Late Glacial fluvial response of the Niers-Rhine (western Germany) to climate and vegetation change

The Niers valley was part of the Rhine system that came into existence during the maximum Saalian glaciation and was abandoned at the end of the Weichselian. The aim of the study was to explain the Late Pleniglacial and Late Glacial fluvial dynamics and to explore the external forcing factors: climate change, tectonics and sea level. The sedimentary units have been investigated by large-scale coring transects and detailed cross-sections over abandoned channels. The temporal fluvial development has been reconstructed by means of geomorphological relationships, pollen analysis and 14C dating. The Niers-Rhine experienced a channel pattern change from braided, via a transformational phase, to meandering in the early Late Glacial. This change in fluvial style is explained by climate amelioration at the Late Pleniglacial to Late Glacial transition (at ca. 12.5k14C yr BP) and climate-related hydrological, lithological and vegetation changes. A delayed fluvial response of ca. 400 14Cyr (transitional phase) was established. The channel transformations are not related to tectonic effects and sea-level changes. Successive river systems have similar gradients of ca. 35-40cmkm-1. A meandering river system dominated the Allerod and Younger Dryas periods. The threshold towards braiding was not crossed during the Younger Dryas, but increased aeolian activity has been observed on the Younger Dryas point bars. The final abandonment of the Niers-Rhine was dated shortly after the Younger Dryas to Holocene transition. Traces of Laacher See pumice have been found in the Niers valley, indicating that the Niers-Rhine was still in use during the Younger Dryas.