LOESSIAL SOILS: THEIR RELATIONSHIP TO WIDTH OF THE SOURCE VALLEY IN ILLINOIS

Abstract

We examined four traverses adjacent to narrow and wide segments of the Mississippi River Valley in Illinois for trends in loess thickness, particle-size distribution, and soil development.

Where the valley is wide, loess thickness, mean particle size, and coarse silt content decrease rapidly with distance from the valley, and clay enrichment within the B horizon is increasingly evident away from the valley. Where the river valley is narrow, the adjacent soils exhibit different trends in loess thickness, mean particle size, clay enrichment, and coarse silt content along the transect. Within the study area, soils adjacent to narrow segments of the Mississippi River Valley are commonly classified as “well-developed” Argiudolls, while soils adjacent to wide valley segments are “weakly developed” Hapludolls.

Local glaciofluvial sediments from the Mississippi River Valley appear to be a major source for loess located leeward of broad valley segments, but apparently are not a major source of loess for those uplands adjacent to narrow valley sections. The primary source of loess for these sites is considered to be from areas west of the Mississippi River Valley and loess deposited by variable winds.