--> --> Marginal Palaeozoic Fault Systems of the Northern Carnarvon Basin, North-West Shelf, Australia

2018 AAPG International Conference and Exhibition

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Marginal Palaeozoic Fault Systems of the Northern Carnarvon Basin, North-West Shelf, Australia

Abstract

The North-West Shelf encompasses the offshore and marginal basins of Australia’s northern and western margin comprising of the Northern Carnarvon, Offshore Canning, Browse and Boneparte basins, as well as the Timor-Banda-Orogen. The margin is related to the fragmentation of Gondwana and contains predominately Mesozoic depocentres that can exceed 15 km in thickness. These Triassic, Jurassic and Lower Cretaceous sediments form the source and reservoirs of Australia's premier hydrocarbon province. The marginal Palaeozoic aged structures of the Northern Carnarvon Basin are fundamental to the formation of the basins that comprise this prolific region. Despite this, they have received relatively limited attention since their original recognition on deep, regional scale seismic sections. We present interpretations of the geometry and tectono-stratigraphy of major Palaeozoic structures from the inboard margins of the Mesozoic Barrow, Dampier and Beagle sub-basins of the Northern Carnarvon Basin based on 2D and 3D seismic data. Two distinct orientations of structures provide evidence for a poly-phase rift history during the Palaeozoic. NNE trending faults of the Barrow sub-basin were initiated in the Carboniferous or Devonian but were underfilled, resulting in erosion of the fault block crest and filling of the remnant rift-related topography by conformable sequences of later Permian and Triassic sediments. By contrast, NE-SW oriented faults of the Dampier sub-basin experienced a distinct phase of Permian activity and are unconformably overlain by Triassic sediments. In the Beagle sub-basin, both orientations of structures are present and are highly segmented. The evolution and structural style of the Mesozoic depocentres was controlled by the major Palaeozoic structures and can account for segmentation and fault patterns in these basins. The marginal fault systems have complex fault geometries. Significant deformation of hanging wall strata is associated with the reactivation of the eroded fault block crests and overprinting of faults during Mesozoic extension. There has been relatively limited exploration of the complex traps that result, and it has met with limited success. The more detailed understanding of the structural evolution presented here will help to better quantify risk associated with these traps. This study also sheds light on the geodynamic evolution of this poly-phase margin and the implications of this for petroleum systems.