| Pitkin Formation | |
|---|---|
| Stratigraphic range: Upper Visean-Serpukhovian[1] | |
| Type | Formation |
| Sub-units | Imo Shale |
| Underlies | Hale Formation |
| Overlies | Fayetteville Formation |
| Thickness | up to and over 400 feet[2] |
| Lithology | |
| Primary | Limestone[1] |
| Other | Shale |
| Location | |
| Region | Arkansas |
| Country | United States |
| Type section | |
| Named for | Pitkin post office, Washington County, Arkansas[3] |
| 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.[4] This formation was first named the "Archimedes Limestone" by David Dale Owen in 1858, but was replaced in 1904.[3] 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.