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.

Early Albian palynoflora of ODP Hole 120-750B

A well-preserved, diverse sporomorph flora of over 60 species has been found in Cores 120-750B-12W through -14R from the Southern Kerguelen Plateau. Analysis of the flora indicates that the terrestrial sediments overlaying the basaltic basement are late Early Cretaceous in age. Ranges of the sporomorphs in other parts of Gondwana and the morphology and paucity of angiosperm pollen grains confine the age of this section to the early to possibly early middle Albian. The Albian palynomorph assemblages in Hole 750B are composed primarily of fern spores and podocarpaceous pollen, and show most similarity to those from southern Australia. Changes in the flora through time reflect the successional vegetation changes on barren volcanic islands, beginning with high percentages of colonizing ferns and maturing into conifer (podocarp) forests. The flora shows some signs of endemism, which may be a result of the isolated position of the Kerguelen Islands during the Early Cretaceous. This endemism is expressed by high percentages of a distinctive monosulcate pollen species Ashmoripollis woodywisei n.sp. of pteridosperm or cycadophytean origin, and by a thick-walled, monosulcate angiosperm pollen species of the genus Clavatipollenites. The climatic conditions were probably cool to temperate (mean annual temperature approximately 7°-12°C) and humid (annual rainfall >1000 mm), analogous to modern Podocarpus-dominated forests in New Zealand and in South American mountain regions.

Census of calcareous nannofossil taxa expressed as percent of total number of individuals counted, ODP Legs 113, 114, 119, 120

Quantitative analysis of upper Eocene-upper Oligocene calcareous nannofossil assemblages from five Ocean Drilling Program sites in the Atlantic and Indian Ocean sectors of the Southern Ocean reveals an abrupt increase in cool-water taxa at the top of magnetic Subchron C13R ca. 35.9 Ma, coincident with an enrichment of ~1? d18O in the planktonic foraminifers at these sites. The synchrony of the abrupt increase in cool-water taxa in the Southern Ocean renders this event a useful biostratigraphic datum at southern high latitudes. This earliest Oligocene cool-water taxa increase was the sharpest and largest during the late Eocene-late Oligocene interval and indicates a drop in surface-water temperature of more than 3°C in the Southern Ocean. This suggests that the earliest Oligocene d18O shift represents primarily a temperature signal; a small portion (~0.2?) is attributable to a global ice-volume increase.