Pliocene–Pleistocene radiolarian and diatom biostratigraphy of ODP Hole 709C (equatorial Indian Ocean)

Abstract. Ocean Drilling Program (ODP) Hole 709C was drilled on Madingley Rise in the equatorial Indian Ocean. Thirteen radiolarian and diatom events were identified in the Pliocene to Early Pleistocene section studied. Five radiolarian zones could be recognized: Anthocyrtidium angulare, Pterocanium prismatium, Anthocyrtidium jenghisi, Stichocorys peregrina, and Phormostichoartus doliolum zones. The LAD of P. prismatium was found to be an unreliable indicator of the base of the A. angulare zone in Hole 709C and in other upwelling areas. Accordingly, the base of the A. angulare zone is redefined here by the FAD of A. angulare. The Phormostichoartus fistula zone, which normally separates the 5. peregrina and P. doliolum zones, could not be identified due to the scarcity of P. fistula. Standard tropical diatom Pliocene–Pleistocene zones and subzones were identified: Nitzschia reinholdii, Rhizosolenia praebergonii, and Nitzschia jouseae zones. The development of oxygen isotope calibrated dates enabled the dating of some radiolarian events: FAD A. angulare 1.65 Ma, LAD Theocorythium vetulum 2 Ma, LAD A. jenghisi 2.21 Ma, FAD Theocalyptra davisiana 2.33 Ma, FAD Theocorythium trachelium 2.33 Ma, and FAD Lamprocyrtis neoheteroporos 2.4 Ma.