Reconstruction of dust flux of ODP Hole 198-1209C

Eolian dust in pelagic deep sea sediments can be used to reconstruct ancient wind patterns and paleoenvironmental response to climate change. Traditional methods to determine dust accumulation involve isolating the non-dissolvable aluminosilicate minerals from deep sea sediments through a series of chemical leaches, but cannot differentiate between minerals from eolian, authigenic and volcanogenic sources. Other geochemical proxies, such as sedimentary 232Th and crustal 4He content, have been used to construct high-resolution records of atmospheric dust fluxes to the deep sea during the Quaternary. Here we use sedimentary Th content as a proxy for terrigenous material (eolian dust) in ~58 Myr-old sediments from the Shatsky Rise (ODP Site 1209) and compare our results with previous dust estimates generated using the traditional chemical extraction method and sedimentary 4He(crustal) concentrations. We find excellent agreement between Th-based dust estimates and those generated using the traditional method. In addition our results show a correlation between sedimentary Th and 4He(crustal) content, which suggests a source older than present day Asian loess supplied dust to the central subtropical Pacific Ocean during the early Paleogene.

Lithology and geochemistry of ODP Leg 198 sites, Shatsky Rise

Samples of chert, porcellanite, and chalk/limestone from Cretaceous chert-bearing sections recovered during Leg 198 were studied to elucidate the nature and origin of chert color zonations with depth/age. Sedimentary structures, trace fossils, compactional features, sediment composition, texture, geochemistry, and diagenetic history were compared among lithologies. Trends in major and minor element composition were determined. Whereas geochemical analyses demonstrate systematic elemental differences among the different lithologies, there are less distinct patterns in composition for the colored cherts. The color of the chert appears to be related primarily to the amount of silica and secondarily to the proportion of other components. Red cherts are almost pure silica with only minor impurities. This may allow pigmentation from fine Fe oxides to dominate the color. These red cherts are from places where geophysical logs indicate that chert is the dominant rock type of the section. These red chert intervals cannot be unequivocally distinguished from surrounding chert-bearing lithologies in terms of sedimentary structures.

Eocene-Oligocene calcareous nannofossil events of ODP Sites from the Southern Ocean

The evolution of the Southern Ocean climate during the late Eocene-late Oligocene interval is examined through highresolution, quantitative calcareous nannofossil analyses on samples from the Southern Ocean sections on Maud Rise and Kerguelen Plateau. We determined the abundance patterns of the counted species to clarify the biostratigraphy, which we correlated with high-resolution magnetostratigraphy [Roberts, A.P., Bicknell, S.J., Byatt, J., Bohaty, S.M., Florindo, F., Harwood, D.M., 2003a. Magnetostratigraphic calibration of Southern Ocean diatom datums from the Eocene-Oligocene of Kerguelen Plateau (Ocean Drilling Program Sites 744 and 748). In: Florindo, F., Cooper, A.K., O'Brien, P.A. (Eds.), Antarctic Cenozoic Palaeoenvironments: Geologic Record and Models. Palaeogeogr., Palaeoclimatol., Palaeoecol. 198 145-168; Florindo, F., Roberts, A.P., in press. Eocene-Oligocene magnetobiochronology of ODP Sites 689 and 690, Maud Rise, Weddell Sea, Antarctica. Geol. Soc. Am. Bull.], and used this data to interpret paleoceanographic changes through the late Eocene to late Oligocene. Percentage plots of the individual species, compared with R-mode principal component and cluster analysis results, allowed us to divide the assemblages into three groups: temperate-water taxa, cool-water taxa, and no temperature-affinity taxa. We attempt correlations between these paleoecological groups and the major sea-surface temperature (SST) variations with tectonic and paleoceanographic changes in the Southern Ocean. During the late Eocene, the nannofossil assemblage data reveal that there were several minor SST decreases (coolings) from 36 to 34 Ma, before the Eocene/Oligocene (E/O) boundary. A sharp cooling event, dated at 33.54 Ma (earliest Oligocene), occurred about 160 kyr after the E/O boundary, which is dated at 33.7 Ma. Relatively stable, cool conditions are interpreted to persist until the latest Oligocene, when an increase in abundance of temperate-water taxa, which corresponds to an antithetical decrease in abundance of cool-water indicators, is recorded. On the basis of our dating, the opening of the Drake Passage, allowing shallow-water circulation, began by 33.54 Ma at the latest, while the establishment of deep-water connections through the Tasmanian Gateway occurred at 33 Ma, as suggested by Exon et al. [Proc. ODP, Init. Rep. 189 (2001) 1].