VALLEY ORIENTATION AS A FACTOR FOR LOCAL SAND SOURCES ON THE IOWAN EROSION SURFACE

Iowan Erosion Surface (IES) sediments had multiple sources of eolian materials during the Late Wisconsinan. The main source was from rivers that drained the Des Moines Lobe glacial advance, namely the Iowa and Cedar rivers; dunes, sand sheets, and loess deposits are located primarily to the southeast of these river valleys. Peoria Formation loess is found in areas where the outwash-derived sand could not deflate the landscape, e.g. downwind of steep channels. The area between the Iowa and Cedar rivers demonstrates this relationship and was investigated using a combination of slope values derived from 1m LiDAR, SSURGO soil information, and newly collected core. The results showed certain 2^nd to 5^th order stream channels in this region provide a second, local sand source. Where these valleys are wide (>0.5 km), contain thick (>5 m) Wisconsinan-aged sand and gravel deposits, and oriented perpendicular to the NW wind, their lee sides lack loess. The stoss side have steep, thick (>5 m) loess deposits and sometimes paha (NW-SE aligned elongated hillocks comprised of >5 m of loess burying a paleosol formed in glacial diamicton). The sand and gravel bodies which provided the sand are derived from the local landscape due to periglacial erosion. While not as significant a source as outwash, these deposits provide enough eolian sand to alter the slope downwind. Had they not provided a local deflation source, loess thickness would be more uniform across the area between the Iowa and Cedar rivers. Deciphering the depositional and erosional processes and chronology of this area will increase our understanding of periglacial environment destabilization due to climate change as well as eolian controls on the landscape.