HR: 08:30h
AN: PP51F-03    [Abstracts]
TI: Canterbury Drifts, SW Pacific Ocean: Record of Antarctic Intermediate Water Flow Since 24 Ma
AU: * Carter, R M
EM: bob.carter@jcu.edu.au
AF: Marine Geophysical Laboratory, James Cook University, Townsville, Qld 4811 Australia
AB: The Canterbury Drifts were deposited in water depths between 400 and 1500 m by northward flowing, cold, intermediate depth water masses - Subantarctic Mode Water, Antarctic Intermediate Water, and their predecessor current flows. Drift accumulation started at 24 Ma, fed by terrigenous sediment derived from the newly rising Alpine Fault plate boundary in the west, which has built a progradational shelf-slope sediment prism up to 130 km wide at rates of eastward advance of up to 5.4 km/My. These regionally extensive, intermediate-depth sediment drifts can be examined in outcrop, in marine drillcore (ODP Site 1119) and at the modern seabed. The drifts comprise planar-bedded units up to several metres thick. Sand intervals have either reverse graded or sharp, erosive bases and normally graded tops. Bioturbation is moderate and the sands occur within a pervasive background of cm-scale, planar or wispy alternating muddy and sandy silts, consistent with deposition from rhythmically fluctuating bottom currents. In the Plio-Pleistocene, the sand:silt lithological rhythmicity occurs in synchroneity with Milankovitch-scale climate cycling; periods of inferred faster current flow (sand beds) mostly correspond to warm climatic intervals. The drifts vary in thickness from 300 m near the early Miocene shoreline, where they were accumulating in limited shallow water accommodation, to 2000+ m under the modern shelf edge. Mounded drifts first occur at 15 Ma (Middle Miocene), their appearance perhaps reflecting more vigorous intermediate water flow consequent upon the worldwide climatic deterioration between 15 and 13 Ma. A further change from large (more than 10 km wide) to smaller (1-3 km wide) mounded slope drifts occurs at 3.1 Ma, marking further cooling, the inception of discrete SAMW flows, and initiation of the Subantarctic Front. The natural gamma ray record from Site 1119 contains a history since 3.9 Ma of the waxing and waning of the New Zealand mountain ice cap. Back to 0.37 Ma, this record closely mirrors the climate history of Antarctica, as manifested in the Vostok ice core, at 0.1-0.6 ky resolution. Beyond, and back to 3.9 Ma, the gamma record reflects southern mid-latitude ice-volumes and perhaps Antarctic polar plateau temperature at a resolution of 1.3 ky.
DE: 4558 Sediment transport (1862)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4938 Interhemispheric phasing
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005