10 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 496 



LAKE MICHIGAN CORE IOOI-3A 



• < i % 



30 5 5 10 20 



Percent of total pollen 



Fig. 3 - Diagram of percentages of pollen for Lake Michigan core 1001-3A. 



other cores, the percentage pollen diagram for core 1000-3C (fig. 4) shows a dom- 

 ination by pine and oak throughout the length of the core and by pine, oak, and 

 ragweed in the upper section. Ambrosia starts to increase between 13 cm and 14cm 

 (base of zone 4), rising from 5 percent to 20 percent in this 1 -cm interval. Ambrosia 

 reaches a maximum of 43 percent at 7 cm . There is a similar increase in the 

 Chenopodiineae above 14 cm. 



Pollen assemblage zone 2 extends from the bottom of the core to 75 cm 

 and exhibits low percentages of pine, slightly higher oak percentages than in the 

 higher zone, and pollen concentrations as low as 12,00 grains per gram. At 70 

 cm, pine concentration abruptly increases by 20 percent, oak concentration de- 

 clines slightly, and the total pollen concentration increases to 35,000 grains per 

 gram. This shift marks the base of zone 3, which extends from 75 cm to 14 cm. 

 Gramineae, Chenopodiineae, and Cyperaceae also decline at this boundary to 

 less than 1 percent each in zone 3 . In the upper part of zone 3, pine begins to 

 decrease in percentage, oak increases slightly, and ragweed starts to increase. 



In zone 4a, pollen concentrations are lower than in either zone 3 or zone 

 4b. Throughout zone 4a, concentration of pine declines.; concentration of oak 



