U-Pb single zircon grain dating of Present fluvial and Cenozoic aeolian sediments from Gabon: consequences on sediment provenance, reworking, and erosion processes on the equatorial West African margin

Abstract

U-Pb ages obtained from detrital zircon from terrigenous sediments are used to determine the sources. Present fluvial sand-bars of the Ogooue river yield age spectra of detrital zircons in agreement with Archean and Early Proterozoic Sources found in the drainage. The large proportion of Late Proterozoic zircons cannot be derived from primary erosion of the watershed basement rocks, since there is no formation of that age in the area. This later group of zircons is in good agreement with reworking of the aeolian Paleogene Bateke Sands, by regressive erosion in the upper reaches of the Ogooue river, as they contain a majority of Late Proterozoic age zircons. The sources of Late Proterozoic zircons in the Bateke Sand are very distant, and transported and reworked - at least in part - by aeolian processes. Our results, together with the widely distributed Paleogene sediments over continental Africa, suggests that Paleogene was it time of subdued erosion of the cratonic areas and extensive reworking, transport and deposition within continental Africa. In contrast, our results from the Ogooue river indicate active present incision of the cratonic area, erosion of the previous continental sediments, and export of the river bed-load to the continental margin. This temporal evolution of erosion-transport-deposition is correlated with the drastic climate change that occurred during the Cenozoic, leading to a more efficient mechanical erosion, and it correlates with the increase of terrigenous flux to the margin, observed during the Neogene

Marine Communities on Oil Platforms in Gabon, West Africa: High Biodiversity Oases in a Low Biodiversity Environment

“…In addition, the Ogooué River in central Gabon has an average discharge rate of 4,758 m 3 s −1 , making it the third most important river in west equatorial Africa [8], [9]. Although the water discharge is one order of magnitude lower compared to the Congo River, the particulate load of the two rivers is similar [10]. Collectively these river systems greatly influence the marine ecosystem of Gabon.…”

Accelerated Contribution of the Paleo–Congo River to Global Seawater 87Sr/86Sr Change Following Eocene‐Oligocene Collapse of the African Surface

“…The upper part of this basement exposes vast Cryogenian-Ediacaran carbonate platforms with relatively low 87 Sr/ 86 Sr (0.706-0.710; Delpomdor & Préat, 2015). U-Pb detrital zircons geochronology identified three main sources for the Congo Basin sediments derived from the Precambrian terrains Séranne et al, 2008). The most prominent peaks at 1,000 and 650 Ma (Figure 2b) are interpreted to represent abundant zircons derived from the Central Gondwana Mountains that formed during continental collisions and final amalgamation of the Gondwana supercontinent, and thereafter exhumed rapidly between 650 and 500 Ma.…”

The Ogooue Fan (Gabon): a modern example of deep-sea system on a complex sea-floor topography

“…Despite the relatively small size of the Ogooue River basin (215,000 km²), the river mean annual discharge reaches 4,700 m 3 /s due to the wet equatorial climate prevailing on the drainage basin (Lerique et al, 1983;Mahé et al, 1990). The Ogooue River flows on a low slope gradient in a drainage basin where very thick lateritic soils develop over the Congo craton and Proterozoic orogenic belts (Séranne et al, 2008). The estuary area includes several lakes ( Fig.…”

“…These features contribute to the mainly muddy composition of the particle load of the Ogooue River that is estimated between 1 and 10 M t/yr (Syvitski et al, 2005). The limited portion of sand particles in the river originates mainly from the erosion of the poorly lithified Batéké Sands located on a 550-750 m-high perched plateau that forms the easternmost boundary of the Ogooue watershed (Séranne et al, 2008) (Fig. 1a).…”