Silicoflagellate abundance in ODP Holes 183-1138A and 183-1140A

The biostratigraphic distribution and abundance of lower Oligocene and Miocene to Pleistocene silicoflagellates are documented from Ocean Drilling Program Leg 183 Holes 1138A and 1140A, on the Kerguelen Plateau. The Distephanus speculum speculum forma pseudofibula plexus is found in the upper Miocene in Hole 1138A, but other important biostratigraphic markers are not available. Diversity and abundance of silicoflagellates vary considerably in Hole 1138A, with silicoflagellates more abundant in the Pliocene and Pleistocene and some intervals of the Miocene barren of silicoflagellates or containing only limited numbers of specimens. The silicoflagellates of Hole 1140A include a new skeletal morphology, described here as Distephanus speculum speculum forma cylindrus. Silicoflagellates were generally abundant throughout the lower and middle Miocene in Hole 1140A.

Diatom biostratigraphy and datum events of ODP Hole 183-1140A

Ocean Drilling Program (ODP) Leg 183 Site 1140 provided a lower Oligocene to middle Miocene record of diatom assemblages from the northern Kerguelen Plateau. Samples were examined to improve the resolution of shipboard diatom biostratigraphy. The material is complementary to that recovered during ODP Legs 119 and 120, and the diatom zonation of Harwood and Maruyama could be readily applied. A standard succession of biostratigraphic zones from the middle Miocene and lower Oligocene was delineated, although some zones were unrecognizable because of poor core recovery. The detailed diatom biostratigraphy presented here agrees well with shipboard calcareous nannofossil biostratigraphy. Sediment accumulation rates based on diatom bioevents average 1.26 cm/k.y.