30. RELATIONSHIP BETWEEN THE BENTHIC FORAMINIFERS AND THE OSTRACODES IN THE PLIOCENE-PLEISTOCENE TYRRHENIAN DEEP-SEA RECORD (ODP LEG 107, SITE 654)1

Deep-water benthic ostracodes from the Pliocene-Pleistocene interval of ODP Leg 107, Hole 654A (Tyrrhenian Sea) were studied. From a total of 106 samples, 40 species considered autochthonous were identified. Detailed investigations have established the biostratigraphic distribution of the most frequent ostracode taxa. The extinction levels of Agrenocythere pliocenica (a psychrospheric ostracode) in Hole 654A and in some Italian land sections lead to the conclusion that the removal of psychrospheric conditions took place in the Mediterranean Sea during or after the time interval cor­ responding to the Small Gephyrocapsa Zone (upper part of early Pleistocene), and not at the beginning of the Quater­ nary, as previously stated. Based on a reduced matrix of quantitative data of 63 samples and 20 variables of ostracodes, four varimax assem­ blages were extracted by a Q-mode factor analysis. Six factors and eight varimax assemblages were recognized from the Q-mode factor analysis of the quantitative data of 162 samples and 47 variables of the benthic foraminifers. The stratigraphic distributions of the varimax assemblages of the two faunistic groups were plotted against the cal­ careous plankton biostratigraphic scheme and compared in order to trace the relationship between the benthic foramini­ fers and ostracodes varimax assemblages. General results show that the two populations, belonging to quite different taxa, display almost coeval changes along the Pliocene-Pleistocene sequence of Hole 654A, essentially induced by pa­ leoenvironmental modifications. Mainly on the base of the benthic foraminifer assemblages (which are quantitatively better represented than the ostracode assemblages), it is possible to identify such modifications as variations in sedimen­ tation depth and in bottom oxygen content.