Figure 20--Diagrammatic cross section on the east side of the Forest City basin showing relation of surface anticlines to folds in older rocks with strong regional dips. A, Mississippian rocks were deposited upon a peneplaned surface of northwestward dipping rocks. B, Post-Mississippian erosion on a low post-Mississippian fold followed by deposition of early Pennsylvanian rocks. Note structural closure in beds at base of Mississippian but lack of closure in underlying tilted formations. C, Increased folding during deposition of early Pennsylvanian rocks. Note lack of structural closure in the St. Peter sandstone. D, Further increase of folding during deposition of Pennsylvanian produces a limited area of closure in pre-Mississippian rocks. E, A regional northwestward tilting of the entire section in post-Permian time. Low folds in upper Pennsylvanian rocks are reduced to structural noses or terraces; closure of stronger folds in lower Pennsylvanian and Mississippian rocks is reduced in areal extent and closure in pre-Mississippian rocks is lost.
Kansas Geological Survey, Forest City Basin
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Web version July 2005. Original publication date Dec. 1943.