ALBERT

Description: Analyses of 87Sr/86Sr in foraminifera and sedimentological observations suggest that the Chicxulub impact was not the trigger for slumps or a hiatus within the Maastrichtian section recovered at Ocean Drilling Program Sites 1049, 1050, and 1052 (subtropical western North Atlantic). The slumps and hiatus occur within a sequence dominated by pelagic chalk. The 87Sr/86Sr measurements show a general increase through the Maastrichtian at each site, but suggest chronostratigraphic gaps on the order of 10 Myr across the slumps. Some of the slumps have burrowed upper surfaces and are composed of material that is older and coarser grained than the bounding chalks. Pelagic deposition punctuated by gravity flows easily explains the Maastrichtian record on Blake Nose, whereas an impact-based explanation for slumping is difficult to reconcile with sedimentological and geochemical observations.

Description: We examined near-surface, late Holocene deep-sea sediments at nine sites on a north-south transect from the Congo Fan (4°S) to the Cape Basin (30°S) along the Southwest African continental margin. Contents, distribution patterns and molecular stable carbon isotope signatures of long-chain n-alkanes (C27-C33) and n-alkanols (C22-C32) are indicators of land plant vegetation of different biosynthetic types, which can be correlated with concentrations and distributions of pollen taxa in the same sediments. Calculated clusters of wind trajectories and satellite Aerosol Index imagery afford information on the source areas for the lipids and pollen on land and their transport pathways to the ocean sites. This multidisciplinary approach on an almost continental scale provides clear evidence of latitudinal differences in lipid and pollen composition paralleling the major phytogeographic zonations on the adjacent continent. Dust and smoke aerosols are mainly derived from the western and central South African hinterland dominated by deserts, semi-deserts and savannah regions rich in C4 and CAM plants. The northern sites (Congo Fan area and northern Angola Basin), which get most of their terrestrial material from the Congo Basin and the Angolan highlands, may also receive some material from the Chad region. Very little aerosol from the African continent is transported to the most southerly sites in the Cape Basin. As can be expected from the present position of the phytogeographic zones, the carbon isotopic signatures of the n-alkanes and n-alkanols both become isotopically more enriched in 13C from north to south. The results of the study suggest that this combination of pollen data and compound-specific isotope geochemical proxies can be effectively applied in the reconstruction of past continental phytogeographic developments.