Keokuk Limestone

The Keokuk Limestone is named for Keokuk, Lee County, Iowa. At the type locality about 70 feet of Keokuk Limestone overlying the Burlington Limestone is well exposed along Soap Creek and in the Mississippi River bluff near the mouth of the creek. Like the Burlington, the Keokuk is primarily a biocalcarenite. In the type region the lower 30 feet is very cherty and is differentiated as the Montrose Chert Member. The part of the Keokuk above the Montrose is composed of beds of fossiliferous, crinoidal limestone interbedded with fine-grained limestone, argillaceous dolomite, and calcareous gray shale. The limestone is light gray, speckled with darker gray, brown, or black, and contains beds and nodules of chert. It is generally thinner bedded and darker than limestone of the Burlington, and the shale partings are more numerous. In contrast to the crinoidal limestone of the Burlington, the Keokuk shows a great heterogeneity of skeletal remains, with abundant bryozoans, corals and brachiopods.