Unraveling the three-dimensional character of clinoforms: Gulf of Papua, Papua New Guinea

The clinoform developing on the Fly River shelf, Gulf of Papua, Papua New Guinea has been examined in detail. Coring, water-column, seismic, and multibeam mapping studies have revealed that under close inspection, clinoforms exhibit three-dimensional heterogeneity that was poorly quantified previously.; Multibeam mapping revealed the presence of three extant shelf valleys on the Fly River margin. The morphology of the valleys are analogous to modern river valleys and evidence of subaerial modification is described. The presence of the valleys in a relatively pristine state is unusual because transgressive processes typically modify the shelf and erase evidence of ancient river valleys. The differing morphology of the valleys produces different modes of valley filling. Kiwai valley is filling in three stages: (1) hemipelagic sedimentation at distal sites, (2) gravity-driven flows spreading far down the valley, and (3) subsequent clinoform progradation that completely fills the valley. Umuda valley is filling predominantly via clinoform progradation that is driven by deposition of 100-150-cm thick deposits of sediment on the topset, and steady-state supply to the foreset of the clinoform that fills the valley. Purutu valley is similarly being filled by a prograding clinoform. Overall, filling in the valleys is only a minor sink (<1%) for Fly River sediment because of their small areal extent.; Sedimentation outside the valleys is characterized by seven distinct styles of accumulation. The southwestern section of the margin is characterized by little or no modern accumulation and the northeastern section has rapid non-steady-state accumulation. Accumulation in the central region shows characteristics of both end members. Variability in non-steady-state accumulation may record the incidence of El Nino events in this area.; A sediment budget with high resolution compares well with previous low-resolution estimates. Inner-shelf sedimentation is not found to be a major sink for Fly River sediment, although some accumulation does occur there. Clinoform morphology is related to sediment accumulation with high accumulation rates generating steeper foreset slopes.