PALYNOLOGY AND SEDIMENTOLOGY OF HOLOCENE DEPOSITS 

 IN SOUTHERN LAKE MICHIGAN* 



James E. King, 1 Jerry A. Lineback, and David L. Gross 



ABSTRACT 



An examination of the fossil pollen in the sediment shows 

 that the upper part of the Waukegan Member (Holocene) of the 

 Lake Michigan Formation can be divided into four pollen assem- 

 blage zones on the basis of subtle changes in percentages of the 

 dominant types of pollen and in total numbers of pollen grains 

 per gram of sediment. Three of these zones are distinguished 

 on the basis of the relative abundance of pine and oak pollen, 

 and the fourth is characterized by a high percentage of ragweed 

 pollen. Zone 1, the oldest, has lower percentages of pine and 

 higher percentages of oak than the other zones. The total pollen 

 concentration in the sediment is highest in zone 1. Zone 2 is 

 distinguished from zone 1 by a lower concentration of total pollen. 

 Zone 3 has the highest percentages of pine. Zone 4 is distin- 

 guished by high percentages of ragweed, a result of forest clear- 

 ance for agriculture about 1840 A.D. 



On the basis of the ragweed increase, calculated sedi- 

 mentation rates in southern Lake Michigan for the postsettlement 

 period are 0.49 mm/yr for the central area of the southern basin 

 of the lake and 0.9 to 1.02 mm/yr for areas along the east side 

 of the lake. In agreement with results of studies of the other 

 Great Lakes, the pre settlement sedimentation rates in Lake Mich- 

 igan were generally lower than the postsettlement rates. 



INTRODUCTION 



Fossil pollen preserved within Lake Michigan sediments reflects changes 

 in the vegetation surrounding the lake. Such changes are well known from stud- 

 ies of the Great Lakes region (Cushing, 1965) and provide one method of determi- 

 ning the age of the sediments. Most vegetation changes took place over thousands 

 of years, however, and short-term fluctuations are not always apparent in the pol- 

 len record. One short-term vegetation change that has been correlated and dated 

 throughout the Great Lakes region is a dramatic increase in ragweed ( Ambrosia ) 

 pollen resulting from the initiation of large-scale forest clearance and agriculture 

 in the middle of the nineteenth century (Davis, Brubaker, and Beiswenger, 19 71; 

 Fries, 1962; McAndrews, 1966). Forest clearance started with European settlement 



This publication is also Contribution No. 31, Quaternary Studies Center, Illinois State 

 Museum, Springfield, IL 62706. 



1 Illinois State Museum, Springfield, II 62706. 



2 Illinois State Geological Survey, Urbana, II 6l801. 



1 



