Normal fault growth analysis using 3D seismic datasets located along Australia’s southern margin

Abstract

Understanding and constraining the growth of normal faults continues to remain a grand challenge for geoscientists. Normal faults have long been interpreted to grow symplistically with an elliptical fault surface growing radially and accrued displacement increasing from the fault tip‐line to the centre of the fault surface. However, continued rigorous analysis of normal fault arrays in rock outcrop and 3D seismic datasets has revealed that normal fault growth is substantially more complex. This is due to the growth and interaction of multiple fault segments, spatial heterogeneity in rock properties and a more detailed three‐dimensional analytical approach to understanding displacement variations, rather than in two‐dimensional analysis in the plane of view. The interpretation of normal fault growth has long been analysed on the centimetre and metre scale in rock outcrop. However, with increasingly available, high quality seismic datasets, constraints on normal fault growth can now be interpreted on the kilometre scale. Our present understanding of small‐scale normal fault growth using rock outcrop is crucial information if we are to constrain the growth of normal faults on the kilometre scale in 3D seismic datasets, with limitations such as data quality, resolution, depth penetration and spatial coverage. Seismic interpretation of normal fault geometry and development, explicitly or implicitly, will be influenced by, and in some cases rely on, preconceived and idealized conceptual models. Continued analysis of high quality seismic datasets, in order to further understand the development of normal fault systems, will create greater predictive ability in seismic interpretation and static modelling of the subsurface when a poorer quality seismic dataset does not provide a complete and obvious answer. Factors controlling normal fault growth, such as crustal extension, gravitational instability, thermal subsidence and sediment loading need to be better understood and constrained to allow for greater prediction of normal fault evolution in any given tectono‐stratigraphic setting. This thesis consists of four papers, each of which analyses the growth of Upper Cretaceous normal fault arrays along Australia’s rifted‐to‐passive southern margin providing implications for other rifted and passive margins around the world, including the North Sea, Suez Rift, East African Rift, Niger Delta, Gulf of Mexico and Baram Delta. Australia’s southern margin and its constituent basins (Bight, Otway, Sorell, Gippsland and Bass basins) was formed from the Australian‐Antarctica continental break‐up since the Middle to Late Jurassic. The four papers comprising this thesis provide analysis, interpretation and discussion on the development of normal fault arrays located in the Ceduna Sub‐ Basin of the Bight Basin and the Gambier Embayment, the present‐day shelf‐edge break and the Shipwreck Trough of the Otway Basin. This thesis aims to qualitatively constrain the influence of controls such as crustal extension, gravitational instability, deltaic sediment loading, perturbation of stress orientations and basin compartmentalisation on the spatial and temporal development of normal fault arrays in differing tectono‐stratigraphic settings. Therefore, the findings of this thesis may be used as a predictive tool for normal fault geometry, linkage, displacement distribution and the spatial and temporal development of normal fault arrays in known tectono‐stratigraphic settings around the world.