Stratigraphy of Outcropping Rocks
Pennsylvanian System--Missourian Series
Pedee GroupWeston Shale
The Weston Shale conformably overlies the Stanton Limestone and is overlain disconformably by the Stranger Formation and the Lawrence Shale. Locally the Weston Shale is absent where post-Weston erosion cut deep channels through the shale into the Stanton Limestone, and the younger rocks of the Douglas Group directly overlie the Stanton Limestone. The shale is thickest where the Stranger Formation is thin, and is best exposed in the Vinland and Clearfield areas.
The Weston Shale consists of slightly more than 100 feet of gray-blue and gray marine shale. The lower 50 to 60 feet is a hard medium-gray or bluish laminated and fissile clayey shale containing several zones of dense pinkish-gray clayey-ironstone concretions, which weather yellowish brown or reddish brown. The concretions are elliptical, flattened parallel to the bedding, and 2 to 12 inches in diameter occurring both in layers and as scattered concretions. The upper part of the formation is commonly more bluish than the lower part, is a slightly silty clayey shale, and at least locally has carbonized plant fragments at the bedding planes. The upper part also contains clay-ironstone concretions, but they are generally smaller and less numerous than those in the lower part.
Marine fossils in the formation are sparse, but thin fossiliferous zones contain fragments of bryozoans, crinoids, and brachiopods. Weathered outcrops of the shale are mottled olive and gray, or tan, the color depending on the degree of oxidation of the beds.
Some exposures of the Weston Shale directly underlying the unconformity show evidence of a soil development, as represented by a more massive blocky claystone indicative of the B horizon of a soil enriched with clay, and lacking the fissile shaly texture typical of Weston Shale. A caliche zone is present also in some places.
Kansas Geological Survey, Geohydrology of Douglas County
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Web version Aug. 1999. Original publication date Dec. 1960.