Ocean Drilling Program (ODP) Site 1139 was drilled in 1415 m of water at 50°11´S, 63°56´E on the isolated outlying Skiff Bank off the western edge of the Northern Kerguelen Plateau (Fig. F1). The drilling objectives included a determination of the facies of the seismic stratigraphic sequences, a definition of the ages of the seismic sequence boundaries, and a determination of the paleoceanographic history of the site. A detailed calcareous nannofossil stratigraphy, which is presented here, is necessary to help fulfill these objectives.
At Site 1139, a thin (19 m) Quaternary section of foraminifer diatom-bearing nannofossil ooze (lithologic Subunit IA) is underlain by a greatly expanded 364-m middle Miocene to mid-Oligocene nannofossil ooze/chalk and clay/claystone sequence with generally well preserved siliceous and calcareous microfaunas and floras (lithologic Subunit IB-Unit III) (Fig. F2). There is no appreciable chert within this section, which was deposited well above the calcite compensation depth. This pelagic sequence overlies nearly 80 m of poorly dated reddish orange sandy packstones and grainstones, which, in turn, rest on basement units (Shipboard Scientific Party, 2000).
Minimum overall sedimentation rates are ~18 m/m.y. in the Miocene and 29 m/m.y. in the Oligocene or 23 m/m.y. for the entire Tertiary pelagic section (Shipboard Scientific Party, 2000; fig. F9). The high sedimentation rates have been attributed to high regional pelagic productivity plus the influx of fine terrigenous clastic sediments derived from the weathering of exposed portions of the volcanic edifice, Skiff Bank, on which the sediments were deposited (see "Lithostratigraphy" in Shipboard Scientific Party, 2000) (Reusch, this volume). The clastic input colored the normally white calcareous oozes and chalks gray to brownish gray. Only at the bottom of the section, where such input was minimal, are the sediments oxidized to a pinkish color.