The influence of mechanical stratigraphy on multi-layer gravity collapse structures: insights from the Orange Basin, South Africa

Gravity collapse structures are common features on passive margins and typically have a tripartite configuration including an updip extensional domain, a transitional domain and a downdip compressional domain with a common detachment underlying the system. A number of studies have classified these systems, yet few document the wide variations in geometry. This study documents the gravity collapse structures of the Namibian and South African Orange Basin; these structures represent some of the best imaged examples of this important process. We first demonstrate the geometry and kinematic evolution of these systems, focusing on examples of the tripartite configuration from a typical collapse. We then highlight the significant variability in the structures of the system and describe features such as cross-cutting in margin-parallel sections, portions of the system with multiple detachments, systems with stacked synchronous detachments and the temporal evolution of faults within the system. By integrating our observations from a number of sections, we present a model explaining the spatial and temporal evolution of the system. This enables us to discuss likely causes of collapse structures and also, by placing the system into a well-constrained stratigraphic context, how the presence of both maximum flooding surfaces and early margin deltaic sequences have a fundamental control on the resulting collapse geometry.