HOLOCENE PALYNOLOGY AND S E D I M E N T O L O G Y 3 



Gross, and Meyer, 1974). The tills are overlain by glaciolacustrine and lacus- 

 trine silts and clays (fig. 1). 



in the southern basin, two types of glaciolacustrine sediments overlie 

 the till (Lineback et al., 1971; Lineback, Gross, and Meyer, 1972). The older 

 type is the Carmi Member of the Equality Formation, which consists of silts, 

 sands, clays, and clay-pebble conglomerates that were deposited in close prox- 

 imity to the glaciers. It is generally thin (less than 1 m) except near lake-floor 

 terminal moraines. The younger glaciolacustrine sediment is included in the lower 

 two members of the Lake Michigan Formation, the South Haven and Sheboygan 

 Members; they are reddish gray glaciolacustrine clay derived from the melting of 

 the last ice sheet (Valderan Substage) to occupy the northern half of the Lake 

 Michigan Basin (fig. 1). The Winnetka , Lake Forest, and Waukegan Members 

 are postglacial clays and silty clays derived from sediment carried into the lake 

 by surface drainage and from shoreline erosion (Gross et al., 1972). The Ravinia 

 Member is sand and is confined to the beach areas (Willman and Frye, 1970) . 



This report on fossil pollen is based on four cores from the southern basin 

 of the lake between Waukegan, Illinois, and Benton Harbor, Michigan (table 1, 

 fig. 2). Cores 969-2A and 1000-3C are from an area of high Holocene sedimen- 

 tation rates in intermediate water depths along the east side of the lake (Lineback 

 and Gross, 1972). Core 1001-3A is from deep water, where Holocene sedimenta- 

 tion rates are moderate, and core 1002-3A is from the west side, where little 

 Holocene sediment has accumulated. Core 800-5, near core 1001-3A, and core 

 836-5, which is geologically similar to core 1000-3C, were previously dated by 

 radiocarbon (Lineback and Gross, 1972; Gross, Coleman, and Lineback, 1973). 



Circulation of water and air is important to the distribution and deposi- 

 tion of pollen in lake sediments. Water circulation patterns in southern Lake 

 Michigan are complex and seasonal, and interpretation of them is somewhat con- 

 troversial. Most surface observations indicate that net water circulation affecting 

 sedimentation patterns is generally counter-clockwise and that sediment entering 

 the west side of the lake is swept around to the east side before deposition (Line- 

 back and Gross, 19 72; Federal Water Pollution Control Administration, 1967; and 

 Harrington, 1895). Recent studies by Monahan andPilgrim (1975), however, have pro- 

 duced contradictory evidence indicating that clockwise currents dominated the south- 

 ern basin during the time of their study. Air movement data collected by the U.S. 

 Weather Bureau at Chicago's O'Hare Airport show that the dominant wind direction 

 is from the southwest and that lesser wind components are from the northwest and 



TABLE 1 - CORE LOCATIONS AND WATER DEPTH 





Core 













diameter 









Water depth 



Core no. 



(mm) 



Latitude 



Longitude 



(m) 



800-5 



120 



42°25.0' N. 



87°09.3' 



W. 



128.9 



836-5 



120 



42°02.7' N. 



86°43.5' 



w. 



55.5 



969-2A 



47 



42°14.05' N. 



86°39.2' 



w. 



49.9 



1000-3C 



67 



42°18.0' N. 



86°42.0' 



w. 



73.4 



1001-3A 



67 



42°22.0' N. 



87°11.0' 



w. 



120.5 



1002-3A 



67 



42°23.0' N. 



87°34.9' 



w. 



70.1 



