Along-Strike Variation of Halokinesis and Structural Inheritance Along the West African Salt Basin, South Atlantic

Abstract

Along the West African margin from Gabon to southern Angola, the Loeme Aptian salt deposited during the late rift break-up process. Following the Atlantic opening, passive margin subsidence, large deltas and dynamic topography triggered and shape gravity tectonic systems.

Evaporite deposition occurred during the break-up process, from the rupture of the continental crust to the spreading, thus providing an early inheritance (in term of thickness and geographic distribution of evaporites) for future salt tectonics, which is largely controlled by the genetic domain compartmentalizing the margin, namely the proximal margin, the neck basin, the distal margin, and the outer high and exhumed mantle.

Classically, since the mid-90s the gravity gliding system pattern, with the usual triptych extension-translation-compression, has been over-applied along the West African margin. Recent data from Angola show mini-basins in a context of gravity spreading in addition to pure gliding-spreading roll-overs, rafts and diapirs, as well as mini basins developed during the early phase of evolution, and were later on squeezed by the gliding cell.

We present here a regional study to compare major internal and external factors controlling halokinesis structural styles and we propose new maps and cross-sections up to 300 km long from onshore to ultra-deep offshore, to describe the main domains and styles across the Gabon, Lower Congo, Kwanza, Benguela and Namibe sub-basins. This work is based on an extensive 2D and 3D seismic reflection data, wells and internal reports. Margin scale cartographic compilation of both pre- and post-salt tectono-sedimentary trends provide elements to constrain both geometries and kinematics.

This study documents the spatial and temporal distribution of both the inherited salt controlled basins (i.e. minibasins, salt ridges, etc.) as well as the superimposed gravitational systems, their characteristics and drivers (e.g. gliding, spreading), and by linking them to the genetic domains of the margin to highlight their various roles.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019