Historical:Grove Church Shale
Elwood Atherton, Charles Collinson, and Jerry A. Lineback
The Grove Church Shale (Swann, 1963, p. 44-45), the uppermost formation in the Chesterian Series in Illinois, is named for Cedar Grove Church, Johnson County.
The type section for the Grove Church is in a roadcut and near-by gullies, 1.25 miles east of Lick Creek (W line NE NW 31, 11S-2E), where the formation is 16 feet thick.
Extent and Thickness
The formation has been largely eroded from Illinois by pre-Pennsylvanian erosion, and it occurs only in patches in Johnson, Pope, and Saline Counties, and probably in parts of adjacent counties. The maximum known thickness is 67 feet in the northern half of Johnson County.
The Grove Church is a gray, fossiliferous shale and includes interbedded fossiliferous limestone. It was originally part of the Kinkaid Formation, but it was split off because it is dominantly shale. As a result, the Kinkaid is a dominantly limestone formation.
It has a distinctive fauna; some species have affinities to Pennsylvanian fossils, particularly the fusuline Millerella and some ostracodes (Cooper, 1947). The conodont fauna differs strikingly from that of the Kinkaid (Rexroad and Burton, 1961). The genus Streptognathodus comprises over one-third of the fauna of the Grove Church and there is a marked decrease in Cavusgnathus. Transitional forms show that the change is evolutional, rather than being a migratory influx.
COOPER, C. L., 1947, Upper Kinkaid (Mississippian) microfauna from Johnson County, Illinois: Journal of Paleontology, v. 21, p. 81-94; Illinois State Geological Survey Report of Investigations 122.
REXROAD, C. B., and R. C. BURTON, 1961, Conodonts from the Kinkaid Formation (Chester) in Illinois: Journal of Paleontology, v. 35, p. 1143-1158; Illinois State Geological Survey Reprint 1962-B.
SWANN, D. H., 1963, Classification of Genevievian and Chesterian (Late Mississippian) rocks of Illinois: Illinois State Geological Survey Report of Investigations 216, 91 p.
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