Pitkin Formation

The Pitkin Formation, or Pitkin Limestone, is a fossiliferous geologic formation in northern Arkansas that dates to the Chesterian Series of the late Mississippian. This formation was first named the "Archimedes Limestone" by David Dale Owen in 1858, but was replaced in 1904. The Pitkin conformably overlies the Fayetteville Shale and unconformably underlies the Pennsylvanian-age Hale Formation. Some workers have considered the top of the Pitkin Formation to be a separate formation called the Imo Formation. However more recently, others have considered it as an informal member of the Pitkin Formation.