Post-breakup Evolution of the Ceduna Sub-basin and understanding of processes that occur on Rifted Continental Margins

Abstract

Understanding the characteristics and evolution of normal growth faults has proved critical for interpreting the geological development of delta systems and the petroleum system of sedimentary basins within passive margins. In general. normal faults control the distribution of sedimentary deposits, the stratigraphic architecture and can provide migration pathways or traps for fluids (e.g. water and hydrocarbons). The interpretation of 3D seismic surveys has permitted a better understanding of fault evolution and control the migration of fluids. However, there are still knowledge gaps regarding the variability of normal growth faults geometrical features (length, strike, dip angle and displacement), fault evolution, changes in the distribution of sediments near the fault planes, and variation in the risk of fault reactivation and their control on magma flow. This thesis consists of four chapters that detail the structural complexity of normal growth faults in the Ceduna Sub-basin (Great Australian Bight Basin) and provide a detailed interpretation of the Ceduna 3D MSS seismic survey, an analysis and discussion of the normal growth fault complexity in terms of fault evolution, potential risk of reactivation, and influence the transport of magma. The seismic interpretation used in this study permitted a detail characterization of 530 normal growth fault segments in terms of displaced sedimentary sequences, length, dip angle, strike, and changes in displacement along the fault plane. This study classifies these faults segments in the Ceduna Sub-basin in three different fault groups related to the displaced sequences and includes three different analyses: (1) Fault kinematic analyses to assess three different evolution styles that include constant growth and reactivation by either dip-linkage or reactivation during the deposition of upper sequences. (2) Assessment of risk of fault reactivation using the fault analysis seal technology to demonstrate that areas of the fault with steep dip angles and oblique strikes from the current maximum horizontal stress are at higher risk of reactivation. (3) Interpretation and statistical lineal alignment prediction to demonstrate the substantial control that normal growth faults have on the geometry and emplacement of eruptive centres magma, flow regions and intrusions. This is the first study in the Ceduna Sub-basin to include a 3D seismic data that extends 12, 030 km2 to understand the variation in geometrical characteristics and the variability in the fault evolution of normal growth faults, exposing differences in their evolution styles and the importance of the detachment in the fault displacement configuration in delta systems. It established the importance of the changes in the fault roughness in the prediction of fault reactivation where regions of the faults with steeper dip angles and oblique strike orientations are at higher risk of fault reactivation. It also demonstrates that normal growth faults strongly influence the transport and emplacement of magma by stablishing a preferential northwest-southeast alignment between igneous bodies and the fault strike orientations.