The kinematics of normal faults in the Ceduna Subbasin, offshore southern Australia: Implications for hydrocarbon trapping in a frontier basin

The geometry and growth of normal faults is fundamental to the evolution and petroleum prospectivity of sedimentary basins, controlling trap development, source, reservoir and seal rock distribution, and fluid flow. The poorly studied, petroliferous Ceduna Sub-basin located offshore southern Australia contains an ESE-striking, gravity driven fault array, which soles out onto a SW- dipping detachment horizon. Within the sub-basin, structural closures bound by these gravity driven faults represent the main exploration targets. Determining when these faults and associated traps formed relative to petroleum generation and migration and, more specifically, if the faults reactivated, is thus critical to understanding the prospectivity of the Ceduna Sub-basin. In this study, we use a high-quality, time-migrated 2D seismic reflection survey covering the central Ceduna Sub-basin to constrain the geometry and kinematics of the fault array. Fault throw patterns reveal that most nucleated in the Cenomanian. Although some faults display evidence for continuous growth by upper tip propagation throughout the Cenomanian to Maastrichtian, others grew via either dip linkage of isolated segments or fault reactivation. It is apparent that some faults were inactive during the Turonian-Santonian before reactivating and propagating upwards or dip-linking with overlying, newly formed faults. Continuously growing faults primarily occur in the center of the study area, whereas reactivated faults occur proximal to the sediment source and dip-linked faults developed oceanwards. We suggest that this spatial variation fault growth style was primarily controlled by compositional and mechanical heterogeneities in the Tiger and lower Hammerhead supersequences. In addition to providing insights into the petroleum prospectivity of the Ceduna Sub-basin, this study shows how 2D seismic reflection data can be used to probe the kinematics of normal faults