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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 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.
