HIGH-RESOLUTION SEISMIC PROFILING IN THE SEA OF MARMARA (NORTHWEST TURKEY) - LATE QUATERNARY SEDIMENTATION AND SEA-LEVEL CHANGES

High-resolution sparker seismic profiling was carried out in the Sea o f Marmara (northwest Turkey) to study the late Quaternary tectonics an d sedimentation of this important active basin at the western end of t he North Anatolian fault zone. A sedimentary unit interpreted as the c linoforms of a prograding delta was observed in places along the outer part of the southern shelf. The topset-foreset transitions of the lat est clinoforms cluster around 100 m below present sea level; they were probably deposited during the last glacial maximum and early phase of deglaciation, between 25 and 13 k.y. B.P., when the level of the Aege an was below that of the Dardanelles sill (60 - 70 m below sea level a t present). Therefore, the Sea of Marmara was isolated from the Aegean during the last glacial maximum, but it is possible that a fluvial ov erflow existed across the Dardanelles during this time, stabilizing th e level of the ''Marmara Lake'' and allowing the delta progradation. R ivers that drain into the Sea of Marmara from the south have a much gr eater combined drainage basin area and sediment flux than those draini ng the region to the north. This may explain the much broader shelf to the south: half graben bounded by north-dipping normal faults observe d within the southern shelf would tend to trap sediment sourced from t he south and subdue any sea-bed morphology on the shelf.