakterize edeilen neotektonik dửneme geỗiin Geỗ Pliyosende gerỗekletii, baka bir deyile neotektonik dửnemin balangỗ yann Geỗ Pliyosen olduunu yanstmaktadr Anahtar Sửzcỹkler: Dou Anadolu fay sistemi, Palu-Uluova doğrultu atımlı fay havzası, dağarası havza, Türkiye Introduction One of the best-known intracontinental transform fault systems is the NE-trending East Anatolian fault system (EAFS) located between Karlıova in the northeast and Samandağ-Karataş counties in the southwest (Figure 1a) It meets the NW-trending dextral North Anatolian fault system (NAFS) around Karlıova and forms a conjugate system with it The EAFS is an intra-continental sinistral strike-slip shear zone about 80 km wide and 700 km long It cuts across and sinistrally displaces the Bitlis Suture Zone formed by the final continent-continent collision of the Arabian plate to the south with the Eurasian plate to the north during the Late Middle Miocene (Şengör & Yılmaz 1981; Dewey et al 1986) However, the timing of transition from the fold- and thrust-dominated to the reverse fault-dominated palaeotectonic stage to the strike-slip faultingdominated neotectonic stage, i.e the initiation age of the neotectonic stage and formation of related major structures such as the Anatolian platelet, the NAFS and the EAFS in east-southeastern Turkey, is still under debate Several views on this problem have been expressed The first is that the Late Serravalian continent-continent collision of the Arabian and Eurasian plates is the initiation age of the strike-slip neotectonic stage (Şengör 1980; Şengör et al 1985; Şaroğlu & Yılmaz 1987) The second idea, expressed by Faccenna et al (2006), is that the ‘NAFS’ resulted from slab-detachment beneath the Bitlis Suture Zone in the Late Miocene–Early Pliocene They suggested that slab detachment beneath the collisional belt triggered: (a) accretion of slab-retreat to the west owing to the increase in the slab pull-force, (b) the indentation of the continent in the collisional area, and (c) the emergence of conditions that permitted the lateral westward escape of material and formation of the ‘NAFS’ Although the slab-detachment model 548 seems to be a more plausible explanation for the formation of both the Anatolian platelet and its boundary fault systems (NAFS and EAFS), the time range (Late Miocene–Early Pliocene) fits poorly with the initiation age of the neotectonic regime in eastern Anatolia, as there were a series of coeval processes linked to the major slab-detachment event which predated the onset of a strike-slip neotectonic regime in eastern Anatolia, indicating a Late Pliocene initiation age of the neotectonic regime The third idea, suggested by Göğüş & Pysklywec (2008), related to the nature of the neotectonic regime on the eastern Anatolian plateau, is that the eastern Anatolian plateau is the site of lithospheric thinning, plateau uplift, heating and synconvergent extension resulting from delamination of the mantle lithosphere, i.e the huge central section of the east Anatolian plateau is extensional while only its northern and southern fringes are compressional They also reported that the Kağızman, Tuzluca, Hınıs, Karlıova and Muş basins are E–W-trending, normal fault-controlled extensional basins developed as a natural response to the synconvergent extension In contrast to the idea of these authors, there is a big discrepancy between the site of extension they suggested and the nature of both the structures and style of deformation patterns observed in eastern Anatolian plateau (Koỗyiit et al 2001) The central part of the east Anatolian plateau is shaped by en échelon folds, E–W-trending thrust-reverse faults, N–S-trending extensional features such as normal faults and fissures, NE- and NW-trending strike-slip faults and related pull-apart basins, i.e the Kağızman, Tuzluca, Hınıs, Karlıova and Muş basins are strikeslip fault-controlled pull-apart basins, not normal fault-controlled grabens These locally extensional but regionally compressional features characterize strike-slip faulting and the related prominent Mediterranean Sea FS BSZ Karlıova basin infill Malatya pull-apart basin Lake Hazar negative flower structure Hazar pull-apart basin Palu-Uluova pull-apart basin Kovancılar pull-apart basin rm -Çe Palu Ge collision zone strike-slip fault with normal component strike-slip fault with reverse component strike-slip fault settlement LEGEND one lt z M w : 6.1 N 25 km 39 KGFZ− Karlıova-Göynük fault zone KFZ− Karakoỗan fault zone DSFS Dead Sea fault system EAFS: East Anatolian fault system NAFS− North Anatolian fault system au f nỗ lt BNGệL ầevrimpnar KARAệMER DAI PUSH-UP KF Z Figure 08.03.2010 au ik f 16.03.2010 M w : 4.1 Lice Karakoỗan pull-apart basin Bingửl pull-apart basin Lake Hazar Atatürk Dam an m ya ı Ad Dam ASKER DAĞI Yolüstü fault zone Keban e on tz l u fa one t z Sivrice 100 200 km N Arabian Plate Samandağ EA e n zo ul Uluova fa lt Eurasian Plate e zığ Figure b Platetet NAFS Karataş Ankara Anatolian African Plate au on lt z Ela fau ELAZIĞ zon e 40 KG FZ Figure (a) Simplified map showing major plates and their boundary faults in Turkey and surrounding areas (b) Simplified map showing the Yarpuzlu-Bingöl section of the East Anatolian fault system, its major fault zones and the studied area (box-shaped insert on the map; Koỗyiit et al 2003) a f ce r ive Black Sea ri Siv us subd ypr uct n-C ion z one gea e South A b Yarpuzlu Karakaya Dam Fır at r t aul k te t ault Fırat f kil f Bas r Pe Keban Dam ul DSFS fa Aegean Sea 39 S ÇOLAK ET AL 549 PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM compressional neotectonic regime rather than a tensional tectonic regime in the eastern Anatolian plateau This was also indicated by the fault plane solution diagrams of large destructive earthquakes such as the 1966 Varto, 1971 Bingưl, 1976 Çaldıran, 1983 Horasan-Narman and 2000 Karlıova (Bingöl) earthquakes (Tan et al 2008) The fourth idea (Koỗyiit et al 2001) was based on the field data They stated that 9.5 Ma elapsed between the earlier palaeotectonic stage and the onset of the strike-slip faulting-dominated neotectonic stage in the east Anatolian plateau This transitional period is an elapsed time interval during which occurred a series of regional inversions such as the inversion in tectonic regime, style and pattern of deformation, nature of magmatic activity, the type of basins and their stratigraphy, drainage system and also in the source of seismic activity For this reason, the Late Pliocene initiation age of the strike-slip neotectonic regime post-dates both the slab-detachment and mantle lithosphere delamination (Hempton 1987; Koỗyiit & Beyhan 1998; Koỗyiit et al 2001) Various inversions are well-recorded and reflected by basin infills and their deformation patterns For this reason, detailed stratigraphy, sedimentology and structural analyses of major and minor structures or fault arrays recorded in deformed and undeformed basin infills have a key importance in determining the transition from the palaeotectonic stage to the neotectonic stage A number of basins occur along the EAFS, as along the NAFS (Hempton et al 1983; Hempton & Dunne 1984; Westaway & Argar 1996; Koỗyiit 1989; Aksoy et al 2007) They include, from NE to SW, the Bingửl, Karakoỗan, Kovanclar, PaluUluova, Lake Hazar, Hazar and Malatya strike-slip basins (Figure 1b) These basins have two basin infills separated from one another by an intervening angular unconformity, i.e they are superimposed basins (Koỗyiit 1996) This stratigraphical relationship and the records of other inversions together reveal that the strike-slip neotectonic regime emerged in eastsoutheast Turkey from the Late Pliocene onwards The present paper aims to introduce new field data obtained from the Palu-Uluova strike-slip basin in the EAFS These data fit well with the Late Pliocene onset age of the neotectonic regime in this basin The Bingöl-Yarpuzlu section of the EAFS is structurally very complicated In this section, 550 the master fault of the EAFS displays numerous srike-slip complexities such as extensional to compressional step-overs, single and double bending and bifurcations resulting in a series of push-ups (e.g., Karaömerdağı, Askerdağı and Mastardağı push-ups) and strike-slip basins of dissimilar nature, geometry and size (e.g., the Bingöl pull-apart basin, and the Palu, Uluova, Lake Hazar, Hazar and Malatya fault-wedge types of strike-slip basins) (Figures 1b & 2) The master fault of the EAFS begins to bifurcate into several fault zones and single faults around Palu County, namely the Pertek, Elazığ, Uluova, Yolüstü, Sivrice and Adıyaman fault zones (Figure 1b) With regard to the Palu-Uluova strike-slip basin, these structures are described in more detail below Apart from these, other significant structures include the Baskil fault, the Lice-ầermik fault zones, the Genỗ fault and the Frat fault Of these the first-named two form the northwestern and the southeastern boundaries of the EAFS respectively (Figure 1b) However, these latter four structures are outside the scope of the present paper Stratigraphic Outline Palaeotectonic Units Based on their age and deformation pattern, the rocks exposed in and around the Palu-Uluova basin can be classified into two categories: (1) palaeotectonic rock units, and (2) neotectonic rock units Palaeotectonic units are the intensely deformed (folded and thrust to reverse-faulted) rocks of pre-Late Pliocene age Palaeotectonic units consist of the Jurassic–Lower Cretaceous Guleman ophiolites, the Senonian Elazığ magmatic rocks, Maastrichtian–Upper Palaeocene Hazar Group, the Middle Eocene Maden Group, the MiddleUpper Eocene Krkgeỗit Formation and the Upper Miocene–Lower Pliocene Çaybağı Formation (Sungurlu et al 1985; Hempton 1985; Herece & Akay 1992; Aksoy 1993; Çelik 2003; Koỗ Tagn 2009) All but the latter rock-stratigraphic unit (Çaybağı Formation) which is the youngest palaeotectonic unit, are outside the scope of the present paper However, in order to distinguish between the palaeotectonic units and the neotectonic units, the stratigraphy and deformation pattern of the Çaybağı Formation will be described in more detail S ÇOLAK ET AL Çaybağı Formation The Çaybağı Formation, first named by Türkmen (1988), was later studied in more stratigraphical and sedimentological detail by Koỗ Tagn (2009) It comprises a thick (measured maximum thickness is 1987 m) fluvio-lacustrine sedimentary sequence made up of numerous lithofacies (Figure 3) Both the top and bottom contact relationships, particularly its lower half and bottom contact relationship with older rocks, are poorly exposed owing to superimposed palaeotectonic and neotectonic structures such as overturned folds, reverse and strike-slip faults within the zone of active deformation (East Anatolian fault system) in the study area Therefore, only faulted, dissected and exposed parts of the Çaybağı Formation could be measured in the study area (a in Figure 2; Figure 3) For this reason, the thickness of the Çaybağı Formation varies from ~2 km to 0.8 km in places However, its normal stratigraphical basal contact relationships with older rocks are well exposed in other areas including Perisuyu River, Darıkent, Akpazar and Ekinözü settlements located outside the study area from 11 to 34 km north-northwest of Palu County (Koỗyiit 2003) At these localities, the ầayba Formation overlies with angular unconformity a shallow marine to fluvial sedimentary sequence comprising a sandstone-marl and Nummulite-bearing limestone alternation (Krkgeỗit Formation) of Middle–Late Eocene age (Türkmen 1991), and it displays both a lateral and vertical transitional contact relationships with the Middle Miocene–Lower Pliocene volcano-sedimentary Karabakır Formation (Çetindağ 1985; Sungurlu et al 1985; Koỗyiit 2003) In the same region, both the Karabakr and the Çaybağı formations are underlain comformably by a flysch sedimentary sequence (‘Kuşaklı Flysch’) with abundant intercalations and olistholiths of Aquitanian–Burdigalian reef structures (Koỗyiit 2003) Volcanic rocks (dacite, andesite, rhyolite, basalt and their pyroclastites) of the Karabakır Formation were previously reported to be the west-southwestern continuation of the Upper Miocene–Lower Pliocene Solhan Volcanics (Seymen & Aydın 1972; Yılmaz et al 1987; Ercan et al 1990) Consequently, the Çaybağı Formation is not exposed within the Uluova basin due to a thick cover (Quaternary neotectonic infill) and water accumulation behind the Keban Dam In addition, it may have been faulted and considerably downthrown For easy understanding of the various lithofacies of the Çaybağı Formation and their depositional settings, the measured stratigraphical section (Figure 3) of the Çaybağı Formation and other measured sections carried out outside the study area were compiled, modified and simplified into four members These are, from bottom to top, the Hacısamdere, the Yılankaya, the Ziyarettepe and the Arılar members (Figure 4) The Hacısamdere member is the lowest facies of the Çaybağı Formation It overlies with angular unconformity the Upper Eocene–Lower Oligocene clastics and Nummulite-bearing limestones exposed northeast of Palu, but outside the study area (Sungurlu et al 1985) The Hacısamdere member is a fining-upward sequence deposited by a fluvial system It consists of polygenetic basal conglomerate and sandstone at the bottom but an alternation of siltstone, mudstone, channel conglomerate and claystone towards the top (Figure 5) The measured thickness of this member is about 350 m (1 in Figure 4) The Yılankaya member consists of a thick-bedded conglomerate, sandstone and red mudstone alternation It displays welldeveloped graded bedding, planar cross-bedding and pebble imbrication sequence about 200 m thick which indicates a braided fluvial depositional system Both the Hacısamdere and the Yılanlı members characterize marginal facies comprising the lower part of the Çaybağı Formation These two members are not exposed within the Palu-Uluova basin owing to faulting and deep burial However, they display both lateral and vertical gradations with the Ziyaret Tepe member outside the study area (Figure 4) The Ziyarettepe member is the most widespread unit in the study area (Figure 2) Its measured thickness is about 1175 m (3 in Figure 4) It is represented by a thick fluvio-lacustrine sedimentary sequence composed of an alternation of cross-bedded conglomerate, cross-bedded to parallel laminated sandstone, red mudstone, clayey lacustrine limestone and marl with coal and tuffite intercalations In addition the Ziyaret Tepe member is full of softsedimentary features such as slump folds, broken formation, normal and reverse growth faults, load casts, flame structures, sand dykes and convolute 551 552 Kavaktepe ca UO VA S BA basin infill Siv IN rice e e Lak 1647 E Ha zar Ýlemi Gezin va uo l U d 38 30 an am y ı Ad Kumyazý Siv Yolüstü a N ne zo o lt z km lt fau au ef ric Öre e n PA k nci a MF LU SI N MF b Palu strike-slip fault strike-slip fault with normal component strike-slip fault with reverse component oblique-slip normal fault oblique-slip reverse fault master fault (Y-shear) settlements location of measured sections in Figure Baltaşı BA ASKER DAĞI PUSH-UP Yolüstü fault zone Hazar Basin c 2171 zon e e on tl z u fa Aa ỗme Keban Dam Lake ne t zo faul laz ult k fa Per te Figure Simplified map showing the Palu-Uluova strike-slip basin and its bounding faults Ballı UL upper Pliocene−Pleistocene Palu Formation upper Pliocene travertine deposits upper Miocene−Lower Pliocene Çaybağı Formation 39 15 pre-Upper Miocene basement rocks Quaternary alluvial fan PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM 400 alluvial fan PALU FORMATION S ÇOLAK ET AL EXPLANATIONS horizontal lamination 800 Gastropoda Lamellibranch Lamellibranch fragments Ostracoda macrophyte fragments alluvial fan (distal fan) 300 palaeocurrent direction imbrication lag deposit conglomerate FORMATION ÇAYBAĞI 200 rhizoliths gravel orientation matrix-supported conglomerate planar cross-stratified conglomerate sandstone ÇAYBAĞI FORMATION delta front - shallow - open lacustrine 700 macrophyte 600 lenticular shaped sandstone planar cross-stratified sandstone trough cross-stratified sandstone ripple cross-laminated sandstone red mudstone delta front - open lacustrine 100 500 siltstone grey claystone carbonaceous claystone clayey limestone marlstone limestone Keban Dam Lake fmc 210 sand gravel clay silt clay silt meter coal fmc sand 21530 gravel Figure Measured stratigraphic column of the Çaybağı and Palu formations (2 km N of Yolüstü village) For location of the section, see Figure (modified and simplified from Koỗ Tagn 2009) 553 Thick 812 Lithology (m) Description 4− alluvial fan facies association represented by massive conglomerate, red mudstone and grey-red mudstone alternation 200 1175 3− delta top, delta front, shallow lacustrine and open lacustrine facies association represented by clayey limestone, marl, conglomerate, sandstone, mudstone with organic material, claystone and peat 2− low-sinuosity river facies association represented by conglomerate, sandstone and red mudstone 350 total: 1987 2− Yılankaya Member 3− Ziyaret Tepe Member 1− Hacısam Dere Member Çaybağı Formation Unit Figure Generalized stratigraphic column of the Çaybağı formation 554 1− braided river facies association represented by conglomerate and sandstone preMiocene Late Miocene − Early Pliocene Age 4− Arılar Member PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM angular unconformity older rocks: mostly ophiolitic, magmatic and sedimantary rocks S ÇOLAK ET AL b a Figure General view of the red mudstone (a) and conglomerate (b) alternation comprising the Hacısamdere member of the Çaybağı formation (2 km NE of Yolüstü village, view to NW) For location of the photograph, see Figure bedding which indicate the fault-controlled sedimentation of the ầayba Formation (Hempton & Dewey 1983; Koỗ Tagn & Türkmen 2009) Both the lithofacies and syn-sedimentary structures in the Ziyaret Tepe member reveal that it was deposited in delta front and shallow to open lake depositional settings (Figure 3) The fourth and final member is the Arılar member, measured to be about 812 m thick (4 in Figure 4), which comprises the uppermost part of the Çaybağı Formation It is a coarsening-upward sequence and consists of a matrix-supported, polygenetic boulder-block conglomerate and red-grey mudstone alternation Pebbles in the conglomerates reach up to 65 cm in diameter and have been derived from the northerly located Senonian magmatic rocks and the MiddleUpper Eocene Krkgeỗit Formation The various lithofacies types comprising the Arılar member reveal that it was deposited by braided to meandering high energy fluvial systems including alluvial fans and flood plain Consequently, the entire Çaybağı Formation is characterized by a thick fluvio-lacustrine sedimentary sequence about km thick It is assigned a Late Miocene–Early Pliocene age, based on its rich fossil content, including Candona neglecta Sars, Candona (Candona) paralella pannonica Zalanyi, Heterocypris salina (Bradyi), Cyprideis sublitoralis (Pokorny), Cyprideis anatolica Bassiouni, Cyprideis (Cyprideis) anatolica Bassiouni, Cyprideis pannonica (Mehes), Cyprideis torosa (Jones), Valvata debilis Fuchs, Valvata piscinalis (Müler), Hydrobia ventrosa Montfort, Margaritafera (Pseudounio) flabellata trajani Michailovsky, Potomida (Potomida) sibinensis (Penecke), Unio (Crassunio) batavus (Nillsson), Unio aff hilberi Penecke, identified at its different levels (Koỗ Tagn 2009) This age is also supported by some other field observations As mentioned previously, the Çaybağı Formation rests conformably on the Aquitanian–Burdigalian ‘Kuşaklı Flysch’ and displays both vertical and lateral gradations into the volcanosedimentary sequence of the Upper Miocene–Lower 555 PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM Pliocene Karabakır Formation in the north and outside the study area (Sungurlu et al 1985; Koỗyiit 2003) The radiometric age of the youngest volcanic rocks comprising the uppermost horizon of the Karabakır Formation is 4.1±0.32 Ma (Sanver 1968), showing that the Karabakır Formation extends into the Lower Pliocene Neotectonic Units (Strike-slip Basin Infill) Except for the units deformed in the pressure ridges, these are, in general, nearly horizontal, undeformed and weakly lithified to unconsolidated sedimentary deposits of Plio–Quaternary age Neotectonic units are of two major categories: (1) travertine, and (2) fluvio-lacustrine sedimentary sequence (Palu Formation) They mostly occur in the strike-slip basin (Figure 6) Travertines – Based on the age, degree of lithification and the depositional setting, travertines exposed in the study area are either older and highly lithified travertines (Baltaşı travertines) or actively forming recent travertines Older travertines are well exposed as uplifted and fault-suspended outcrops ranging in area from a few 10 m2 to a few km2 along the fault segments comprising the northeastern parts of the Adıyaman fault zone around Baltaşı village (Figure 2) These are laminated, thick-bedded to massive, highly porous and iron-rich carbonate accumulations precipitated from the CaCO3-rich ground water springs along fault segments and open cracks (fissure ridges) formed during the initial stage of strike-slip faulting They overlie with angular unconformity the underlying Jurassic–Lower Cretaceous ophiolitic rocks (Guleman ophiolite), but have a free erosion surface at the top The Baltaşı travertines begin with basal thin and non-mappable basal clastics, which are overlain by an alternation of thin- and thick-bedded to massive travertine horizons up to about 35 m thick around Baltaşı village Development of the Baltaşı travertines has now ceased The Baltaşı travertines are one of the lithofacies formed during the early development stage of the strike-slip basin Later, the Baltaşı travertines were uplifted, dissected and exposed as fault-suspended terraces at higher elevations above the present basin floor, while their lateral clastic counterparts are being locally deformed and thrown 556 into folds and reverse faults along the pressure ridges bounded by the strike-slip faults with reverse-slip component One such well-developed pressure ridge is exposed on Orta Hill located approximately km south-southwest of Örencik village This locality could not be indicated on the Figure owing to the small scale of the map Based on their structure, texture, origin, stratigraphical position, and tectonic setting, the Baltaşı travertines can be correlated with both the Kzlca Travertine exposed in Kzlca village (Karakoỗan-Elaz) (Koỗyiit 2003) and the Hỹdaihamam Travertine (Sandkl-Kỹtahya) (Saraỗ 2003) The Kzlca travertine is also laminated to thick bedded, iron-rich, nearly horizontal and 80 m thick It overlies with angular unconformity the Upper Miocene–Lower Pliocene Karabakır Formation volcanics at its base, while it is overlain conformably by Early Quaternary coarse-grained terrace conglomerate The Hüdaihamamı travertines are likewise thick-bedded to massive, overlie with an angular unconformity the Palaeozoic metamorphics beneath, and display both vertical and lateral transitions into Plio–Quaternary fluvial conglomerates A mammalian fossil, Mimomys Plioacenicus, which indicates a Upper Pliocene horizon (MN 16), was identified within these fluvial clastics (Saraỗ 2003) Consequently, a relative Late Pliocene–early Quaternary age can also be assigned to the Baltaşı travertine comparable with both the Kızılca and Hüdaihamamı travertines The second category of travertines is actively growing carbonate precipitations exposed along the master fault of the Sivrice fault zone cutting across the basin floor These travertines occur in diverse-sized (a few m2 to 300 m2) and fault-parallel aligned patchlike outcrops located approximately km west of the Kumyazı village (c in Figure 2) These are the fissureridge type of travertine made up of partly lithified, laminated to massive and highly porous Quaternary carbonate precipitations These conformably overlie the fan-apron deposits beneath, and they have a free depositional to erosional surface at the top The measured thicknes of the actively growing travertines is about m (c in Figure & Figure 7c) Palu Formation – First recognized and named by Çetindağ (1985) in Palu County, it consists mainly S ÇOLAK ET AL Lithology I N F I L L ) ( B A S I N U N I T S N E O T E C T O N I C braided river deposits travertine 35 angular unconformity pre-Late Pliocene fan delta deposits lacustrine deposits 140 PA L U F O R M AT I O N BALTAŞI LATE PLIOCENE L AT E P L I O C E N E − P L E I S T O C E N E HOLOCENE fluvial deposits (m) travertine Age Unit Thick older rock (palaeotectonic units) Figure Generalized stratigraphic column of the Palu Formation 1– matrix-supported conglomerate, 2– planar cross-bedded conglomerate, 3– trough cross-bedded conglomerate, 4– planar cross-bedded sandstone, 5– trough cross-bedded sandstone, and 6– travertine of coarse clastics with finer-grained lacustrine sedimentary intercalations (Figure 6) The Palu Formation is well-exposed along the northnortheastern margin of the Palu-Uluova basin, particularly in the west of Palu County It rests with angular unconformity on the erosional surface of the intensely deformed (steeply tilted to folded) various facies of the palaeotectonic units (Figures 7f & 8) The basal clastics representing the lowermost facies of the Palu Formation consists of unsorted, polygenetic, weakly lithified and matrix-supported boulderblock conglomerates Pebbles to blocks (up to m in diameter) are partly well-rounded to sub-rounded and partly angular clasts of mostly ophiolitic rocks such as spilite, peridotite, serpentinite, radiolarite, recrystallized limestone, sandstone, andesite, and basalt set in a sandy matrix These basal clastic rocks are succeeded conformably in turn by an alternation of coarse-grained conglomerate, sandstone, troughto planar cross-bedded sandstone, planar- to troughcross-bedded conglomerate (Figures & 9) These well-bedded and nearly flat-lying coarse clastics are overlain by another diagnostic facies (fandelta deposit) (Winsemann et al 2009) made up of an alternation of claystone, mudstone, siltstone, rippled sandstone and Gilbert-type cross-bedded conglomerate (Figures & 10) The thickness of the Gilbert-type cross-bedded conglomerate packages may reach up to m in places The uppermost part of the Palu Formation consists of weakly consolidated to loose mudstone, sandstone and conglomerate lenses Although the topmost part of the Palu Formation is a free erosional surface, it is also overlain by a series of fault-parallel aligned alluvial fans along the marginboundary faults of the Palu-Uluova strike-slip-basin (Figures & 7b–e) The total thickness of the Palu Formation is 130 m, based on the measured sections and geological cross-section studies No fossils could be identified in the Palu Formation However, as previously explained, outside the study area it conformably overlies the Upper Pliocene Kızılca travertine, which is both the litho- and bio-stratigraphical equivalent of the Baltaşı travertines in the study area In addition, both the non-deformed pattern and the stratigraphical relationship (angular unconformity) between the nearly horizontal undeformed Palu Formation and the intensely deformed (steeply tilted, folded and reverse-faulted) Upper Miocene–Lower Pliocene Çaybağı Formation together reveal that the relative age of the Palu Formatiın is Plio–Quaternary 557 Late Pliocene − Pleistocene Quaternar y Unit a Keban Dam north of Yolüstü village (modified and simplified from Koỗ Tagn 2009) m 120 f AU b near southwest of Palu town TQp c southwest of Kumyaz village Tỗ d upper Cretaceous volcanic rocks Yolỹstỹ village e west of İlemi village fluvio-lacustrine sedimentary braided river deposits: poligenetic basal conglomerate, sandstone, channel conglomerate and claystone meandering river and flood plain deposits: thick-bedded conglomerate, sandstone and red mudstone alternation cross-bedded conglomerate, cross-bedded to parallel laminated sandstone, red mudstone m sequence: 20 alluvial fan deposits: matrix-supported, polygenetic, boulder-block conglomerates and red-grey mudstone alternation fan delta and alluvial fan deposits, travertine: unsorted, polygenetic, weakly lithified and matrix-supported boulder-block conglomerates; claystone, mudstone, siltstone Explanation Figure Correlation chart of the Palu-Uluova basin; (a–e) are measured stratigraphic columns; (f) field photograph showing the angular unconformity (AU) between the Çaybağı Formation (Tỗ) and the Palu Formation (TQp) Late Miocene Early Pliocene B a s i n i n fi l l Pa l u Fo r m a t i o n 558 Çaybağı Formation Age PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM S ÇOLAK ET AL AU TQp Tỗ Figure Close-up view of the angular unconformity (AU) between the steeply-tilted ầayba Formation (Tỗ) and the nearly horizontal Palu Formation (TQp) (2 km NW of Palu) For location of the photograph, see Figure The early deposited fluvial clastics of the Palu Formation are full of syn-sedimentary growth faults, mostly strike-slip and normal faults Another diagnostic lithofacies of the neotectonic infill is the travertine, precipitated from the CaCO3-rich water circulating along the strike-slip faults and emerging as springs Early deposited boulder-block conglomerates occur in two patterns: pressure ridges and fault terraces Either they have been deformed into a series of strike-slip fault-bounded lensoidal pressure ridges with long axes parallel or slightly oblique to the general trend of the master fault, or both the travertine and the early deposited boulderblock conglomerates have been elevated and dissected as fault-bounded terraces as a natural response to the activity on the marginal strike-slip faults of the PaluUluova basin Hence, fault-parallel alluvial fans have also been degraded Consequently, the combination of type of syn-depositional growth fault features, fault terraces, pressure ridges and degraded alluvial fans together reflect strike-slip faulting-induced deformation in the Palu-Uluova basin during the Plio–Quaternary neotectonic period At present, this is also indicated by the fault plane solution diagrams of the fault-related earthquakes, which reveal the neotectonic configuration of the Palu-Uluova complex strike-slip basin (Figures 1b & 2) Structural Geology Palu-Uluova Basin The morphotectonic characteristics of this basin were previously studied for a Master Thesis by Çolak 559 PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM Figure Close-up view of the nearly horizontal conglomerate-sandstone alternation comprising the Palu Formation (5 km NE of Yolüstü village) For location of the photograph, see Figure (2007) The Palu-Uluova depression is a two-armed strike-slip basin 78 km long and between and 14 km wide, located between Palu County in the northeast and Ballıca village in the southwest (Figure 2) Based on its nature and general trend, the Palu-Uluova basin is divided into three sub-sections These are, from east to west, the Palu-Kumyazı section, the Yolüstü section and the Uluova section The PaluKumyazı section is a NE-trending fault wedge-type of strike-slip basin about km wide and 26 km long located along the Sivrice fault zone and its master fault (Figure 2) The Uluova section is a NE-trending strike-slip basin 14 km wide and 40 km long located along the Elazığ and Uluova fault zones between Ballca-Kavaktepe and Aa ỗme-lemi settlements The intervening Yolüstü section, which links the other two sections, is an E–W-trending ramp-type of 560 basin about km wide and 12 km long located along the Yolüstü fault zone (Figure 2) Consequently, the Palu-Uluova basin is controlled by several fault zones of dissimilar trends and nature For this reason, it has a complex evolutionary history The angular unconformity, folds, reverse faults and the major fault zones to single faults which took a key role in the evolutionary history of the Palu-Uluova strikeslip basin are described and documented below Palaeotectonic Structures: Unconformities Folds and Angular In general, angular unconformities indicate the end of an earlier tectonic regime and seal the palaeotectonic regime-induced deformation pattern (Figures 7f & 8) In this frame, the latest palaeotectonic unit, the S ÇOLAK ET AL Gcb Ld Figure 10 Close-up view of the fan-delta deposits characterizing the Palu Formation Gcb– Gilbert-type of cross-bedding, Ld– Lacustrine deposits (2 km NW of Palu) For location of the photograph, see Figure Upper Miocene–Lower Pliocene Çaybağı Formation, has been steeply tilted and deformed into a series of anticlines and synclines trending E–W with limb angles of 20–80° (Figure 11) The Çaybağı Formation is folded both in the study area located along the EAFS, and also outside the study area and the EAFS (Koỗyiit 2003) The same formation has also been thrust or reverse-faulted in places (Koỗ Tagn & Tỹrkmen 2009) This deformation, caused by the NS-directed intra-continental convergence (Koỗyiit et al 2001), occurred towards the end of the deposition of the last and youngest palaeotectonic unit, the Upper Miocene–Lower Pliocene Çaybağı Formation This is indicated by both the regressive nature of the topmost sedimentary package of the Çaybağı Formation and the kinematic analysis of mappable folds developed in it (Figures 11 & 12) In contrast, the Plio–Quaternary Palu Formation, which rests with angular unconformity on the Çaybağı Formation, is weakly consolidated and nearly horizontal, i.e it experienced no regional deformation except for the pressure ridges and the fault-bounded margins of the strike-slip basin This clear contrast in age and deformation patterns of the units beneath and above the angular unconformity reveals strongly an inversion in the type of the tectonic regime and related style of deformation (folding and thrust to reverse faulting-dominated palaeotectonic regime) and the first emergence of a new tectonic regime, namely the strike-slip faultingrelated neotectonic regime in the study area Neotectonic Structures: Strike-Slip Faults Sivrice Fault Zone (SFZ) – This is a sinistral strike-slip fault zone 3–6 km wide, 138 km long and trending N60°E, located between Palu in the northeast and Yarpuzlu in the southwest (Figure 1b) 56 km of it traverse the study area (Figure 2) The Sivrice fault zone, which also contains the master fault of the EAFS, consists of closely-spaced, parallel to subparallel and diverse-sized (0.2–18 km) numerous fault segments However, most of the fault segments could not be plotted on the map due to its small scale Fault segments cut across the older ophiolitic rocks, displacing them, mostly sinistrally, up to 6.5–9 km (Aksoy et al 2007) and tectonically juxtaposing them with the younger Plio–Quaternary strike-slip basin 561 PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM Figure 11 General view of a mappable asymmetrical fold developed within the Çaybağı Formation (2 km NE of Yolüstü village, view to W) For location of the photograph, see Figure infill The Palu-Kumyazı section of the Palu-Uluova basin is located along the northeasternmost part of the Sivrice fault zone and controlled by numerous strike-slip fault segments Fault-parallel and actively growing travertine occurrences, elongated ridges with long axes subparallel or oblique to the master fault, shutter ridges, sag ponds, triangular facets, tectonic juxtaposition of older rocks with Quaternary basin infill, long and linear fault valleys, deflected and S-shaped bent drainage system (Figure 13), well-preserved slickensides recorded in the Plio–Quaternary Palu Formation (Figure 14), together with steeply sloping fault scarps are both the morphotectonic and faultplane related criteria observed within the Sivrice fault zone All of these reveal that the Sivrice fault zone is an active zone of deformation characterized by sinistral strike-slip faulting The Sivrice fault zone, or at least its master fault and some other fault segments closely-spaced to it, are also seismically active This is indicated by both historical and recent seismic 562 activity, such as the historical May 1874 ground surface rupture-forming earthquake, and the recent February 2007 Mw= 5.7 Sivrice and the March 2010 Mw= 6.1 Palu earthquakes (Ambraseys & Jackson 1998; Güneyli 2002; Çetin et al 2003; KOERİ 2007; Tan et al 2010) In addition, both the stereographic plot (Figure 15) of slip-plane data and the fault plane solution diagrams of the recent February 2007 Sivrice and the March 2010 Palu earthquakes along the Sivrice fault zone indicate that it is an active sinisral strike-slip fault zone governed by a NNE– SSW-oriented compressive principal stress system (σ1) (Figure 1) in and adjacent to the study area (see Aksoy et al 2007 for more information about the Sivrice fault zone) Adıyaman Fault Zone (AFZ) – This 3-km-wide, 210-km-long and N50°E-trending active zone of deformation is characterized by sinistral strike-slip faulting It marks and controls the southeastern margin of the Palu-Kumyazı section of the PaluUluova strike-slip basin (Figure 2) The Adıyaman S ÇOLAK ET AL Northern Limb 0 N 20 E, 30 NW 0 N 55 E, 32 NW 0 N 65 E, 39 NW 0 N 67 E, 28 NW 0 N 70 E, 38 NW 0 N 70 E, 38 NW 0 N 80 E, 38 NW 0 N 80 E, 40 NW 0 N 80 E, 41 NW 0 N 85 E, 35 NW 0 N 55 W, 25 NE 0 N 65 W, 42 NE 0 N 70 W, 40 NE 0 N 75 W, 34 NE 0 N 80 W, 40 NE 0 N 80 W,48 NE Southern Limb 0 N 78 E, 75 SE 0 N 80 E, 60 SE 0 N 80 E, 65 SE 0 N 80 E, 70 SE 0 N 82 E, 68 SE 0 N 83 E, 71 SE 0 N 85 E, 76 SE 0 N 85 E, 80 SE 0 N 87 E, 72 SE E-W, 75 S E-W, 75 S E-W, 78 S 0 N 80 W, 70 SW 0 N 82 W, 73 SW Figure 12 (a) Attitudes of bedding planes, and (b) poles to bedding planes comprising the limbs of a fold Large arrows facing each other indicate operation direction of the principal stress at the end of the deposition of the Upper Miocene–Lower Pliocene Çaybağı Formation fault zone splays off the master fault of the EAFS just west of Palu County (Figure 2) and then runs SW across both the study area and beyond, as far as just east of Narlı Town (Kahramanmaraş) (Aksoy et al 2007) The Adıyaman fault zone consists of numerous closely-spaced, parallel to sub-parallel and variable-sized fault segments Fault parallel travertine occurrences, long deep and narrow depressions (fault corridors), very young pull-apart basins (e.g., Hazar Figure 13 Close up view of the deflected and S-shaped bent stream course indicating sinistral strike-slip faulting cutting the Plio–Quaternary Palu formation (S of Örencik village, view to N) For location of the photograph, see Figure Figure 14 Close-up view of the strike-slip faulting-induced slickenside (near Örencik village) For location of the photograph, see Figure pull-apart basin), a well-developed anastomosing pattern peculiar to strike-slip faulting, linear to steeply sloping fault scarps, strips of intensely sheared, crushed to pulverized fault gouge and deflected, bent or offset (up to 1.5 to km) drainage systems such as the Caru and Maden streams (outside the study area) and the Euphrates River are common morphotectonic criteria indicating both the existence and activity of the Adıyaman fault zone Some of fault segments of the Adıyaman fault zone were reactivated and moved by both the May 1874 devastating historical 563 PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM Strike 0500 0470 0430 3170 0070 3580 0690 0420 0510 Dip 740 S 870 S 850 S 880 W 750 E 770 E 650 W 560 S 680 W Rake 200 NW 010 NW 030 NW 10 NW 150 NW 150 NW 30 NW 330 NW 230 NW N M local extention direction local contration direction Figure 15 (a) Slip-plane data and (b) Stereographic plot of slip-plane data on the Schmidt Lower hemisphere net Large arrows facing each other indicate operation direction of principal stress or localized shortening direction in the neotectonic regime earthquake and a series of recent seismic events with magnitudes of Mw= 2.5–4.3 (KOERİ 2007) Uluova Fault Zone (UFZ) – This is a NE-trending active zone of deformation about km wide and 60 km long characterized by strike-slip faulting It is confined in the area between the Yolüstü fault zone in the northeast and the Fırat fault in the southwest, outside of the study area (Figures 1b & 2) The Uluova fault zone forms a mountain front marking the northwestern slope of the Mastardağı horst (Figure 2) It marks and controls the southwestern margin of the Uluova section of the Palu-Uluova strike-slip basin The Uluova fault zone consists of numerous closely-spaced, NE- to NW-trending conjugate dextral to sinistral strike-slip fault segments (Figure 2) cutting the Jurassic–Lower Cretaceous Guleman ophiolitic rocks and the Upper Cretaceous–Paleocene Hazar complex, displacing them up to km in a dominantly left-lateral direction and tectonically juxtaposing various facies of older rocks with each other and with the Plio–Quaternary basin infill The Uluova fault zone also contains a limited number of NNW-trending oblique-slip normal faults and WSW- to WNW-trending oblique-slip reverse fault segments Steeply sloping fault scarps, triangular facets, fault-parallel aligned and scoured alluvial fans (Figure 16), deflected and S-shaped stream courses, strips of intensely sheared and crushed fault rocks and the tectonic juxtaposition of older ophiolitic rocks with the Quaternary alluvial sediments are 564 common morphotectonic criteria which indicate both existence and activity of the fault segments comprising the Uluova fault zone Elazığ Fault Zone (EFZ) – This is a NE-trending zone of active sinistral strike-slip faulting about km wide and 54 km long The Elazığ fault zone is confined to an area between the NW-trending dextral Pertek fault zone and a NNW-trending oblique-slip normal fault in the northwest (Figure 1b) An approximately 35-km-long portion crosses the study area The Elazığ fault zone marks and controls the northwestern margin of the Uluova section of the Palu-Uluova strike-slip basin (Figure 2) It consists of numerous NE-trending closely-spaced, parallel-subparallel, variable-sized (0.3–15 km) fault segments They cut Senonian Elazığ magmatic rocks and tectonically juxtapose them with the Plio–Quaternary basin infill (Figure 2) The steeply sloping and linear fault scarps, triangular facets, basinward facing step-like topography (Figure 16), offset drainage system (e.g., the Fırat River and some of its tributaries are offset by up to km sinistrally by fault segments of the Elazığ fault zone (Figure 1b), fault-parallel aligned alluvial fans with apices against the fault scarp and the tectonic juxtaposition of older rocks with Quaternary deposits, are common morphotectonic criteria for both the existence and activity of the Elazığ fault zone This is also proved by epicentre distribution of small seismic events throughout the fault zone (Tan et al 2010) S ÇOLAK ET AL Ke alluvial fan Figure 16 General view of the tectonic juxtaposition between older rocks in the background (Ke– Senonian Elazığ magmatic complex) and the scoured Holocene alluvial fan in the foreground (south of Yolüstü village, view to SE) For location of the photograph, see Figure Pertek Fault Zone (PFZ) – This is another NW to WNW-trending zone of active deformation 5–9 km wide, 70 km long and dominated by strikeslip faulting with a minor reverse-slip component It extends from west of Ovacık County in the northwest (outside the study area) to Palu County in the southeast Its 33-km-long south-eastern part traverses the study area (Figure 2) The Pertek fault zone links the NE-trending Ovacık sinistral strike-slip fault system with the East Anatolian fault system and acts as a transfer structure between these major structures It consists of numerous closely- to medium-spaced, variable-sized (2–15 km), parallel to sub-parallel NW-trending dextral strike-slip fault segments and WNW-trending strike-slip faults with reverse component (Figure 2) They cut and form a conjugate system with the NE-trending sinistral strike-slip fault segments including both the Uluova and Elazığ fault zones They also intersect with the E–W-trending reverse fault segments of the Yolüstü fault zone (Figure 2b) These fault segments cut across the Senonian magmatic rocks, the Middle– Upper Eocene sedimentary sequence of the Krkgeỗit Formation, older reverse faults and displace them up to km, predominantly dextrally (Figure 17), and tectonically juxtapose these older rocks with each other and the Plio–Quaternary strike-slip basin infill (Figure 2) Yolüstü Fault Zone (YFZ) – This is an E–W-trending zone of active deformation with oblique-slip reverse faulting and a minor strike-slip component about km wide and 20 km long The Yolüstü fault zone is confined to the area between the Sivrice fault zone in the east and the Uluova fault zone in the west (Figure 2) It controls the E–W-trending middle section of the Palu-Uluova strike-slip basin The Yolüstü fault zone consists of several, closely-spaced, varioussized (1.5–12 km), parallel-subparallel, northerly 565 PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM KEBAN DAM LAKE Figure 17 General view of the northwestern bounding faults (Elazığ fault zone) and their step-like topography controlling the Uluova section of the Palu-Uluova strike-slip basin Vertically-oriented white arrows indicate traces of the fault segments (SW of Yolüstü village, view to SW) For location of the photograph, see Figure and southerly steeply dipping reverse fault segments (Figure 2) They cut and displace, predominantly vertically, both older rocks (Senonian Elazığ magmatic complex, the Jurassic–Lower Cretaceous Guleman ophiolitic rocks, the Middle–Upper Eocene Krkgeỗit sedimentary sequence and the Upper MioceneLower Pliocene ầayba Formation), and tectonically juxtapose them with each other and the Plio–Quaternary strike-slip basin infill In the E–Wtrending middle section of the Palu-Uluova basin, the basin infill has been uplifted, dissected and perched on the boundary faults at different elevations owing to the oblique-slip reverse faulting (Figure 2) The existence and nature of reverse faulting, the activity of some fault segments comprising the Yolüstü fault zone, and the N–S orientation of the principal stress (σ1) in and adjacent to the study area were also proved once more by the occurrence of the 16 March 2010 Mw= 4.1 Yolüstü earthquake and its fault plane solution diagram (Figure 1) (Tan et al 2010) Here the deviation of the general NE trend of the faults into an E–W trend, the formation of the E–Wtrending reverse fault zone and the related ramp type of basin along it, and the push-up nature of both the Askerdağı and Mastardağı blocks are attributed to anticlockwise rotation of the Mastardağı blocks between the NE-trending Sivrice and Uluova fault zones (Figure 2) Discussion and Conclusion Turkey is a seismically very active and geologically complicated area in the Eastern Mediterranean seismic belt The geological complexity is dominated by both the palaeotectonic fold-thrust to reverse fault belt and the neotectonic overprinting strike566 slip faulting and related basin formation The geologically complicated deformation pattern of east-southeastern Turkey has resulted from both the entire demise of the Tethyan seaway, the Bitlis Ocean, between the Indian Ocean and Mediterranean Sea, and the continent-continent collision of the northerly moving Arabian plate with the Eurasian plate to the north in Late Serravalian time (Şengör & Yılmaz 1981; Dewey et al 1986) These authors also accepted that the Late Serravalian continentcontinent collision marks both the onset age of the neotectonic regime and the first emergence of related major structures such as the Anatolian platelet and its boundary faults, the NAFS and the EAFS in eastern Turkey However, the time range of these authors (Late Miocene–Early Pliocene) does not fit well with the onset age of the neotectonic regime in eastern Anatolia, where the Late Miocene–Early Pliocene interval marks the occurrence of a series of geodynamic processes related to the intracontinental convergence and a major slab-detachment event (Faccenna et al 2006) which pre-date the onset age of the strike-slip neotectonic regime in eastern Anatolia; i.e the initiation age of the neotectonic regime is not Late Serravalian in eastern Anatolia After the final collision and formation of the Bitlis suture zone, the N–S intra-continental convergence between the Arabian and the Eurasian plates lasted for approximately Ma (Late Miocene–Early Pliocene), an interval termed the transitional period by Koỗyiit et al (2001) A series of deformations occurred during this Late Miocene–Early Pliocene transitional period These include, in sequence, crustal overthickening, regional tectonic uplift, development of numerous asymmetric to overturned S ÇOLAK ET AL folds with E–W-trending axes, thrust to reverse faults, E–W-trending ramp-type intermontane basins with bounding reverse faults, resetting of newly formed drainage systems, disappearance of marine conditions, the development of short- to long-term stratigraphical gaps and widespread calcalkaline magmatic activity (Şengör & Kidd 1979; Innocenti et al 1980; Dewey et al 1986; Şaroğlu et al 1987; Yılmaz et al 1987; Ercan et al 1990; Koỗyiit & Beyhan 1998; Koỗyiit et al 2001) One of the last palaeotectonic units to experience earlier pronounced contractional deformation is the Upper Miocene–Lower Pliocene Çaybağı Formation It was deposited in an approximately E–W-trending intermontane basin controlled by thrust to reverse TQp faulting This is indicated by the widespread occurrence of broken formations, slump structures, reverse type of growth faults and the coarsening upward nature of the Çaybağı Formation Towards the end of sedimentation, the Çaybağı Formation was deformed into a series of asymmetrical to overturned folds (Figures 11 & 12), and dissected by reverse faults (Figure 18) Hence, the depositional setting of the Çaybağı Formation cannot be as previously interpreted, as a strike-slip basin located along the EAFS by Koỗ Tagn & Tỹrkmen (2009), because neither the strike-slip faulting-dominated neotectonic regime nor the related major structures (the Anatolian platelet and its margin-boundary faults) had developed at that time This is indicated AU Ke RF RF Tk Tỗ SF RF Tk Tỗ Figure 18 General view of various mappable structures (RF– reverse fault; AU– angular unconformity; SF– strike-slip fault along which older rocks; Ke– Senonian Elaz magmatic complex; Tk MiddleUpper Eocene Krkgeỗit formation) were emplaced on the Upper MioceneLower Pliocene ầayba Formation (Tỗ) and deformed it TQp– Plio–Quaternary Palu Formation, which overlies with angular unconformity all the pre-Upper Pliocene rocks and compressional structures (2 km SE of Osmanağa village, view to NE) For location of the photograph, see Figure 567 PALU-ULUOVA BASIN IN THE EAST ANATOLIAN FAULT SYSTEM by: (1) the Çaybağı Formation contains very frequent repetition of coarsening- and fining-upward sequences, and ends with coarser-grained regressive clastics, (2) it is full of soft-sediment deformational features related mostly to folding or reverse faulting, such as slump folds, slump thrust, convolute lamination, load structures and sand injections, (3) thrusts to reversed growth faults, (4) the Çaybağı Formation is intensely and synchronously deformed (steeply tilted, folded and reverse-faulted) on a regional (mappable) scale (Figure 17), (5) the Çaybağı Formation and its contractional deformation pattern are truncated, sealed and overlain with angular unconformity by the weakly lithified to unconsolidated and nearly horizontal undeformed Plio–Quaternary Palu Formation (Figures 7f & 8) The development of fold-thrust to reverse faults zones and related contractional deformation of the Çaybağı Formation continued under the control of the N–S principal compressive stress system (Figure 12) until the end of Middle Pliocene Subsequently, it was replaced by the first emergence of a strikeslip neotectonic regime This is indicated by the widespread occurrence of regional inversions in the type of tectonic regime (e.g., the orientation of σ2 changed from horizontal to vertical), the type of geological structures, the style of deformation (e.g., from folding and thrust-reverse faulting to predominantly strike-slip faulting), the type of basin (e.g., from thrust to reverse fault-bounded intermontane basin to strike-slip basin), type of sedimentation (e.g., from a fining-upward sequence to a coarsening-upward sequence), and in particular, in the nature of seismic activity triggered by the formation of two intracontinental transform fault boundaries (e.g., the North Anatolian dextral strikeslip fault system and the East Anatolian sinistral strike-slip fault system) Lastly, the west-southwestward escape of the Anatolian platelet along these two megashear zones was established (Hempton 1987; Koỗyiit & Beyhan 1998; Ylmaz et al 1998; Koỗyiit et al 2001) For this reason, the onset age of the strike-slip faulting-dominated neotectonic regime in east-southeastern Turkey and its neighbourhood is Late Pliocene (Koỗyiit et al 2001) Since the Late Pliocene, the early rugged topography, which reflects the compressional 568 deformation pattern of the Çaybağı Formation and older rocks, was cut and dissected into numerous blocks by strike-slip faulting and newly formed neotectonic structures such as the Sivrice, Adıyaman, Uluova, Elazığ, Pertek and Yolüstü fault zones These blocks were shaped by the strike-slip faulting complexities such as the bifurcation, double bends and step-overs developed as a result of the rheology of the earth’s crust and variation in the general trends of the strike-slip faults mentioned above Lastly these neotectonic structures led to the formation of the Palu-Uluova strike-slip basin The first stratigraphic units accumulated in it were the Baltaşı travertines and the Palu Formation, which were deposited under a strike-slip neotectonic regime The early fluvial clastics of the Palu Formation are full of syn-sedimentary growth faults, mostly strikeslip and normal faults Another diagnostic lithofacies of the neotectonic infill is the travertine, which was precipitated from the CaCO3-rich water circulating along the strike-slip faults and emerging as springs Early deposited boulder-block conglomerates occur in two settings: pressure ridges and fault terraces Deformed into a series of strike-slip fault-bounded lensoidal pressure ridges with long axes parallel or slightly oblique to the general trend of the master fault, both the travertine and the early deposited boulderblock conglomerates have been uplifted, dissected and elevated again on the fault-suspended terraces as a manifestation of the activity on the bounding strike-slip faults of the Palu-Uluova basin Faultparallel aligned alluvial fans have also been deformed Consequently, the combination of growth faultassociated syn-depositional features, such as fault terraces, pressure ridges and deformed alluvial fans all reflect strike-slip faulting-induced deformation in the Palu-Uluova basin during the Plio–Quaternary neotectonic regime At present, this is also indicated by the fault plane solution diagrams (Figure 1) of earthquakes sourced from the faults, which show the Plio–Quaternary neotectonic configuration of the Palu-Uluova complex strike-slip basin (Figures 1b & 2) Evolution of the Palu-Uluova strike-slip basin and deposition of its neotectonic infill have continued under the control of the bounding strike-slip fault zones mentioned above since the Late Pliocene S ÇOLAK ET AL References Aksoy, E 1993 Geological features of the western and southern area of the Elazığ Turkish Journal of Earth Sciences 2, 113–123 Aksoy, E., İnceöz, M & Koỗyt, A 2007 Lake Hazar basin: a negative flower structure on the East Anatolian fault system (EAFS), SE Türkiye Turkish Journal of Earth Sciences 16, 319– 338 Ambraseys, N.N & Jackson, J.A 1998 Faulting associated with historical and recent earthquakes in the Eastern Mediterranean region Geophysical Journal International 133, 390–406 Çelİk, H 2003 Stratigraphic and Tectonic Features of Vicinity of Mastar Mountain (SE of Elazığ) PhD Thesis, Fırat University 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slip faultingdominated neotectonic stage, i.e the initiation age of the neotectonic stage and formation of... between the earlier palaeotectonic stage and the onset of the strike- slip faulting-dominated neotectonic stage in the east Anatolian plateau This transitional period is an elapsed time interval during... or fault arrays recorded in deformed and undeformed basin infills have a key importance in determining the transition from the palaeotectonic stage to the neotectonic stage A number of basins