What Controls Salt‐Detached Contraction in the Translational Domain of the Outer Kwanza Basin, Offshore Angola?

It is now well‐established that base‐salt relief drives complex deformation patterns in the mid‐slope domain of salt‐bearing passive margins, in a location classically thought to be dominated by simple 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 structural restorations of the Outer Kwanza Basin, offshore Angola to examine the controls on the evolution of variably oriented salt anticli...  more

It is now well‐established that base‐salt relief drives complex deformation patterns in the mid‐slope domain of salt‐bearing passive margins, in a location classically thought to be dominated by simple 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 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, this contractional deformation occurs where the seaward flow of salt is inhibited due to: (a) it flowing being forced to flow up, landward‐dipping ramps; (b) it encountering thicker, slower‐moving salt near the base of seaward‐dipping ramps; or (c) 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, more regional scale, primary salt thickness. As a result of these along‐strike changes in translation rate, 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, extension and rotation are fundamental processes controlling the structural style of the mid‐slope translational domains of salt basins.