Structural Geomorphology of Rock Shelters in Metasedimentary Rocks of the Lagoa da Velha Archaeological Complex, Morro do Chapéu, Bahia

Abstract

This study investigates the genesis and morphology of rock shelters in the Lagoa da Velha Archaeological Complex (Morro do Chapéu, Bahia, Brazil) through a structural geomorphology lens, using aerial photogrammetry techniques, field fracture measurement, and digital elevation models. The analysis uses a cantilever beam mechanical model to explain the projection of competent rock layers over voids created by preferential basal retreat. Situated within the São Francisco Craton, the study area contains siliciclastic rocks of the Morro do Chapéu Formation, deformed during the Brasiliano Orogeny. The research establishes a hierarchy of controls: morphostructural (large-scale folds), lithostructural (binary mechanical stratigraphy), and internal geometric (fracture networks). Results indicate that alternating layers of silicified sandstones and less resistant pelitic levels drive shelter formation. Roof instability is governed by negative bending moments that lead to slab falls, triggered by either catastrophic failure or subcritical stress corrosion cracking. The study concludes that the resulting morphology results from Proterozoic structural heritage interacting with contemporary surface processes, showcasing the principle of geomorphological equifinality.