Relationship Between Sodium Affected Soil Distribution and Relict Patterned Ground On the Loess Covered Illinoian till Plain of South Central Illinois II.

High pH, sodium affected soils (SAS) occupy approximately 383,512 ha in south central Illinois. SAS occurs on extremely low-relief, planar landscapes where 1-2 m of Wisconsin Episode loess overlies a leached, lower permeability Sangamon Geosol. Previous research suggests that differential water movement and variations in evapotranspiration were the mechanisms responsible for sodium redistribution. Recent updating and digitization of Illinois soil surveys has revealed the occurrence of large areas of polygonal patterned ground associated with SAS. Not all SAS is associated with polygonal patterned ground. The polygonal patterned ground is interpreted to have formed as a result of Wisconsin Episode permafrost formation and degradation. Most polygons are 10 to 80 m in diameter with 4 to 6 m borders. Polygon interiors are darker colored with lighter colored borders. SAS are associated with the polygon borders. While there are multiple pathways responsible for the formation of SAS, we will focus our discussion on the geomorphic significance of permafrost related processes and how they have led to a unique microtopography that has in turn led to the formation of SAS in south central Illinois.