Bonita Barrett, David Hodgson, Christopher Aiden-Lee Jackson , Christopher Lloyd, Junia Casagrande, Richard E.Ll Collier 

Interactions between footwall-, hangingwall- and axial-derived depositional systems make syn-rift stratigraphic architecture difficult to predict, and preservation of net-erosional source landscapes is limited. Distinguishing between deposits derived from fault-scarp degradation (consequent systems) and those derived from long-lived catchments beyond the fault block crest (antecedent systems) is also challenging, but important for hydrocarbon reservoir prospecting. We undertake geometric and volumetric analysis of a fault-scarp degradation complex and adjacent hangingwall-fill associated with the Thebe-2 fault block on the Exmouth Plateau, NW Shelf, offshore Australia, using high resolution 3D seismic data. Vertical and headward erosion of the complex and fault throw are measured. Seismic-stratigraphic and seismic facies mapping allow us to constrain the spatial and architectural variability of depositional systems in the hangingwall. Footwall-derived systems interacted with hangingwall- and axial-derived systems, through diversion around topography, interfingering, or successive onlap. We calculate the volume of footwall-sourced hangingwall fans (VHW) for nine quadrants along the fault block, and compare this to the volume of material eroded from the immediately up-dip fault-scarp (VFW). This analysis highlights areas of sediment bypass (VFW>VHW) and areas fed by sediment sources beyond the degraded fault scarp (VHW>VFW). Exposure of the border fault footwall and adjacent fault terraces produced small catchments located beyond the fault block crest that fed the hangingwall basin. One source persisted throughout the main syn-rift episode, and its location coincided with: (i) an intra-basin topographic high; (ii) a local fault throw minimum; (iii) increased vertical and headward erosion within the fault-scarp degradation complex; and (iv) sustained clinoform development in the immediate hangingwall. Our novel quantitative volumetric approach to identify through-going sediment input points could be applied to other rift basin-fills. We highlight implications for hydrocarbon exploration and emphasise the need to incorporate interaction of multiple sediment sources and their resultant architecture in tectono-stratigraphic models for rift basins.