Aeolian Sand Stringers in the Upper Midwest, USA: Morphology, Stratigraphy, and Paleoenvironmental Significance

Sand stringers are subtle (~1-10 m high), elongate (several km long, up to 100 m wide) aeolian landforms that lack a slip face and generally have a northwest-southeast orientation. They are ubiquitous across the Upper Midwest, including southeast Minnesota and western Wisconsin. Despite their prevalence, the timing, processes, and environmental conditions during sand stringer formation and evolution are poorly understood. This research aims to describe sand stringer morphology and stratigraphy, reconstruct regional paleoclimate, and characterize the timing and geomorphic processes of sand stringer formation and evolution in response to shifts in environmental conditions. This study investigates two sand stringers: Good-1 (Goodhue County, Minnesota) and ECC (Eau Claire County, Wisconsin). The morphology of each stringer was described using geospatial tools in ArcGIS. To obtain samples for analysis, a Giddings hydraulic soil coring machine was used to collect soil-sediment cores from Good-1 and ECC. Internal stratigraphy and paleoenvironmental conditions for each sand stringer were characterized by completing detailed soil profile descriptions and conducting particle size, magnetic susceptibility, and stable carbon isotope analyses. Optically stimulated luminescence (OSL) and radiocarbon dating provided age control for this study. Good-1 and ECC morphology are comparable to other sand stringers described in the literature. Their northwest-southeast orientation indicates formation via northwesterly winds. Stratigraphy suggests sediment sources for Good-1 and ECC are different from one another. Good-1 is primarily composed of silt-rich, regional Peoria Loess, while ECC is primarily composed of sand derived from local sources. Timing of formation for the two sand stringers differ as well, with ages indicating Good-1 began forming following the Last Glacial Maximum (LGM) ~15-20 ka and ECC began forming during the Pleistocene-Holocene transition ~12-10 ka. Paleoenvironmental proxy data is consistent between the two stringers. Stable carbon isotopes generally decrease over time, indicating temperatures were colder than modern during sand stringer formation, and magnetic susceptibility data shows higher levels of pedogenic influence in the surface horizons, suggesting a prolonged period of stabilization and pedogenesis over the last several hundred to several thousand years. Outcomes from this research help expand the knowledge surrounding Midwestern aeolian systems and paleoenvironmental change since at least the LGM