AbstractThis study explores and develops the application of Polycystine radiolarian microfossils to the investigation of Late Cenozoic deep-sea sediments recovered by the Deep Sea Drilling Program (DSDP) and Ocean Drilling Program (OOP), and utilizes these advances in undertaking a detailed palaeoenvironmental study of the Plio-Pleistocene Olduvai magnetosubchron (1.95-1.79Ma) of the equatorial Indo-Pacific Oceans. A number of radiolarian tools are used as palaeoceanographic proxies, including the recognition of distinct glacial and interglacial assemblages, which form the basis of a new Radiolarian Temperature Index (RTI), and the further development and refinement of the Upwelling Radiolarian Index (URI), shown here for the first time to be applicable to upwelling regions throughout the Plio-Pleistocene equatorial Oceans.
Radiolarian biostratigraphy is also investigated, confirming that a recently devised Plio-Pleistocene biozonation scheme for the Indian Ocean is also largely applicable in the Atlantic, and also provides the first astronomically calibrated radiolarian biodatums for the Indian Ocean Plio-Pleistocene. Stratigraphy based on synchronous abundance variations of Cycladophora daws/ana, previously only used in highlatitude regions, is assessed in low-latitudes with encouraging results, including a significant abundance peak coincident with the Plio-Pleistocene boundary in both the Indian and Pacific Oceans. The potential of this dating technique for intra- and inter-oceanic correlation at all latitudes is demonstrated.
The palaeoceanographic reconstruction of the Indo-Pacific Olduvai subchron indicates a tripartite palaeoceanographic division of the subchron, with conditions analagous to the modern El Nino prevalent during the middle part of the Olduvai. In the eastern equatorial Pacific at this time, trade wind intensity, upwelling, and bioproductivity is reduced, with a concomitant rise in sea-surface temperatures. A comparison with land sequences indicate palaeoenvironmental changes consistent with known El Nino phenomena, although these conditions are likely to lay beyond the present-day natural limits of interannual El Nino variability.
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