Geomorphological evolution of the Paraguay River fluvial plain in the Corumbá reach, Pantanal, Brazil

Abstract

The Pantanal wetland, located in the Upper Paraguay River Basin, is the world's largest tropical wetland and a key region for understanding fluvial system responses to Late Quaternary climatic changes. This study investigates the geomorphological evolution of the Paraguay-Corumbá Fluvial Plain (PCFP; approximately 18.3°S to 19.4°S and 57.0°W to 57.8°W) using remote sensing, sedimentological analysis, and OSL dating. We identified three main geomorphological compartments: (1) a floodbasin with topographically elevated channels; (2) an abandoned meander belt; and (3) the active meander belt (floodplain) of the Paraguay River. Sedimentary and chronological data indicate that the floodbasin and its topographically elevated channels developed prior to the Last Glacial Maximum (>23 ka), under conditions of high sediment supply and variable discharge. A meandering system (paleomeander belt) was active during the late Pleistocene to early Holocene (ca. 10–9 ka OSL), with its initial formation possibly occurring earlier under wetter late Pleistocene conditions. A final avulsion event near Castelo Bay around 2–1.5 ka resulted in the current meander belt. These changes reflect primarily variations in hydro-sedimentary dynamics, likely driven by regional climatic shifts during the Late Quaternary. Our results provide new insights into the complex evolution of large tropical floodplains and highlight the role of sediment supply and discharge regimes in controlling fluvial style in the Pantanal.