Dense shelf water cascading and Messinian Canyons: A new scenario for the Mediterranean salinity crisis

The salt giant beneath the deep Mediterranean seafloor is the impressive record of the “Messinian salinity crisis,” a dramatic event that occurred about 6Ma ago following the reduction of the connections with the Atlantic Ocean. According to the shallow-water deep-basin model, developed for these deposits (Hsu¨ and others, 1973a, 1973b, 1978a, 1978b), the Messinian evaporites formed in a deep but desiccated Mediterranean, while shelves and slopes underwent subaerial erosion due to fluvial rejuvenation triggered by a 1500 m sea level drawdown. Deeply incised Messinian canyons in the continental slopes surrounding the Mediterranean are the main argument supporting this scenario. Using a state of the art model and idealized but realistic numerical simulations, here we demonstrate that the activation of downslope flows of hypersaline, dense waters, in a process similar to present-day “dense shelf water cascading,” but much more energetic, may account for both slope erosion and progressive salinity rise leading to the formation of deep-seated supersaturated brines. Our findings support a deep-water deep-basin model (Schmalz, 1969, 1991; De Benedetti, 1976, 1982; Dietz and Woodhouse, 1988), thus implying that evaporite deposition may have occurred in a non-desiccated basin with strongly reduced ocean connections.