Why are there no Messinian evaporites in the Black Sea?

摘要

An unconformity has been observed along the Black Sea shelf on seismic reflection profiles and wells which is broadly similar to the one associated with that formed during the Messinian salinity crisis (MSC) in the Mediterranean. Therefore, this intra- (or Middle) Pontian unconformity has been traditionally interpreted as the manifestation of the MSC in the Black Sea Basin. However, the magnitude of the sea-level fall associated with this erosive surface does not appear to be nearly as significant as was assumed previously. Also, the inferred MSC surface itself cannot be easily followed into the palaeo-deep-water basin as a regional unconformity in the same manner as in the Mediterranean. Moreover, around the Black Sea, there is no evidence of major river incisions during the MSC, unlike the well-documented cases in the Mediterranean region. If the MSC evaporites in the Mediterranean indeed deposited in a subaerial setting at the basin floor, the lack of a major drawdown in the Black Sea explains why there are no Messinian evaporites in the Black Sea. Owing to the approximately 500 m MSC sea-level drop the Black Sea basin system, this basin did not even get close to the conditions required for the formation of evaporites in the basin centre. As the magnitude of the sea-level drop and the overall impact of the MSC in the Black Sea is interpreted to be less significant than in the Mediterranean, the risk of breaching pre-existing hydrocarbon traps during the MSC is less than has been suggested before.