Description: A record based on counts of the relative abundance of the dominant calcareous nannofossil taxa Coccolithus pelagicus and Reticulofenestra spp. in sediments recovered from Ocean Drilling Program Hole 747A (Kerguelen Plateau, Southern Indian Ocean) is established in this paper. This record (17 m.y. long) virtually spans the entire Miocene. Broad, steplike variations in the abundance of C. pelagicus range between 0% and 96%. Based on these variations, five stratigraphic units characterized by high abundance in C. pelagicus are delineated. We suggest that these variations are caused by water-mass movements (such as the north/south shifting of a front). This pronounced signal is compared with paleoceanographic events revealed by isotopic (d18O and d13C) studies. The five defined units are tentatively correlated to well-known global isotopic events. In particular, Units A and D correlate respectively with the Oligocene/Miocene boundary glaciation and the middle Miocene cooling event. Time-series analysis indicates the presence of the three main periodic components of the eccentricity of the Earth's orbit. A 200-k.y. cycle is also present. The stratigraphic and paleoceanographic significance of this record is discussed.

Description: Stable carbon and oxygen isotope analyses were conducted on well-preserved planktonic and benthic foraminifers from a continuous middle Eocene to Oligocene sequence at Ocean Drilling Program (ODP) Site 748 on the Kerguelen Plateau. Benthic foraminifer d18O values show a 1.0 per mil increase through the middle and upper Eocene, followed by a rapid 1.2 per mil increase in the lowermost Oligocene (35.5 Ma). Surface-dwelling planktonic foraminifer d18O values increase in the lowermost Oligocene, but only by 0.6 per mil whereas intermediate-depth planktonic foraminifers show an increase of about l.0 per mil. Benthic foraminifer d13C values increase by 0.9 per mil in the lowermost Oligocene at precisely the same time as the large d18O increase, whereas planktonic foraminifer d13C values show little or no change. Site 748 oxygen isotope and paleontological records suggest that southern Indian Ocean surface and intermediate waters underwent significant cooling from the early to late Eocene. The rapid 1.2 per mil oxygen isotope increase recorded by benthic foraminifers just above the Eocene/Oligocene boundary represents the ubiquitous early Oligocene d18O event. The shift here is unique, however, as it coincided with the sudden appearance of ice-rafted debris (IRD), providing the first direct link between Antarctic glacial activity and the earliest Oligocene d18O increase. The d18O increase caused by the ice-volume change in the early Oligocene is constrained by (1) related changes in the planktonic to benthic foraminifer d18O gradient at Site 748 and (2) comparisons of late Eocene and early Oligocene planktonic foraminifer d18Ovalues from various latitudes. Both of these records indicate that 0.3 per mil to 0.4 per mil of the early Oligocene d18O increase was ice-volume related.