Evolution of the Southern Guinea Plateau: Implications on Guinea-Demerara Plateau formation using insights from seismic, subsidence, and gravity data

Title of Publication: 
Evolution of the Southern Guinea Plateau: Implications on Guinea-Demerara Plateau formation using insights from seismic, subsidence, and gravity data
Olyphant, Jared R., Johnson, Roy A., Hughes, Amanda N.
Publication Info: 
Tectonophysics Volume 717, 16 October 2017, Pages 358-371. https://doi.org/10.1016/j.tecto.2017.08.036

The Guinea Plateau (offshore Guinea) and its conjugate, the Demerara Plateau (offshore French Guiana), comprise two of the most prominent passive continental margins in the Atlantic Ocean. The conjugate plateaus formed as a result of two periods of rifting, the Jurassic opening of the Central Atlantic Ocean and the northward-propagating Cretaceous opening of the Southern Atlantic Ocean. Although several studies are published on the Demerara Plateau that explain the evolution of its multi-rift history and the effect of rifting on its distinct geometry, the Guinea Plateau, and in particular its south-eastern margin, remain relatively unexplored in the literature. Here we present interpretations of the structure and evolution of the Guinea Plateau using recent 2-D and 3-D seismic-reflection data collected at the intersection of the southern and eastern margins. We substantiate our study with calculated subsidence curves at four locations along the southern margin, as well as two 2-D gravity forward models along regional seismic-reflection profiles to estimate stretching factors (β) and crustal thicknesses. We combine our results with previous studies concerning the south-western Guinea margin, and compare them to published interpretations regarding the conjugate margins of the Demerara Plateau. The resolved amounts of rift-related volcanism, listric-style normal faults, and moderate stretching factors suggest that a component of upper-crustal asymmetry (simple shear) and depth-dependent stretching may have persisted at the Demerara-Guinea conjugate margins during Cretaceous rifting of the equatorial segment of the Southern Atlantic Ocean.

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Fig. 1. (Top): Present-day geodynamic setting of equatorial segment of the Southern Atlantic Ocean. The Guinea Plateau (G.P.) and Demerara Plateau (D.P.) are outlined along West Africa and South America, respectively. Fracture zones (FZs; light-gray lines) and the Mid-Atlantic Ridge (red line), modified from Edge (2014), show the paths along which the two conjugate plateaus have been separating since the Cretaceous. The Marathon FZ represents the dividing line between the (Jurassic) Central Atlantic Ocean to the north and the (Cretaceous) Southern Atlantic Ocean to the south. (Bottom) Contoured bathymetric map of the Guinea Plateau showing locations of seismic data used in this study. Red boxes outline the two 3-D surveys, A & C, while red lines highlight the 2-D seismic lines shown in this paper. Purple circles show the two exploration wells, GU-2B-1 and SABU-1, the yellow circles, PW-1 and PW-2, are pseudo-well locations used in subsidence analysis discussed in the text (5. Backstripping and Tectonic Subsidence). Inset map in bottom-left shows the named sections/segments of the South Atlantic Ocean. The segments are divided by prominent FZs. Map shown at plate-reconstruction time of Chron-34 (83 Ma) as presented in Moulin et al. (2010) and emphasizes the north-ward propagation of the Southern Atlantic Ocean rifting event. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)