Chert nodules in limestone (Columbus Limestone, Middle Devonian; Ohio Caverns, western Ohio, USA) 14
Ohio Caverns is the largest cave system in Ohio. It is located in a bedrock knob called Mt. Tabor on the southern side of the Bellefontaine Outlier (= Ohio's elevationally highest area). The cave is hosted in the Middle Devonian Columbus Limestone, which is part of a widespread shallow marine carbonate succession in eastern and midwestern America.
In the above photo, the nodules projecting from the limestone wall are chert, a cryptocrystalline quartzose sedimentary rock. These chert nodules are diagenetic chert masses, formed by dissolution and remobilization of silica after burial. Visible marine fossils such as rugose corals and brachiopods are present in some of these nodules (= chertified limestone).
The various colors are due to iron oxide staining. The lighter-colored material at left and upper left is travertine speleothem (microgours).
Locality: Ohio Caverns, Mt. Tabor, east of the town of West Liberty, northern margin of Champaign County, western Ohio, USA
For a recent technical article on the geology of Ohio Caverns, see: