• Denizhan Vardar

      Articles written in Journal of Earth System Science

    • Seismic stratigraphy and depositional history of the BüyükÇekmece Bay since Latest Pleistocene, Marmara Sea, Turkey

      Denizhan Vardar Hakan Alp Bedri Alpar

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      High-resolution seismic data shed light on latest Pleistocene and Holocene sedimentation beneath the BüyükÇekmece Bay, northern shelf area of the Marmara Sea, Turkey. Discontinuous fluvio-marine and marine deposits overlying the erosional truncation surface of Oligocene–Lower Miocene deposits are as thick as 30 m and preserved preferentially within the incised valleys that were controlled by some old faults. A series of prograding shoreline, laterally passing to the latest Pleistocene–Holocene valley-fill deposits, are thought to have accumulated mainly during times of shoreline transgression and sealevelrise. The overall morphology and stratigraphic setting observed in the BüyükÇekmece Bay and at the southern outlet of the Bosphorus Strait have nearly same characteristics, implying that similar hydrodynamic conditions, erosional and depositional processes were mainly under the control of strong northerly flows during the Late Quaternary. These flows were less powerful in the BüyükÇekmece region with decreased sediment input and smaller accommodation space.

    • Evidence for active faulting in the eastern part of the Gulf of Saros, northern Aegean, from high-resolution seismic data

      Denizhan Vardar

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      This study focuses on the determination of the near-surface tectonic features in the eastern part of the Gulf of Saros, a highly active seismic region within the North Anatolian Fault Zone. Approximately 350-km-line high-resolution seismic data were acquired to understand the active tectonic setting of the inner side of the gulf. The Ganos Fault, which generated the 9 August 1912 earthquake (Mw = 7.3) in western Turkey, enters into the Gulf of Saros from the east, cuts the southern margin of the gulf forming a trough which becomes broader and deeper westward. The seismic data reveal that the fault is not made up of a single segment or a pair of border faults bounding the trough. According to the seismic images of the fault segments, however, the emanating earthquake energy will possibly be carried by two different faults; namely the Ganos and Saros segments. These fault segments will be presented first in this paper in detail from new collected seismic data at the inner part of the gulf, and will be used to help a new tectonic model that explains how the Ganos segment controls the northern margin of the trough while the Saros segment controls the central part of the main trough. The latter is responsible from the development of an active basin and it forms the sudden deepening observed on the trough.

    • Stratigraphical and morphological aspects of the northern Marmara shelf based on seismic data

      Aslihan Nasif Derman Dondurur Denizhan Vardar

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      Recent sedimentation and Plio-Quaternary stratigraphy of northern Marmara shelf has been investigated by high-resolution seismic datasets. Seismic data indicate that a thin cover of Plio-Quaternary unit (termed Unit 1) overlies the Miocene/Oligocene age older sediments (termed Unit 2). The erosional surface between Unit 1 and Unit 2 is the regional unconformity for the shelf formed during the last sea level low stand. Unit 1 is subdivided into two sub-units as Unit 1a for Holocene deposits accumulated after the last glacial maximum (LGM) and Unit 1b for fluvial sediments deposited during the last low stand of the Marmara Sea. The thickness of the Holocene sediments is maximum at SW of Bosphorus outlet, in the Buyukcekmece Bay and along the coastal area between Silivri and Buyukcekmece reaching approximately 32 m. Mean sedimentation rate of the entire northern shelf is calculated as 0.4 m/1000 yr for the last 12,000 yr based on the Holocene sediment thickness. There are four depressions in the western part of the shelf, which correspond to palaeolakes during the LGM filled by Plio-Quaternary sediments. Transition from lacustrine to marine conditions in the palaeolakes occurred when the Marmara Sea level exceeded −62 m threshold depth during the sea level rise following the LGM at approximately 12,500–13,000 yr before present (BP).

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