Kemal Tasli

Tectonic evolution of the South Tethyan ocean: evidence from the Eastern Taurus Mountains (Elaziğ region, SE Turkey)

Abstract Geological information from the Eastern Taurus Mountains, part of the Tethyan (South Neotethyan) suture zone exposed in the Elaziğ region, is used here to test existing tectonic hypotheses and to develop a new tectonic model. Five main tectonic stages are identified: (1) Mid-Late Triassic rifting-spreading of Southern Neotethys; (2) Late Cretaceous northward subduction-accretion of ophiolites and arc-related units; (3) Mid-Eocene subduction-related extension; (4) Early-Mid-Miocene collision and southward thrusting over the Arabian Foreland; (6) Plio-Quaternary, post-collisional left-lateral tectonic escape. During the Late Cretaceous (c. 90 Ma) northward intra-oceanic subduction generated regionally extensive oceanic lithosphere as the İspendere, Kömürhan, Guleman and Killan ophiolites of supra-subduction zone type. A northward-dipping subduction zone was activated along the northern margin of the ocean basin (Keban Platform), followed by accretion of Upper Cretaceous ophiolites in latest Cretaceous time. As subduction continued the accreted ophiolites and overriding northern margin (Keban Platform) were intruded by calc-alkaline plutons, still during latest Cretaceous time. The northern margin was covered by shallow-marine mixed clastic-carbonate sediments in latest Cretaceous-Early Palaeogene time. Northward subduction during the Mid-Eocene was accompanied by extension of the northern continental margin, generating large fault-bounded, extensional basins that were infilled with shallow- to deep-water sediments and subduction-influenced volcanic rocks (Maden Group). Thick debris flows (‘olistostromes’) accumulated along the oceanward edge of the active margin. The partly assembled allochthon finally collided with the Arabian continental margin to the south during Early-Mid-Miocene time in response to oblique convergence; the entire thrust stack was then emplaced southwards over the downflexed Arabian Foreland. Left-lateral strike-slip (tectonic escape) along the East Anatolian Fault Zone ensued.

Late Cretaceous–Early Eocene tectonic development of the Tethyan suture zone in the Erzincan area, Eastern Pontides, Turkey

Six individual tectonostratigraphic units are identified within the Izmir–Ankara–Erzincan Suture Zone in the critical Erzincan area of the Eastern Pontides. The Ayikayasi Formation of Campanian–Maastrichtian age is composed of bedded pelagic limestones intercalated with polymict, massive conglomerates. The Ayikayasi Formation conformably overlies the Tauride passive margin sequence in the Munzur Mountains to the south and is interpreted as an underfilled foredeep basin. The Refahiye Complex, of possible Late Cretaceous age, is a partial ophiolite composed of ~75% (by volume) serpentinized peridotite (mainly harzburgite), ~20% diabase and minor amounts of gabbro and plagiogranite. The complex is interpreted as oceanic lithosphere that formed by spreading above a subduction zone. Unusual screens of metamorphic rocks (e.g. marble and schist) locally occur between sheeted diabase dykes. The Upper Cretaceous Karayaprak Melange exhibits two lithological associations: (1) the basalt + radiolarite + serpentinite association, including depleted arc-type basalts; (2) the massive neritic limestone + lava + volcaniclastic association that includes fractionated, intermediate-composition lavas, and is interpreted as accreted Neotethyan seamount(s). The several-kilometre-thick Karadag Formation, of Campanian–Maastrichtian age, is composed of greenschist-facies volcanogenic rocks of mainly basaltic to andesitic composition, and is interpreted as an emplaced Upper Cretaceous volcanic arc. The Campanian–Early Eocene Sutpinar Formation (~1500 m thick) is a coarsening-upward succession of turbiditic calcarenite, sandstone, laminated mudrock, volcaniclastic sedimentary rocks that includes rare andesitic lava, and is interpreted as a regressive forearc basin. The Late Paleocene–Eocene Sipikor Formation is a laterally varied succession of shallow-marine carbonate and siliciclastic lithofacies that overlies deformed Upper Cretaceous units with an angular unconformity. Structural study indicates that the assembled accretionary prism, supra-subduction zone-type oceanic lithosphere and volcanic arc units were emplaced northwards onto the Eurasian margin and also southwards onto the Tauride (Gondwana-related) margin during Campanian–Maastrichtian time. Further, mainly southward thrusting took place during the Eocene in this area, related to final closure of Tethys. Our preferred tectonic model involves northward subduction, supra-subduction zone ophiolite genesis and arc magmatism near the northerly, Eurasian margin of the Mesozoic Tethys.

Subduction, ophiolite genesis and collision history of Tethys adjacent to the Eurasian continental margin: new evidence from the Eastern Pontides, Turkey

This paper presents several types of new information including U–Pb radiometric dating of ophiolitic rocks and an intrusive granite, micropalaeontological dating of siliceous and calcareous sedimentary rocks, together with sedimentological, petrographic and structural data. The new information is synthesised with existing results from the study area and adjacent regions (Central Pontides and Lesser Caucasus) to produce a new tectonic model for the Mesozoic–Cenozoic tectonic development of this key Tethyan suture zone. The Tethyan suture zone in NE Turkey (Ankara–Erzincan–Kars suture zone) exemplifies stages in the subduction, suturing and post-collisional deformation of a Mesozoic ocean basin that existed between the Eurasian (Pontide) and Gondwanan (Tauride) continents. Ophiolitic rocks, both as intact and as dismembered sequences, together with an intrusive granite (tonalite), formed during the Early Jurassic in a supra-subduction zone (SSZ) setting within the İzmir–Ankara–Erzincan ocean. Basalts also occur as blocks and dismembered thrust sheets within Cretaceous accretionary melange. During the Early Jurassic, these basalts erupted in both a SSZ-type setting and in an intra-plate (seamount-type) setting. The volcanic-sedimentary melange accreted in an open-ocean setting in response to Cretaceous northward subduction beneath a backstop made up of Early Jurassic forearc ophiolitic crust. The Early Jurassic SSZ basalts in the melange were later detached from the overriding Early Jurassic ophiolitic crust. Sedimentary melange (debris-flow deposits) locally includes ophiolitic extrusive rocks of boninitic composition that were metamorphosed under high-pressure low-temperature conditions. Slices of mainly Cretaceous clastic sedimentary rocks within the suture zone are interpreted as a deformed forearc basin that bordered the Eurasian active margin. The basin received a copious supply of sediments derived from Late Cretaceous arc volcanism together with input of ophiolitic detritus from accreted oceanic crust. Accretionary melange was emplaced southwards onto the leading edge of the Tauride continent (Munzur Massif) during latest Cretaceous time. Accretionary melange was also emplaced northwards over the collapsed southern edge of the Eurasian continental margin (continental backstop) during the latest Cretaceous. Sedimentation persisted into the Early Eocene in more northerly areas of the Eurasian margin. Collision of the Tauride and Eurasian continents took place progressively during latest Late Palaeocene–Early Eocene. The Jurassic SSZ ophiolites and the Cretaceous accretionary melange finally docked with the Eurasian margin. Coarse clastic sediments were shed from the uplifted Eurasian margin and infilled a narrow peripheral basin. Gravity flows accumulated in thrust-top piggyback basins above accretionary melange and dismembered ophiolites and also in a post-collisional peripheral basin above Eurasian crust. Thickening of the accretionary wedge triggered large-scale out-of-sequence thrusting and re-thrusting of continental margin and ophiolitic units. Collision culminated in detachment and northward thrusting on a regional scale. Collisional deformation of the suture zone ended prior to the Mid-Eocene (~45 Ma) when the Eurasian margin was transgressed by non-marine and/or shallow-marine sediments. The foreland became volcanically active and subsided strongly during Mid-Eocene, possibly related to post-collisional slab rollback and/or delamination. The present structure and morphology of the suture zone was strongly influenced by several phases of mostly S-directed suture zone tightening (Late Eocene; pre-Pliocene), possible slab break-off and right-lateral strike-slip along the North Anatolian Transform Fault. In the wider regional context, a double subduction zone model is preferred, in which northward subduction was active during the Jurassic and Cretaceous, both within the Tethyan ocean and bordering the Eurasian continental margin.

Kilop Cretaceous Hardground (Kale, Gümüshane, NE Turkey):description and origin

Abstract A hardground surface is well exposed in the Kilop area of Kale (Gumushane, NE Turkey) which forms part of the Eastern Pontides. Here, the hardground is underlain by shallow water Lower Cretaceous limestones, and overlain by Upper Cretaceous red limestones/marls which contains a planktonic microfauna including Globotruncanidae. In the field, the recognition of the hardground is based on the presence of extensive burrows (especially vertical burrows), the encrusting rudistid bivalve Requienia , neptunian-dykes with infills of pelagic sediments and synsedimentary faults. Skolithos and Thalassinoides -type burrows are present. Some burrow walls show iron hydroxide-staining. The extensive burrowing occurred prior to lithification. On the other hand, the neptunian-dykes and synsedimentary faults, which cut the hard ground, occurred after the lithification. These features indicate the progressive hardening of the substrate. The burrowed limestone consists of an intrabioclastic peloidal grainstone which was deposited in an intertidal to shallow, subtidal, moderate to relatively high energy environment. The peloidal limestone shows little or no evidence of submarine cementation, characterized by only scarce relics of isopachous cement rims of bladed calcite spar. The grainstone cement is composed predominantly of blocky calcite and overgrowth calcite cements on the echinoid-fragments. The origin of this cement is controversial. Biostratigraphic analysis of the limestones demonstrates that there is a marked stratigraphic gap (hiatus), spanning the Aptian to the Santonian, in the Cretaceous of the Kilop area. The formation of the Kilop Hardground is related to the break-up and subsidence of the Eastern Pontides carbonate platform during the formation of the Black Sea backarc basin. Hardground development was initiated in a shallow marine environment of slow sedimentation and with moderate to high energy indicating slow subsidence. Later, the hardground subsided abruptly, as shown by the deposition of pelagic sediments on the hardground surface. During drowning, the Kilop area was converted to a bypass-margin where currents were effective. The formation of the hardground may also have been associated with an eustatic rise in sea-level.

Evidence from the Kyrenia Range, Cyprus, of the northerly active margin of the Southern Neotethys during Late Cretaceous–Early Cenozoic time

Sedimentary geology and planktonic foraminiferal biostratigraphy have shed light on the geological development of the northern, active continental margin of the Southern Neotethys in the Kyrenia Range. Following regional Triassic rifting, a carbonate platform developed during Jurassic–Cretaceous time, followed by its regional burial, deformation and greenschist-facies metamorphism. The platform was exhumed by Late Maastrichtian time and unconformably overlain by locally derived carbonate breccias, passing upwards into Upper Maastrichtian pelagic carbonates. In places, the pelagic carbonates are interbedded with sandstone turbidites derived from mixed continental, basic volcanic, neritic carbonate and pelagic lithologies. In addition, two contrasting volcanogenic sequences are exposed in the western-central Kyrenia Range, separated by a low-angle tectonic contact. The first is a thickening-upward sequence of Campanian–Lower Maastrichtian(?) pelagic carbonates, silicic tuffs, silicic lava debris flows and thick-bedded to massive rhyolitic lava flows. The second sequence comprises two intervals of basaltic extrusive rocks interbedded with pelagic carbonates. The basaltic rocks unconformably overlie the metamorphosed carbonate platform whereas no base to the silicic volcanic rocks is exposed. Additional basaltic lavas are exposed throughout the Kyrenia Range where they are dated as Late Maastrichtian and Late Paleocene–Middle Eocene in age. In our proposed tectonic model, related to northward subduction of the Southern Neotethys, the Kyrenia platform was thrust beneath a larger Tauride microcontinental unit to the north and then was rapidly exhumed prior to Late Maastrichtian time. Pelagic carbonates and sandstone turbidites of mixed, largely continental provenance then accumulated along a deeply submerged continental borderland during Late Maastrichtian time. The silicic and basaltic volcanogenic rocks erupted in adjacent areas and were later tectonically juxtaposed. The Campanian–Early Maastrichtian(?) silicic volcanism reflects continental margin-type arc magmatism. In contrast, the Upper Maastrichtian and Paleocene–Middle Eocene basaltic volcanic rocks erupted in an extensional (or transtensional) setting likely to relate to the anticlockwise rotation of the Troodos microplate.

Tectonostratigraphic evolution of the Upper Cretaceous–Cenozoic central Anatolian basins: an integrated study of diachronous ocean basin closure and continental collision

Abstract The Upper Cretaceous–Mid-Eocene Kırıkkale, Tuz Gölü, Haymana and Çankırı basins are bounded by the Pontide (Eurasian) continental margin to the north, the Niğde–Kırşehir microcontinent to the east and the Tauride–Anatolide continental unit to the south. The basins developed during northward subduction/collision of the İzmir–Ankara–Erzincan Ocean (‘northern Neotethys’) in the north and the inferred Inner Tauride Ocean in the south. Subduction of the İzmir–Ankara–Erzincan Ocean resulted in latest Cretaceous collision of the Niğde–Kırşehir microcontinent with the Pontide active margin and ophiolite emplacement. Some mid-ocean ridge-type oceanic crust remained to the SW and formed the basement of the Kırıkkale and Tuz Gölü basins. These basins are partially floored by an accretionary wedge to the west and by the Niğde–Kırşehir microcontinent to the east. Locally volcaniclastic, the sediment infill switched to terrigenous after latest Cretaceous. The Haymana Basin, further NW, developed as a forearc basin on the Mesozoic accretionary wedge and Pontide continental fragments. The Çankırı Basin also developed on an accretionary wedge, bounded by the Eurasian active margin to the north. An extensional setting prevailed during the latest Cretaceous related to subduction of remnant oceanic crust, followed by a switch to regional compression during Late Paleocene–Mid Eocene progressive and diachronous collision.

Late Palaeozoic–Cenozoic tectonic development of carbonate platform, margin and oceanic units in the Eastern Taurides, Turkey

Abstract Continental margin-type, ophiolitic and mélange units are exposed throughout central eastern Turkey (e.g. Gürün, Hekimhan and Pınarbaşı areas). These restore as a north-verging Triassic-rifted continental margin that underwent Jurassic–Early Cretaceous passive margin subsidence. Chemically ‘enriched’ basaltic lavas of seamount type are interbedded with and overlain by Middle Jurassic–Early Cretaceous ribbon cherts. Ophiolitic rocks (e.g. Pınarbaşı, Dağlıca, Kuluncak, Hekimhan, Divriği) formed by spreading above a Late Cretaceous northwards-dipping intra-oceanic subduction zone. Emplacement of continental margin units, mélanges and ophiolites onto the East Tauride platform was driven by trench-margin collision during latest Cretaceous. The northern part of the East Tauride neritic carbonate platform detached and overthrust the continent to the south (Malatya Metamorphics) which was deeply underthrust, metamorphosed at least to greenschist facies and exhumed by latest Cretaceous. Collision-related Mid-Eocene southwards thrusting strongly affected the western part of the region (e.g. Pınarbaşı), whereas areas further east (e.g. Darende, Hekimhan, Divriği, Sivas) mainly experienced folding. Taking account of the regional tectonic setting, we infer that the Gürün platform, with its distinctive unbroken up to Lutetian-aged succession, represents a small exotic terrane that was translated from a relatively southerly (‘internal’) part of the Tauride platform (Geyik Dağ), related to strike-slip displacement (syn/post-Eocene to pre-Pliocene). Supplementary material: Two supplementary tables giving the GPS coordinates of the samples of basic intrusive and extrusive igneous rocks that were analyzed during this work are available at www.geolsoc.org.uk/SUP18569

Eocene development of the northerly active continental margin of the Southern Neotethys in the Kyrenia Range, north Cyprus

We focus on an active continental margin related to northwards subduction during the Eocene in which sedimentary melange (‘olistostromes’) forms a key component. Maastrichtian – Early Eocene deep-marine carbonates and volcanic rocks pass gradationally upwards into a thick succession (<800 m) of gravity deposits, exposed in several thrust sheets. The lowest levels are mainly siliciclastic turbidites and debris-flow deposits. Interbedded marls contain Middle Eocene planktonic/benthic foraminifera and calcareous nannofossils. Sandstones include abundant ophiolite-derived grains. The higher levels are chaotic debris-flow deposits that include exotic blocks of Late Palaeozoic – Mesozoic neritic limestone and dismembered ophiolite-related rocks. A thinner sequence (<200 m) in one area contains abundant redeposited Paleogene pelagic limestone and basalt. Chemical analysis of basaltic clasts shows that some are subduction influenced. Basaltic clasts from unconformably overlying alluvial conglomerates (Late Eocene – Oligocene) indicate derivation from a supra-subduction zone ophiolite, including boninites. Taking account of regional comparisons, the sedimentary melange is interpreted to have formed within a flexurally controlled foredeep, floored by continental crust. Gravity flows including large limestone blocks, multiple debris flows and turbidites were emplaced, followed by southwards thrust imbrication. The emplacement was possibly triggered by the final closure of an oceanic basin to the north (Alanya Ocean). Further convergence between the African and Eurasian plates was accommodated by northwards subduction beneath the Kyrenia active continental margin. Subduction zone rollback may have triggered collapse of the active continental margin. Non-marine to shallow-marine alluvial fans prograded southwards during Late Eocene – Oligocene time, marking the base of a renewed depositional cycle that lasted until latest Miocene time.

Late Triassic rifting and Jurassic–Cretaceous passive margin development of the Southern Neotethys: evidence from the Adıyaman area, SE Turkey

Evidence of rifting and continental break-up to form the S Neotethys is found within the volcanic-sedimentary Koçali Complex. This is a folded, thrust-imbricated succession that includes lavas, volcaniclastic sediments, pelagic carbonates, radiolarites and manganiferous deposits. Interbedded ribbon cherts contain radiolarians of Late Triassic to Late Jurassic age. The lower part of the succession of Mid?-Late Triassic age (Tarasa Formation) is dominated by enriched mid-ocean ridge basalt (E-MORB). The overlying Late Triassic to Mid-Jurassic interval (Konak Formation) is characterised by intercalations of ocean island basalt and E-MORB. Taking account of structural position, the basalts erupted within the outer part of a continent–ocean transition zone. Continental break-up probably occurred during the Late Triassic (Carnian–Norian). Early to Mid-Jurassic lavas and volcaniclastic sediments record volcanism probably after continental break-up. In addition, the Karadut Complex is a broken formation that is located at a relatively low structural position just above the Arabian foreland. Pelagic carbonates, redeposited carbonates and radiolarites predominate. Radiolarians are dated as Early to Mid-Jurassic and Late Cretaceous in age. The pelagic carbonates include planktic foraminifera of Late Cretaceous age. The Karadut Complex resulted from the accumulation of calcareous gravity flows, pelagic carbonate and radiolarites in a relatively proximal, base-of-slope setting. After continental break-up, MORB and ophiolitic rocks formed within the S Neotethys further north. Tectonic emplacement onto the Arabian platform took place by earliest Maastrichtian time. Regional interpretation is facilitated by comparisons with examples of Triassic rifting and continental break-up in the eastern Mediterranean region and elsewhere.

BIOSTRATIGRAPHY OF THE LOWER JURASSIC CARBONATES FROM THE AYDINCIK AREA (CENTRAL TAURIDES, S. TURKEY) AND MORPHOLOGICAL ANALYSIS OF LITUOLIPORA TERMIERI (HOTTINGER, 1967)

Benthic foraminiferal biostratigraphy of the Lower Jurassic platform carbonate succession from the Aydincik area (Central Taurides, Southern Turkey) has been carried out. Three main biozones comparable to those from the Lower Jurassic of Morocco and Northern Italy have been identified. The Lituosepta recoarensis Phylozone has a well-defined relative biostratigraphic position as well as the overlying Orbitopsella Phylozone, which is widespread all over the southern Tethys platforms of the Lower Jurassic. The species Lituosepta compressa Hottinger is first recorded in this biozone, i.e. , below the Orbitopsella Zone. The Lituolipora termieri Interval Zone defined by the disappearance of the genus Orbitopsella characterizes the upper part of the Lower Jurassic sections. A generic revision of the species Mayncina termieri Hottinger, afterwards attributed to the genus Paleomayncina Septfontaine, has been made. This species has a keriothecal wall, nearly plani- to streptospirally coiled test, and an ontogenetic evolution of the aperture from basal-central to cribrate; it is considered herein as a junior synonym of Lituolipora polymorpha GusIc and Velic. It is proposed that the genus Lituolipora should be retained due to priority. The variability of the species Lituolipora termieri is also described.