Elwood Atherton, Charles Collinson, and Jerry A. Lineback
The Joppa Member of the Ste. Genevieve Limestone (Swann, 1963, p. 29, 71), the uppermost member, is named for Joppa Junction, Johnson County.
The type section of the Joppa Member of the Ste. Genevieve Limestone is located about a half a mile east of Joppa Junction, Johnson County (SW SW 32, 13S-2E), where the member comprises 32 feet of shale and limestone overlying the Karnak Limestone Member.
Extent and Thickness
The Joppa is 20-50 feet thick.
In southeastern Illinois the Joppa generally includes prominent limestones that allow it to be readily separated from the Aux Vases Sandstone. However, in most of the western and northern parts of the basin it is impractical to separate the Joppa from the Aux Vases, and there the Joppa is terminated by a vertical cut-off. Most of the limestone is sandy and oolitic, and part of it is red and hematitic. The sandstone is generally very fine grained and calcareous, resembling that of the Aux Vases. The shale is largely dark greenish gray, but red and green shales are common.
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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