Salt-Detached Strike-Slip Faulting, Outer Kwanza Basin, Offshore Angola

Abstract

We here use a 3D seismic reflection dataset from the Outer Kwanza Basin, offshore Angola to examine the structure and growth of salt-detached strike-slip faults. The faults occur in four, up to 13.8 km-long, NE-trending arrays that are physically linked by restraining bends and releasing stepovers, and which presently overlie Aptian salt and base-salt relief related to pre-salt faulting. We suggest that these faults formed to accommodate along-margin variations in the rate and magnitude of differential seaward translation and salt diapirism, which commenced in the Early Cretaceous. We illustrate that the arrays grew by tip propagation of isolated fault segments, some of which linked during the Albian-Cenomanian (i.e., 113–100.5 Ma, or the initial 11%–13% of their deformation history). Some arrays then reached their near-final length within the subsequent ca. 77 Ma (or the next 69%–81% of their deformation history), while others attained this later, during the subsequent ca. 18 Ma (i.e., after 95% of their deformation history). During this time, the segments formed and then breached releasing and restraining stepovers, with the arrays as a whole growing by alternating periods of lengthening and throw accumulation, punctuated by phases of inactivity. Our results also show that scatter in the D-L scaling of strike-slip faults reflects the propagation, interaction, and linkage of individual segments.