Three-Dimensional Heterogeity of Processes, Sedimentation and Morphology for a Modern Shelf Clinoform: Gulf of Papua

Charles Nittrouer, Andrea Ogston, John Crockett, and D. Preston Martin
University of Washington, Seattle, WA

During highstands of sea level, fluvial sources supply substantial amounts of sediment and commonly form major sinks on adjacent continental shelves – clinoforms. A number of studies have delineated across-clinoform differences among topset, foreset and bottomset environments. Similar observations have been made for the clinoform being created by sediment supplied from the Fly and other rivers entering the Gulf of Papua, Papua New Guinea. In addition, detailed investigations have demonstrated a range of sedimentary processes and products that show distinct differences along strike. 1) The clinoform is prograding across a lowstand and transgressive surface with irregular topography (in particular, shelf valleys) that imposes bathymetric variability. This can cause tidal and gravity flows to be accentuated through valleys that are still filling. Consequently, sedimentary character (e.g., texture, structure) differs from open-clinoform regions. 2) On the topset, heterogeity is imposed by proximity to rivers and deltaic distributaries, which supply and temporarily store sediment. 3) Convergent transport associated with along-clinoform currents causes the central Gulf to concentrate the sediment suspended in the water column and accumulating in the seabed. The greater sediment concentrations cause seaward transport as fluid muds, which extend onto the bottomset region. This is likely the reason that shelf valleys are filled in the central Gulf. 4) The shelf width substantially decreases from southwest to northeast, impacting factors ranging from tidal exchange to off-shelf transport. Understanding the causes of along-clinoform heterogeneity will allow better interpretation of stratigraphy in ancient clinoform deposits.