Dinoflagellate and other palynomorph abundance in sediments from ODP Leg 189 sites

At Ocean Drilling Program (ODP) Leg 189 Sites 1170-1172, the climatologically critical Eocene-Oligocene (E-O) transition is barren of any calcareous microfossils but contains rich marine organic walled dinoflagellate cyst (dinocyst) and diatom assemblages, suitable for detailed biostratigraphic and paleoenvironmental analysis. The resulting first-ever integrated dinocyst/diatom magnetostratigraphy allows confident correlation of the E-O interval between all Leg 189 sites, including Site 1168. Our correlations indicate that the (deep) opening of the Tasmanian Gateway occurred quasi-synchronously throughout the Tasmanian region, starting at ~35.5 Ma. At Sites 1170-1172, quantitatively, three distinct dinocyst assemblages may be distinguished that reflect the relatively rapid and pronounced stepwise environmental changes associated with the E-O transition in the Tasmanian region, from a pro-deltaic setting to a deep marine pelagic setting. Moreover, synchronous with the deepening of the gateway, at the southern and eastern Sites 1170-1172, typical endemic Antarctic assemblages were replaced by more cosmopolitan dinocyst communities. In marked contrast, at Site 1168 off western Tasmania, endemic Antarctic taxa are virtually absent during the E-O transition. At Sites 1170-1172, the endemic Antarctic dinocyst assemblage (Transantarctic Flora) drastically changes into a more cosmopolitan assemblage at ~35.5 Ma, with a more offshore character, reflecting the arrival of different oceanographic and environmental conditions associated with the deepening of the Tasmanian Gateway. In turn, this assemblage grades at ~34 Ma into one more typical for even more offshore and/or upwelling conditions at Site 1172. In slightly younger deposits at all sites, organic microfossils are virtually absent, reflecting winnowing and oxidation, indicative of a next step of oceanographic development. This phase may be dated as close to the Oceanic Anoxic (Oi)-1 18O (Antarctic glaciation) event (~33.3 Ma). In a single productive sample from the earliest Oligocene the northern Site 1172, a relatively warm-water cosmopolitan assemblage has been recovered. This aspect contrasts findings from coeval deposits from the Ross Sea, where endemic Antarctic species remain dominant. Somewhere between the paleogeographic positions of Site 1172 and the Ross Sea, a strong differentiation of surface waters occurred in the earliest Oligocene, possibly reflecting the onset of the Antarctic Circumpolar Current.

Calcareous nannofossil abundance in ODP Site 185-1149 sediments

Basal carbonate sediments recovered at Ocean Drilling Program (ODP) Site 1149 lie directly on magnetic Anomaly M12. They contain abundant and moderately well preserved calcareous nannofossils. Two nannofossil zones are recognized: the lower Calcicalathina oblongata Zone and the upper Lithraphidites bollii Zone, indicating a late Valanginian-late Hauterivian age. The close occurrence of two significant bioevents, the first occurrence (FO) of L. bollii and the FO of Rucinolithus terebrodentarius in Core 185-1149B-20R, together with dip data recorded during in situ geophysical logging, suggest the presence of an unconformity that corresponds to the lower Hauterivian sedimentary section. The continuous occurrence of L. bollii is reported for the first time in sediments from the Pacific Ocean. Other marker species regarded as cosmopolitan (e.g., C. oblongata) have a sporadic occurrence. Nannoconids, very useful zonal markers for Tethyan areas, are virtually absent. The presence of an unusually high abundance of Diazomatolithus lehmanii is also recorded and correlates with the Valanginian 13C positive excursion.

Mollusc biostratigraphy and Bolboforma abundance in sediments obtained near Gross Pampau, north Germany

A thirty-six meter thick section of Miocene mica clay of Gross Pampau was studied for molluscs and bolboformas. The molluscs define the regional substages of late Reinbekian to late Langenfeldian. The bolboformas enable the cross-correlation with the nannoplankton subdivision and the geological time scales of BERGGREN et al. (1995). New species are Periploma ariei, Ringicula tiedemanni, Bolboforma robusta badenensis, and Bolboforma contorta.

Nannofossil datums and abundance in sediments from ODP Leg 164 sites

Twenty routinely used nannofossil datums in the late Neogene and Quaternary were identified at three Blake Ridge sites drilled during Leg 164. The quantitative investigation of the nannofossil assemblages in 236 samples selected from Hole 994C provide new biostratigraphic and paleoceanographic information. Although mostly overlooked previously, Umbilicosphaera aequiscutum is an abundant component of the late Neogene flora, and its last occurrence at ~2.3 Ma is a useful new biostratigraphic event. Small Gephyrocapsa evolved within the upper part of Subzone CN11a (~4.3 Ma), and after an initial acme, it temporarily disappeared for 400 k.y., between 2.9 and 2.5 Ma. Medium-sized Gephyrocapsa evolved in the latest Pliocene ~2.2 Ma), and after two short temporary disappearances, common specimens occurred continuously just above the Pliocene/Pleistocene boundary. The base of Subzone CN13b should be recognized as the beginning of the continuous occurrence of medium-sized (>4 µm) Gephyrocapsa. Stratigraphic variation in abundance of the very small placoliths and Florisphaera profunda alternated, indicating potential of the former as a proxy for the paleoproductivity. At this site, it is likely that upwelling took place during three time periods in the late Neogene (6.0-4.6 Ma, 2.3-2.1 Ma, and 2.0-1.8 Ma) and also in the early Pleistocene (1.4-0.9 Ma). Weak upwelling is also likely to have occurred intermittently through the late Pliocene. Due to the sharp and abrupt turnover of the nannofossils, which resulted from an evolution of very competitive species, the paleoproductivity of the late Pleistocene is not clear. The site was mostly in an oligotrophic central gyre setting during the 4.6- to 2.3-Ma interval, intermittently between 2.1 and 1.4 Ma, and continuously for the last several tens of thousand years.