Paleogene planktonic foraminifera from the southern Kerguelen Plateau

An essentially complete Paleogene record was recovered on the Central and Southern Kerguelen plateaus (55°-59°S) in a calcareous biofacies. Recovery deteriorated in the middle Eocene and down to the upper Paleocene because of the presence of interbedded cherts and chalks. The stratigraphic distribution of about 70 taxa of planktonic foraminifers recovered at Sites 747-749 is reported in this paper. Faunas exhibited fairly high diversity (approximately 20-25 species) in the early Eocene, followed by a gradual reduction in diversity in the middle Eocene. A brief incursion of tropical keeled morozovellids occurred near the Paleocene/Eocene boundary, similar to that recorded on the Maud Rise (ODP Sites 689 and 690). The high-latitude Paleogene zonal scheme developed for ODP Leg 113 sites has been adopted (with minor modifications) for the lower Eocene-Oligocene part of the Kerguelen Plateau record. A representative Oligocene (polarity chronozones 7-13) and late Eocene-late middle Eocene (questionably polarity chronozones 16-18) magnetostratigraphic record has allowed the calibration of several biostratigraphic datum levels to the standard Global Polarity Time Scale (GPTS) and established their essential synchrony between low and high latitudes.

Chemistry of bulk-rocks and minerals of ODP Hole 120-748C

Five hundred meters of a unique Upper Cretaceous Cr-rich glauconitic sequence (Unit III) that overlies a 3-m-thick alkali-basalt flow with underlying epiclastic volcanogenic sediments was drilled at ODP Leg 120 Site 748. The Cr-rich glauconitic sequence is lithostratigraphically and biostratigraphically divided into three subunits (IIIA, IIIB, IIIC) that can also be recognized by the Cr concentration of the bulk sediment, which is low (<200 ppm) in Subunits IIIC and IIIA and high (400-800 ppm) in Subunit IIIB. The Cr enrichment is caused by Cr-spinel, which is the only significant heavy mineral component beside Fe-Ti ores. Other Cr-bearing components are glauconite pellets and possibly some other clay minerals. The glauconitic sequence of Subunit IIIB was formed by reworking of glauconite and volcanogenic components that were transported restricted distances and redeposited downslope by mass-transportation processes. The site of formation was a nearshore, shallow inner shelf environment, and final deposition may have been on the outer part of a narrow shelf, at the slope toward the restricted, probably synsedimentary, faulted Raggatt Basin. The volcanic edifices uncovered on land were tholeiitic basalts (T-MORB), alkali-basaltic (OIB) and (?)silicic volcanic complexes, and ultramafic rocks. The latter were the ultimate source for the Cr-spinel contribution. Terrestrial aqueous solutions carried Fe, K, Cr, Si, and probably Al into the marine environment, where, depending on the redox conditions of microenvironments in the sediment, green (Fe- and K-rich) or brown (Al-rich) glauconite pellets formed. The Upper Cretaceous glauconitic sequence at Site 748 on the Southern Kerguelen Plateau constitutes the transition in space and time from terrestrial to marine, from magmatically active subaerial to magmatically passive submarine conditions, and from a tranquil platform to active rifting conditions.