Erosional dynamics and escarpment retreat at the southern end of the South American passive margin escarpment

Understanding how continental plateaus and their escarpments evolve is essential for explaining the formation and evolution of elevated passive margins. How and when the Brazilian Great Escarpment formed remains highly debated, as studies suggest it is a recent tectonic feature, while others conclude it is the erosion remnant of the Atlantic rifting. The southernmost segment of the escarpment, the Aparados da Serra features a 1 km high escarpment, providing an excellent opportunity to study escarpment evolution in detail. Here, we combine topographic analysis and isotopically determined escarpment retreat rates to resolve the geological evolution of this escarpment. Based on catchment-averaged 10 Be analysis of stream sediment, we determine that the escarpment is retreating inland at 40 to 920 m Myr −1 , eight to ten times faster than regional erosion rates. Geological observations suggest that retreat rates are influenced by lithology that varies across the escarpment face; basins with a higher proportion of strong basaltic rocks compared to weaker sedimentary rocks exhibit lower retreat rates. In addition to impacting retreat rates, erodibility indirectly controls the nature of divide migration, as differential erosional unloading leads to spatially variable flexural responses: faster retreat rates in the north result in greater flexural deflections that help fix the divide to the escarpment edge. In contrast, slower retreat rates in the south induce a modest flexural response insufficient to maintain an uplifted escarpment edge, thus facilitating the capture of plateau segments by escarpment-draining rivers. These results provide a mechanism for post-uplift topographic diversification of the escarpment that is independent of initial tectonic and topographic heterogeneity. This model may apply to other escarpments with strong unloading gradients. Collectively, geological observations and calculated retreat rates favor an ancient (Cretaceous) origin for the Aparados da Serra escarpment. Combined with observations from other continental escarpments, our results support the long-term preservation of continental escarpments and their associated highlands as prominent geological features over timescales >10 8 years. • Escarpment retreat rates are highly variable, reaching up to 920 m Myr −1 . • Lithology is the primary control on retreat rates. • River captures, guided by joint sets, drive divide migration. • Erosion-flexural feedback set divide position relative to the escarpment.