Pitkin Formation
| Pitkin Formation | |
|---|---|
| Stratigraphic range: Upper Visean-Serpukhovian | |
| Type | Formation |
| Sub-units | Imo Shale |
| Underlies | Hale Formation |
| Overlies | Fayetteville Formation |
| Thickness | up to and over 400 feet |
| Lithology | |
| Primary | Limestone |
| Other | Shale |
| Location | |
| Region | Arkansas |
| Country | United States |
| Type section | |
| Named for | Pitkin post office, Washington County, Arkansas |
| Named by | George Irving Adams and Edward Oscar Ulrich |
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 shales at the top of the Pitkin Formation to be a separate formation called the Imo Formation. More recently, others have considered the Imo to be informal member of the Pitkin Formation.