Burdigalian-Serravallian (Miocene) radiolarians from Havelock Island, Northeast Indian Ocean and their paleoecological significance.

Adetailed study on radiolarian biostratigraphy and paleoecology has been carried out from three outcrops on Havelock Island, belonging to theRitchie'sArchipelago of Andaman and NicobarGroup of islands. Though most of the radiolarian taxa aremoderately preserved, it was possible to demarcate an age ranging from late early to early middleMiocene based on index radiolarians of RN4 andRN5 zones. An attempt has been made to correlate the radiolarian events recorded hereinwith earlier reports on radiolarians from differentDSDP, ODP, and IODPsites of the Indian Ocean and the onshore sections of different islands of theAndaman and NicobarBasin.A total of 119 radiolarian taxa belonging to 70 genera have been recorded in the present study, out of which 4 species are being reported for the first time from the northeastern part of the Indian Ocean. Diversity analyses were performed to deduce the Shannon Diversity Index, Simpson Index, Margalef Richness, and Pielou's Evenness. TheWater Depth Ecology index (WADE) has been analyzed for a better understanding of the paleoecological perspectives, and the Nassellaria-Spumellaria ratio of each outcrop has been calculated to ascertain the water depth. Comparison of the data obtained from diversity analysis andWADE index provides a clear picture of the environment during the late early to early middleMiocene. The overwhelming dominance of warm species of radiolarians may be linked to the Miocene Climate Optimum (MCO) event. [ABSTRACT FROM AUTHOR]