HR: 08:30h
AN: OS11A-03 INVITED     [PDF]
TI: Evidence for Low Sea Level Incision of the Gulf Of Papua Shelf by the Fly River and by Tidal Currents During the Quaternary
AU: * Harris, P T
EM: Peter.Harris@ga.gov.au
AF: Geoscience Australia, GPO Box 378, Canberra, ACT 2601 Australia
AU: Heap, A
AF: Geoscience Australia, GPO Box 378, Canberra, ACT 2601 Australia
AU: Passlow, V
AF: Geoscience Australia, GPO Box 378, Canberra, ACT 2601 Australia
AU: Hughes, M
AF: School of Geosciences, University of Sydney, Sydney, NSW 2006 Australia
AU: Daniell, J
AF: Geoscience Australia, GPO Box 378, Canberra, ACT 2601 Australia
AU: Anderson, O
AF: Kort & Matrikelstyrelsen, Geodetic Division Rentemestervej 8, Copenhagen, DK-2400 Denmark
AB: Multibeam sonar and seismic mapping at the northern end of Australia's Great Barrier Reef in the Gulf of Papua, have revealed a shelf valley system up to 220 m deep that extends for more than 80km across the continental shelf. Two valley types are evident. Relict fluvial valleys located in the Gulf of Papua exhibit lateral accretion surfaces in seismic profiles and incised margins that intersect and truncate underlying strata. Over-deepened valleys located adjacent to the northern Great Barrier Reef exhibit closed bathymetric contours and are floored with well-sorted carbonate gravely sand containing a large relict fraction. The deepest valley segments were probably the sites of lakes during the last ice age, when Torres Strait formed an emergent land-bridge between Australia and Papua New Guinea. Post-glacial transgression of the shelf transformed the relict fluvial valleys into estuaries where terrigenous and marine sediments were deposited, as documented by cores and seismic data. Radiocarbon ages of mangrove peat samples range from 8,597 to 11,733 years BP in water depths of from 35 to 81 m. The southern valleys, however, would have formed estuarine embayments, whose origin owed nothing to fluvial erosion processes, and where minimal terrigenous deposition occurred. Numerical modelling indicates that the strongest tidal currents occur over the deepest, outer shelf segment of the valleys when sea level is about 40-50 m below its present position, suggesting the channels are Pleistocene in age and of relict origin. At such low sea-level times, strong tidal currents at the northern end of the Great Barrier Reef prevents the deposition of sediment derived from Papua New Guinea's rivers that would otherwise bury the coral reefs.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3022 Marine sediments--processes and transport
DE: 3210 Modeling
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting