Tectonics and sedimentation in the Gulf of Corinth and the Zakynthos and Kefallinia channels, Western Greece

Abstract Single-channel seismic reflection profiling data are presented from the Gulf of Corinth and from the continental margin outside the Gulf of Patras. Different tectonic styles are exhibited in the two regions. The Gulf of Corinth is occupied by a complex asymmetrical graben structure with major faults trending nearly perpendicular to the local tectonic zones of the Internal Hellenides. The Gulf is interpreted to have formed during the Quaternary in response to approximately north-south extensional stress. The deep floor of the Gulf is underlain by a sequence of turbidites up to 1 km thick affected by normal growth faulting that extends up to the sea floor. The sea areas inside the Ionian Islands of Zakynthos and Kefallinia (Zakynthos and Kefallinia Channels) occupy a broad structural depression that trends parallel to the local tectonic zones of the External Hellenides and is situated on the continental side of the Strophades continental margin rise. The Channels contain local NW-SE trending structural basins (Zakynthos and Kefallinia basins) whose geometry is controlled by reverse faults or thrusts with associated diapirism in Triassic evaporites. Hydra Bank is interpreted as a tilted fault block with a diapiric core and its faulted western margin can be traced into the zone of thrusting and diapirism in southeast Kefallinia at the boundary between the Ionian and pre-Apulian (Paxos) zones of the External Hellinides. The Zakynthos and Kefallinia structural basins are filled with a variety of sediments including prodeltaic deposits (in front of the modern delta complex of the Acheloos river), slumped masses and debris flow deposits and, in the Zakynthos basin, occasional turbidites. The boundary separating zones of extensional and compressional focal mechanisms for shallow earthquakes crosses the Gulf of Patras, the inner part of which exhibits WNW-ESE trending graben tectonics apparently related to the Gulf of Corinth tectonic province. Onshore neotectonic studies around the Gulf of Patras are required in order to understand the nature and cause of the westward tectonic transition from WNW-ESE graben structures in the Gulfs of Corinth and Patras to NW-SE oriented zones of subsidence with associated compressional tectonics and diapirism in the Zakynthos and Kefallinia Channels.