Lo Importante De La Vida

Marine and Petroleum Geology 26 (2009) 1000–1017

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Marine and Petroleum Geology
journal homepage: www.elsevier.com/locate/marpetgeo

Neocomian to early Aptian syn-rift evolution of the normal to oblique-rifted North Gabon Margin (Interior and N’Komi Basins)
M. Mbina Mounguengui a, M. Guiraud b, *
a b

´ ´ ´ Universite des Sciences et Techniquesde Masuku, Departement de Geologie, BP 943, Franceville, Gabon ´ ´ Universite de Bourgogne, Centre des Sciences de la Terre et UMR CNRS 5561 Biogeosciences, 6, Bd Gabriel, 21000 Dijon, France

a r t i c l e i n f o
Article history: Received 23 October 2008 Accepted 3 November 2008 Available online 13 November 2008 Keywords: Rift segmentation Oblique rifting Normal rifting End-rift erosionPrecambrian heritage Early Cretaceous Gabon

a b s t r a c t
The North Gabon coastal rift basins consist of a set of 130–150 long-segment asymmetrically tilted half ´ grabens (Interior Basin) and 000–020 short-segment en echelon half grabens (N’Komi Basin) separated by 040–060 major transverse faults. Tectono-sedimentary analysis of field and subsurface data reveals the control exerted byextensional tectonism over continental sedimentation. During Berriasian to early Barremian times, uniform uniaxial 040–060 extension was responsible for the stretching of the brittle upper crust over a 100-km wide domain. During late Barremian–early Aptian times, the main locus of extension stepped westward resulting in severe end-rift uplift and erosion of the failed Interior and N’Komi rift basins. EarlyCretaceous coastal rifts in North Gabon display a wide range of styles from oblique rifting (N’Komi Basin), normal rifting (Interior Basin) to transform rifting. The pre-existing Precambrian tectonic fabric exerts a strong control over the mode and over the 100–300 km-scale segmentation of the rifting. Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction Several of the world’s rifted(passive) margins are highly segmented. In the South Atlantic Ocean, variously oriented segments up to 700 km long are bounded by oceanic fracture zones and volcanic lines such as the Romanche, Chain, Ascension and Walvis Ridge structures (Davison, 1999; Turner et al., 2003). Two extremes are characterized: (a) rifted margins sensu stricto, associated with a plate divergence vector that is orthogonalto the strike of the margin (e.g. southern Gabon, Teisserenc and Villemin, 1990; ´ Dupre, 2003); and (b) transform margins, on which plate diverˆte gence is subparallel to the strike of the margin (e.g. Co d’Ivoire: Mascle and Blarez, 1987; Basile et al., 1993; Guiraud et al., 1997. Rio Muni: Dailly, 2000; Turner et al., 2003; Wilson et al., 2003). Obviously a whole range of oblique-riftedvariations may exist between these extremes. However, the relationship with fracture zones that may control various rift segments along the North Gabon Margin has not been analysed in detail. In this paper, we analyse the principal tectonic and stratigraphic features of the Interior and N’Komi rift basins of the North Gabon Margin in terms of their structure, fault kinematics and stratigraphy. Thesebasins have been little explored but their history is

connected with the Early Cretaceous and even Late Jurassic separation of South America and Africa (Reyre, 1984; Scotese et al., 1988; Guiraud, 1990; Guiraud and Maurin, 1991). This paper also illustrates the control exerted by the pre-existing Precambrian fabric during syn-rift extension and its effect on the style of rifting (normal riftingversus oblique to transform rifting). 2. Tectono-sedimentary history The coastal basins of Gabon belong to a set of coastal basins associated with the opening of the South Atlantic Ocean during Early Cretaceous times (Teisserenc and Villemin, 1990; Reyre, 1984; Guiraud and Maurin, 1991). The Gabon Interior and the N’Komi rift basins are both 100 km long and 70–50 km wide (Fig. 1). They lie ´ ´...