Mehmet Sakınç

An abrupt drowning of the Black Sea shelf

Abstract During latest Quaternary glaciation, the Black Sea became a giant freshwater lake. The surface of this lake drew down to levels more than 100 m below its outlet. When the Mediterranean rose to the Bosporus sill at 7,150 yr BP 1 , saltwater poured through this spillway to refill the lake and submerge, catastrophically, more than 100,000 km2 of its exposed continental shelf. The permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of Europe at that time.

Palaeogeographical evolution of the Thrace Neogene Basin and the Tethys-Paratethys relations at northwestern Turkey (Thrace)

Abstract The Thrace Neogene Basin situated in northwestern Turkey was initiated by strike-slip faulting that was active from the Early Miocene until the end of the Pliocene. During the Early Miocene, it began to form under the control of the Thrace–Eskisehir Fault Zone, initiated by continental collision in northwestern Anatolia (Late Oligocene–Early Miocene). During the late Early Miocene, the basin was a site of mainly fluviatile and limnic sedimentation to the west and marine sedimentation via the Paratethyan transgression in the north. With the onset of the Middle Miocene, the Thrace Block started to rotate in a counterclockwise sense and escaped westward with respect to the Strandja–Istanbul block owing to rejuvenation of fossil fault systems within it. In this period, warm marine conditions were also established around the Gulf of Saros through a Mediterranean originated transgression. During the Middle–Late Miocene fluviatile and limnic conditions were created over the western Thrace by the westerly propagation of the Thrace–Eskisehir Fault Zone. One of the principal results of the Early–Middle Miocene tectonics is the tilting of the Strandja–Istanbul Block to the south, severing the Tethys and the Paratethys. During the latest Miocene–Early Pliocene period, the Thrace–Eskisehir Fault Zone was deactivated because of the evolution of the North Anatolian Fault Zone to the south. The resurrected Ganos Fault Zone situated on the dissected fossil suture zone in the Sea of Marmara also joined the North Anatolian Fault Zone, uplifting the Gelibolu Peninsula and, thus, severing the connection that existed between the Sea of Marmara and the Paratethys. The Sea of Marmara eventually became an endemic basin by the activity of the North Anatolian Fault Zone.

Origin of the Sea of Marmara as Deduced from Neogene to Quaternary Paleogeographic Evolution of its Frame

The Sea of Marmara Basin (SMB) is connected to the fully marine Mediterranean by the Dardanelles strait and to the brackish Black Sea by the Thracian Bosporus. This linkage to two different marine realms with contrasting water chemistry has been a prime control on the sedimentary history of the SMB, which in turn was controlled by its tectonics. Isolation from any of these realms resulted in drastic changes in its paleoceanographic conditions and made it a part either of the global ocean system or of a brackish-marine environment, depending on the realm from which the connection was severed. The SMB represents the inundated part of the northwestern Anatolian graben system that resulted from the interaction between the North Anatolian fault (NAF) zone and the present N-S extensional tectonic regime of the Aegean. The geologic history of this basin began during the late Serravallian when the NAF was initiated. The first inundation of the basin coincided in both time and space with this initiation. The invad...

Late Pleistocene uplift history along the southwestern Marmara Sea determined from raised coastal deposits and global sea-level variations

Pleistocene raised coastal deposits characterized by locally abundant shells, aragonite-cemented beachrock and associated nearshore deposits border the western Marmara Sea at elevations of 0–50 m. Field observations confirm that these deposits formed during a series of transgressive and regressive events. U/Th dates in 16 in situ shells from four localities show that the peak of the transgressions occurred during the highstands of oxygen isotopic stages 7 and 5, between ∼53 and ∼210 ka. The elevations of these dated deposits can be used to quantify their post-depositional uplift and indicate that the entire western Marmara shelf, including the Strait of Canakkale (Dardanelles) has been rising at an average rate of ∼0.40 mm yr−1 since ∼225 ka. The primary cause of uplift is the local compression associated with a restraining bend in the western segment of the North Anatolian Fault. Paleogeographic maps constructed using the average rate of tectonic uplift and detailed topographic and bathymetric maps reveal that prior to glacial oxygen isotopic stage 8 the Marmara Sea was never isolated from the Aegean Sea, even when global sea level was low, because the floor of the Strait of Canakkale was too deep early in its uplift history. The dominance of Mytilus edulis in raised coastal terraces dating from the lowstand of glacial oxygen isotopic stage 8 suggests that the degree of communication between the Aegean Sea and Marmara Sea was comparable to that of the present. During the peak of glacial oxygen isotopic stage 6, the floor of the strait was subaerially exposed, isolating the Marmara Sea for the first time in the Pleistocene from the higher salinity Mediterranean water inflow and possibly causing it to become a blackish-water lake. During interglacial isotopic stages 9, 7 and 5, the Strait of Canakkale was very wide and deep (∼100–125 m), and there were two subsidiary channels (Bolayir and Eceabat channels), providing additional links between the Aegean Sea the Marmara Sea, further promoting significant water exchange between these basins. The dominance of Ostrea edulis in the raised terraces dating from isotopic stages 5 and 7 confirms an enhanced penetration of the Mediterranean water mass into the Marmara Sea. The history of communication between the Black Sea, fed by central and northern European drainage systems, and the low-latitude Mediterranean Sea is of fundamental importance in understanding the genesis of organic-rich sapropel deposits throughout the region. The results presented in this paper caution against the simple assumption that sea-level change alone controlled the degree of connection across this oceanographic gateway. Instead, the physiography and paleoceanography of the region were controlled both by variations in global sea level and the rate of uplift in an area of active transpression.

The effects of the North Anatolian Fault Zone on the latest connection between Black Sea and Sea of Marmara

Abstract The development of the Strait of Istanbul is also one of the principal results of the tectonics which led to the evolution of the North Anatolian Fault Zone (NAFZ) in the Marmara Region 3.7 Ma ago. High resolution seismic profiles from the Marmara entrance of the Strait of Istanbul show a folding which occurred after the deposition of the parallel reflected Tyrrhenian sediments. Over the Tyrrhenian strata, a fondoform zone of a deltaic sequence and marine sediments of the latest sea level rising are present. These sediments also display syn-depositional folding. This situation implies that a local compressional stress field was created over the area probably since the Wurm Glacial age. This recent variation of the tectonic regime in the northern shelf of the Sea of Marmara may indicate a significant change in the development of the NAFZ through the Sea of Marmara. This variation of evolution of the NAFZ affected the latest development of the Strait of Istanbul via clockwise rotation of the Istanbul and Kocaeli peninsulas by right-lateral shearing between two zone bounding faults. This rotation has led to the development of NNE–SSW left-lateral faults in the Strait of Istanbul and local compressional and tensional areas explaining the compressional structures seen in the southern entrance of the Strait of Istanbul. Therefore, the latest Mediterranean–Black Sea connection was established by means of the sufficient deepening of the Bosphorus channel by a variation in the evolution of NAFZ through the Sea of Marmara.

Neogene Paratethyan Succession in Turkey and Its Implications for the Palaeogeography of the Eastern Paratethys

Abstract The Neogene marginal succession of the Eastern Paratethys (EP) crops out along the southern Black Sea coast and in the Marmara region of Turkey, and provides important clues to the tectono-sedimentary and palaeoceanographic conditions. In the Tarkhanian stage, the southern margin of the EP basin was largely a carbonate platform covered by warm, marine waters. From the end of the Tarkhanian to the Early Chokrakian there was an overall emergence throughout the basin, which is indicated by an influx of siliciclastic sediments. The fossil assemblage indicates that normal marine conditions persisted during most of this period, except for a salinity reduction towards the end due to an eustatic isolation of the basin, which in turn led to anoxic bottom water conditions. The Late Chokrakian isolation became even more severe during the Karaganian as indicated by the endemic fossil assemblage indicating brackish-marine conditions. Carbonate platform conditions prevailed in the northern Pontides during this time. In the Early Konkian, the basin was reconnected briefly with the world ocean by a transgression from the Indo-Pacific Ocean. In the Late Konkian there was a return to brackish-marine conditions. Lower Sarmatian sediments are absent in the southern margin of the EP, but elsewhere in the basin this stage is characterized by a widespread marine transgression. In the Middle-Late Sarmatian, the EP basin was partially isolated with freshening and anoxic bottom-water conditions. During this time there was a brief marine transgression from the Mediterranean into the Marmara region, but it did not reach the Paratethyan basin. The Pontian is characterized by an extensive transgression from the EP that inundated the Marmara and northeastern Aegean regions. The connection with the Marmara Basin was cut off during the Kimmerian and re-established during the Late Akchagylian, when the EP basin was inundated by the Mediterranean waters via the Sea of Marmara as a result of increased North Anatolian Fault activity and a short-term global sea level rise.