Brine formation and gypsum precipitation in the Bannock Basin, Eastern Mediterranean

Sixty kilograms of gypsum crystals were collected at two dredging stations from the anoxic, hypersaline Bannock Basin, close to the Sirte Abyssal Plain. The basin was investigated by means of ten precision-positioned piston and gravity cores, one Nansen-bottle hydrocast and three CTD stations. The sediments of the basin floor are dark, H sub(2)S rich and commonly laminated, and contain centimetric crystals of gypsum. The water column above the basin has normal salinity down to a depth of 3150 m; below this depth the basin is filled with hypersaline brines, formed from the dissolution of Messinian evaporites, outcropping on the steep eastern wall. When the brines reach the necessary concentration in Ca and in SO sub(4), gypsum may precipitate along the steep eastern wall and within the sediments on the basin floor. The very recent age of the gypsum is proved by the inclusions of Quaternary planktonic fauna (foraminifera and pteropods) and by radiometric techniques.