Abstract:
We studied the composition of Oligocene-Miocene benthic foraminiferal assemblages in relation to stable isotope values and sedimentological data at Site 1148 (ODP Leg 184), situated at the northern margin of the South China Sea. Our results have the following implications for understanding the evolution of deep water environments in the South China Sea and the evolutionary patterns of deep water benthic foraminifers during the Oligocene and Miocene: Deep water agglutinated foraminifers, including tubular suspension feeding forms and other "flysch-type" agglutinated foraminifers characterize Oligocene assemblages and indicate that bottom currents exerted a strong influence in deep water depositional environments. A significant change is observed from Early Oligocene Nothia-dominated assemblages to Late Oligocene Rhabdammina-assemblages, which probably reflects the transition from turbidity currents to contour currents. Oligocene and Miocene benthic foraminifers are cosmopolitan, and indicate consistent deep-water (lower bathyal) conditions at Site 1148 since the Early Oligocene (bottom of Hole 1148B). However, Oligocene assemblages exhibit a strong similarity to Tethyan assemblages, whereas Miocene assemblages are typically "Pacific". The first occurrence of some prominent "modern" benthic foraminifers, including Planulina wuellerstorfi, is recorded during the Middle Miocene. Their evolution appears to be linked to the mid-Miocene events (i.e. Monterey carbon isotope excursion).