Alluvial stratigraphic evidence for channel incision during the Mediaeval Warm Period on the central Great Plains, USA

Alluvial valley fills from tributaries to the upper Republican River, southwest Nebraska, USA, provide soil- and morpho-stratigraphic evidence for an episode of channel incision that occurred between c. I 100 and 800 C-14 yr BP, based on 11 new radiocarbon ages. This local episode of channel incision correlates with other alluvial stratigraphic studies from the central Great Plains and demonstrates regionally synchronous fluvial behaviour. Proxy records of palaeohydrologic conditions in and around the Great Plains (including lacustrine, aeolian and geomorphological sources) indicate that channel incision correlates with a multicentennial episode of common, widespread drought. Temporally, this drought episode corresponds to the period recognized in many regions as the Mediaeval Warm Period (MWP). Therefore, this research demonstrates: (1) a relationship in the semi-arid central Great Plains between drought and increased fluvial incision; and (2) a local/regional geomorphic response to a particular episode of global climate change.