DEEP-SEA BENTHIC FORAMINIFERAL CHANGES AND TERMINAL MIOCENE EVENT AT TROPICAL INDIAN-OCEAN DSDP SITE-214

Quantitative data of Late Miocene deep-sea benthic foraminifera from the tropical Indian Ocean DSDP Site 214 have been combined with oxygen and carbon isotope values to understand the history of deep thermohaline circutation in the Indian Ocean. The important faunal changes include a significant increase in Uvigerina proboscidea percentages at c. 8.5 to 7.5 Ma and during 6.2 to 5.2 Ma. reaching their maximum values at the Miocene/Pliocene boundary. The increase in U. proboscidea percentages are accompanied by decreasing abundances of Bulimina alazanensis, Cibicides kullenbergi, and C. wuellerstorfi, and lower values of H (S) and E'. The delta-O-18 values are, in general, higher during these intervals while delta-C-13 values show a decreasing trend. The interval between 7.5 and 6.2 Ma is marked by a major increase in B. alazanensis which coincides with slightly higher delta-C-13 and lower delta-O-18 values. C. kullenbergi and C. wuellerstorfi, interestingly, reveal significant variations with higher values before Chron - 6 Carbon Shift at about 6.2 Ma and a prominent peak immediately preceding the shift, but remain low and less variable following the shift during the remainder of the Late Miocene as do the delta-C-13 values. The well-known Late Miocene Chron - 6 negative carbon shift is marked by significantly higher U. proboscidea percentages, and lower C. kullenbergi, C. wuellerstorfi and B. alazanensis values. Our data support the hypothesis that the shift was caused by excess organic carbon input to the system, and higher rate of upwelling and ocean productivity. The Miocene/Pliocene boundary marks a warming event and is typified by highest percentages of U. proboscidea and Osongularia culter, lighter delta-O-18 and lighter delta-C-13 values, and lowest values of H(S) and E'. The sediment accumulation rates were remarkably higher at the Miocene/Pliocene boundary. These events reflect high rates of surface productivity intensified by strong upwelling.