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Ludden J N Plank T and Escutia C Eds Proceedings of the Ocean Drilling Program Scientific Results Volume 185 4 SILICOFLAGELLATE BIOSTRATIGRAPHY HOLE 1149A ODP LEG 185 NADEZHDA BASIN NORTHWESTERN PACIFIC 1 Francesca Lozar2 3 and Massimo Mussa2 ABSTRACT Silicoflagellate assemblages have been studied from Hole 1149A northwestern Pacific Ocean Drilling Program Leg 185 in a continuous record of pelagic clay from lithologic Unit I The biostratigraphic framework of D Bukry adapted in this work is calibrated to tropical and subtropical fossil floras Four biozones and three subzones have been recognized from the lower Pliocene Dictyocha fibula Zone to the Quaternary Dictyocha aculeata aculeata Zone and their zonal boundaries have been calibrated to the magnetostratigraphic scale In particular the boundary between the Dictyocha perlaevis delicata and the Dictyocha perlaevis ornata Subzones approximates the Pliocene Pleistocene boundary The identification of three closely spaced climatic events the asperoid fibuloid reversal at 75 11 meters below seafloor mbsf the sharp decrease in abundance of Distephanus sp at 70 05 mbsf and the last occurrence of Distephanus boliviensis at 68 46 mbsf indicates the increased strength of the warm Kuroshio Current in the interval between 3 3 and 2 8 Ma due to the final closure of the Central American Seaway and leading to the present day hydrodynamic regime The beginning of the acme of Mesocena quadrangula at 37 01 mbsf 1 1 Ma also shows a sharp warming in surface waters 1 Lozar F and Mussa M 2003 Silicoflagellate biostratigraphy Hole 1149A ODP Leg 185 Nadezhda Basin northwestern Pacific In Ludden J N Plank T and Escutia C Eds Proc ODP Sci Results 185 1 18 Online Available from World Wide Web http www odp tamu edu publications 185 SR VOLUME CHAPTERS 009 PDF Cited YYYYMM DD 2 Dipartimento di Scienze della Terra Universit degli Studi di Torino via Accademia delle Scienze 5 I 10123 Torino Italy Correspondence author francesca lozar unito it 3 CNR



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