Messinian Salinity Crisis - Confirmation and Further Evidence

Confirmation and Further Evidence

In 1961, seismic surveying of the Mediterranean basin revealed a geological feature some 100–200 m (330–660 ft) below the seafloor. This feature, dubbed the M reflector, closely followed the contours of the present seafloor, suggesting that it was laid down evenly and consistently at some point in the past. The origin of this layer was largely interpreted as related to salt deposition. However, different interpretations were proposed for the age of salt and its deposition.

Earlier suggestions from Denizot in 1957 and Ruggieri in 1967 proposed that this layer was Late Miocene in Age, and the same Ruggieri coined the term Messinian Salinity Crisis.

New and high quality seismic data on the M-reflector were acquired in the Mediterranean Basin in 1970, published by e.g. Auzende et al. (1971) At the same time, the salt was cored during Leg 13 of the Deep Sea Drilling Program conducted from the Glomar Challenger under the supervision of co-chief scientists William B.F. Ryan and Kenneth J. Hsu. All these deposits were indisputably dated and interpreted for the first time as deep-basin products of the Messinian Salinity Crisis.

The first drilling of the Messinian salt at the deeper parts of the Mediterranean Sea came in the summer of 1970, when geologists aboard the Deep Sea Drilling Program drillship Glomar Challenger brought up drill cores containing arroyo gravels and red and green floodplain silts; and gypsum, anhydrite, rock salt, and various other evaporite minerals that often form from drying of brine or seawater, including in a few places potash, left where the last bitter, mineral-rich waters dried up. One drill core contained a wind-blown cross-bedded deposit of deep-sea foraminiferal ooze that had dried into dust and been blown about on the hot dry abyssal plain by sandstorms and ended up in a brine lake interbedded between two layers of halite. These layers alternated with layers containing marine fossils, indicating a succession of drying and flooding periods.

The massive presence of salt does not require a desiccation of the sea. The main evidence for the evaporative drawdown of the Mediterranean comes from the remains of many (now submerged) canyons that were cut into the sides of the dry Mediterranean basin by rivers flowing down to the abyssal plain. For example, the Nile cut its bed down to several hundred feet below sea level at Aswan (where Ivan S. Chumakov found marine Pliocene foraminifers in 1967), and 2,500 m (8,200 ft) below sea level just north of Cairo.

In many places in the Mediterranean, fossilized cracks have been found where muddy sediment had dried and cracked in the sunlight and drought. In the Western Mediterranean series, the presence of pelagic oozes interbedded within the evaporites suggests that the area was repeatedly flooded and desiccated over the course of 700,000 years.