Strato-structural evolution of the deep-water Orange Basin: Constraints from high-resolution 3D seismic data

Abstract. We use high-resolution 3D reflection seismic data to constrain the strato-structural evolution of the transitional and compressional domains of a Late Cretaceous deep-water fold-and-thrust belt (DWFTB) system and its influence on the overlying Cenozoic megasequence in the Orange Basin, South Africa. Multiple shale detachment surfaces have given rise to a complex structural framework, allowing for the redistribution of stress and strain, along progressive deformation and sedimentation. High-resolution 3D seismic data show that the compressional domain exhibits large-scale landward-dipping DWFTBs with faults initially detaching the Turonian shale detachment surface. Thrust sheets are segmented along strike by extensive oblique-slip faults which extend from the transitional domain into the down-dip compressional domain. the transitional domain is imaged as a complex region containing listric normal, thrust and oblique-slip faults. Many faults in the transitional domain have been reactivated to detach onto an older Albian shale detachment surface at depth, transferring stress and distributing strain during gravitational sliding. Smaller, localized fold-and-thrust belts are subsequently formed in the down-dip compressional domain directly below the kilometre-scale DWFTB system between the upper Turonian and lower Albian shale detachment surface. Mass erosional processes of the Cenozoic are confined above the transitional domain including a large, roughly slope-perpendicular Oligocene submarine canyon formed by turbidity currents, and a smaller series of slope-parallel, sinusoidal channel-like features in the Miocene formed by bottom currents. Normal and oblique-slip faults from the transitional domain have been reactivated to terminate at either one of the Oligocene or Miocene sequence boundaries. This, together with a present-day seafloor slump scar above a buried Late Cretaceous syncline, indicates how the stratigraphy and structural geometry of a buried DWFTB system controls fundamental sedimentary processes in an evolving continental margin.