Sedimentation on a mixed siliciclastic/carbonate continental margin over decadal to millennial timescales: Gulf of Papua
Sediments from the Gulf of Papua were examined to estimate particle flux and sediment mass accumulation rates on multiple timescales. Patterns of sediment mass accumulation and inventory-derived 210Pb fluxes display regional variations, decreasing seaward, and along isobaths seaward from the northeastern shelf edge. The amount of terrigenous sediment load being discharged annually from the shelf and accumulating in Pandora Trough is approximately 7-14×106 tonnes. The existence of possible turbidity-current transport and deposition have been documented in deeper parts of the Gulf of Papua. High excess 210Pb fluxes estimated from seabed inventories at the shelf edge and upper slope are consistent with the combined effects of sediment focusing and boundary scavenging of oceanic water masses. Sediments may be transported from inner-shelf depocenters by oceanic processes, focused in depocenters near the northeastern Gulf of Papua shelf edge, and distributed downslope through a combination of nepheloid-layer flow and possible turbidity-currents. For the cores located between shelf edge and lower slope, biodiffusion coefficients and mixing depths exhibit a decreasing trend with increasing water depth. Using a two-layer model, biodiffusion coefficients in these cores are in the range of 0.007-60 cm2 y-1 for the upper layer and 0.002-2.9 cm2 y-1 for the bottom layer. Sediment mass accumulation rates without the influence of physical mixing are probably overestimated by a factor of ~1.4. Jumbo piston cores taken from the shelf edge and upper and middle slope in the northern Pandora Trough suggest variation in sediment mass accumulation rates during post-Last Glacial Maximum (LGM) sea level rise. Upper 12 m of the sediment on the northeastern shelf edge has deposited in < 12 ky BP after post-LGM sea level rise. The bulk of this mud deposit, with mass accumulation rates as high as 3900 g cm-2 ky-1, is constrained between the time of Last Glacial Maximun and Younger Dryas. The findings from this study suggest that physical processes building the mud wedge on the northeastern Gulf of Papua shelf were similar to the physical processes acting today building the clinoform in the western Gulf of Papua shelf.
magnetic susceptibility, bioturbation, Pb-210 flux, sediment inventory
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