Structural style in a Messinian (intra-Pontian) gravity-driven deformation system, western Black Sea, offshore Romania

摘要

Miocene sediments of the western Black Sea failed gravitationally during the intra-Pontian (Messinian) sea-level fall. In the region of the Histria Trough, this generated two independent collapse systems detaching on the upper part of Oligocene-Lower Miocene shale. This contribution focuses on the eastern system. The eastern linked system is approximately 60 km long in the dip direction, containing about 10 major extensional faults in the updip domain, with a cumulative extension (heave) of 11.4 km. This extension is accommodated downdip partially by 6 - 7 km of lateral compaction and on a single toe thrust with 4.8 km of shortening. The thin-skinned extension generated both basinwards-dipping faults and counter-regional faults (dip towards the basin margin), with associated rollovers, tilted fault blocks and keystone graben. Broad shale pillow (3 km across) and cuspate shale upwelling developed due to reactive shale diapirism. The collapse of the rollover anticlines into the half-graben suggests a high deformation rate. Downdip, the thrust follows the top of the Oligocene-Lower Miocene unit and steps up into the top of Sarmatian. The thrust hanging-wall anticline collapsed and triggered a mass transport complex (MTC). The top of the MTC is a rugose surface, and we suggest that it remained under water during the Messinian event due to its lack of visible erosion.