Fluvial archives as records of the late quaternary landscape evolution in the southeastern Brazilian highlands

Abstract

This paper discusses the role of fluvial archives as records of the landscape evolution and geomorphological configuration of the southeastern Brazilian highlands (Brazilian Atlantic Plateau), particularly in the Espinhaço meridional ridge. A cartographic bases search was carried out, complemented by fieldwork to support the definition of the studied 10 valleys. During fieldwork, depositional levels and sequences were described in terms of composition, thickness, organization, and transitions, vertical sections were selected and described. Different fluvial levels in each valley were identified mainly by the heights and characteristics of the sediments of which they were composed. Sediments were sampled at 24 representative points and dated using the Single-Aliquot Regenerative Optically Stimulated Luminescence technique (SAR OSL, five aliquots). The depositional archives allow the reconstruction of six regional relief evolution phases associated with fluvial processes throughout the Late Quaternary (from 26 ka to present). On the upper quartzite surfaces, the bottom valleys are wider, and the channels are straighter, with beds and/or rocky banks than the down surfaces. In this context, the current river dynamics have been controlled by local baseline levels that have reduced the intensity of downcutting. In the lower crystalline areas, valleys tend to be narrower and deeply dissected, favoring the mischaracterization of older archives. Stepped depositional levels in these compartments indicate the role of the Brazilian Shield tectonics (epirogenetic uplifts) in regional geomorphological evolution. Furthermore, the set of deposits and river system characteristics, which show filled valley bottoms, reflect the current stabilization of the regional base level and indicate the importance of lithostructural, climate, and anthropic aspects for understanding the role of fluvial processes in landscape configuration.