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

Abstract

The geometry and growth of normal faults are 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 Subbasin located offshore southern Australia contains an east–southeast-striking, gravity-driven fault array, which soles out onto a southwest-dipping detachment horizon. These gravity-driven faults displace the White Pointer delta and overlying Hammerhead delta. Within the subbasin, 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 Subbasin. In this study, we use a time-migrated two-dimensional (2-D) seismic reflection survey covering the central Ceduna Subbasin to constrain the geometry and kinematics of the fault array. Throw patterns reveal that most faults nucleated in the Cenomanian. Although some faults display evidence for continuous growth by upper tip propagation throughout the Cenomanian to Maastrichtian, it is apparent that other faults were inactive during the Turonian–Santonian, before reactivating and propagating upward or dip-linking with overlying, newly formed faults during the Campanian and/or Maastrichtian. Faults that grew continuously during the Cenomanian to Maastrichtian primarily formed in the center of the study area, whereas reactivated faults developed in landward positions. Faults that formed because of dip linkage developed in seaward positions. We suggest that this spatial variation in fault growth style was controlled by compositional and mechanical heterogeneities in the Tiger and lower Hammerhead supersequences, which mark the boundary between the two delta systems. In addition to providing insights into the petroleum prospectivity of the Ceduna Subbasin, this study shows how 2-D seismic reflection data can be used to probe the kinematics of normal faults.