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Öğe Clay mineralogy, chemistry, and diagenesis of Late Devonian K-bentonite occurrences in northwestern Turkey(SCIENTIFIC TECHNICAL RESEARCH COUNCIL TURKEY-TUBITAK, 2015) Gunal-Turkmenoglu, Asuman; Bozkaya, Omer; Goncuoglu, M. Cemal; Unluce, Ozge; Yilmaz, Ismail Omer; Okuyucu, CengizThin beds of tephra (K-bentonites) formed by the diagenesis of volcanic ash are exposed within the limestone-dolomitic limestone successions of the Yilanli formation at Zonguldak and Bartin in northwestern Turkey. They were deposited on the Middle Devonian-Lower Carboniferous shallow carbonate platform of the Zonguldak terrane. In this study, K-bentonite samples collected from Gavurpinari and Yilanli Burnu limestone quarries are investigated in order to reveal their mineralogical and geochemical characteristics and diagenetic evolution. Illite is the major clay mineral in the studied K-bentonites. Additionally, kaolinite and mixed-layer illite-smectite are identified in some samples. The nonclay minerals calcite, dolomite, quartz, gypsum, feldspar, pyrite, and zircon are also found. Crystal-chemical characteristics (Kubler index, d(060) values, and polytypes of illites) from two different sampling locations do not show significant variations. Kubler index values for the Yilanli Burnu and Gavurpinari sampling locations, 0.47-0.93 (average: 0.71 Delta degrees 2 theta) and 0.69-0.77 (average: 0.72 Delta degrees 2 theta), respectively, indicate that illites were affected by high-grade diagenetic conditions. The swelling (or smectite) component (similar to 5%), crystallite size (N = 10-20 nm), and polytype (2M(1) > 1M(d)) data of illites support the same conditions. Illite d(060) values of 1.491-1.503 angstrom correspond to a range of octahedral Mg+Fe values of 0.27-0.51 atoms per formula, indicating a composition between end-member muscovite and phengite unit. Trace and rare earth element-based chemical classification of the K-bentonite samples revealed that composition of original volcanic ash is basaltic. Illitization took place by fixation of K from volcanic minerals and ash, and diffusion of elements (Mg+Fe) into and out of the beds during diagenesis. Mineralogical-chemical data point out that these K-bentonites evolved in high-grade diagenetic conditions (approximately 100-150 degrees C) from the products of volcanic eruptions of disputed sources and distances during the Late Devonian time.Öğe Discovery of an earliest Triassic, post-extinction foraminiferal assemblage above the Permian-Triassic boundary, Strandzha nappes, north-west Turkey(POLISH GEOLOGICAL INST, 2014) Okuyucu, Cengiz; Ivanova, Daria; Bedi, Yavuz; Ergen, AliA new foraminiferal fauna from Early Triassic (Induan) strata of the Caglayik section on the "Strandzha Massif", north-west Turkey, comprises five species precisely determined and five species in open nomenclature belonging to ten genera. They belong to the post-extinction foraminiferal assemblage of the Permian-Triassic crisis, characterized by the presence of both disaster taxa (Earlandia and Postcladella kalhori) and Lazarus taxa (Diplosphaerina inaequalis, ?Rectostipulina quadrate, Arenovidalina sp. and Glomospira sp.). The present study at Tutunluktepe Formation identified for the first time the Permian foraminifers on the Strandzha Massif as relict members of a post-extinction foraminiferal assemblage.Öğe Foraminifera, Radiolaria and Conodont assemblages from the Early Mississipian (late Tournaisian)/Early Pennsylvanian (early Bashkirian) blocks within the Mersin Melange, southern Turkey: Biochronological and paleogeographical implications(ELSEVIER, 2018) Okuyucu, Cengiz; Tekin, U. Kagan; Noble, Paula J.; Bedi, Yavuz; Saydam-Demiray, D. Gulnur; Sayit, KaanThe Mersin Melange, a sedimentary complex in southern Turkey, includes blocks of various origins within a Late Cretaceous matrix. Two blocks in the Mersin Melange are herein recognized to be of Carboniferous age. One block (the Kozan Block) is composed of alternating chert and mudstone, and includes radiolarian and conodont assemblages revealing a late Tournaisian (Early Mississippian) age. The other (Keven-West Block) consists of platform carbonate containing abundant foraminifera indicating Bashkirian (Early Pennsylvanian) age. These dates are so far the oldest obtained from the blocks within the Mersin Melange. A correlation of the lithostratigraphies of blocks in the Mersin Melange with the coeval Tauride sequences indicates that they correspond to the successions in the Beysehir-Hoyran Nappes. In these nappes, the late Tournaisian is characterized by radiolarian rich chert and mudstone of an open marine environment, whereas the Bashkirian succession represents a shallow water environment with Foraminifera-bearing limestone. The Tournaisian deepening can be ascribed to the opening of a deep marginal basin to the north of the Tauride Platform and uplifting of the northern Tauride-Anatolide Platform margin during the Late Mississippian and Early Pennsylvanian. A shallowing upward sequence started in the Tournaisian with a pelagic sequence followed by platform carbonates of Bashkirian age in the Beysehir-Hoyran Nappes, and could be related to a major glaciation event during late Visean-Serpukhovian resulting in a sea-level drop and deposition of platform carbonates in the Bashkirian. Given the stratigraphic properties of northerly originated nappe packages (Cataloturan, Hadim and Bolkardag) and parautochthonous/autochthonous sequences in Taurides, sedimentation on the Tauride-Anatolide Platform mainly terminated after the Moscovian, except in the Hadim Nappe with sedimentation in a very shallow sea conditions until the end of the Permian. A depositional break corresponding to the Kasimovian-Wordian time interval in these sequences in the Tauride-Anatolide Platform could be related to the effects of both late Paleozoic Gondwanan glaciation and a possible mantle plume occurrence evidenced by the geochemistry of lavas in the Mersin Melange causing major uplift in the Northern NeoTehys Ocean. However; at the center of the plume, pelagic sequences (e.g., ribbon chert and pelagic limestone) were deposited associated with these lavas due to a progressive developing rift system during the Permian, based on previous studies. (C) 2018 Elsevier Ireland Ltd Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved.Öğe Fusulinid zonation of the Late Moscovian-Early Sakmarian sequences from the Taurides, southern Turkey(E SCHWEIZERBARTSCHE VERLAGSBUCHHANDLUNG, 2013) Okuyucu, CengizLate Moscovian-Early Sakmarian fusulinid faunas of the Anatolian Platform were examined in three stratigraphic sections (Ozbek Tepe, Eskibey and Bademli) from the Eastern and Central Taurides. Eight fusulinid zones were identified and include 1.) the Fusulinella (Fusulinella) colaniae-Fusiella praetypica concurrent range zone, 2.) the Fusulinella (Fusulinella) bocki bocki concurrent range zone, 3.) the Protriticites ovatus-Quasifusulinoides aff. quasifusulinoides concurrent range zone, 4.) the Protriticites pseudomontiparus-Obsoletes cf. obsoletes concurrent range zone, 5.) the Montiparus paramontiparus range zone, 6.) the Triticites oezbekensis-Rauserites subobsoletus concurrent range zone, 7.) the Daixina (B.) ex gr. bosbytauensis-Daixina (D.) ex gr. robusta range zone and 8.) the Zellia nunosei-Pseudofusulinoides instabilis-Pseudofusulinoides convexus assemblage zone.Öğe Late Permian (Tatarian) fluvio-lacustrine successions in NW Anatolia (Zonguldak Terrane, Turkey): palaeogeographic implications(CAMBRIDGE UNIV PRESS, 2017) Okuyucu, Cengiz; Dimitrova, Tatyana K.; Goncuoglu, Mehmet Cemal; Gedik, IbrahimLate Permian fluvio-lacustrine successions of the Cakraz Formation in the Zonguldak Terrane between the regions of Akcakoca and Ereli were investigated in order to describe the litho- and biostratigraphic properties and explain the depositional environment. The studied succession with black, dark-grey to greenish-grey shales, siltstones and limestones is named the Alapl Member to distinguish it from the classical red clastic successions, which are tentatively named the Ereli Member of the Cakraz Formation. The organic-rich black shales, mudstones and limestones of the Alapl Member yielded palynological assemblages suggesting a Lopingian (Tatarian) age. The lack of any marine macro- or microfossils, the fine-grained character of the lithofacies with abundant plant material and the association of poorly sorted conglomerates in the middle part of the succession indicate possible deposition in a broad range of fluvial and lacustrine environments. Successions of similar age and depositional environment are known from the East European Variscan Belt in Bulgaria and Romania. Common successions were also developed in actively extending shallow-marine platforms on the NW Palaeotethyan margin at the end of the Permian Period.Öğe Middle Triassic back-arc basalts from the blocks in the Mersin Melange, southern Turkey: Implications for the geodynamic evolution of the Northern Neotethys(ELSEVIER, 2017) Sayit, Kaan; Bedi, Yavuz; Tekin, U. Kagan; Goncuoglu, M. Cemal; Okuyucu, CengizThe Mersin Melange is a tectonostratigraphic unit within the allochthonous Mersin Ophiolitic Complex in the Taurides, southern Turkey. This chaotic structure consists of blocks and tectonic slices of diverse origins and ages set in a clastic matrix of Upper Cretaceous age. In this study, we examine two blocks at two different sections characterized by basaltic lava flows alternating with radiolarian-bearing pelagic sediments. The radiolarian assemblage extracted from the mudstone-chert alternation overlying the lavas yields an upper Anisian age (Middle Triassic). The immobile element geochemistry suggests that the lava flows are predominantly characterized by sub-alkaline basalts. All lavas display pronounced negative Nb anomalies largely coupled with normal mid ocean basalt (N-MORB)-like high field strength element (HFSE) patterns. On the basis of geochemical modelling, the basalts appear to have dominantly derived from spinel-peridotite and pre-depleted spinel-peridotite sources, while some enriched compositions can be explained by contribution of garnet-facies melts from enriched domains. The overall geochemical characteristics suggest generation of these Middle Triassic lavas at an intra-oceanic back-arc basin within the northern branch of Neotethys. This finding is of significant importance, since these rocks may represent the presence of the oldest subduction zone found thus far from the Neotethyan branches. This, in turn, suggests that the rupturing of the Gondwanan lithosphere responsible for the opening of the northern branch of Neotethys should have occurred during the Lower Triassic or earlier. (C) 2016 Elsevier B.V. All rights reserved.Öğe Ordovician graptolites from the basal part of the Palaeozoic transgressive sequence in the Karadere area, Zonguldak Terrane, NW Turkey(ESTONIAN ACAD PUBLISHERS, 2014) Goncuoglu, M. Cemal; Sachanski, Valeri; Gutierrez-Marco, Juan Carlos; Okuyucu, CengizThe Karadere area to the east of Safranbolu in NW Anatolia is one of the very few localities in Turkey where the contact between the Cadomian basement and the Lower Palaeozoic transgressive succession is well exposed. The Ordovician graptolite Rhabdinopora flabelliformis (Eichwald) ssp. was found in the basal part of the Bakacak Formation, indicating an Early to early Late Tremadocian age for the beginning of the Palaeozoic transgression in the Zonguldak terrane. A few metres above this occurrence, another horizon contains Paradelograptus cf. antiquus (T. S. Hall), which mainly ranges into the Late Tremadocian. Higher up in the Ordovician succession, a new graptolite bed confirms an early Darriwilian (Dw1) age for the middle part of the Karadere Formation with the occurrence of the biozonal index Levisograptus austrodentatus (Harris & Keble) and the first record of Tetragraptus cor (Strandmark) in the area. The palaeobiogeographic distribution of these Karadere fossils is in agreement with a peri-Gondwanan affinity of the Zonguldak Terrane of the Pontides, NW Anatolia, during the Early-Middle Ordovician.Öğe Radiolarian biochronology of upper Anisian to upper Ladinian (Middle Triassic) blocks and tectonic slices of volcano-sedimentary successions in the Mersin Melange, southern Turkey: New insights for the evolution of Neotethys(PERGAMON-ELSEVIER SCIENCE LTD, 2016) Tekin, U. Kagan; Bedi, Yavuz; Okuyucu, Cengiz; Goncuoglu, M. Cemal; Sayit, KaanThe Mersin Ophiolitic Complex located in southern Turkey comprises two main structural units; the Mersin Melange, and a well-developed ophiolite succession with its metamorphic sole. The Mersin Melange is a sedimentary complex including blocks and tectonic slices of oceanic litosphere and continental crust in different sizes. Based on different fossil groups (Radiolaria, Conodonta, Foraminifera and Ammonoidea), the age of these blocks ranges from Early Carboniferous to early Late Cretaceous. Detailed fieldwork in the central part of the Mersin Melange resulted in identification of a number of peculiar blocks of thick basaltic pillow-and massive lava sequences alternating with pelagic-clastic sediments and radiolarian cherts. The oldest ages obtained from the radiolarian assemblages from the pelagic sediments transitional to the volcano-sedimentary succession in some blocks are middle to late Late Anisian. These pelagic sediments are overlain by thick sandstones of latest Anisian to middle Early Ladinian age. In some blocks, sandstones are overlain by clastic and pelagic sediments with lower Upper to middle Upper Ladinian radiolarian fauna. Considering the litho- and biostratigraphical data from Middle Triassic successions in several blocks in the Mersin Melange, it is concluded that they correspond mainly to the blocks/slices of the Beysehir-Hoyran Nappes, which were originated from the southern margin of the Neotethyan Izmir-Ankara Ocean. As the pre-Upper Anisian basic volcanics are geochemically evaluated as back-arc basalts, this new age finding suggest that a segment of the Izmir-Ankara branch of the Neotethys was already open prior to Middle Triassic and was the site of intraoceanic subduction. (C) 2016 Elsevier Ltd. All rights reserved.Öğe Refinements in biostratigraphy of the foraminiferal zone MFZ11 (late early Visean, Mississippian) in the Cebecikoy Limestone (Istanbul Terrane, NW Turkey) and palaeogeographic implications(CZECH GEOLOGICAL SURVEY, 2013) Okuyucu, Cengiz; Vachard, Daniel; Goncuoglu, Mehmet CemalThe Cebecikoy Limestone from the Variscan flysch of the Istanbul Terrane is assigned to the foraminiferal MFZ11 zone (late early Visean, formerly V2a). This zone is essentially the range zone of Uralodiscus rotundus. Additional bioevents are proposed for characterizing the upper part of this biozone (MFZ11B subzone): the LAD of Eoendothyranopsis and the FAD of Pararchaediscus and Conilidiscus. The majority of foraminifers and algae, belonging locally to MFZ11 are well-known, except for the following taxa: Issinella luteotubulifomis sp. nov., I. enormis sp. nov., Vicinesphaera parasqualida sp. nov., Planogloboendothyra modesta sp. nov. and Endothyra irinaeformis sp. nov. The Istanbul Terrane is connected with the southern branch of the Palaeotethys, whereas the Zonguldak Terrane is connected with the northern branch of this one.
