How do detachment properties influence the kinematics of normal growth faults? Insights from 3D seismic reflection data from the Ceduna sub-basin.

The growth of gravity-driven normal faults exerts a critical control on multiple elements and processes of the petroleum system. However, there is still a poor understanding of the interactions between the properties of detachment layers and the evolution of growth faults in delta systems underlain by mechanically-weak detachments. This study is focused on the White Pointer Delta system in the Ceduna sub-basin, which detaches on an overpressure shale layer deposited during the AlbianCenomanian. Using the Ceduna 3D seismic survey, we present evidence of how changes in thickness, dip angle and geometry of the Albian-Cenomanian detachment influences the kinematics of overlying, detachment-linked growth faults. In the proximal region of the study, the detachment is relatively thin (0.2 to 0.5 s) with basal dips of 5-10. Normal faults located at this region, show constant growth during the Cenomanian-Maastrichtian. In central and distal areas of the seismic survey, the thicker detachment has basal dips <2 with thrust faulting and `dome' structures. Faults at this area grew by dip-linkage. Our study shows that a more consistent and active evacuation of the detachment resulted in non-interrupted fault growth, while a thicker and more complex detachment can outcome in minimum accumulation that caused irregular fault growth.