HR: 14:10h
AN: H53E-03    [Abstracts]
TI: Massive Siliciclastic Accumulation on Slopes off Northeast Australia During the Last Sea Level Transgression: Response of an Intensified Monsoon at 10 ka?
AU: * Francis, J M
EM: jfrancis@rice.edu
AF: Rice University, Department of Earth Science - MS-126, 6100 Main Street, Houston, TX 77005 United States
AU: Dickens, G R
EM: jerry@rice.edu
AF: Rice University, Department of Earth Science - MS-126, 6100 Main Street, Houston, TX 77005 United States
AU: Opdyke, B
EM: bno@ems.anu.edu.au
AF: The Australian National University, Department of Earth and Marine Science, Canberra, ACT 0200 Australia
AU: Eggins, S
EM: Stephen.Eggins@anu.edu.au
AF: The Australian National University, Department of Earth and Marine Science, Canberra, ACT 0200 Australia
AU: Droxler, A W
EM: andre@rice.edu
AF: Rice University, Department of Earth Science - MS-126, 6100 Main Street, Houston, TX 77005 United States
AB: The continental margins of southern Papua New Guinea and northeastern Australia collectively form the world's largest extant tropical mixed siliciclastic-carbonate depositional system where rivers supply large amounts of terrigenous sediment to a shelf with substantial carbonate production. Over the last 30 kyr, the flux and composition of sediment shed from these margins to surrounding slopes and basins has changed dramatically. This is not unexpected given the two dominant sediment sources and the large amplitude variations in sea level. Importantly, though, the observed accumulation of siliciclastic material deviates significantly from generic sequence stratigraphic models, at least for slopes off northeast Australia. Recent studies in this region clearly show greatly increased siliciclastic fluxes coincident with late transgression ca. 12-7 ka rather than lowstand ca. 25-18 ka. Two end-member models have been proposed to explain elevated siliciclastic discharge to the slopes during late transgression: (1) sediment was stored behind a subaerially exposed inactive barrier reef tract during lowstand, and released to the slope when the shelf was flooded; (2) sediment was not supplied during arid climates coincident with the glacial world, but intensified precipitation greatly increased river fluxes and siliciclastic supply coincident with transgression. Increased siliciclastic accumulation during late transgression has been identified offshore the Ganges dispersal system, and attributed to intensified monsoons (e.g., Weber et al., 1997; Goodbred and Kuehl, 2000). Combined oxygen isotope measurements of planktic foraminifera tests and alkenone paleotemperature measurements also suggest that intensified monsoons caused anomalously fresh surface water off the Ganges system (Kudrass et al., 2001). This study examines oxygen isotopes and Mg/Ca ratios of G. ruber (white) tests in well-dated cores offshore northeast Australia to see if increased river run-off and surface water freshening also occurred in this region during the last transgression.
DE: 9330 Australia
DE: 4863 Sedimentation
DE: 4556 Sea level variations
DE: 3022 Marine sediments--processes and transport
DE: 1050 Marine geochemistry (4835, 4850)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting