THE LATE WOODFORDIAN JULES SOIL 

 AND ASSOCIATED MOLLUSCAN FAUNAS 



John C. Frye, A. Byron Leonard, H. B. Willman, 

 H. D. Glass, and Leon R. Follmer 



ABSTRACT 



The Jules Soil formed during the late Woodfordian 

 episode of maximum glacial retreat in the Lake Michigan 

 Glacial Lobe during the interval between 15,500 and 

 16,500 radiocarbon years B.P. The soil is directly 

 radiocarbon dated and stratigraphically framed by a group 

 of dates. The molluscan faunas above and below the 

 soil indicate a cool, moist climate. The significantly 

 higher content of expandable clay minerals (montmorillo- 

 nite) in the Jules Soil than in the loess above and below 

 indicates that there was a decrease in Lake Michigan 

 outwash discharged to the Illinois Valley during the 

 episode of soil formation. 



GENERAL STATEMENT 



The Jules Soil was named in 1970 (Willman and Frye, 1970) from its 

 occurrence in the Peoria Loess at the Jules Section (Frye, Glass, and Willman, 

 1968), Cass County, Illinois. The soil had earlier been recognized as an un- 

 named soil in the Peoria Loess in the Frederick South Section (Leonard and Frye, 

 1960), and in other loess sections in the lower Illinois Valley and the East 

 St. Louis area (Frye, Glass, and Willman, 1962; Frye and Willman, 1963). The 

 stratigraphic significance of this weakly developed soil was discussed by Frye 

 and Willman (1973), who suggested an age of slightly more than 17,000 radio- 

 carbon years B.P. The presence of this minor soil in the Peoria Loess is evi- 

 dence of a pause in loess deposition that reflects a significant glacial retreat 

 during late Woodfordian time in the region of the type Wisconsinan. 



In the steepest valley bluffs at the margin of the lower Illinois Valley 

 and in the Mississippi Valley bluffs in Madison and St. Clair Counties, the 

 Jules Soil is split into a complex of two or more A-horizons separated by a foot 

 or more of typical loess. However, where the exposures are extensive enough 

 to trace the soil as much as 100 yards away from the bluff line, the multiple 



