Sea level changes and depositional environments in the Izmit Gulf, eastern Marmara Sea, during the late glacial-Holocene period

Offshore and onshore stratigraphic studies, together with high-resolution shallow seismic reflection profiling and multibeam bathymetric mapping, were carried out in the western and central part of the Izmit Gulf. These studies indicate that the Izmit Gulf was a lacustrine environment as part of the Marmara “lake” during the late glaciation and early deglaciation until ~12 kyr BP, when the Marmara basin was inundated by the Mediterranean waters. Correlation of 14C-dated onshore and offshore stratigraphic units in the western Izmit Gulf indicates that generally coarse late glacial sediments overlie a marked erosion surface formed during the low water level of the Marmara “Lake”. These coarse sediments are succeeded by 10.4-7 kyr BP old transgressive and by late Holocene post-transgression mud units. The bathymetry and subbottom chirp profiles clearly show that the palaeoshoreline of this lake was located at -85 m, having been controlled by the bedrock sill depth of the Çanakkale Strait. Another palaeoshoreline observed –65 m on northern margin of the Western Izmit and Karamürsel basins was probably formed during the Younger Dryas sea-level stillstand. The shelf areas during about this time were colonized by bioherms, which were subsequently drowned and disappeared after further rise of the sea level. The presence of a –65 m marine paleoshoreline in the Karamürsel basin indicate that the sill restricting this basin to the west was much deeper than its present –55 m level and placed further south. The Gölcük basin restricted by a –38 m sill to its west, was probably not flooded by marine waters until ~9 kyr BP.