Tectonic evolution of the northern shelf of the Marmara Sea (Turkey): interpretation of seismic and bathymetric data

This study is based on the geological interpretation of 250 km2 of multibeam bathymetric data coupled with 300 km of seismic profiles recorded on the northern shelf of the Marmara Sea offshore Büyükçekmece and Küçükçekmece Lagoons. The sea bottom morphology has a highly chaotic structure at the exit of the Büyükçekmece and Küçükçekmece lagoons. This chaotic surface structure is controlled by a basin-ridge system lying in the NE–SW direction at the exit of the Büyükçekmece Lagoon and by a relatively deep entrance observed at the exit of the Küçükçekmece Lagoon. In addition, the linear submarine slope parallel to the shoreline between the Istanbul Strait and the Küçükçekmece Lagoon is an important morphological structure of this area. The Istanbul Strait’s canyon on the northern shelf of the Marmara Sea and the elevated submarine plain west of this canyon are other important morphological structures observed at the sea bottom. The geologic interpretation of seismic profiles has allowed us to distinguish two seismo-stratigraphic units. The lower one is separated from the overlying units by a seismic sequence having a seismic facies from chaotic to parallel and the top represented by a high amplitude seismic reflector. Since these units get close to the sea bottom rising landwards, they are inferred to be the seaward continuation of the Oligocene–Upper Miocene units widely exposed on land. The upper unit, overlying the acoustic basement, whose parallel internal reflections onlap and downlap on the top of the acoustic basement, is interpreted as a Quaternary basin fill. Two groups of faults have been identified on seismic profiles and identified based on their characteristics in the study area. The first group consists of dip-slip faults trending NNE–SSW. These faults border the western slope of the Bosporus and the NNE–SSW trending basins offshore of the Büyükçekmece Lagoon. The second group of faults consists of NW–SE oriented strike-slip faults. These faults have created the linearities in the same direction at the sea bottom. As the result of comparison of these NW–SE-faults to the North Anatolian Fault Zone (NAFZ), this group of faults is likely to have a relation with the NAFZ. Therefore, it is considered that the mentioned faults may be reactivated in the region due to the stress created by the NAFZ.