Exploring the links between climate, weathering, and dynamic topography during the upper Cretaceous : a geochemical and mineralogical approach within a source-to-sink system

Abstract

The major uplift phase encountered by southern Africa during the late Cretaceous leaded to a drastic increase in denudation rates. This event provides a unique opportunity to explore the long-term response of chemical weathering and erosion to intense tectonic uplift within the greenhouse climate context of the late Cretaceous. The respective importance of these two processes in the evolution and distribution of detrital fluxes and in the formation of reservoirs is a key question that still remains to be elucidated. The aim of this PhD is to apply a novel geochemical approach, combining clay mineralogical analyses with Hf-Nd isotopic analyses (ΔεHf) on clay fractions to (1) decipher the respective evolution of chemical weathering and erosion during the late Cretaceous uplift of southern Africa, (2) explore the links between erosion and weathering processes and the evolution and distribution of detrital fluxes in this tectonic setting, and (3) explore the potential impact of this uplift on late Cretaceous climate evolution, through CO2 consumption by silicate weathering reactions.Three sites (DSDP core 361, borehole O-A1, borehole P-A1) located in a proximal-distal transect along the Cape Basin were targeted to track the evolution of denudation processes by applying a source-to-sink approach. The record from these sites shows consistent provenace of the sediments for all the sites coming from southwestern-central areas of the South African Plateau during the late Cretaceous. The clay mineralogy and the ΔεHf indicate an increase in chemical weathering along the late Cretaceous starting around the Cenomanian-Turonian (ca. 97 Ma), while an increase in physical erosion is observed between the Campanian – Danian (77-62 Ma). This enhancement in denudation occurs while the global climate is under a cooling trend that started around the Turonian (ca. 94 Ma), which is not favourable to enhanced denudation episodes. This suggests that this increase in denud