Zhiyuan Ge, Robert Leslie Gawthorpe, Leo Zijerveld, Ayodeji Oluboyo

In passive margin salt basins, the distinct tectonic domains of thin-skinned extension and contraction exert important controls on the geometry and evolution of minibasins. In this study, we use a semi-regional 3D seismic dataset from the Lower Congo Basin to investigate the spatial and temporal evolution of a network of salt-related minibasins and intervening salt walls and diapirs during thin-skinned salt tectonic deformation. Widespread thin-skinned extension occurred during Cenomanian to Coniacian created numerous normal faults, typically 5–10 km long and spaced 1–4 km apart within the supra-salt cover across the study area. Subsequently, during the Santonian–Paleocene, multiple, 10–25 km long, 5–7 km wide depocentres progressively grew and linked along strike to form elongate minibasins separated by salt walls that are several tens of kilometres long. Simultaneous with the development of the minibasins, thin-skinned contraction occurred in the southwestern downslope part of the study area, forming folds and thrusts that are up to 20 km long and have a wavelength of 2–4 km. The elongate minibasins further developed into turtle structures and the depocentres migrated towards the flanks of the minibasins during Eocene to Oligocene. From the Miocene onward, contraction of the supra-salt cover caused salt walls to be uplifted and created elongate and confined depocentres within the minibasins. Minibasin development is dependent on the kinematic domains in which they form. Distinct geometries develop due to extension, sediment loading and contraction. Variability in structural style and evolution within minibasins occurs due to along-strike growth of early formed depocentres. As minibasins have different subsidence rates and maturity, their geometry varies from one minibasin to another. Upslope migration of contraction further complicates the structural style and stratigraphic architecture of the minibasins. This study suggests that minibasin growth is variable both within individual minibasins as well as across the network of minibasins and is more complex than simple domain-controlled models of extension, translation and contraction would predict.