Paleoceanographic Significance of Changes in Miocene Deep-Sea Benthic foraminiferal Diversity on the Wombat Plateau, Eastern Indian Ocean

In the present work, late Oligocene to latest Miocene (-28 6 5 Ma) Deep-Sea benthic foraminifeia(over 149 μm size fraction) were studied from ODP sites 760A and 761B on Wombat Plateau in the eastern lndian Ocean to understand the faunal diversity pattern. The samples were commonly examined at about 0 75m intelva at both the sites. The bentic foraminifeia species diversity was measured in terms of Shannon-Weaver Index [H(S)] Hurlbe lts Diversity Index (S₁₀₀), Alpha Index (α) and Equltability (Ε), all of which show almost similar trends with few exceptions. The Miocene section at both the sites show marked fluctuations in the values of various diversity indices of Beep-Sea benthic foraminiteral assemblages. Distinctly low vatues of diversity indices across the Oligocene-Miocene transition correspond well with the higher values of benthic δ¹⁸0 and δ¹³c reflecting relatively cold, nutrient depleted, young bottom waters which possibly indicate the influence of Antarctic Circumpolar Current (ACC) in this region Faunal diversity reached to maximum values at both the sites near the end of Miocene climatic optimum at about 15 Ma reflecting warm bottom wateis with low trophic levels. The low bottom water temperature, expansion of East Antarctic Ice Sheet (EATS) and possibly higher trophic level appear to be responsible for less diverse fauna during the middle Miocene 1 e -14Ma and younger. Further, decrease in the values of diversity during latest Miocene (-7 5-6 5 Ma) is suggested to be due to increased surface water productivity in response to the intensified monsoonal activity in the eastern Indian Ocean.