What Controls Contraction in the Translation Domain of the Outer Kwanza Basin, Offshore Angola?
It is now well-established that base-salt relief drives complex deformation in the mid-slope domain of salt-bearing passive margins, in a location classically thought to be dominated purely by horizontal translation. However, due to a lack of detailed studies drawing on high-quality, 3D seismic reflection data, our understanding of how base-salt relief controls four-dimensional patterns of salt-related deformation in natural systems remains poor. We here use 3D seismic reflection data from, and
... tion data from, and structural restorations of the Outer Kwanza Basin, offshore Angola to examine the controls on the evolution of variably oriented salt anticlines, rollers, and walls, and related normal and reverse faults. We show that the complex geometries and kinematics of predominantly contractional salt structures reflect up to 22 km of seaward flow of salt and its overburden across prominent base-salt relief. More specifically, contractional deformation occurs where seaward salt flow: (i) is retarded, and salt thickens and overburden buckles above landward-dipping ramps; (ii) encounters thick, slower-moving salt at the base of seaward-dipping ramp; (iii) translates across an array of concave-into-the-basin ramps; (iv) is retarded due to the formation of primary salt welds at the upper hinge of seaward-dipping ramps. The rate at which salt and its overburden translates seaward varies along strike due to corresponding variations in the magnitude of base-salt relief and, at a larger scale, primary salt thickness. As a result, overburden rotation accompanies bulk contraction. Our study improves our understanding of salt-related deformation on passive margins, highlighting the key role of base-salt relief, and showing contraction and rotation are fundamental processes in mid-slope translational domains of salt basins.