Enhanced erosion and silicate weathering of the West African craton during the late Cretaceous cooling evidenced by mineralogical and HfNd isotope proxies

Abstract

The evolution of oceanic temperatures between the Turonian and the K/T boundary indicates a long-term cooling coincident with a decrease of atmospheric CO₂ levels, yet the cause of climate cooling at that time still remains debated. In this study, we evaluated the possible implication of enhanced silicate weathering as a sink for atmospheric CO₂ by applying paired NdHf isotope measurements to detrital clay records from the West African margin. The use of this novel proxy for chemical weathering intensity (Δɛ_Hf(t)clay) was complemented by additional mineralogical and major-trace element analyses in order to investigate the variability of mechanical erosion patterns and further explore potential linkages between tectonics, weathering and climate during the late Cretaceous.

Our Δɛ_Hf(t)clay data suggest more intense silicate weathering on the West African Craton during the Santonian to the middle Campanian period, coincident with enhanced physical erosional inputs as inferred from higher Quartz/Clays and Feldspar/Clays ratios. This observation suggests that the shift towards intensified chemical weathering at that time was driven by enhanced mechanical erosion, possibly related to a moderate tectonic event on the West African craton. Evidence for increasing kaolinite contents and higher Δɛ_Hf(t)clay values during the Maastrichtian point towards more hydrolysing conditions, inducing either destabilization of older Mesozoic lateritic material or favouring the development of kaolinite-rich soils.

Overall, this study was compared with several new data of chemical weathering evolution along the south Atlantic margins, adding new insights on tectonic-weathering-climate interactions during the late Cretaceous, suggesting a possible link between silicate weathering feedbacks and global cooling at that time.