Quantification of architectural variability and controls in an Upper Oligocene to Lower Miocene carbonate ramp, Browse Basin, Australia

Integration of seismic geomorphology and trajectory analysis of the Oligocene through Lower Miocene distally-steepened carbonate ramp system in the subsurface Browse Basin of the Northwest Shelf of Australia introduces a new way to parameterize carbonate slope channel systems and their stability, and sheds light on how basinward sediment transport is influenced by allogenic and autogenic controls. Seismic geomorphologic analysis identified large-scale prograding clinoforms with an extensive slope channel system and slope angles of up to 12°. Clinoforms have an average slope angle of 8°, a height of ∼500 m, and prograded 9 km during the Upper Oligocene through the Lower Miocene. Relative sea level changes overprinted the effect of intermediate-scale and small-scale antecedent topography, and determined progradation, aggradation and slope angles of the system. We introduce cumulative channel cross sectional area (CCCSA) as the product of number of slope channels, slope channel depth, and slope channel width. CCCSA quantifies the capability of the slope channel system to transport sediment basinward and highlights phases of autogenic slope system re-organization in response to changes in relative sea level. Abruptly increasing values of CCCSA correlate with slope sediment bypass through the incision of new slope channels during system re-organization phases at slope angles of 10°. Thus, we propose that CCCSA can be used as a proxy for slope system stability. Incision of new slope channels into the ramp margin created strike-parallel variability of the ramp margin trajectory. Our seismically-derived relative sea level curve and subsidence rates of 9-30 m/Myr indicate a good preservation of the subsidence and sea level signal in the data.