Cenozoic calcareous nannofossil biomagnetochronology on the Exmouth Plateau, eastern Indian Ocean

Integration of biostratigraphy and magnetostratigraphy is essential to the development of a worldwide biomagnetochronology. Drilling on the Exmouth Plateau during Ocean Drilling Program Leg 122 recovered an almost complete Cenozoic stratigraphic sequence at Site 762. Sediments at this site contain abundant, diverse, and generally well-preserved calcareous nannofossils. The continuity of the stratigraphic sequence, good preservation of the taxa, and availability of magnetostratigraphic measurements on the same cores offered an opportunity to construct a detailed first-order biomagnetochronology for Cenozoic calcareous nannofossils at Site 762. In the authors study, 104 nannofossil evolutionary first occurrences/last occurrences are correlated with magnetostratigraphy for the first time. The new biomagnetochronologic determinations include 28 dates in the Paleocene, 47 in the Eocene, 14 in the Oligocene, 11 in the Miocene, one in the Pliocene, and three in the Pleistocene. In addition, 71 first/last occurrences are determined for species whose first/last occurrences have previously been reported from other areas. The accurate assessment of the reliability (the synchroneity and/or diachroneity) of magnetically dated first occurrences/last occurrences over a wide latitudinal range depends on a data base consisting of many such age assignments. The large number of new dates reported here, and the complementary information on previously published dates, willmore » add significantly to the refinement of Cenozoic biomagnetochronology.« less