Conduits, timing and processes of sediment delivery across a high relief continental margin: Continental shelf to basin in Late Quaternary, Gulf of Papua
Abstract The Gulf of Papua (GoP) between Australia and Papua New Guinea, is the receiving basin for multiple substantial rivers draining southern Papua New Guinea with collective sediment discharge 220 million metric tons (Mt) per year, comparable to a continental scale river, but draining a combined catchment area of only ~160,000 km 2 This study of the deepest marginal basins in the Gulf of Papua was undertaken to build a regional late Quaternary lithofacies and stratigraphic framework to better understand processes, timing, and conduits of sediment delivery from terrestrial and shelf settings to deep marginal basins, using the GoP as a natural laboratory. Methods include observations of sediment core stratigraphy and physical properties, accelerometer mass spectrometry (AMS) C 14 dates, core x radiographs and thin sections. Six lithofacies across the deep water Gulf of Papua (GoP) are identified based on core visual and textural observation. Chronological constraints permit an assessment of changes in sediment supply and depositional environments across time and space, from marine isotope stage (MIS) 3 to 1, or in the last 40 cal ka. The sediment delivery to the deep water GoP is dominated by two mechanisms, gravity driven flows down slopes and into deep sea basin primarily during lowstands in the western portions of the study area, and hemipelagic sediment accumulation during transgression and highstand. Although the sediment flux appears to be overall dominated by sediment gravity flows, hemipelagic sediment delivery is widespread during periods of sea level highstand. In the eastern portions of the study area, off shelf sediment delivery continued into the Holocene in sufficient local volumes to produce turbidity currents. This late, localized sediment delivery appears to have been facilitated by oceanographic processes that allowed seaward sediment transport after flooding of the shelf. A simple sediment budget comparing basinal sediment accumulation to modern estimated river sediment discharge indicates that peak sediment accumulation in proximal basins occurred during MIS 2; and declined thereafter, generally shifting to upper slope locations, except for the eastern margin of Moresby Trough. There, turbidite deposition continued until 7.4 cal ka, well after drowning of the shelf edge. This continued Holocene deep sea sediment delivery is likely explained by the local narrow shelf width, and the presence of oceanographic processes capable of transporting sediments from shore to shelf edge.