CONCLUSIONS

The 170.1-m-long hemipelagic sediment sequence recovered at ODP Site 1002 in the Cariaco Basin (Venezuela) contains a continuous late Quaternary record that spans the last ~580 k.y. A newly available planktonic foraminiferal ¹⁸O stratigraphy, coupled with a revised set of shore-based biostratigraphic datums, clearly indicates that the basal age of Site 1002 is approximately twice as old as initially surmised from the single tentative biostratigraphic identification available from shipboard sampling of core catchers. Sedimentation rates at Site 1002 average in the range of 350 m/m.y., in line with estimates available from shorter piston-core records.

Although ¹⁸O variations at Site 1002 can be clearly correlated to the standard open ocean stratigraphy, the amplitude of the glacial-interglacial signal is large, well in excess of 2, and there is a significant component of high-frequency variability visible in the record where sampling intervals are close enough to resolve millennial-scale events. Both changes in local sea-surface temperature and salinity offer plausible explanations for the unusual features of the Cariaco Basin ¹⁸O record. We consider it likely that the effects of both variables are recorded, with the relative contributions of each varying through time.

Large-scale variations in sediment lithology in the Cariaco Basin can be related to glacial-interglacial climate cycles, most likely as a consequence of glacioeustatic sea-level changes and their effect on basin morphology. During glacial sea-level lowstands, local rivers would have discharged their terrigenous sediment load more directly into the semi-isolated basin, whereas the shallower sill depths would have disrupted the supply of nutrient-rich thermocline waters that support high surface productivity along the Venezuelan coast. These effects can be seen in the changing relative contributions of biogenic carbonate, TOC, and terrigenous matter in the Site 1002 record on glacial-interglacial time scales. Higher frequency variability visible in the records of TOC and carbonate presumably requires a climate/oceanographic mechanism related to circulation and nutrient supply.

The oxygenation history of the Cariaco Basin, as inferred from the presence or absence of preserved sediment laminae, does not appear to be related in a simple way to climate or sea-level cycles of the late Quaternary. Further studies are required to unravel the complicated linkages between climate variability and the processes that control export production, carbon burial, and anoxia in this important tropical setting.