Large-scale variability in style and magnitude of footwall rift-related unconformities, northern Carnarvon Basin, offshore NW Australia

Abstract

Fault-scarp degradation complexes record rift-related erosion of normal fault scarps. At the scale of an individual fault segment, the magnitude and distribution of erosion are related to the total and along-strike variability in fault throw. However, previous studies on degradation complexes focused on one type of rift-related erosional unconformity, with the factors controlling the development, magnitude, and style of footwall erosion at a far larger scale (i.e., several fault blocks) being poorly constrained. This study uses high-resolution subsurface data to constrain the timing, magnitude, and style of footwall erosion across the NW Shelf of Australia. By doing so, we test conceptual and numerical model predictions for rift-related unconformities development. We show that footwall erosion complexes development is dependent on the occurrence and duration of footwall exposure and that fault throw and footwall uplift control the magnitude of erosion. Furthermore, the style of footwall erosion depends on the driving process(es), with gravitational instabilities resulting in cuspate footwall crest erosional surfaces, whereas peneplain-style surfaces develop in response to wave-driven erosion dictated by the base level. The results of this study can help refine rift-related faults evolution and the effects of sea level changes in tectono-stratigraphic models of rift basins.