PLEISTOCENE PALEOSOLS AND THE CLARINDA SOIL SERIES IN ADAMS COUNTY, SW IOWA
During the 2006 Adams County soil survey update, 78 locations were logged where gray paleosols lay exposed along roadcuts and hillslopes. The top elevations of the exposures fell into four groups, separated by 5-9 m. We propose that these paleosols represent four Pre-Illinoian interglacial stages. Projecting these elevations onto the Clarinda series map may give an initial approximation of the distribution of Pre-Illinoian tills in the county.
Drilling in 2006 and 2014 allowed for textural and morphological study of the upper three paleosols in a buried state. Solum thickness varies from >7 m in the uppermost paleosol (Yarmouth-Sangamon) to <2 m in the lower Pre-Illinoian paleosol (PIP-2). All three have clay or silty clay textures with >45% clay. The two younger paleosols are welded soils and include an upper solum in a non-till parent material, most likely loess. PIP-2 is sandier and very dark with an organic carbon content more typical of a Late Wisconsinan paleosol. Solum depth to secondary carbonates decreases markedly with paleosol age due to re-saturation by overlying tills. Thin-sections show frequent channels and fused granular structure at the top of PIP-1 and PIP-2, probable evidence for preservation of an A-horizon. Strongly developed vertic features (wedge structure, slickensides, and stress-oriented clay) on both macroscopic and microscopic scales attest to intense or prolonged conditions of wetting and drying. Future collaborative work will attempt to correlate the tills to a regional stratigraphic framework and characterize organic carbon stabilization in PIP-2.