Erosional Response to Pleistocene Climate Changes in the Brazilian Highlands

Abstract

Plio-Quaternary climatic changes are considered to be a key driver of landscape evolution, but many unresolved questions remain, such as the extent of the impact of major climatic shifts such as the Mid-Pleistocene Transition (MPT). Various geochronological methods are available to infer changes in surface processes over the Plio-Quaternary, and Terrestrial Cosmogenic Nuclides (TCN) have proven to be one of the most efficient tools to reconstruct paleo-denudation. Implementing these approaches requires very specific conditions, such as well-preserved and extensive sediment sequences. Developing alternative methods to document the evolution of denudation is thus of major interest to retrieve information on the evolution of denudation in places where recent detrital sediment records are absent. We explore the evolution of landscape erosion over a $\sim$1 Ma timescale in an intra-cratonic setting, the Espinhaço mountain range (Brazil), with a new data set of detrital cosmogenic nuclide concentrations (²⁶Al–¹⁰Be). We observe a systematic disequilibrium in the ²⁶Al/¹⁰Be ratio, which we interpret as resulting from the combination of soil mixing and a significant increase in the intensity of surface processes, close to the MPT. We discuss the different scenarios with respect to available local and global data concerning the relationships between climate evolution and erosion over this time period. Our results have important implications for the interpretation of the denudation rates derived from TCN concentrations under steady states assumption, in landscapes with low erosion rates, which have a long memory for surface processes history.