| Blakely Sandstone | |
| Type: | Formation |
| Age: | Ordovician |
| Prilithology: | Sandstone |
| Namedfor: | Blakely Mountain, Garland County, Arkansas |
| Namedby: | Albert Homer Purdue[1] |
| Region: | Arkansas, Oklahoma |
| Country: | United States |
| Unitof: | none |
| Subunits: | none |
| Underlies: | Womble Shale |
| Overlies: | Mazarn Shale |
| Thickness: | up to 700 feet[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.[1] 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.
C. horridus[6]
H. holodentata[6]
L. quadratus[6]
P. costatus[6]
P. aculeatus[6]
D. euodes[7]
D. manus[7]
D. spinosus[7]
G. echinatus[7]
G. horridus[7]