Psychrospheric and Continental Ostracoda from Ancient Sediments in the Floor of the Mediterranean

Pliocene ostracods, typical of the upper psychrosphere of the open ocean floor, were found in drill cores of the Deep Sea Drilling Project (Leg 13) from the Tyrrhenian Basin at Site 132, and from the Balearic Basin at Site 134.No ostracods were recorded including other shallower species, in the cores examined from the Ionian Basin (Sites 125, 128) and the Levantine Basin (Site 129-Hole 129A) except in the latest Miocene portions thought to represent the "Melanopsis-Cyprideis zone" of the upper Messinian lago mare continental, alkaline facies.The deep-sea ostracod fauna is also known from outcrops in Italy, chiefly in early Pliocene sediments from immediately above the unconformity and conglomerate which commonly overlies strata of Messinian age.This considerable difference in faunas suggests a rapid change in regimen in the western Mediterranean from continental to deep, cold marine conditions.The absence of the psychrospheric ostracod fauna in the Pliocene of the Ionian Basin in the eastern Mediterranean may have been caused by the presence of an effective threshold between the two major basin complexes during this time.The Pleistocene sections of the cores of both the eastern and western basins contain the record of the Calabrian replacement of the psychrosphere by the thermosphere and the ultimate extinction in the Mediterranean of all but the most eurytropic psychrospheric ostracods.It is remarkable that no ostracods characteristic of normal marine sublittoral environments were found.