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Structural Controls on Sequence Stratigraphic Architecture During Rift Basin Development: An Example From the Northern Carnarvon Basin, North West Shelf, Australia


Structural geology and sequence stratigraphy often have a complementary relationship where observations from each discipline can be combined to improve the understanding of the other. An integrated approach can greatly aid reconstruction of the geological evolution of a basin and consequently improve the characterisation of petroleum systems, plays and prospects therein. In this paper, structural and stratigraphic transitions observed in the Northern Carnarvon Basin are related to typical phases of rift evolution described in many basins around the world. The onset of Mesozoic rifting in the Late Triassic (end of the Norian) is characterised by downwarping and sediment growth across small faults, coinciding with a change from prograding-aggrading to retrograding stacking patterns of the clastic delta system. Fluvial and alluvial deposition dominated the inboard rift area as in the earlier parts of the Triassic, however, increasing marine influence is observed in well data. The change in stacking pattern and depositional environments is interpreted to be driven by a relatively minor increase in accommodation during the initiation phase of rifting. The start of the rift climax phase is interpreted to occur at the beginning of the Rhaetian when discernible syn-rift wedge packages are observed in seismic data. This change in structural architecture resulted in the rapid creation of accommodation in the inboard rifts (Barrow, Dampier, Exmouth Sub-basins), sufficient to cause the major, rapid and long-lived transgression (~300km landward shoreline shift) observed at this time. A significant change in sequence architecture also occurs after this time with a series of depositional cycles, linked to pulses of extension and growth faulting, characterised by rapid basal transgressions and longer-lived coarsening upwards highstand deposits. The sudden cut off in clastic sediment supply to the outboard region, due to capture of the deltas in inboard rifts, resulted in the development of a drowned shelf and promoted carbonate deposition and buildups on fault blocks on the Exmouth Plateau.