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Paleogeographic and Structural Evolution of Northwestern Africa and Its Atlantic Margins Since the Early Mesozoic GEOSPHERE

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Paleogeographic and Structural Evolution of Northwestern Africa and Its Atlantic Margins Since the Early Mesozoic GEOSPHERE Research Paper GEOSPHERE Paleogeographic and structural evolution of northwestern Africa GEOSPHERE; v. 13, no. 4 and its Atlantic margins since the early Mesozoic doi:10.1130/GES01426.1 Jing Ye1,2, Dominique Chardon1,3, Delphine Rouby1, François Guillocheau4, Massimo Dall’asta2, Jean-Noel Ferry2, and Olivier Broucke5 1Géosciences Environnement Toulouse, Université de Toulouse, CNRS, IRD, UPS, CNES, F-31400, France 16 figures; 1 table; 2 supplemental files 2TOTAL R&D, Frontier Exploration, Centre Scientifique et Technique Jean Féger (CSTJF), Avenue Larribau, F-64018 Pau Cedex, France 3Institut de recherche pour le développement (IRD) & Département des Sciences de la Terre, Université Ouaga I Professeur Joseph Ki-Zerbo, 01 BP 182, Ouagadougou 01, Burkina Faso 4Géosciences-Rennes, UMR 6118, Université de Rennes 1, CNRS, F-35042 Rennes CEDEX, France CORRESPONDENCE: yiren20100521@ gmail .com; 5TOTAL E&P, Middle East and North Africa–Technical Excellence, La Défense, F-92078 Paris, France dominique .chardon@ ird .fr CITATION: Ye, J., Chardon, D., Rouby, D., Guillocheau, F., Dall’asta, M., Ferry, J.-N., and Broucke, O., 2017, ABSTRACT of the Gondwana supercontinent by breakup between South America and Af- Paleogeographic and structural evolution of north- rica during the Early Cretaceous (Fig. 1). Counterclockwise rotation of the Afri- western Africa and its Atlantic margins since the The geological evolution of northwestern Africa and its continental mar- can plate produced a northward rift propagation leading to the formation of the early Mesozoic: Geosphere, v. 13, no. 4, p. 1254–1284, doi:10.1130/GES01426.1. gins is investigated in the light of nine Meso-Cenozoic paleogeological maps, South Atlantic Ocean under dominantly normal divergence, whereas the future which integrate original minimal extent of sedimentary deposits beyond their equatorial Atlantic domain underwent dextral-oblique divergence (e.g., Moulin Received 8 September 2016 present-day erosional limits. Mapping is based on a compilation of published et al., 2009; Frizon de Lamotte et al., 2015). The intracontinental African rifts, Revision received 21 February 2017 original data on the stratigraphy and depositional environments of sediments, which were connected to the southern Atlantic and equatorial rift systems by a Accepted 30 March 2017 structures, magmatism, and low-temperature thermochonology, as well as on triple junction, aborted before the African continent could split into three sub- Published online 26 May 2017 the interpretation of industrial seismic and borehole data. plates along the Western and Central rift system (Burke and Whiteman, 1973; We show that rifting of the equatorial domain propagated eastward from Fairhead, 1988; Binks and Fairhead, 1992; Guiraud and Maurin, 1992; Fig. 1). the Central Atlantic between the Valanginian (ca. 140 Ma) and the Aptian (ca. Given their transform character, the margins of the equatorial Atlantic 112 Ma) as an en echelon strike-slip and rift system connected to an inland rift Ocean were mainly investigated through the kinematics of ocean opening network. This network defines a six-microplate synrift kinematic model for the (e.g., Basile et al., 2005; Moulin et al., 2009; Heine et al., 2013; Basile, 2015) with African continental domain. We document persistent, long-wavelength erod- an emphasis on the fracture zones and the vertical movements induced along ing marginal upwarps that supplied clastic sediments to the offshore margin the margins (Bouillin et al., 1998; Clift et al., 1998; Bigot-Cormier et al., 2005; basins and a large intracratonic basin. The latter acted as a transient sediment Mercier de Lépinay, 2016). The abruptness of the equatorial margins of Af- reservoir because the products of its erosion were transferred both to the rica results from the strong control of strike-slip faults (i.e., future transforms) Tethys (to the north) and the Atlantic Ocean. This paired marginal upwarp- during rifting. These steep margins have specific thermal and subsidence intra cratonic basin source-to-sink system was perturbed by the growth of the histories that are not yet well understood but are crucial in controlling—and late Paleogene Hoggar hotspot swell that fragmented the intracratonic basins unraveling—their high hydrocarbon potential (MacGregor et al., 2003). Pub- into five residual depocenters. By linking the evolution of the continental mar- lished exploration studies have provided insights (Delteil et al., 1974; Kjem- OLD G gins to that of their African hinterland, this study bears important implications perud et al., 1992; Bennett and Rusk, 2002; MacGregor et al., 2003) but only at for the interplay of long-wavelength deformation and sediment transfers over the scale of individual subbasins and/or along cross sections that do not allow paired shield-continental margin systems. apprehending the fully three-dimensional nature of the tectonostratigraphic evolution of the margins. OPEN ACCESS Integrated regional studies linking the stratigraphic history of the equa- INTRODUCTION torial Atlantic margins to their deformation since pre-rift configuration are still lacking. Such studies require structural and paleogeographic reconstructions The equatorial Atlantic Ocean opened as a consequence of oblique diver- (i.e., maps showing past depositional environments) of their adjoining con- gence along what were to become the best known examples of transform and tinental domain in order to address the coupling between margin evolution oblique continental margins of northern South America and West Africa (Emery and the erosional, depositional, and deformational history of their hinterland This paper is published under the terms of the et al., 1975; Mascle and Blarez, 1987; Basile et al., 2005; Figs. 1 and 2). Those in a “source-to-sink” perspective. So far, paleogeographic reconstructions for CC-BY license. margins belonged to a large-scale network of rifts that led to the final dispersion northwestern Africa did not include the equatorial margin domain (Guiraud © 2017 The Authors GEOSPHERE | Volume 13 | Number 4 Ye et al. | Evolution of northwestern Africa and its Atlantic margins Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/13/4/1254/3995218/1254.pdf 1254 by guest on 26 September 2021 Research Paper 40°W ic 0° 40°E SOUTH ALGERIAN BASIN STUD 20°W 10°W 0° 10°E ral Atlant NEO-TETH Cent Y AREA MARGIN MURZUQ T SHIELD AYA BASIN YS Wester REGUIBAT HOGGAR Equa n TARF Rift System an 0° SHIELD TIBESTI 0° torial Atlantic d Ce SEGMEN ntr al Amded PACIFIC WEST GONDWANA Western and 20°N S N Aïr N Central T South Atlantic TAOUDENI BASI Rift ANIA EN NIDE TA System IULLEMMEDEN Meso-Cenozoic 40°S MAURI CHAD BASIN 40°S Gao BASIN sediment thickness: Nara >10 km MARGIN SEGM MARGIN A 40°W 0° SENEGALO-MAURIT 10 Guinea FZ NIGERIAN BOVE SHIELD SHIELD Early Cretaceous Variscan Belt 10°N BASIN Rifts LEO-MAN VOLTA 7 Jurassic to Early BASIN Bida gh Continental domain GUINEA-LIBE Cretaceous Rifts MARGIN SEGMENT Benue Trou N 5 Shallow marine R Niger Active Mountain Belt IA Delt environment a CONGO 0 500 km 3 Deep marine GHANA-BENIN SHIELD Subduction Front environment ss FZ MARGIN SEGMENT GUINEA 2 Grand Ce MARGIN SEGMENT Y COAST IVOR 1 OF 0° St Paul FZ Romanche FZ GULF B 0 Transform faults Other faults activated Main Ceno-Mesozoic Neoproterozoic - in the Meso-Cenozoic volcanics and plutons Paleozoic sediments Cretaceous normal West African Meso-Cenozoic Crystalline rocks faults craton limit sediments Figure 1. (A) Map showing the African and South American rift systems at ca. 120 Ma during dispersal of Gondwanaland (modified after Frizon de Lamotte et al., 2015). (B) Structural map of north- western Africa showing Meso-Cenozoic faults and sedimentary basins (modified after Kogbe, 1981, and Milesi et al., 2010). Geologic contours are simplified from Figure 2. The names of the main Early Cretaceous intracontinental rifts are indicated (bold font). The frame of Figure 1B is shown in red on Figure 1A. et al., 2005). Furthermore, those paleogeographic reconstructions were biased of 28°N, west of 17°E) as well as the conjugate equatorial margin of north- from a methodological viewpoint. Indeed, they often consider the preservation ern South America (Fig. 1). Our work is based on a series of large-scale, off- limits of sedimentary deposits of a given age as the limits of the sedimentation shore-onshore geologic cross sections and nine maps showing successive area of that age. Such is never the case, however, because the edges of coastal geological configurations since 200 Ma, taking into account (1) restoration and intracratonic basins undergo erosion that leads to significant reduction of of the position of northern South America relative to northwestern Africa, their original extent (Sloss, 1963). (2) fault patterns and magmatic occurrences, (3) extent of erosion and/or sedi- In this contribution, we reassess the Meso-Cenozoic geological evolution menta tion areas and associated depositional environment of sediments, and of the Atlantic margins of northwestern Africa and their hinterland (south (4) constraints provided by low-temperature thermochronology data on the GEOSPHERE | Volume 13 | Number 4 Ye et al. | Evolution of northwestern Africa and its Atlantic margins Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/13/4/1254/3995218/1254.pdf 1255 by guest on 26 September 2021 Research Paper 500 km 20°W 10°W 0° 10°E Reggane N Taoudeni Nouadhibou 20°N Bilma CENTRAL ATLANTIC OCEAN Gao Figure 2. Simplified geologic map of West Dakar Africa compiled from Choubert and Faure- Muret (1988), Fabre et al. (1996), Milesi Lake et al. (2010), and this work. Quaternary Chad sand cover has been omitted, and small Bamako Triassic– Jurassic sedimentary outcrops in the Tim Mersoi basin were included in N’Djamena Lower Cretaceous sediment map units. Lower Cretaceous and Paleogene con- Guinea FZ Conakry tinental sediments are grouped as the 10°N Abuja “Continental Intercalaire” and “Continen- tal Terminal,” respectively. Only outcrop- ping faults that were potentially activated Guinean Plateau during the Meso-Cenozoic are shown.
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