18O; and the early Miocene terrigenous pulse follows an increase in benthic foraminiferal 18O near the Oligocene/Miocene boundary.
Skiff Bank accomplished most of its subsidence prior to the Oligocene and had stabilized by 32 Ma. Skiff Bank is probably too remote from the Kerguelen archipelago to have been affected by plume activity there during the Oligocene.
Noncarbonate variations are large (10-90 wt%) at the ~100-m scale. Additional analyses show intermediate-scale (>1 m) variations up to 40 wt%, and reflectance measurements show previously unrecognized small-scale (<1 m) variations up to 20 wt%.
Carbonate concentration probably reflects glacioeustatic sea level and/or climate changes because it varies inversely with sedimentation rate, grain size, and opal concentration and by analogy with similar mixed terrigenous-pelagic sequences where relatively constant carbonate input was diluted by terrigeneous sediment during glacials. Specifically, the large mid-Oligocene terrigenous pulse at Site 1139 may correlate with a glacioeustatic lowstand (TB1.1 of Haq et al., 1987; Oi2 of Miller et al., 1991); the late Oligocene period of low terrigenous flux follows a large decrease in benthic foraminiferal 18O; and the early Miocene terrigenous pulse follows an increase in benthic foraminiferal 18O near the Oligocene/Miocene boundary.
Low organic carbon concentrations (and fluxes) throughout the Oligocene and early Miocene are attributed to a hostile terrestrial environment, lack of mineral surface area (predominance of silt), and deposition followed by extensive bioturbation below the oxygen minimum zone.
Although silicate weathering is high in comparable modern settings (southwestern Iceland), a paucity of clay minerals and clay-sized sediment (and presence of primary igneous minerals and predominance of silt) suggests that physical processes dominated over chemical weathering. It is likely that Skiff Bank was attacked by waves and perhaps was eroded by ice during the Oligocene and early Miocene. Site 1139 is a strategic site because of the intercalated terrigenous and pelagic components. The cores, however, are difficult to work with; specifically, the microfossil components are both difficult to extract from lithified material and difficult to clean.
