Messinian event in the black sea: Evidence of a Messinian erosional surface

Abstract

In 1975, sediment cores from leg DSDP 42b (sites 380A and 381) revealed a thin sediment layer in the Black Sea basin which points to a shallow water environment at the Miocene-Pliocene boundary. With these facts and in the wake of hypothesis of the Messinian Salinity Crisis (MSC), it was proposed that the Black Sea, like the Mediterranean Sea, suffered a desiccation period at the end of the Messinian (Hsü, K.J. and Giovanoli, F., 1979. Messinian event in the Black Sea. Palaeogeography, Palaeoclimatology, Palaeoecology, 29: 75–93). Whereas the main topics of the MSC in the Mediterranean Sea is now widely accepted, the lack of evidence for a Messinian erosional surface in the Black Sea left the debate about the Messinian desiccation of this basin open until today. The analysis of high resolution multi-channel seismic data acquired during the BlaSON surveys brings important new elements for this scientific debate: (1) Down the slope offshore the Bosporus, we show a clear erosional surface correlated to the top of the Upper Miocene shallow water environment unit of site DSDP 381. The overlying Lower Zanclean unit inevitably dates this erosional surface of the Messinian event. (2) A wide intra-Pontian erosional surface (IPU) is evidenced on the Romanian shelf. The IPU is characterized by a sharp decrease in the incision rate from outer (deep canyons) to inner shelf (superficial incisions network). According to the most recent Paratethyan and Mediterranean stratigraphic scale correlations, the IPU erosional surface is considered as the analogue to the Messinian erosional surface described down the slope offshore the Bosporus. In addition to recently discovered inland erosional signature, the wide regional erosional surface we underline on the Western Black Sea margins validates the Black Sea Messinian desiccation hypothesis. We also demonstrate that evaporative draw-down of the Black Sea implied the installation in the basin of a negative hydrologic budget during the Messinian. The lack of a major Messinian Danube canyon on the Romanian shelf supports the hypothesis of a Messinian Danube trapped in the Dacic basin. However, the presence of a Messinian superficial incision network connecting the location of the modern Danube delta to deeply incised Messinian canyons on the outer shelf (IPU) makes the hypothesis of a Danube reaching the partially desiccated Black Sea still possible.