Episodic Holocene loess deposition in central Nebraska

The Mirdan Canal section in central Nebraska, USA, provides evidence for multiple episodes of Holocene loess deposition in the central Great Plains. This irrigation canal cut exposes more than 4 m of Holocene sediment that overlies the late Wisconsinan Peoria Loess. The oldest Holocene sediment is local slopewash that fills gullies, but overlying beds are interpreted as Holocene loess (Bignell Loess). Three buried soil profiles occur within the Holocene sediment, and have yielded uncalibrated C-14 ages of 3010 yr BP (uppermost buried soil) and 8790 yr BP (third buried soil from top). A fourth buried soil yielded an age of 9330 yr BP, and is correlated with the Brady Soil. The Bignell Loess has a darker color? slightly more organic matter, more clay, more coarse silt and sand, less smectite, and less volcanic glass than the underlying Peoria Loess. The Bignell Loess is most plausibly interpreted as dust from local flood plains, containing a mixture of reworked Peoria Loess and older silts with contrasting mineralogy. Episodes of loess deposition occurred in the early, middle and late Holocene, probably during periods of dry climate but possibly also as a consequence of large erosive floods that made wind-erodible sediment available on nearby flood plains. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.