Radiolaria and diatom stratigraphy of ODP Hole 182-1128C sediments

The radiolarian assemblages from the Eocene-Oligocene sequence at Site 1128 lack zonal marker species reported from regions further south or north, and thus, age estimates cannot be made using previously published zonations. However, the presence of diverse and well-preserved radiolarians in these assemblages indicates that it should be possible to establish a zonation for this intermediate latitude sub-Antarctic region as more comparable material becomes available.

The ebridian Ammodochium ampulla Deflandre is present at Site 1128. A. ampulla was originally described from the upper Eocene diatomite of Oamaru, New Zealand, and was previously recorded in assemblages from the sub-Antarctic southwest Pacific, Deep Sea Drilling

Project

Sites 277, 281, and 283. Diatoms were either absent or rare and poorly preserved in the samples examined between Cores 182-1128C-9H and 21X. Zonal markers for both the low-latitude and the high southern latitude diatom zonations for the Oligocene are absent, and precise correlation of this interval is impossible.

The diatom assemblage in Sample 182-1128C-8H-4, 130-132 cm, contains a combination of oceanic and neritic diatoms, and the presence of Rocella vigilans and Coscinodiscus rhombicus suggests a late Oligocene or earliest Miocene age. Between Cores 182-1128C-22X and 26X, the diatom assemblages contain a combination of neritic and oceanic taxa, including the species Cestodiscus reticulatus and Cestodiscus convexus, which are indicative of an early Oligocene age.