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Links Between Fault Evolution and Drainage Development, and the Influence on Deep Rift Sedimentation, Northwest Shelf Australia’s Dampier Sub-Basin


Abstract: The shelf-edge in rifts is often a structurally complex region where high accommodation interacts with a variety of depositional processes to generate thick reservoir units. The Dampier sub-basin in the offshore Northern Carnarvon basin of the North West shelf of Australia is a marine, rifted basin which fills with Jurassic-age syn-rift sediments. Seismic data, whole core and well logging suites are used to examine the relationships between drainage catchment and submarine fan development in this basin. The results show that the rift's west-margin, Rankin terrace (footwall), supplies huge amounts of sediment into the Kendrew Trough throughout all rift phases, but no obvious axial sediments are entering the Kendrew Trough. Thus, the development of drainage catchments along the uplifting footwalls is critical for the development of transverse-fed submarine fan systems. The J40.0 SB is the most broadly occurring subaerial unconformity across the basin. Its paleogeomorphology was reconstructed to examine the drainage catchments on the Rankin terrace. The Jurassic-age drainage area of the Rankin terrace is about 1900 km2 in which 1/6 of the total exposed area is developed as footwall catchments. We consider the fault length controls the width of drainage basins, and a total of five fault segments are identified and corresponding to five drainage basins. As indicated by paleo-geomorphology and stratal slicing, from north to south, five sub-drainages with catchments areas of ~ 56 km2 (Lambert), 58 km2 (Eaglehawk), 106 km2 (Perseus), 39 km2 (Goodwyn) and 49 km2 (Dixon) are focused through breached relay ramp eastward into the Kendrew trough and generate sub-marine fans with areas of 98 km2, 61 km2, 180 km2, 25 km2 and 18 km2, respectively. The amplitude extraction on the J53.0 SB shows morphologic features that appear to be reworked by longshore current-generated processes from south to north and relocating sediments along the footwall shoreline. Such reworking and re-sedimentation of deposits are supported by the lack of mass-balance in some fan systems. The ratio of catchment area to fan area shows the Dixon fan aprons to appear smaller than would be suggested by their source area volumes, while the Lambert fan aprons volumes seem to be outside of the fan volume trends. These types of studies express both the promise and the potential of S2S studies in rift basins. Keywords: rift basin; drainage catchment; longshore current; seismic geomorphology