Integrated environmental records in Late Pleistocene Poland: The paleofluvial regime and paleoclimate inferred from Krosinko site

Multiproxy analyses performed at the Krosinko site in the Warsaw–Berlin ice marginal valley have provided data that characterize the depositional conditions, the paleofluvial regime, and the paleoclimate and help reconstruct the paleo-environment at a time of significant sediment (alluvium) accumulation (starting in central Poland ca. 45 ka BP). The sedimentological study, including sand-grain morphology and micromorphology analyses, reveals the presence at Krosinko of a meandering river and of a braided river during the Eemian (MIS 5e) and Upper Pleniweichselian (MIS 2), respectively. The fluvial regime changed over time, from low-energy, through high-energy, to low-energy, as documented by the differently formed sedimentary units A–D (vertical sedimentary succession from base to top: sandy silt, sand, gravelly sand, and sand). Sedimentary unit A and the lower part of unit B were accumulated in the Eemian interglacial (MIS 5e) by the low-energy meandering river. The high-energy fluvial environment during the Weichselian is associated with long, intense sediment transport, organic remains, and flints, as confirmed by taphonomic studies on conifer cones (Picea cf. abies) and wood remains (Juniperus). The river operated under distinct environmental conditions. First, during the accumulation of the upper part of unit B and unit C, there was a strong influence of freezing and aeolian weathering, which weakened significantly over time (unit D). This in turn indicates a change in climate from periglacial (upper part of unit B and unit C), when we also document the presence of permafrost in the subsurface or relatively deep seasonal frost, to temperate (unit D). With warming in the Holocene (MIS 1), an oxbow lake developed in Krosinko, the presence of which is recorded by peat.