8 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 496 



Pollen Assemblage Zones 



Pine and oak pollen dominate throughout percentage diagrams constructed 

 for Lake Michigan cores; in the upper few centimeters, Ambrosia pollen is also 

 abundant. However, presence or absence of pollen taxa is not a major factor in 

 establishing pollen assemblage zones. Rather, zonation relies on subtle changes 

 in percentages of the dominant types and in the numbers of total grains per gram 

 of sediment. The pollen-zone boundaries are not always clearly defined, and they 

 could be shifted several centimeters either way without appreciably affecting the 

 definition of a zone. The important consideration is that these pollen zones are 

 pre sent in all of the core s . 



Within the Lake Michigan sediment cores, the following pollen assem- 

 blage zones are described: 



Zone 4 - The Ambrosia zone is characterized by high percentages of rag- 

 weed, low percentages of arboreal pollen, and a high number of total 

 grains per gram. This zone can be divided into two subzones, 

 an early Ambrosia zone (4a), with lower pollen concentrations, 

 and a late Ambrosia zone (4b), with high concentrations, that 

 extends to the present. The base of zone 4a is defined in this 

 paper as the point at which Ambrosia exceeds 5 percent of the 

 total pollen. 



Zone 3 - This zone is characterized by the highest pine percentages in 

 the cores and a high total pollen concentration. 



Zone 2 - This zone is characterized by slightly lower percentages of pine 

 and by higher percentages of oak than zone 3, and by very low 

 pollen concentrations per sample. The numbers of grains per 

 gram in this zone are the lowest encountered in the cores. 



Zone 1 - Zone 1 is similar to zone 2 in percentages of oak and pine, but 

 has higher pollen concentrations per sample. The average num- 

 ber of grains per gram is twice that of zone 2. Zone 1 is appar- 

 ent only in the deeper part of core 969-2A. 



To further test the validity of the boundaries between the four pollen as- 

 semblage zones, chi-square tests ( x 2 ) of homogeneity were calculated for pairs 

 of adjacent samples (Mosimann, 1965). The counts of Pinus , Querous , Ambrosia, 

 and Chenopodiineae were used to test the null hypothesis that each of a tested 

 pair of samples was similar to the other. These tests, however, did not take into 

 account the total pollen concentration, which was one of the criteria for visually 

 locating the assemblage zones. Thus, the x 2 tests did not distinguish all of the 

 pollen assemblage zones. 



Sediment Cores 



Core 1002-3A 



The pollen in most of core 10 02-3A was quite poorly preserved and was 

 present in such low numbers that counts were not meaningful except for the upper 

 lcm, from which a total of 100 exotic grains were counted to determine current pollen 

 deposition on the bottom in the western part of the southern lake basin. The data 

 indicate that 4000 grains per gram are present in the upper 1 cm of sediments, a 

 low value even for Lake Michigan. 



