ILL OLOGICAL 



SU MBRARY 



MAY 28 1986 



WISCONSINAN MOLLUSCAN FAUNAS 

 OF THE ILLINOIS VALLEY REGION 



A. Byron Leonard and John C. Frye 



ABSTRACT 



In the Illinois Valley region, the Altonian Substage (between 

 50,000 and 70,000 to 28,000 B. P.), Farmdalian Substage (28,000 to 

 22,000 B. P.), and Woodfordian Substage (22,000 to 12, 500 B. P.) of 

 the Wisconsinan Stage are represented by loess, water-laid elastics, 

 and glacial till. Molluscan faunas of these sediments are here listed 

 both geographically and stratigraphically, and 61 species are illus- 

 trated. Woodland faunas distinctive of the Roxana silt (Altonian) are 

 found at 11 localities. Two of the Farmdalian localities yielded a- 

 quatic faunas and one woodland fauna. Faunas characteristic of the 

 Woodfordian are abundant but differ in the various geographic areas. 

 The faunas of the several Woodfordian rock-stratigraphic units are 

 not distinguishable, but those of the three substages are distinctly 

 so. During Wisconsinan time the glaciers did not produce rigorous 

 climates in Illinois very far from the ice fronts. During Altonian and 

 part of Farmdalian time the southern half of Illinois was heavily for- 

 ested, but this was not so in Woodfordian time. 



INTRODUCTION 



Deposits of glacial till and associated outwash, loess, and alluvium of 

 Wisconsinan age are the surficial materials of a large part of Illinois and thereby 

 determine to a considerable extent the character of the soils, affect the occurrence 

 of ground-water supplies, and pose problems for engineering construction. Conse- 

 quently, in order to enable more precise recognition and better comprehension of 

 these materials and their relationships, the Illinois State Geological Survey has been 

 investigating the nature of these sediments, conducting fundamental studies of their 

 mineralogy, stratigraphy, and content of fossil mollusks. This report deals with 

 fossil mollusks and is integrated with Illinois Geological Survey studies of the stra- 

 tigraphy of the deposits and with radiocarbon determinations of their age made by 

 the United States Geological Survey. 



For the most part the fossils reported on were collected from the loesses, 

 but some were taken from terrace deposits, outwash sands, and silt and sand in- 

 clusions within glacial till. The geographic distribution of the faunal localities 

 and geologic sections are shown in figure 1 . 



[1] 



