USING THE PI-SWERL TO EVALUATE SOURCES OF LOESS IN NEBRASKA

Recent provenance studies of the Pleistocene Peoria Loess implicate the White River Group as a primary dust source, while the Holocene Bignell Loess may have a large component of silt reworked from nearby dunes and sand sheets. We used the Portable in situ Wind Erosion Lab (PI-SWERL) to test the emission potential of dust sources from dry washes, braided streams, dunes, and exposures of White River Group and Pierre Shale in Nebraska. Dry washes, braided streams, and dunes had the potential to produce large volumes of dust. Silt-rich White River Group bedrock produced limited dust unless reworked into fluvial systems. In this case, the availability of saltating sand (including White River Group aggregates) resulted in large dust emissions. The Pierre Shale produced surprisingly high amounts of dust on weathered exposures. Small aggregates of the Pierre Shale were easily entrained at lower wind speeds and continuously broken down allowing for high dust production. Sand dunes, despite containing <5% silt and clay, are relatively large emitters of dust because of saltation that liberates dust particles; however, dunes are not as large emitters compared to fluvial sources. Our work complements conclusions of previous research regarding sources of loess. Mechanistically, during more arid climates with lower vegetation density, all landforms tested have the potential to generate dust. Weathered bedrock, especially the White River Group (incorporated into fluvial sediment) and Pierre Shale which cover large areas upwind of the loess, are potentially large dust sources.