Effects of basement uplift on passive-margin salt basins: new insights from the Kwanza Basin, Angola

Basement beneath the Kwanza Basin, Angola, has been reactivated several times since the end of Neocomian rifting and continental separation. Basement uplift has played a major role in controlling the timing and magnitude of seaward translation detached above Aptian salt.<br>The first major basement deformation was a hitherto unrecognized period of crustal uplift beneath the continental rise that began around 75 Ma (Campanian). Uplift of an overlying thick salt plateau in deep water led to line-sourced salt extrusion and seaward advance of the Angola Salt Nappe over the abyssal plain. Exposure of the nappe toe removed the buttress provided by abyssal-plain cover, which triggered gravity-driven seaward translation of Kwanza Basin sediments.<br>A second period of basement uplift in the Miocene was more complex. A group of uplifts below the shelf steepened the bathymetric slope and greatly accelerated downslope translation. Other uplifts located farther inboard had negligible effect on regional bathymetric slope. Instead, only a few small fold-and-thrust belts formed in sediments next to and above the basement blocks. Finally, Miocene–Recent uplift and erosional unroofing of the African continental interior supplied abundant new sediment to the passive margin. Most of this sediment flux bypasses the Kwanza Basin and is accumulating on the abyssal plain. Aggradation of sediments on the abyssal plain has reduced the overall relief of the system and blocked salt-nappe advance. Detached deformation and translation are thus currently slowing to near zero in distal regions.