CHARACTERIZATION AND IMPLICATIONS OF GEOMORPHIC RESPONSE TO LATE-QUATERNARY CLIMATE VARIATIONS IN A SANDY, LOW-RELIEF TERRAIN

Loess and loess-derived colluvium blanket the deeply dissected, bedrock controlled, topography west of the Black River in Jackson County, Wisconsin. East of the Black River, loess is largely absent and the low-relief Cambrian terrain is instead blanketed by a few meters of sandy sediment. Based on the low-relief terrain and nearby relict permafrost features, this sand mantle may partially be the result of periglacial pedimentation during the last glaciation. Additionally, the thin sandy mantle with infrequent low dunes commonly overlies ventifacts, suggesting the mantle is partially the result of eolian processes. Alternatively, the sand mantle and stone line may have formed largely due to subsequent Holocene hillslope and/or bioturbation processes.

Each of these scenarios present different geomorphic responses to climate fluctuations since the last glaciation, and each have different implications to modern landuse practices. A mantle that resulted from periglacial pedimentation and/or eolian activity suggest geomorphic stability for the last ~18-12 ka, despite climate and land use variations. On the other hand, a mantle produced by bioturbation and Holocene hillslope processes suggests a more dynamic landscape that is prone to erosion and degradation.

Surface soil samples were collected across the study area and analyzed for particle size distribution. Silt content was used to make interpolation maps in ArcMap, the results of which suggest the highest surface silt contents occur southeast of topographic barriers. This is consistent with regional northwesterly paleowinds and an eolian interpretation. Soil profile data also suggest Holocene hillslope processes are largely absent. Future work is necessary to explore the role of bioturbation in this landscape.