Paleogeographic and structural evolution of northwestern Africa and its Atlantic margins since the early Mesozoic

Jing Ye,Dominique Chardon,Massimo Dall’Asta,Olivier Broucke,Delphine Rouby,François Guillocheau,Jean-Noel Ferry

doi:10.1130/ges01426.1

Abstract

The geological evolution of northwestern Africa and its continental margins is investigated in the light of nine Meso-Cenozoic paleogeological maps, which integrate original minimal extent of sedimentary deposits beyond their present-day erosional limits. Mapping is based on a compilation of published original data on the stratigraphy and depositional environments of sediments, structures, magmatism, and low-temperature thermochonology, as well as on the interpretation of industrial seismic and borehole data. We show that rifting of the equatorial domain propagated eastward from the Central Atlantic between the Valanginian (ca. 140 Ma) and the Aptian (ca. 112 Ma) as an en echelon strike-slip and rift system connected to an inland rift network. This network defines a six-microplate synrift kinematic model for the African continental domain. We document persistent, long-wavelength eroding marginal upwarps that supplied clastic sediments to the offshore margin basins and a large intracratonic basin. The latter acted as a transient sediment reservoir because the products of its erosion were transferred both to the Tethys (to the north) and the Atlantic Ocean. This paired marginal upwarp-intracratonic basin source-to-sink system was perturbed by the growth of the late Paleogene Hoggar hotspot swell that fragmented the intracratonic basins into five residual depocenters. By linking the evolution of the continental margins to that of their African hinterland, this study bears important implications for the interplay of long-wavelength deformation and sediment transfers over paired shield-continental margin systems.

Highlights

The equatorial Atlantic Ocean opened as a consequence of oblique divergence along what were to become the best known examples of transform and oblique continental margins of northern South America and West Africa (Emery et al, 1975; Mascle and Blarez, 1987; Basile et al, 2005; Figs. 1 and 2)
The margins of the equatorial Atlantic Ocean were mainly investigated through the kinematics of ocean opening (e.g., Basile et al, 2005; Moulin et al, 2009; Heine et al, 2013; Basile, 2015) with an emphasis on the fracture zones and the vertical movements induced along the margins (Bouillin et al, 1998; Clift et al, 1998; Bigot-Cormier et al, 2005; Mercier de Lépinay, 2016)
The geometry is spatially consistent across the Central Atlantic and equatorial margins, with continental margin basins separated from intra cratonic basins by a marginal upwarp

Summary

Introduction

The equatorial Atlantic Ocean opened as a consequence of oblique divergence along what were to become the best known examples of transform and oblique continental margins of northern South America and West Africa (Emery et al, 1975; Mascle and Blarez, 1987; Basile et al, 2005; Figs. 1 and 2). The intracontinental African rifts, which were connected to the southern Atlantic and equatorial rift systems by a triple junction, aborted before the African continent could split into three subplates along the Western and Central rift system (Burke and Whiteman, 1973; Fairhead, 1988; Binks and Fairhead, 1992; Guiraud and Maurin, 1992; Fig. 1) Given their transform character, the margins of the equatorial Atlantic Ocean were mainly investigated through the kinematics of ocean opening (e.g., Basile et al, 2005; Moulin et al, 2009; Heine et al, 2013; Basile, 2015) with an emphasis on the fracture zones and the vertical movements induced along the margins (Bouillin et al, 1998; Clift et al, 1998; Bigot-Cormier et al, 2005; Mercier de Lépinay, 2016). Published exploration studies have provided insights (Delteil et al, 1974; Kjemperud et al, 1992; Bennett and Rusk, 2002; MacGregor et al, 2003) but only at the scale of individual subbasins and/or along cross sections that do not allow apprehending the fully three-dimensional nature of the tectonostratigraphic evolution of the margins

Results

Discussion

Conclusion