HOLOCENE PALYNOLOGY AND S E DI M E NT O LO GY 9 



Core 1001-3A 



Core 1001-3A, taken from the center of southern Lake Michigan, pene- 

 trated down to the middle of the Sheboygan Member of the Lake Michigan Forma- 

 tion (fig. 2, table 1). However, only enough pollen was present for analysis to 

 a depth of 0.70 m in the Waukegan Member. Throughout the core, pollen was 

 very sparse and badly eroded. No pollen concentration data are available from 

 this core . 



The percentage pollen diagram (fig. 3) shows that the Waukegan Member 

 in core 1001-3A is dominated by pine and oak throughout its length, and that in 

 the upper part significant quantities of ragweed pollen are present. Other tree 

 pollen present include spruce {Pioea) , juniper {Juniperus) , willow (Salix) , and 

 ash {Fraxinus ) . Above 10 cm there is a greater abundance of such arboreal taxa 

 as fir {Abies), birch ( Betula) , walnut {Juglans) , hickory {Carya), sycamore 

 (Platanus), elm {Ulmus), and maple (Acer) than below. Many of these latter 

 taxa are prevalent in the Ambrosia -dominated sediments above 6 cm (zone 4) . 

 The consistent presence of Platanus in the lake sediments probably reflects the 

 riparian plant communities along the rivers flowing into the lake. These rivers 

 are one of the major means of transporting pollen into the lake system. 



The dramatic increase of Ambrosia pollen (zone 4) starts between 6 and 7 

 cm below the surface. Below this point ragweed abundance is never more than 8 

 percent and usually is less than 5 percent. Between 7 cm and the surface, rag- 

 weed increases from 4 percent to 36 percent. The Chenopodiineae, a group of weeds 

 which grow on disturbed land and which include lamb' s-quarters (Chenopodium ) and 

 pigweed {Amaranthus) , also increase in zone 4. Other herbaceous pollen in the 

 core include sage {Artemisia), the tubuliflorae tribe of the Compositae, grass 

 (Gramineae), sedge (Cyperaceae) , and an unknown member of the Papilionoideae 

 (legume family) . 



In addition to the Ambrosia zone (zone 4), the percentage pollen diagram 

 for core 1001-3A can be divided into zones 2 and 3. Zone 2 lies between 70 cm 

 and 35 cm. In zone 2 pine averages 20 to 25 percent and oak is approximately 

 50 percent of the total pollen. The sharp decrease in oak pollen at 50 cm is not 

 believed to represent a vegetational change. Herbaceous pollens are persistent 

 throughout zone 2. Between 40 cm and 30 cm, pine increases, and oak and the herbs 

 such as Ambrosia, Gramineae, and Chenopodiineae decrease. Thus a depth of 

 35 cm marks the boundary between zones 2 and 3. The zone of high percentages 

 of pine pollen (zone 3) extends from 3 cm to 7 cm in depth and contains pine 

 percentages 15 to 20 percent higher than either zone 2 or zone 4 contains. At the 

 beginning of the Ambrosia increase, zone 4, pine and oak percentages decline. 



Chi-square tests identified significant differences at the .95 confidence 

 level between the sample at 30 cm and the one at 40 cm and between the one at 

 3 cm and the one at 4 cm. The beginning of the Ambrosia rise at 6 to 7 cm was 

 not identified precisely, because the percentage changes, especially of Ambrosia, 

 are gradual. A significant difference was found between 3 cm and 4 cm and may 

 represent the boundary between subzones 4a and 4b. However, because the pol- 

 len zones are based in part on pollen concentrations, this x 2 ~determined boundary 

 is not plotted on the pollen diagram (fig. 3) . 



Core 1000-3C 



Core 1000-3C, located on the eastern side of the southern basin (fig. 2, 

 table 1), was taken from the upper part of the Waukegan Member, which is up 

 to 8 m thick in this part of the basin (Lineback and Gross, 1972). As in the 



