FOX RIDGE STATE PARK AND ITS GEOLOGY

by Todd Danielczyk

 

INTRODUCTION

Fox Ridge State Park is located in central Illinois, eight miles south of Charleston. The Late Wisconsinan glacial ice advanced from the north leaving the Shelbyville end moraine at the park and an outwash plain grading down onto the Springfield Plain (Jorstad, 1991) figure 1.

Figure 1. View of the outwash plain grading down onto the Springfield Plain.

 

The young and mature landscape developmental and stream stages are readily observed in the deep valleys of the park. The streams have cut into the formations and have caused 100 feet of relief to be formed. These valleys are steep walled and have a V shape to them which is characteristic of youthful intermittent streams (figure 2). This is expected, since these valleys have been eroded in less than 20,000 years. The bottom of the valley floors also have streams that meander and form cut banks which are examples of mature streams. Sometimes a glacial erratic that was transported by the ice and consolidated into the till, and now may be found in stream channels, figure 3. These erratics may have rolled down a hillside to their present location when undercut by a laterally migrating stream.

Figure 2. V-shaped valleys with steep walls.

Figure 3. An example of an erratic in the stream bed.

STRATIGRAPHY

The Illionian Glasford and Wisconsinan Wedron Formations are exposed at Fox Ridge and unconformably overlie the unexposed Pennsylvanian Mattoon Formation, figure 4. Strata of the Late Pennsylvanian Mattoon Formation and other portions of the MacLeansboro Group are exposed in stream cuts elsewhere in the local area. The oldest unit exposed in the park is the Vandalia Till Member of the Glasford Formation. Both the Illionian Glasford and the Wisconsinan Wedron Formations were deposited by glaciers advancing from the same general northerly direction at different times; this makes field recognition difficult at times.

Figure 4. A generalized lithostratigraphic column of Pleistocene units presented in Fox Ridge, from Jorstad 1991.

GLASFORD FORMATION

The Illionian Glasford Formation is represented in the park by the Vandalia Till Member. The Vandalia Till Member is a brown clay-rich till containing some pebbles. South of the Shelbyville Moraine, this unit grades upward into the modern soil and is recognizable in the field by the slopes it forms on top of a very thick sandstone (Hardesty, 1982). In the park, it can be recognized by its strength. The Glasford Formation has a strength over five tons per square foot and the younger Wedron formation has a strength less than four tons per square foot (Nelson, 1990). The Vandalia Till Member is usually 2 to 5 feet thick with a Sangamonian paleosol overlying it (Hardesty, 1982). In the park, there are only a few stream cuts that penetrate the Vandalia Till (Jorstad, 1991).

WEDRON FORMATION

The Wedron Formation makes up 95% of the glacial drift exposed at the surface of Coles County, Illinois (Hardesty, 1982). The Wisconsinan Wedron Formation is olive-grey to yellowish brown. It contains roughly 30% sand, 40% silt, and 30% clay. The till is silty to sandy, and contains irregularly distributed pods and lenses of silt, sand, and gravel in the upper portions of the unit (Hardesty, 1982) and has a strength of less than four tons per square foot.

PALYNOLOGY

METHODOLOGY

The pollen sample was taken from Vandailia Till exposed in a stream cut that leads to the Embarass River figures 5 and 6. The methods used to obtain the pollen was to first locate the Glasford Formation and then excavate it by digging down through recent alluvium to obtain fresh samples.

Figure 5. Todd collecting the soil sample.

Figure 6. Click here for a panoramic view of the sample site, requires QuickTime, 126. kb.

Figure 7. Click here for a panoramic view of the cut bank,, requires QuickTime, 158 kb.

 

The sample was broken up with a mortar and pestil. The sample was then soaked in a Calgon solution to deflocculate the clay particles. The sample was then centrifuged and washed with water three times. The sample was then washed in a zinc chloride solution with a specific gravity of 2.0 to separate organic and mineral matter. The sample was then centrifuged and washed with water three times. Hydroflouric acid was added to the sample to remove any remaining matter. The sample was then centrifuged and washed with water three times. The pollen was left at the bottom and collected and mixed with glycerin jelly and mounted on the slide. This method was described by Kapp's (1969).

Pollen grains were then identified using descriptions and illustrations in Kapp's (1969) publication. The relative pollen frequency is shown in Table 1. The total number of grains looked at was 75, this is a preliminary report and more data is to be collected in the future. Diatoms were also encountered while looking at the pollen grains that were not identified or counted.

Table 1. A list of pollen grains from Fox Ridge and the relative frequency.

COMPARISON OF MODERN AND ANCIENT FLORAS

Table 2 shows comparison of modern and ancient flora. Ebinger (1970) and Barlow's (1976) publications were used for the modern taxa. There are 13 taxa that are common between the ancient and modern flora. Grasses and gymnosperms make up a large portion of the pollen shown due to the fact that they produce massive amounts of pollen or are abundant members of the floral community.

Table 2. List comparing modern members of the fossil pollen assemblages.

 

INTERPRETATION OF FLORA

The floristic diversity of the fossil pollen assemblage is very similar to the present day temperate mixed hardwood forest of the area. This suggests that during the Pleistocene the area was a temperate forest similar to that which exists in the area today. These floristic similarities also suggest that the climate and ecological community in the past were also similar. This preliminary report is consistent with Willman's ideas on biological changes in the Sangamon Interglacial (Willman, 1970).

REFERENCES CITED

Barlow, S. J. and Ebinger, J. E., 1976, Herbaceous Spring Flora of East-Central Illinois; Eastern Illinois University, Charleston, Illinois, pp 143-146.

Ebinger, J. E. and Thut H.F., 1970, Woody Plants of East Central Illinois; Kendall/Hunt Publishing Company Dubuque, Iowa, pp 131-135.

Hardesty, A.F., 1982, The Distribution of the Piatt Till Member of the Wedron Formation in Coles County, Illinois; Department of geology in the Graduate School Southern Illinois University, pp 13.

Jorstad R.B., 1991, Geology of Fox Ridge State Park, Illinois; in Guidebook for the 55th Annual Tri-State Geological Field Conference. Eastern Illinois University Charleston, Illinois, pp 31-33.

Kapp R.O., 1969, How to Know Pollen and Spores; WM. C. Brown Company Publishers Dubuque, Iowa, pp 9-249.

Willman, H.B. and Frye, J.C., 1970, Pleistocene Stratigraphy of Illinois. Illinois State Geologic Survey Urbana, Illinois bulletin 94, pp 28.

 

 

4/22/99