Submarine valley systems in the Gulf of Papua

Andrew Donald, James Cook University, School of Earth Sciences, Townsville, Australia, [email protected]

Bathymetric maps and several scientific cruises depict a valley system extending for more than 80 km from the eastern Torres Strait to across the northern end of the Great Barrier Reef. Landward are infilled channels, which may represent paleo-river channels filled with post-glacial transgressive deposits. The valleys, on the outer edge of the shelf however, do not exhibit fluvial features. These deep channels are u-shaped and have closed bathymetric contours with the valley floors in <100 m water depth. This means that during the Last Glacial Maximum when sea level was 120 m lower than present, these valleys probably formed elevated lakes on the subaerial shelf when Torres Strait formed a land-bridge between Australia and Papua New Guinea. However, no lacustrine sediments, as yet, have been found in any of the cores taken during the scientific cruises to the area.

The eustatic sea level curve shows prolonged periods of sea level within a 40-50 m, below present, range occurred during isotope stages 3, 4, 5a and 5c. Tidal scour may have exhumed these valleys during the periods when sea level fell into this range.

Our seismic work shows the valleys have a propensity for channel formation in this area, as there is a succession of channel formations on top of each other. There may have been tidal scouring in this area, at least, during the last two glacial/interglacial cycles.