Cenozoic Landscape Evolution in and Around the Congo Basin: Constraints from Sediments and Planation Surfaces

Abstract

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

“…The last upwarp segment (IV) relates to the South Atlantic margin. Its considerable width (up to more than 500 km) and the uplift it has undergone during the Neogene (Guillocheau et al, 2015) suggest at least a recent mantle support. Rouby et al (2013) have shown that flexure-related rift shoulders of a passive margin are often eroded away 10-20 m.y.…”

Riverine dissolved lithium isotopic signatures in low‐relief central Africa and their link to weathering regimes

“…High Sr isotope ratios are typical of rivers draining the Archean and Proterozoic rocks constituting the border of the Congo Basin [ de Wit and Linol , ]. By contrast, the low Sr isotope ratios are characteristic of the sedimentary region at the center of the Congo Basin [ Negrel et al ., ; Guillocheau et al ., ]. One sample significantly deviates from the calculated mixing trend which can be attributed to the natural heterogeneity in terms of Sr isotope ratios of the Congo River tributaries draining the outer parts of the Congo Basin [ Negrel et al ., ] (Figure a).…”

“…These rivers represent the regional base level and have particularly low dissolved and suspended loads. Geomorphologic analyses of the planation surfaces [ Guillocheau et al ., ] indicate that the present‐day topography of the Congo Basin derives from differential uplift, less pronounced in the central basin, and higher in the surrounding areas. Conversely, dynamic topographic models show that the Cuvette Centrale results from the subsidence of the Congo Basin over the past 30 Myr in response to mantle convective drawdown [ Moucha and Forte , ].…”

“…We thus expect that in such regions of high weathering intensity, the dissolved δ 7 Li will be close to that of the bedrock (or slightly higher if weak but significant reincorporation of Li occurs). The bedrock of the central part of the basin consists of Eocene and Paleocene sedimentary rocks ranging from claystones and silty claystones to grainstones of lacustrice origin (Mbandaka well) [Guillocheau et al, 2015]. Their δ 7 Li value is not known, but it can reasonably be predicted to be close to values typical of shales (À0.5 ± 2‰) .…”

“…The reason why large parts of the Cuvette Centrale in the Congo Basin are permanently or temporally flooded is that the uplift of central Africa over the Cenozoic has been faster in the outer parts of the basin than in the central part. The existence of the Likouala and Sangha wetlands where low δ 7 Li signatures are generated is thus the consequence of large-scale crustal deformation resulting from a long-term thermotectonic evolution following early Neoproterozoic rifting below the central part of the Congo Basin [Guillocheau et al, 2015].…”