As it turns out, evaporite deposits are found across the Mediterranean Sea during the same time period. Drill cores have turned up three kilometers of evaporites in some areas. To crystallize this much salt over such a wide area, geologists think that the entire Mediterranean Sea must have evaporated–an event called the Mediterranean Salinity Crisis (or Messinian Salinity Crisis) which lasted from 5.96 million years ago to 5.33 million years ago.
The Mediterranean Sea is located in the desert latitudes, where evaporation exceeds precipitation. The water level remains constant because water from the Atlantic Ocean enters the basin through the Straits of Gibralter.
But this wasn’t always the case. During the Messinian, a global sea level drop and local tectonics caused the land at the Straits to rise, cutting off the Mediterranean from the ocean. Since evaporation was so high, the water level dropped, concentrating the dissolved ions, and crystallizing evaporites; just like the Dead Sea in Israel, which crystallizes halite on its seafloor. Halfway through the Salinity Crisis, the four kilometers of water that filled the Mediterranean disappeared. A vast, desert basin is all that remained.
Nano and I are studying Messinian river deposits. Before and after the Salinity Crisis, rivers carried sediments from the mountains west of the basin. During the Messinian, however, something different happened.