Paleoenvironmental records across middle to Upper Cretaceous in central part of the West and Central African Rift System: Palynological and geochemical inferences

Abstract

The West and Central African Rifts System (WCARS) is well-known for its Cretaceous deposits. Still, the reliable dating of sedimentary successions, especially in the central part, and the mechanisms causing environmental and climate change over time remained less explored. Two sections of exposed deposits were investigated within the Babouri-Figuil Basin, specifically along the Mayo-Figuil (MF) and Mayo-Dakmoune (MD) rivers. The deposits are primarily composed of wackes formed from felsic and intermediate parent rocks, perhaps originating from the adjacent basement rocks, although there are also mafic components represented by an iron-rich shale layer at the MF section. Relative dating has constrained the MF sediment age to the Albian–Cenomanian and the MD sediment age to the Campanian–Maastrichtian. Using whole-rock organic matter geochemistry and trace element concentrations, we discovered anoxic conditions, well-preserved organic matter, and marine salinity water occurrence in the Albian–Cenomanian deposits, probably related to the first Trans-Saharan seaway. Oxic conditions, poor-preserved organic matter, and brackish salinity water occurrence were established during the Campanian–Maastrichtian. The Hg/TOC spike recorded during the Albian–Cenomanian could be the consequence of proximal volcanism, most likely associated with enhanced rifting tectonic activity, whereas the maximum Hg/TOC ratios observed during the Campanian–Maastrichtian could be the product of distal volcanism. Globally, weathering was slow to moderate, and the climate was interpreted as semi-arid throughout the middle to Late Cretaceous in the central WCARS.