Biostratigraphic and paleomagnetic datum levels in sediments from DSDP Site 85-575

Data on the composition of benthic foraminiferal faunas at Deep Sea Drilling Project Site 575 in the eastern equatorial Pacific Ocean were combined with benthic and planktonic carbon- and oxygen-isotope records and CaCO3 data. Changes in the composition of the benthic foraminiferal faunas at Site 575 predated the middle Miocene period of growth of the Antarctic ice cap and cooling of the deep ocean waters by about 2 m.y., and thus were not caused by this cooling (as has been proposed). The benthic faunal changes may have been caused by increased variability in corrosivity of the bottom waters, possibly resulting from enhanced productivity in the surface waters.

Calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea

The distribution of calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea was quantitatively analysed. The samples contain 11 cyst species and the vegetative coccoid Thoracosphaera heimii. Cyst abundance increases towards the deeper parts of the basins and is generally higher in the eastern Mediterranean Sea. Three major distribution characteristics exist: (1) different assemblages in oceanic and neritic regions, (2) little agreement with the associations of areas studied so far like the Atlantic Ocean, and (3) a unique oceanic assemblage in the eastern Mediterranean Sea. A gradual change in cyst assemblages from the western to the eastern Mediterranean Sea was observed and statistically compared with the main environmental gradients in the upper water column. Temperature, nitrate concentration and possibly salinity appear to be the most important factors controlling cyst production. Three groups containing cysts with similar environmental preferences can be distinguished: (1) an eastern Mediterranean group related to relatively high temperature and salinity but low nitrate concentration, (2) a group of more or less consistently abundant cosmopolitan species tolerating or even preferring relatively low temperature and salinity but high nitrate concentration, and (3) a group containing species that are possibly adapted to neritic environments and have probably been transported from coastal areas into the studied regions. In contrast to other calcareous plankton, calcareous dinoflagellate cysts correlate strongly with the main environmental gradients in the Mediterranean Sea, bearing a high potential for palaeoenvironmental reconstructions.

Geochemistry at DSDP Holes 85-573B and 85-574C

Eocene-Oligocene metalliferous sediments and associated lithologies from the central equatorial Pacific are described in detail. Geochemical analyses of 54 sediment and 2 basalt samples are presented for 34 elements. Detailed stratigraphic and statistical analyses of these data, combined with mineralogic studies, indicate the presence of volcanic glass and seven main mineral phases: biogenic calcite and opal, Fe smectite, goethite, dMnO2, carbonate fluorapatite, and barite. Fe smectite formed by reactions between Fe oxyhydroxides and biogenic opal, causing the dissolution of calcite and the precipitation of barite. Diagenesis was oxic. Sediments have rare earth element distributions similar to those in seawater. The metal content of the sediments is related to competition between the supply rates of hydrothermal and biogenic particles, but has been enhanced by early diagenetic processes. Eocene-Oligocene metalliferous sediments compare closely to those currently being deposited in the Bauer Basin and on the flanks of the East Pacific Rise. There is, however, no evidence that they were deposited in close proximity to an active hydrothermal system.