HR: 1330h
AN: T22A-0494    [PDF]
TI: Quantifying the Growth History of an Ancient Border Fault System, and the Role of Normal Fault Growth on Sedimentation During Basin Formation: a Case Study from the Late Cambrian Owen Conglomerate, West Coast Range, western Tasmania, Australia
AU: * Noll, C A
EM: christian@mail.earth.monash.edu.au
AF: Monash University, PO Box 28E Monash University Clayton, Melbourne, VIC 3800 Australia
AU: Hall, M
EM: mhall@mail.earth.monash.edu.au
AF: Monash University, PO Box 28E Monash University Clayton, Melbourne, VIC 3800 Australia
AB: The stratigraphic and depositional architecture of evolving extensional basins is principally controlled by normal fault growth through the generation of accommodation space. The history of border fault systems therefore controls the evolution of internal drainage patterns and basin facies distributions. Despite recent advances in the understanding of present-day normal fault growth, quantifying the effect of normal fault evolution on the architecture of ancient sedimentary basins has been largely obscured by post-rift deformation and erosion. The Late Cambrian Owen Conglomerate along the West Coast Range of western Tasmania, Australia, includes thick fluvial sandstone and marine turbidite sequences, as well as fluvial and marine conglomerates. The accumulation of this formation provides excellent insights into the rift-fill history of an ancient extensional basin, due to rugged, glaciated topography and exceptional outcrops, and the typically overfilled nature of the basin, which preserves the fault displacement history. Structural traverses have delineated the geometry of the extensional fault system active during deposition of the Owen Conglomerate. The fault system comprises a segmented array of border faults with variable along-strike polarity. Minimum displacements were calculated from present-day stratigraphic thicknesses, and define a roughly symmetric displacement-length profile that resembles that of a single, isolated fault, with maximum displacement (Dmax) located at the centre of the fault array, and decreasing displacement toward the distal segments. Displacement along the fault system, however, indicates a varied growth history through time. Isolated faulting (Stage 1) occurred during the early stages of rifting, when small fault segments grew in isolation. Stage 1 faults exhibit a Dmax at the centre of each individual segment. Rapid propagation of fault segments to maximum strike length occurred early in the basin history, with only limited interaction and feedback between individual segments. Continued growth faulting (Stage 2) resulted in migration of the locus of maximum displacement as individual segments began to interact and link. Eventual linkage of fault segments (Stage 3) occurred during the final stages of rifting, where the overall system exhibits a characteristic, through-going, displacement-length profile. Integration of lithofacies distributions, isopach maps and palaeocurrent data with the structural dataset shows that the stratigraphic architecture is strongly coupled with the development of the border fault system, and offers a high resolution model for fault development. While the generation of accommodation space adjacent to footwall scarps facilitated the development of a hanging-wall, dip-slope fluvial catchment and axial-through drainage networks, tectonic subsidence also provided a crucial trigger for the onset of isolated marine sedimentation where accommodation space generated by the localised accumulation of displacement on individual segments outpaced sediment supply.
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting