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We present an investigation the Late Quaternary seismic stratigraphy of the shelf area of the northern the Sea of Marmara extending from its northern coast (between Silivri and Kumkapi) to approximately 100 m depth, using shallow high-resolution seismic reflection data along 73 N-S and 15 E-W lines. Seismic sequence analysis is used to identify the depositional systems, associated sedimentation conditions, and relative sea level changes. Seismic stratigraphic interpretations indicate the presence of four distinct seismic units (SU I, II, III and IV) underlying the shelf area. Seismic units are bounded by erosional unconformities overlying an acoustic basement. Seismic unit I constitutes the acoustic basement (AB), which is characterized by chaotic, subparallel, and wavy reflections that out locally off the rocky shorelines and along the crests of the positive structures where the sedimentary cover is absent. Seismic unit II is interpreted to represent the pre-Holocene deposits and exhibits subparallel reflections. Seismic unit II is interpreted to have been subjected to sub-aerial erosion during the Last Glacial Maximum. Seismic unit III-IV are interpreted to have formed during the Holocene (Flandrian) transgression and have parallel/subparallel internal reflection patterns. The top of seismic unit IV forms the present-day sea floor. As a result of the presence of fill, seismic facies within seismic unit IV reflect differences in depositional processes. The bathymetry of the study area has a close relation with sedimentation dynamics, tectonic, wave and flow dynamics and palaeotopograpy. Particularly, sudden dip changes determined at the shelf area might have been due to fault and/or fault systems that control the bottom topography. Seismic activity in the Sea of Marmara region has a key role the northern branch of the North Anatolian Fault Zone (NAFZ) affecting on the tectonic activity of the study area. The last two earthquakes in Izmit and Duzce, Turkey, in 1999 have been originated from NAFZ. The presence of several faults on various scales in the seismic profiles of the study area is identified. The active normal faults in the Holocene units that disturb the seafloor are determined. Most of these faults are intense in the eastern part of research area. The isopach map of Holocene sediment (seismic unit III and IV) indicates that the maximum sediment accumulations (up to 36 m) occur in the offshore areas of Bakirkoy and Kumkapi. Young sediment thicknesses are common on the shoreline areas in the investigated area. (C) 2014 Elsevier Ltd. All rights reserved. |
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