Cave sediment chronology and erosion rates in the São Desidério karst reveal a million-year-scale landscape evolution of the Central Brazilian Plateau

Abstract

In central Brazil, regional-scale plateaus and ridges have developed during the Cenozoic in cratonic terrains, after the continental breakup of Pangea. The timing and mechanisms associated with the uplift of such landscape features are poorly understood due to the scarcity of data concerning crustal dynamics and erosion rates. This study used limestone caves containing a rich sedimentary record to obtain new erosion and fluvial incision rate data from the last 3 Ma in the Central Brazilian Plateau. The combination of different geochronological methods (cosmogenic ²⁶Al and ¹⁰Be, OSL, and UTh series), cave passage leveling, and geophysical soundings allowed for the reconstruction of the valley incision history of the São Desidério River since the Late Pliocene. Knickpoint migration rates in the limestone towards the sandstone contact varied from 3782 ± 984 and 1122 ± 198 m/Ma in the São Desidério River and a major tributary. An expressive base level drop of 30–50 m has occurred between 1 and 2 Ma from present and is evidenced by distinct cave levels and the entrenchment of vadose canyons. The average fluvial incision rate in the limestone was determined as 52.5 ± 13.0 m/Ma. The average fluvial incision rate associated with the removal of sediment infill from the conduits was determined as 657.0 ± 31.0 m/Ma. The average erosion rate in the plateau's sandstone-covered catchment areas was 17.1 ± 1.4 m/Ma. Knickpoint retreat and valley incision rates suggest that the onset of the limestone exposure and prominent karst landscape development occurred during the Late Pliocene.