Browsing by Author "Atakul-Ozdemir, Ayse"

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Conodont Biostratigraphy of Upper Devonian Tephra Bearing Deposits in the İstanbul-Zonguldak Terrane, Nw Turkey: Insights on the Kellwasser Events
(Univ Studi Milano, 2024) Atakul-Ozdemir, Ayse; Turkmenoglu, Asuman Gunal; Goncuoglu, M. cemal; Bozkaya, Omer; Okuyucu, Cengiz
New evidence for a biostratigraphic assessment of the limestone succession comprising K-bentonite levels exposed in the Y & imath;lanl & imath; Formation of the Istanbul-Zonguldak Terrane are provided from conodonts at the Gavurp & imath;nar & imath; quarry in Bart & imath;n area (NW Turkey). The succession depicts a shallow marine, nearshore facies setting that comprises rare and low diversity conodont associations mainly exemplified by the species of Ctenopolygnathus, Icriodus and Polygnathus. Conodont faunas from the lower part of the section are of late Frasnian age, including the taxa Icriodus subterminus Youngquist, 1947, Polygnathus aff. xylus Stauffer, 1940, Icriodus iowaensis iowaensisYoungquist & Peterson, 1947 and Ctenopolygnathus brevilaminus Branson & Mehl, 1934, and the upper part is assigned to early Famen-nian marked by the first appearance of Icriodus cornutus Sannemann, 1955. The local biostratigraphic framework of the Y & imath;lanl & imath; Formation is correlated with the upper Frasnian Lower rhenana to the lower Famennian Middle triangularisstandard conodont zonations. Considering the described species, the Frasnian-Famennian boundary corresponds to a slight change in conodont fauna and is assigned within the local Icriodusiowaensis iowaensis Zone. Accordingly, the novel K-bentonite age data potentially indicates the evidence for the Kellwasser events in northern Turkey, improving paleogeographic correlations of the Istanbul-Zonguldak Terrane with other terranes in Laurasia and Peri-Gondwana.
Conodont Zonation and the Devonian/Carboniferous (famennian/Tournaisian) Boundary in the Naltas Section, Eastern Taurides, Turkey
(Pergamon-elsevier Science Ltd, 2017) Atakul-Ozdemir, Ayse
Conodont faunas from the Devonian/Carboniferous Naltas section (eastern Taurides, Turkey) are presented. The faunas include important marker species of the latest Devonian earliest Carboniferous interval, belonging to the genera Siphonodella, Bispathodus, Polygnathus, Pseudopolygnathus, Apatognathus and Branmehla. Four conodont zones, comparable to the standard conodont zonation, are established in the studied succession, from the oldest to the youngest: (1) Bispathodus ultimus, (2) Siphonodella praesulcata Zones (Upper Famennian), (3) Siphonodella sulcata and (4) Siphonodella bransoni Zones (Lower Tournaisian). The Devonian/Carboniferous boundary in the eastern Taurides is recognized by the first appearance of Siphonodella sulcata. (C) 2016 Elsevier Ltd. All rights reserved.
Foraminiferal Responses To Sea Level Changes Across the Mid-Carboniferous Boundary in Central Taurides (Turkey)
(Polish Mineral Eng Soc, 2024) Atakul-Ozdemir, Ayse; Altiner, Demir; Ozkan-Altiner, Sevinc
The response of benthic foraminiferal assemblages to relative sea-level changes during the mid-Carboniferous succession of the Yar & imath;cak Formation in the Central Taurides is assessed with respect to sedimentary cyclicity and sequence stratigraphy by quantitative analysis. The data derived from the relative abundances of foraminifera have critical significance in the understanding of cyclic patterns and sea level changes in carbonate deposits. Calcareous foraminiferal groups including archaediscids, eostaffellids, irregularly coiled bilocular forms, unilocular forms, paleotextularids, biseriamminids, endothyrids, and pseudoendothyrids have been counted and analysed in this study. The mid-Carboniferous boundary succession predominantly covering uniform lithology of carbonates alternated with sandstone layers involves shallowing upward cycles used for the revealing of sea-level fluctuations. The relative abundances of these foraminiferal groups reveal a striking response to cyclicity with the reductions in the abundances towards the upper part of the cycles. Conversely, the abundances of pseudoendothyrids and endothyrids do not exhibit any considerable variations within the studied interval.
Paleogeographic Implications of the Permian Shallow Marine Carbonates in the Eastern Lake Van Region (Eastern Turkey): Foraminiferal Biostratigraphic and Sequence Stratigraphic Constraints
(Wiley, 2019) Atakul-Ozdemir, Ayse
The study focuses on the Middle Permian recrystallized limestone succession, previously considered as Triassic, at the eastern parts of Lake Van (eastern Turkey) representing the northern margin of Gondwana. The Middle Permian successions in the region are mainly composed of slightly metamorphosed, recrystallized limestones. The shallow-water depositional settings of the studied units are characterized by the relative dominance of smaller foraminifers and rare occurrence of fusulinids. Middle Permian foraminifers recorded from eastern Anatolia are typically Tethyan assemblages for the Capitanian (Guadalupian) age. Detailed microfacies analysis by textural analysis and faunal assemblages have been undertaken throughout the studied sections. The Capitanian carbonates of the region are mainly characterized by six major microfacies types representing shallow marine environments, ranging from foreshoal environment to shoal and backshoal environments. Within the scope of sequence stratigraphic interpretations, vertical stacking patterns of these microfacies types reflecting different depositional environments reveal the presence of two third-order depositional sequences, each of which consists of a transgressive systems tract and a highstand systems tract. Within the context of sequence stratigraphy, the microfacies changes point out the relative sea-level fall towards the upper part of the sections, coinciding with the onset of a regression recorded worldwide in the Capitanian.
A Pelagic Upper Devonian Sequence in Sariyer, Istanbul
(Tubitak Scientific & Technological Research Council Turkey, 2020) Okay, Aral; Atakul-Ozdemir, Ayse; Okay, Nilgun
The Palaeozoic sequence in the Istanbul region is made up of a continuous transgressive sedimentary series extending from Ordovician continental clastic rocks to Lower Carboniferous turbidites. The middle part of this sequence consists predominantly of carbonates ranging from shallow marine Upper Silurian limestones to latest Devonian to earliest Carboniferous deep marine limestones and shales. Here, we describe a new Upper Devonian deep marine limestone-siltstone section from the Sariyer region in the European part of Istanbul. The 37-m thick section located in the campus of the Istanbul Technical University consists at the base of dark micritic limestones interbedded with carbonate-rich siltstones, which pass up into siltstones with rare micritic limestone lenses and beds. Conodonts indicate a late Famennian (latest Devonian) age for the ITU campus section; 5 conodont biozones are documented; Pseudopolygnathus granulosus, Polygnathus styriacus, Palmatolepis gracilis manca, Palmatolepis gracilis expansa, and Bispathodus aculeatus aculeatus. The Late Devonian fauna from the ITU Campus section are dominated by the important marker species of Palmatolepis, Bispathodus and Polygnathus. There are also some Branmehla, Mehlina, and Icriodus elements within the succession. The conodont assemblages are representative of the palmatolepid-bispathodid biofacies, which indicate deposition on an outer shelf to slope environment.
Structural Elements and Neogene Lithostratigraphy of the Manavgat Basin (Antalya, Turkey)
(Tmmob Jeoloji Muhendisleri Odasi, 2024) Yilmaz, Yusuf Emrah; Atakul-Ozdemir, Ayse; Koc, Ayten
The Tauride fold-thrusts belt has formed under similar to S-N convergence between the Africa and Eurasian plates since Cretaceous time. This movement also resulted in the development of the complex tectonic structure known as the Isparta Angle. In the Neogene period, the western and central Taurides and the inner part of the Isparta Angle became overlain by marine sedimentary basins (Antalya Basin Complex). The Manavgat Basin is one of these marine basins, and unconformably rests on the Tauride in the north. Basically, the Manavgat Basin has a sedimentation thickness of more than 1 km from the Early Miocene to Pliocene. Hence, it is expected to keep the geological records regarding the crustal deformation, besides the lithostratigraphic records during this time. Lithostratgraphically, seven basic units have been identified in the Manavgat Basin. These are, in line with previous studies; 1) Tepekli Formation (Burdigalian-E. Langhian), 2) Oymapinar Limestone (G. Burdigalian-Langhian), 3) Cakallar Breccia (Langhian), 4) Geceleme Formation (G. Langhian-Serravalian), 5) Karpuzcay Formation (G. Langhian-Tortonian), 6) Pliocene units (Yenimahalle and Kursunlu formations), and 7) Belkis Conglomerate (Quaternary). Biosamples were collected from two different measured sections of the Karpuzcay Formation, and the age of the formation was determined. These show that the Karpuzcay Formation was deposited in a deep marine outer neriticbathyal environment from the Late Langhian to Tortonian. In addition to lithostratigraphic features, structural elements forming the Manavgat Basin were also studied, and the Tortonian aged Cardakkoy Fault was described for the first time in this study. As a result, the presence of two different tectonic regimes in the region was determined. Accordingly, the Manavgat Basin developed under the influence of an extensional tectonic regime before the Tortonian, and of a compressional system during the post-Tortonian. This study indicated that N-S directional convergence between Eurasia and Africa and the kinematics of the fragmented subducted plate under the Isparta Angle should be reevaluated based on these paleostress phases.
X-Ray Nanotomography and Electron Backscatter Diffraction Demonstrate the Crystalline, Heterogeneous and Impermeable Nature of Conodont White Matter
(Royal Soc, 2021) Atakul-Ozdemir, Ayse; Warren, Xander; Martin, Peter G.; Guizar-Sicairos, Manuel; Holler, Mirko; Marone, Federica; Donoghue, Philip C. J.
Conodont elements, microfossil remains of extinct primitive vertebrates, are commonly exploited as mineral archives of ocean chemistry, yielding fundamental insights into the palaeotemperature and chemical composition of past oceans. Geochemical assays have been traditionally focused on the so-called lamellar and white matter crown tissues; however, the porosity and crystallographic nature of the white matter and its inferred permeability are disputed, raising concerns over its suitability as a geochemical archive. Here, we constrain the characteristics of this tissue and address conflicting interpretations using ptychographic X-ray-computed tomography (PXCT), pore network analysis, synchrotron radiation X-ray tomographic microscopy (srXTM) and electron back-scatter diffraction (EBSD). PXCT and pore network analyses based on these data reveal that while white matter is extremely porous, the pores are unconnected, rendering this tissue closed to postmortem fluid percolation. EBSD analyses demonstrate that white matter is crystalline and comprised of a single crystal typically tens of micrometres in dimensions. Combined with evidence that conodont elements grow episodically, these data suggest that white matter, which comprises the denticles of conodont elements, grows syntactically, indicating that individual crystals are time heterogeneous. Together these data provide support for the interpretation of conodont white matter as a closed geochemical system and, therefore, its utility of the conodont fossil record as a historical archive of Palaeozoic and Early Mesozoic ocean chemistry.