Changes in composition of neogene benthic foraminiferal faunas in equatorial Pacific and North Atlantic

Abstract

Deep sea benthic foraminiferal faunas were studied from three DSDP sites in the equatorial Pacific (Leg 85, depth about 4.5 km), and two DSDP sites in the North Atlantic (Leg 94, depth 3.5 and 2.5 km), for the interval between 25 and 0 Ma. The number of first appearances (FA's) and last appearances (LA's) of taxa in the early to middle Miocene was similar at all sites, despite differences in location and depth. Specific events, however, were rarely coeval at several sites, even within the Pacific. Changes in faunal composition began earlier (at about 18 Ma) in the equatorial Pacific than in the North Atlantic (about 15.5 Ma); these changes affected between about 20 and 30% of the total fauna. There is no simple, globally valid correlation between the changes in composition of the benthic foraminiferal faunas and events in oxygen and carbon isotopic records. The FA of Cibicidoides wuellerstorfi, however, appears to be coeval with the increase in oxygen isotopic ratios in the early middle Miocene.