Paleoenvironment of the Messinian Mediterranean "Lago Mare" from Strontium and Magnesium in Ostracode Shells

Abstract

Ostracodes from Deep Sea Drilling Project (DSDP) site 376 (Florence Rise, Levantine Basin) in the eastern Mediterranean have been studied to elucidate the environments of the during the Messinian (Late Miocene). Additional ostracode samples from the Lago Mare from DSDP site 372 (East Menorca Rise, Balearic Basin) in the western Mediterranean, andfrom outcrops in the Sorbas Basin in southeastern Spain, the Polemi Basin in Cyprus, and from the Sitia-Lithinais Basin in Crete, were also studied. All samples contained valves of the euryhaline ostracode genus Cyprideis for which the distribution coefficient KD for Sr and Mg is known from analyses of modern specimens grown in the laboratory and from modern field collections. Because the Sr/Ca of ostracode shells is controlled by the Sr/Ca of the host water, and because the MglCa of the shells is controlled both by the MglCa of the water and by water temperature, Ca, Sr, and Mg analyses of individual fossil Cyprideis shells from the Lago Mare indicate the environment in which they lived. Throughout the sequence atDSDP site 376, the water was fresh or close to fresh, exceptfor layers just above the uppermost gypsum layers, at the base of the sequence where water with some marine affinity is recognized. Above these layers, the continental aspect of the Lago Mare water is indisputable. Chemical analyses of single ostracode shells from site 376 and the other sites mentioned above indicate that at no time during the life of the Cyprideis ostracodes was the Lago Mare connected to the ocean. Furthermore, there is no indication that the individual basins of the Mediterranean studied here were in direct connection to one another.