DISTRIBUTION, CHRONOLOGY, AND PALEOENVIRONMENTAL SIGNIFICANCE OF AEOLIAN SAND STRINGERS BEYOND THE ICE MARGIN, SOUTHEASTERN MINNESOTA AND WESTERN WISCONSIN, USA

Recent LiDAR-derived imagery allowed researchers to identify a variety of stabilized aeolian depositional landforms beyond the margins of late Wisconsin glacial lobes in the upper Midwest, USA. These landforms are noted across parts of MN, IA, WI, IL and consist of sand ramps, climbing dunes, parabolic dunes, cliff-top dunes, sand sheets, dune-dammed drainages, loess, and sand stringers. The most ubiquitous and enigmatic landforms are sand stringers, first discussed by Zanner (1999). Stringers are subtle in height (<1-5m), linear (<1-20km), and lack a discernible slipface. Since Zanner, and until recently, no comprehensive studies have been conducted on these landforms. The recent acquisition of LiDAR data has allowed for rejuvenated recognition of stringers and led to obtaining new, but limited data on their morphology and depositional chronology. However, their regional distribution, chronology, genesis, and paleoenvironmental significance remains poorly understood. We compile and synthesize data from prior research and add new chronological constraints (OSL), interpret sedimentary structure from ground penetrating radar (GPR), and present results from a replicable mapping methodology to determine the quantity and spatial distribution of stringers in this region. 250 stringers are identified and indicate a predominant WNW-ESE orientation, consistent with other regional aeolian landforms (Schaetzl et al. 2018). New and prior OSL ages from four stringers indicate deposition between 13-9 ka, consistent with Zanner’s thermoluminescence ages in SE MN (14.7 – 11.2 ka). 200 MHz GPR data contains horizontal to sub-horizontal and gently undulating reflections throughout the landforms. This is consistent with a low energy depositional genesis suggested for stringers by McKee (1979). We hypothesize that the regional distribution and quantity of stringers, coupled with the abundance of other aeolian landforms of similar age, indicate a pronounced period of sandy sediment deposition between 14.7 – 9 ka. A lack of vegetation, soil moisture, and cold-windy conditions existed, and sediment availability may have initiated as permafrost degraded releasing stored sediment from outwash plains and hillslopes. This work may present an analogue for future landscapes undergoing transition from periglacial/permafrost conditions to warmer regimes as climate changes.