The Black Sea consists of two oceanic basins separated by the mid-Black Sea ridge. The east-west-oriented west Black Sea basin opened as a back-arc rift in the Cretaceous by tearing a Hercynian continental sliver, the Istanbul zone, from the present-day Odessa shelf. The Istanbul zone, which was initially contiguous with the Moesian platform in the west, moved south during the Late Cretaceous-Paleocene with respect to the Odessa shelf along two transform faults: the dextral west Black Sea and the sinistral west Crimean faults. It collided in the early Eocene with a Cimmeride zone in the south, thereby ending the extension in the western Black Sea and deactivating both the west Black Sea and the west Crimean faults as strike-slip faults. The east Black Sea basin opened as a result of the counterclockwise rotation of an east Black Sea block around a rotation pole located north of the Crimea. This block was bounded by the west Crimean fault, the southern margin of the eastern Black Sea, and the southern frontal thrusts of the Greater Caucasus. The rotation of the east Black Sea block was contemporaneous with the rifting of the west Black Sea basin but lasted until the Miocene, resulting in continuous compression along the Greater Caucasus.
