| Stanley Shale | |
| Type: | Formation |
| Age: | Mississippian |
| Prilithology: | Shale |
| Namedfor: | Stanley, Pushmataha County, Oklahoma |
| Namedby: | Joseph A. Taff[1] |
| Region: | Arkansas, Oklahoma |
| Country: | United States |
| Unitof: | none |
| Subunits: | Hatton Tuff Lentil (AR/OK), Hot Springs Sandstone (AR) Member, Chickasaw Creek Shale Formation (OK), Moyers Formation (OK), Tenmile Creek Formation(OK) |
| Underlies: | Jackfork Sandstone |
| Overlies: | Arkansas Novaculite |
| Thickness: | 3,500 to 10,000+ feet[2] |
The Stanley Shale, or Stanley Group, is a Mississippian stratigraphic unit in the Ouachita Mountains of Arkansas and Oklahoma. First described in Arkansas in 1892,[3] this unit was not named until 1902 by J.A. Taff in his study of the Ouachita Mountains of Oklahoma.[1] Taff assigned the town of Stanley in Pushmataha County, Oklahoma as the type locality, but did not designate a stratotype. After introduction into Arkansas in 1909 by Albert Homer Purdue,[4] the unit was redefined in 1918, when the formation known as the Fork Mountain Slate was abandoned and partially combined into the Stanley Shale.[5] As of 2017, a reference section for the Stanley Shale has yet to be designated.
The Stanley Shale is recognized as a geologic formation with two sub-units in Arkansas, the Hatton Tuff Lentil and the Hot Springs Sandstone Member,[2] however, several others have been proposed. These include the Chickasaw Creek Member,[6] Chickasaw Creek Tuff,[7] Gap Ridge Sandstone Member,[8] Moyers Member,[6] Parker Hill Sandstone Member,[8] Polk County Ash Bed,[9] and Tenmile Creek Member.[6] In 1963, it was first proposed to raise the rank of the Stanley Shale Formation to Group status in Arkansas,[10] with proposed sub-units consisting of the Chickasaw Creek Formation, Moyers Formation (with the Gap Ridge Sandstone and Parker Hill Sandstone Members), and Ten Mile Creek Formation.[11] However, the proposal was not accepted and the unit remained as a formation.
In Oklahoma, this unit is recognized as a group called the Stanley Group composed of three formations: the Chickasaw Creek Shale Formation, the Moyers Formation, and the Tenmile Creek Formation. The Hatton Tuff Lentil, recognized in Arkansas, is also in Oklahoma as a unit of the Tenmile Creek Formation. Several informal members have been noted including the Smithville chert lentil, the Faith chert member, and the Chickasaw Creek tuff among others[12]
Mining in the Stanley Shale is limited to cinnabar, barite, and quartz. Cinnabar is primarily used for mercury, however, production in Arkansas essentially ended by the mid-20th century. Barite mining, mostly useful for oil and gas drilling fluid, is ongoing.[13]
A. stanleyanus[14]
A. arkansana[14]
A. coralloides[14]
A. stanleyensis[14]
C. menae[14]
C. miseri[14]
L. subclypeatum[14]
L. peniculus[14]
N. elrodi[14]
P. subgeniculata[14]
R. secalicus[14]
R. goepperti[14]
S. arkansanum[14]
S. dawsoni[14]
T. gillhami[14]
T. vallisjohanni[14]
W. suspecta[14]