Active tectonics of offshore Cide–Sinop (southern Black Sea shelf): from seismic and multibeam bathymetry data

Abstract

Approximately 600 km of multichannel seismic reflection data and multibeam bathymetric data with an area of 2750 km² indicate that offshore Cide–Sinop is filled by the sediments of four main seismic units dating from the Upper Cretaceous–Paleocene to Plio-Pleistocene. The deposits from the Eocene to modern times are highly eroded from their upper surfaces and widely outcropped at the seafloor. These units constitute the large flat shelf plain with an average depth of 100 m. Moreover, there are no significant marine onlaps identified in the shelf area. These stratigraphical and morphological features indicate that, until very recently, the area was a terrestrial landscape. Structurally, the shelf-plain and shelf-slope are primarily deformed by E–W-trending active reverse faults and strike–slip faults with a compressional component. These faults are densely spaced toward the outer shelf as fault segments bordering E–W-oriented dunes on the seafloor. A strike–slip fault with a reverse component delimits the shelf edge at long distances. Toward offshore İnebolu, the fault character changes to a negative flower structure that bends to the WNW direction, which indicates that the strike–slip fault is right lateral. The strike–slip faulting is also effective along the shelf slope deforming the slumps. These tectonic structures demonstrate that the shelf area is widely deformed by E–W-trending active transpressional strike–slip faults and reverse faults. This result reveals that the southern Black Sea shelf is under a recent N–S compressional tectonic regime.