29. QUANTITATIVE ANALYSIS OF BENTHIC FORAMINIFERAL ASSEMBLAGES FROM PLIO-PLEISTOCENE SEQUENCES IN THE TYRRHENIAN SEA, ODP LEG 1071

Plio-Pleistocene benthic foraminiferal assemblages from Holes 652A, 653A, and 654A of ODP Leg 107 (Tyrrhenian Sea, Western Mediterranean) are examined by means of Q-mode factor analysis. As a result, seven assemblages (A, B, Ca, Cb, D, Ea, and Eb) are distinguished in four zones (I-IV). The relationship between zones and assemblages and their stratigraphic ranges are as follows: Zone I. Assemblage A; MP11 biozone in the lowest Pliocene, Zone II. Assemblage B; MP12 biozone to lower part of MP15 biozone in the Pliocene, Zone III. Assemblages Ca (Sites 652 and 653) and Cb (Site 654); middle of MP15 biozone to middle of MP16 bio­ zone in the upper Pliocene, and Zone IV. Assemblages D, Ea, and Eb; upper of MP16 (uppermost Pliocene) and the Pleistocene. These faunal changes suggest that the whole Tyrrhenian Basin has become deeper from upper epibathyal to lower mesobathyal depths since the beginning of the Pliocene. This increasing depth was the differential that become more and more with the advance of time: Site 652 was deepest and Site 654 was shallowest, consistently. This basin sank rap­ idly during late Pliocene (Zone III). The assemblages in Zone III and lower part of Zone IV indicate that the Tyrrhenian Basin has been occupied by the modern Mediterranean-type warmer deep water since the late Pliocene. At the same time, these assemblages also sug­ gest that this region was affected in some degree by cool deep water like NADW in the Atlantic during late Pliocene to early Pleistocene. Less oxygenated bottom conditions are represented by Assemblage E which prevailed in the three-site area as early as early Pleistocene time.