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Öğe Aeolian imprints of multiple Mediterranean invasions of the Black Sea during Pleistocene(Elsevier, 2022) Erginal, Ahmet Evren; Kiyak, Nafiye Gunec; Makaroglu, Ozlem; Bozcu, Mustafa; Ozturk, Muhammed Zeynel; Selim, Haluk Hamit; Nowacyzk, Norbert R.Climate changes determined the repeated connections between the Black Sea, Caspian Sea and Mediterranean Sea. The landlocked anoxic Black Sea basin was exposed to several transgressions throughout Quaternary by the Mediterranean Sea through the Straits of Istanbul (Bosphorus) and by the Caspian Sea through the Manych-Kerch spillway. Sedimentological records of these connections are limited mostly to the marine terrace deposits of Marine Isotope Stage (MIS) 5e while the pre-MIS 5e period remains uncertain due to a lack of robust facies and chronological data from deep-sea sedimentary sequences. Here we discuss the imprints of multiple Mediterranean transgressions during Middle Pleistocene in the Black Sea based on facies analysis and the optical age of coastal carbonate aeolianites. Contrary to today's hydro-climate of the Black Sea, the aeolianites bear witness to the transformation of the Black Sea into a warm inland sea during successive Mediterranean invasions. Prior to the onset of aeolian deposition, paleosols were formed on the Eocene-aged hardened sandy silts, suggesting strongly washed soil. This is evidenced by no calcium carbonate and a high Rb/Sr ratio, with quartz amounting to of 99.8%. According to our OSL ages, carbonates deposited on the shelf plain under higher temperature and increased evaporation conditions in MIS 15 and the later interglacial phases were transported to the coastal sand dunes during the transitional phases of MIS 15-14, MIS 13-12, MIS 11-10 and MIS 9-8. We suggest that the carbonate-rich and ooid-containing aeolianites were repeatedly formed in the multiple Mediterranean transgression stages, beginning with an increasingly severe dry phase following the Brunhes-Matuyama magnetic reversal.Öğe Cementation characteristics and age of beachrocks in a fresh-water environment, Lake Iznik, NW Turkey(Elsevier, 2012) Erginal, Ahmet Evren; Kiyak, Nafiye Gunec; Ozturk, Muhammed Zeynel; Avcioglu, Mustafa; Bozcu, Mustafa; Yiğitbaş, ErdinçThis paper focuses on the cement characteristics and optical luminescence age of late Pleistocene-Holocene beachrock, exposed on the southeast shore of freshwater Lake Iznik in northwest Turkey, based on field observations, various spectroscopic analyses and optical dating results. The studied beachrock is a poorly-sorted coastal conglomerate composed mostly of gravels derived from surrounding volcanic rocks and marbles as well as quartz and carbonate grains. We identified different types of cements; dominated by micritic envelopes, bladed isopachous aragonite rims, void fills, radial aggregates and meniscus bridges, implying no single origin. Cementation characteristics indicate that marine-like cement micro-fabrics may occur in freshwater lake environments where the lake-water chemistry favors carbonate precipitation. OSL data revealed the existence of older beachrock dating back to 20.2 ka, together with younger Holocene-age beachrock of between 5.6 and 2.4 ka. This suggests that younger beachrocks have been superimposed on older cemented carbonates through the removal of carbonates by wave motion (splash and spray) during lower lake level conditions. (C) 2011 Elsevier B.V. All rights reserved.Öğe Depositional Characteristics of Carbonate-Cemented Fossil Eolian Sand Dunes: Bozcaada Island, Turkey(Coastal Education & Research Foundation, 2013) Erginal, Ahmet Evren; Ekinci, Yunus Levent; Demirci, Alper; Avcioglu, Mustafa; Ozturk, Muhammed Zeynel; Turkes, Murat; Yiğitbaş, ErdinçErginal, A.E.; Ekinci, Y.L.; Demirci, A.; Avcioglu, M.; Ozturk, M.Z.; Turkes M., and Yigitbas, E., 2013. Depositional characteristics of carbonate-cemented fossil eolian sand dunes: Bozcaada Island, Turkey. Journal of Coastal Research, 29(1), 78-85. Coconut Creek (Florida), ISSN 0749-0208. Coastal eolianite on the south coast of Bozcaada Island, Turkey, was investigated by field observations, petrographic and climatological examinations, and electrical resistivity tomography data. The 4- to 7-m-thick eolianite, including rhizolith morphotypes characterized by root tubules and bifurcated root casts, demonstrates dune-sand accumulation during the Upper Pleistocene. Our results showed that paleowind drift and recent windblown sand drift on the island are similar. The dune sands exhibit various cement types formed of calcite and aragonite, such as micrite encrustations, meniscus and gravitational cements, and in particular, void fills. Dune-sand accumulation took place on the truncated surface of Miocene deposits. Geophysical data showed the existence of large weathered cavities within the eolianite and a high-angle normal fault, which displaces the eolianite, together with the underlying Miocene unit.Öğe Eolianite and coquinite as evidence of MIS 6 and 5, NW Black Sea coast, Turkey(Elsevier Sci Ltd, 2017) Erginal, Ahmet Evren; Kiyak, Nafiye Gunec; Selim, Hamit Haluk; Bozcu, Mustafa; Ozturk, Muhammed Zeynel; Ekinci, Yunus Levent; Demirci, AlperThis paper discusses the implications of a lowstand carbonate eolianite and overlying transgressive sequence of coquinite at Sile on the Turkish Black Sea coast based on composition, depositional characteristics and optical age estimations. The cross-bedded eolianite is a mixed ooid quartz grainstone in composition, yielding a depositional age matching MIS 6. It formed at the backshore of the paleobeach with the supply of sediment the from the beach face and offering insights into the drift of mixed shallow marine carbonates and siliciclastics together with radial ooids by onshore winds from a subaerially exposed high- to low-energy ooid shoals and oolitic sand complexes which developed parallel to the shoreline on the shallow shelf margin. During this lowstand, a low-relief dune retaining a record of opposing paleowind directions than that of prevalent northeasterly winds of today appears to have been lithified to form dune rock (aeolinite) under drier conditions compared to the present. Coinciding with MIS 5e, shallow marine coquina beds resting unconformably on the eolianite indicate the occurrence of the Mediterranean transgression during the last interglacial, as confirmed by benthic foraminifera within the high-salinity tolerant coquina shells. (C) 2017 Elsevier B.V. All rights reserved.Öğe First record of beachrock on Black Sea coast of Turkey: Implications for Late Holocene sea-level fluctuations(Elsevier, 2013) Erginal, Ahmet Evren; Ekinci, Yunus Levent; Demirci, Alper; Bozcu, Mustafa; Ozturk, Muhammed Zeynel; Avcioglu, Mustafa; Oztura, ErdalWe present new data on the diagenetic characteristics, subsurface nature and radiocarbon ages of beachrock from the Thracian Black Sea coast of Turkey, indicative of sea-level changes and climatic conditions favoring lithification of beach sands between 5.4 ka and 3.5 ka cal BP. Micrite coatings and succeeding meniscus cements typify diagenetic history and suggest a two-stage cementation over this timeframe. The early cements are typical of upper intertidal zone when the sea-level was likely similar to that of today. The ensuing intergranular bridges refer to an approximate 2 m decline in sea-level, favoring downward percolation of meteoric waters related to subaerial exposure, marked by a reduction in Mg concentration and dissolution pits on early cement coatings. Formation of beachrock during this bimillennial period could be associated with relatively drier conditions promoting the precipitation of connective cements. (C) 2013 Elsevier B.V. All rights reserved.Öğe Records of repeated drought stages during the Holocene, Lake Iznik (Turkey) with reference to beachrock(Pergamon-Elsevier Science Ltd, 2016) Ozturk, Muhammed Zeynel; Erginal, Ahmet Evren; Kiyak, Nafiye Gunec; Demirci, Alper; Ekinci, Yunus Levent; Curebal, Isa; Avcioglu, MustafaThe cement fabrics, subsurface nature and optically stimulated luminescence age of beachrocks along the shores of Lake Iznik in NW Turkey were studied within the context of Holocene lake level changes. With a maximum thickness of 1.5 m, the low-angle (average 5-10 degrees) beds are composed of coarse grains and small gravels and extend up to 5 m offshore at their most lakeward extremities. Cement textures on and around the poorly-rounded grains are made up of micrite envelopes and meniscus bridges as well as acicular aragonite rims. Geoelectrical resistivity sections taken from a representative location along the beach where the beds have maximum thickness showed that the sand-buried beds are followed up to about 24 m landward. Based on the OSL ages of 33 samples, the cemented beds occurred at four drier periods of the following: Pre- and Early Holocene (dated to 15-9 ka), Holocene Climatic Optimum (7.9-5.6 ka), Middle Holocene (4.9 ka-2.8 ka) and Late Holocene (2.0 ka-0.9 ka). (C) 2015 Elsevier Ltd and INQUA. All rights reserved.
