Late Quaternary geomorphology, seabed evolution, and terrigenous sediment delivery to the Pandora and Moresby Troughs, Gulf of Papua
Abstract An integrated geology and geophysics investigation has been carried out to study the late Quaternary deepwater depositional system in the Gulf of Papua (NSF MARGINS focus area) focusing on two contrasting depocentres, Pandora and Moresby troughs. The studies incorporate multi beam bathymetry, sub bottom sonar, and core data in order to define and map acoustic and lithofacies; and relate depositional processes, sediment routing, timing and geomorphic products that have developed since Marine Isotope Stage (MIS) 3, ca. 40 cal ka. 3D seafloor visualisation is used to infer sedimentary processes responsible for observed morphology, which are then placed into a chronostratigraphic framework using recently published age models of sediment cores. The peak depositional period in Pandora Trough occurred during MIS 2. At that time a large deep sea channel network linked the Pandora and Moresby troughs, allowing long distance sediment transport by large turbidity currents from the Papuan mainland to the Coral Sea Basin. Near the LGM, shelf edge failure led to emplacement of mass transport deposits on the floor of the Pandora Trough, blocking this pathway for large turbidity currents. Intermittent turbidity currents continued to feed minibasins upslope of the MTD complex until early MIS 1 (earliest Holocene) Along the shelf edge of the Papuan Peninsula, substantial sediment delivery by turbidity currents continued until middle Holocene and perhaps later; combined with bottom currents, these flows contributed to the formation of large sediment waves of Moresby Fan. However, this Holocene turbidite sedimentation does not extend much farther into the Moresby Trough, based on negligible Holocene sediment accumulation deeper in the basin. This study has shown that sediment delivery from fluvial sources to deep basins in the GoP is controlled by a complex interplay of changing sea level, evolving basin bathymetry (influenced by depositional and tectonic processes) and oceanic transport of sediment from shelf to slope. These conditions have created highly localised conduits for shelf to slope sediment delivery that respond both to global forcing (eustatic sea level) as well as local conditions (shelf gradient, mass wasting, currents, and source proximity) resulting in a complex network of deep sea depositional morphologies active from the Last Glacial Maximum to Holocene time.