Morphology, Sedimentology and OSL Chronology of the Lower Prosna River System Evolution – A Case Study in Rokutów, West-Central Poland

This paper presents comprehensive investigations of the morphological, sedimentological, and stratigraphic features in the lower Prosna River valley infill, situated in west-central Poland. At the Rokutów site, we identified two meander generations and an anastomosing system. Fluvial changes observed depict the response of the extraglacial river system to climate fluctuations post-last glaciation. Following valley aggradation, scouring erosion, reaching depths of 9–10 m, likely occurred during the Bølling Interstadial. ‘Great meanders’ emerged during the Allerød-Younger Dryas, persisting for around 1000 years, with an uncommon upstream rotation influenced by the sub-Quaternary surface slope. A lengthy stabilization phase, lasting 8000–10,000 years, characterized by an anastomosing system with gradual aggradation, followed the great meandering period. About 3600–3900 years ago, the valley shifted back to a fluvial system with small meanders, lasting 600–900 years. Subsequently, the River Prosna reverted to an anastomosing system, remaining so until the 19th–20th centuries when it transformed into a single-channel system through regulatory manipulation. Our research suggests that the evolution of the Prosna River differed from other rivers across Western and Central Europe, exhibiting a blend of anastomosing and meandering phases.