The Mid Pleistocene Climate Transition Recorded in a Hemipelagic Sediment Drift (ODP Leg 194): Implications for the Understanding of Continental Margin Sediment Sources and Sinks

The Marion Plateau (NE Australia margin) provides an ideal setting to study continental margin paleoceanographic history. It is not significantly current scoured and is located at upper continental slope depths, freeing it from the influence of large sediment gravity flows. Atop the plateau, a hemipelagic sediment drift is perched and was drilled on Ocean Drilling Program Leg 194 (site 1198). The lithologic record and other shipboard-acquired data sets (physical properties, downhole logging), as well as the site-survey seismic data all suggest that cyclicity dominates this sedimentary section, which encompasses the Mid Pleistocene climate transition (0.9 to 0.92 Ma). This period contains the transition from a 41 k.y. cycle (ice volume and temperature) to 100 k.y. (ice volume and temperature) cycle dominated world. Preliminary results indicate that the basic stratigraphic units of this drift record terrestrial climate, continental margin, and pelagic processes. Mass accumulation rates of the siliciclastic, neritic carbonate, and pelagic carbonate components represent orbitally-forced cycles that form a predictable sedimentary architecture, and grain size variations are a proxy for fluctuations in bottom current strength. The terrigenous flux varies as a function of both aridity/humidity variation on the adjacent continent and sea-level fluctuations, while the carbonate flux varies as a function of paleoproductivity of the overlying water column plus lateral input from the developing Great Barrier Reef. Examination of the changing sedimentary architecture of this drift during the Mid Pleistocene climate transition will further the understanding of sedimentary sources and sinks along continental margins, including their sensitivity to sea level, climate, and circulation changes.