STRATIGRAPHIC INVESTIGATIONS OF AEOLIAN SAND STRINGERS IN SOUTHEAST MINNESOTA AND WESTERN WISCONSIN

Sand stringers are subtle, linear aeolian deposits that lack a slipface. Limited data exist on the stratigraphy, sedimentology, and depositional chronology of these landforms in the Upper Midwest, USA. We investigate two sand stringers in Minnesota (Good1) and Wisconsin (ECC). Here, we: 1) characterize landform morphology using LiDAR data; 2) collect and describe soil-sediment cores; 4) measure particle size in 1-4-cm intervals; and 5) provide the first age control estimates for deposition of these stringers with 14C and OSL methods.

Good1 is 860 m by 50-80 m with three stratigraphic units: 1) ~80-270-cm-thick silt-rich surface unit with Ap-A-B-C horizonation; 2) ~15->100-cm-thick sand unit; and 3) >25-cm-thick dark brown sandy loam unit. Unit 1 returned 14C ages of 22410±100 and 25440±330 cal yr BP at the base and 9140±110 cal yr BP at the B-C horizon boundary. Unit 3 returned 14C ages of 21730±300 and 20120±210 cal yr BP.

ECC is 945 m by 30-50 m with three stratigraphic units: 1) ~80-100-cm-thick silt loam to loamy sand surface unit with Ap-A-AB-B-BC horizonation; 2) ~60->190-cm-thick stratified fine to medium sand unit; and 3) ~50->80-cm-thick stratified coarse sand unit. Units 2 and 3 contain several iron bands. Unit 1 returned a 14C age of 1320±20 cal yr BP at the top of the BC horizon. Unit 2 returned 14C ages of 6260±40 and 8000±30 cal yr BP at depths of 94-128 cm and OSL ages of 8.9±1.40 to 11.25±1.71 ka from depths of 145-275 cm.

Good1 likely began forming after the Last Glacial Maximum (LGM), while ECC began near the Pleistocene-Holocene transition. Pedogenesis at both sites indicate stabilization and reduced sediment inputs from the mid- to late-Holocene to present. Good1 is primarily composed of loess with minor inputs of outwash sands. ECC is primarily composed of outwash sands with minor inputs of loess. Both sites have similar morphologies and orientations, consistent with predominant NW-SE winds during and post LGM. We hypothesize that sedimentological differences at these two sites result from spatial and temporal variability in glacial retreat and/or permafrost melting and the character of proglacial and periglacial sediment available at each site for aeolian transport. Thus, sand stringers represent a key landform to understand paleoenvironmental change during deglaciation of the Upper Midwest, USA.