| Blakely Sandstone | |
|---|---|
| Stratigraphic range: Ordovician | |
 Blakely Sandstone (Coleman Quartz Mine, Arkansas) | |
| Type | Formation |
| Unit of | none |
| Sub-units | none |
| Underlies | Womble Shale |
| Overlies | Mazarn Shale |
| Thickness | up to 700 feet [1] |
| Lithology | |
| Primary | Sandstone |
| Location | |
| Region | Arkansas, Oklahoma |
| Country | United States |
| Type section | |
| Named for | Blakely Mountain, Garland County, Arkansas |
| Named by | Albert Homer Purdue [2] |
The Blakely Sandstone is a Middle Ordovician geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. First described in 1892, [3] this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas. Purdue had initially named this unit the Caddo Shale at a 1907 Geological Society of America meeting, [4] but later redefined and renamed the unit as the Ouachita Shale. [5] He again renamed the unit to the Blakely Sandstone in a letter to Edward Oscar Ulrich, to which Ulrich used in a 1911 publication, becoming the first reference using this name. [2] Ulrich assigned the Blakely Mountain in Garland County, Arkansas as the type locality, but did not designate a stratotype. As of 2017, a reference section for this unit has yet to be designated.
