Continental margins are commonly characterized by gravity-driven, thin-skinned deformation of overburden above mobile shale or salt. Deformation is classically characterised by kinematically linked zones of up-dip extension, mid-slope translation, and downdip contraction above a smoothly seaward-dipping surface underlying the basal detachment. However, relatively few recent natural examples, and physical and numerical models, show that basal detachment paleo-topography can be rugose, and that deformation can be temporally and spatially complex. The origin of this paleo-topography, and the detailed geometry and kinematic evolution of related overburden deformation, are not fully understood; this forms the focus of this thesis.
This study uses 3D seismic reflection data from two continental margins (i.e. the Outer Kwanza Basin, offshore Angola, and the Tarakan Basin, offshore Indonesia) to document the style and interpret the growth of contractional, extensional and strike-slip structures, and their associated basal salt or shale layers in three-dimensions. This study unravels kinematic in these two basins by using a number of approaches, including structural restorations (i.e. palinsplastic or backstripping), displacement-distance and/or isopach analysis. On the Outer Kwanza Basin, this study identifies variably oriented salt structures (i.e. anticlines, rollers, walls) of up to 3 km height and 47 km length, and their related normal, reverse and strike-slip faults. More specifically to the strike-slip faults, this study shows four arrays of faults of up to 13 km long and 0.8 km tall that form restraining bend and releasing stepover at their lateral tip. In this basin, this study identifies the predominantly contractional structures reflect up to 22 km of seaward translation of salt and its overburden across rugose paleo-topography reliefs. The rate of translation seaward varies along strike, resulting in formation of the strike-slip faults that grew via alternating periods of lengthening, throw accumulation and inactivity. In the Tarakan Basin, however, this study identifies shale structures (i.e. shale rollers and anticline, and mud diapir and volcano) of up to 5 km height and their related normal faults and roller folds. These deformations reflect spatial variation in sedimentary loading during gravitational gliding downslope above irregular dips of along strike paleo-topography. This study concludes that geometry of the paleo-topography can have an important role in the styles and distributions of overburden deformations during gravitational spreading and gliding in both Outer Kwanza and Tarakan Basins.