ILLINOIAN AND KANSAN MOLLUSCAN FAUNAS 



OF ILLINOIS 



A. Byron Leonard, John C. Frye 

 and W. Hilton Johnson 



ABSTRACT 



Molluscan faunas of Kansan and Illinoian age col- 

 lected from 28 localities in Illinois are listed by geograph- 

 ic location and stratigraphic position. Eight of the faunas 

 are of Kansan age, eleven are assigned to the Liman Sub- 

 stage of the Illinoian Stage, and ten are assigned to the 

 Jubileean and Monican Substages of the Illinoian Stage. 

 These faunas are composed predominantly of terrestrial 

 forms, even though they occur largely in water-laid sedi- 

 ments, and they indicate an environment of forest-border, 

 or mixed savanna and woodlands. Pleistocene molluscan 

 faunas in Illinois are of minor value for stratigraphic cor- 

 relation because of their essential similarity through the 

 Quaternary. This history of faunal stability contrasts sharp- 

 ly with data from the Great Plains, where marked composi- 

 tional changes in faunas, resulting from ecologic changes, 

 have occurred during Pleistocene time. 



INTRODUCTION 



Within Illinois there is a nearly complete sequence of Pleistocene glacial 

 and interglacial deposits, and, with the exception of the Nebraskan, or oldest, 

 stage, all of the glacial stages and substages are known to have molluscan faunas, 

 The faunas of the Wisconsinan Stage were reported by Leonard and Frye in 1960, 

 and it is the purpose of this report to describe the molluscan faunas of the Illinoi- 

 an and Kansan Stages. 



During the past decade collections of fossil molluscan faunas have been 

 made from pre-Wisconsinan deposits in Illinois by the three of us and by H. B. 

 Willman. Reported here are 29 local faunal assemblages, 21 from deposits of 

 Illinoian age and 8 from deposits of Kansan age. The fauna localities are distrib- 

 uted widely over the state as shown by the map of localities in figure 1, and, al- 

 though not large in number the faunas are thought to be representative of the fossil 

 mollusks of the Illinoian and Kansan Stages as they occur in the Illinois region. 



1 



