IDENTIFYING EROSIONAL HILLSLOPE DEPOSITS USING FLY-ASH IN SOUTHEAST WISCONSIN

Post settlement alluvium (PSA) has not been intensively studied on floodplains in southeastern Wisconsin. One reason is the difficulty in deciphering PSA from the original floodplain alluvium. The “black-on-black” soil color makes identifying PSA difficult in floodplains. Recent advances in determining fly-ash incidence from soils serve as a potential tool for identifying PSA in southeastern Wisconsin floodplains. The main objective of this study was to perform fly-ash extraction using an established extraction and quantification methodology. We selected soils along hillslopes that had a high probability of containing fly-ash and contained easily recognizable PSA layers burying pre-settlement soil profiles. Three soil cores were extracted from footslope positions of a drumlin in Jefferson County, Wisconsin. All three cores showed clear evidence of erosional deposits over well-expressed pre-settlement soil profiles. Particle size and organic carbon data support the field identification of PSA burying the pre-settlement surface. Extraction of magnetics in the uppermost horizons of the erosional deposits indicate that fly ash is likely present in the PSA with lesser amounts in the pre-settlement soil horizons. Initial indication comes from horizons containing PSA that have higher magnetics when compared to the pre-settlement soil. Continued analyses of the magnetic fraction is necessary for the confirmation of fly-ash. If fly-ash can be identified in the hillslope deposits, we anticipate using the same methodology to examine floodplain soils in southeast Wisconsin.