Fluvial dynamics of the Grande River and paleolandscape evolution in Northeastern Brazil

The Grande River stands out in the landscape of Northeast Brazil as one of the main tributaries of the São Francisco River - the largest river exclusively Brazilian, which supplies water to a significant portion of the country's northeast, a predominantly semi-arid region. Despite its notable natural, social, and economic importance, the Grande River lacks sufficient geomorphological and geochronological studies to provide a reliable landscape reconstruction over the past millennia. In this study, we propose a reconstruction of the fluvial dynamics of the middle Grande River over the last 35 ky through an integrated geomorphological analysis using satellite imagery and Digital Elevation Model (DEM) interpretations, field data collection, Optically Stimulated Luminescence (OSL) dating, and grain-size analyses of sediments. The results suggest the presence of a surface associated with a Pleistocene fluvial terrace (T1), a surface corresponding to a Holocene fluvial terrace (T2), the floodplain (FP) and paleochannel landforms, such as abandoned meanders, scars, and scroll bars. The morphogenesis of these features points to four phases: a predominantly erosive and energetic phase; base-level lowering and the abandonment of the T1 level; aggradation, lateral channel migration, and the development of the T2 surface; and the current phase, characterized by subtle channel incision and abandonment of the T2 terrace level. We conclude that the adjustments in the fluvial dynamics of the middle Grande River responded to cyclical allogenic factors followed by autogenic channel responses. While these transformations have likely occurred at the local level, their manifestations may have varied across the regional level. • A Pleistocene terrace (T1), a Holocene terrace (T2), and the floodplain were dated. • Paleochannel landforms, such as abandoned meanders, scars, and scroll bars, were mapped. • Base-level lowering/incision occurred in two phases during the last 35 ky. • Two phases of lateral migration through erosion or aggradation were also identified. • The coupling of allogenic/autogenic processes triggered these phases and paleoforms.