Response of weathering and erosion to the intense tectonic uplift of the South African Plateau during the Late Cretaceous: Preliminary insights.
Abstract
During the Late Cretaceous the South African Plateau
experienced a period of uneven tectonic uplift. It started during
the Turonian with an early pulse in the eastern margin, which
increased the sediment accumulation rates in the western side,
especially in the Orange and Cape basins. This was followed by
a late uplift stage in the western margin during the Campanian,
which similarly increased the sediment accumulation rates in the
eastern side, particularly in the Transkei and Durban Basins. This
occurred within a greenhouse climate and coincided with a
marked global climate cooling during the Late Cretaceous.
Sediment budget calculations have been performed for this
system, but quantitative constrains on the long-term response of
the denudation processes to this tectonic event and climatic
variations remain unsolved. In this study, we combine two
geochemical techniques to determine the intensity of chemical
weathering and physical erosion. We use a new proxy of
chemical weathering intensity, the ΔHf based on coupled Lu-Hf
and Sm-Nd isotopic systems in clay fractions [1]. This technique
is joint with X-ray Diffraction to determine the concomitant
evolution of clay mineralogical assemblages thus tracking the
progress of physical erosion. Both methods are applied on
sediments from DSDP sites 361 and 249 (Fig. 1). This new data
set will be combined with published sediment budget [2] and
climate records to discuss the links between uplift, margin
denudation, chemical weathering and how they impact the
accumulation rates of sediments in the nearby oceanic basins.