Paleoceanographic implications of a 17-mylong record of high-latitude Miocene calcareous nannoplankton fluctuations

International audienceA record based on counts of the relative abundance of the dominant calcareous nannofossil taxa Coccolithuspelagicus and Reticulofenestra spp. in sediments recovered from Ocean Drilling Program Hole 747A (KerguelenPlateau, Southern Indian Ocean) is established in this paper. This record (17 m.y. long) virtually spans the entireMiocene. Broad, steplike variations in the abundance of C. pelagicus range between 0% and 96%. Based on thesevariations, five stratigraphic units characterized by high abundance in C. pelagicus are delineated. We suggest thatthese variations are caused by water-mass movements (such as the north/south shifting of a front). This pronouncedsignal is compared with paleoceanographic events revealed by isotopic (δ18θ and δ13C) studies. The five definedunits are tentatively correlated to well-known global isotopic events. In particular, Units A and D correlaterespectively with the Oligocene/Miocene boundary glaciation and the middle Miocene cooling event. Time-seriesanalysis indicates the presence of the three main periodic components of the eccentricity of the Earth's orbit. A200-k.y. cycle is also present. The stratigraphic and paleoceanographic significance of this record is discussed