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Johnson, D.A., Schneider, D.A., Nigrini, C.A., Canlet, J.P. and Kent, D.V., 1989. Pliocene-Pleistocene radiolarien events and magnetostratigraphic calibrations for the tropical Indian Ocean. Micropaleontol., 14: 33-64.A composite of four piston cores from the Central Indian Basin and adjacent Ninetyeast Ridge has yielded a continuous magnetobiostratigraphic reference section for most of the Pliocene and the Pleistocene (0.0-4.5 Ma). We identified thirty-three radiolarian events (first-or last-occurrences), and precisely correlated each event to the Neogene geomagnetic polarity time scale. Thirteen of these events are based on revised taxonomic studies of the genera Anthocyrtidium and Pterocorys. Some events show significant departures from synchroneity: five of the radiolarian first-appearances and seven of the last-appearances are time-transgressive by 0.4 m.y. or greater. We here propose a revised, eleven-fold radiolarian zonation for the Pliocene-Pleistocene, using zonal boundaries defined by events which are easily recognized and are demonstrably synchronous in the tropical Indo-Paciflc. The sequence of faunal and floral events reported in this paper will allow high-resolution biostratigraphic correlations within the tropical Indian Ocean; however, the same sequence of events is not necessarily applicable to other tropical or extratropical regions.Pleistocene. We suggest discarding the Spongaster lineage as a criterion for defining zonal boundaries due to its demonstrable non-synchroneity and the scarcity of specimens of this genus in Indian Ocean cores. We propose an alternative zonation based upon several Pliocene radiolarian events which are more sharply defined in the Indian Ocean.

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[1] Stratigraphic data from 63 Deep Sea Drilling Project and Ocean Drilling Program (ODP) sites that sample the lower Neogene and Paleogene sediments of the tropical Pacific have been compiled and put on the biostratigraphic and paleomagnetic timescale refined by ODP Leg 199 scientists. Sediment accumulation rates have been calculated for ten intervals ranging in age from 10 to 56 Ma and have been plotted for the midpoint of each interval at the associated paleoposition for each site used. A fixed hot spot model was used for reconstruction of the Pacific lithospheric plate. All such reconstructed intervals show the development of a tongue of high accumulation rates associated with the oceanographic divergence at the geographic equator. The development of this equatorial band is weakest between 46 and 56 Ma, the time of the peak warmth in Paleogene climate. Possible motion of the Hawaiian hot spot or true polar wander between 46 and 56 Ma appears to have had little effect on the plate rotation estimate of the position of the equator. In addition to temporal changes in the calcite compensation depth and in productivity, the biggest change in the patterns of sediment accumulation rates in the eastern tropical Pacific was the development of a relatively strong divergence between 6°and 10°N, near the region of divergence between the modern North Equatorial Current and the North Equatorial Counter Current. Changes in the equatorial circulation appear to be associated in time with the opening and closing of oceanic gateways, particularly the complex closing of the Caribbean-Pacific gateway.

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