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An Enigmatic Transverse Structural Domain of the Northwest Passive Margin of Australia


Rift-related structural deformation, e.g., faulting and folding, is typically perpendicular to the rift direction. The rift-related structures of most passive margins are strictly aligned with the elongate shape of the margins, which reflect the dispersal direction of the two related continents. The North West Shelf of Australia is a NE-SW trending passive continental margin and most of the faults identified across the entire North West Shelf are NE-SW oriented and attributed to the NW-SE directed Late Jurassic-Early Cretaceous breakup of the Indian Ocean. However, the detailed structural interpretation of the recently released 3D seismic surveys, together with the 2D surveys has identified a large population NW-SE trending Late Jurassic-Early Jurassic faults extending up to 30 kilometers in length and indicate a NW-SE trending structural domain in the Roebuck Basin (central North West Shelf). In the adjacent parts of the Northern Carnarvon Basin, structural trends also show irregularities. The outer board Exmouth Plateau presents both NE-SW and N-S trending Late Jurassic-Early Cretaceous faults, cutting the faulted strata into rhombic-shape compartments. The inboard Beagle Sub-basin is dominated by N-S trending faults. Our study suggests that the development of the NW-SE to N-S structural domain in the central North West Shelf was initiated during the Late Triassic-Early Jurassic deformation and is controlled by the zones of weakness in the basement. The development of this structural domain has exerted a strong influence on the sedimentary architecture in the area. The Triassic sediments show distinct thinning towards the central area, contrasting with the Jurassic sequences that are thickening. The transition of the central area from a basin high to a major depocenter was simultaneous with the initiation of the NW-SE to N-S structural domain in the Late Triassic-Early Jurassic, which support the thermal uplifting-cooling-rifting process. We propose the NW-SE to N-S structural domain we identified could represent an abandoned arm of a Late Jurassic-Early Cretaceous trilete rift system. The results of this study will lead to a better understanding of the rifting process which shaped the structural developments of the North West Shelf. Also, given the fact that there were limited significant petroleum discoveries in the central North West Shelf, the recognition of the transverse structural domain is of crucial importance for the exploration in the area.