| Joachim Dolomite | |
| Type: | Formation |
| Age: | Ordovician |
| Period: | Ordovician |
| Prilithology: | dolomite |
| Namedfor: | Joachim Creek, Jefferson County, Missouri |
| Namedby: | Arthur Winslow[1] |
| Region: | Arkansas, Illinois, Missouri |
| Country: | United States |
| Unitof: | Ancell Group |
| Underlies: | Pecatonica Formation and Plattin Limestone |
| Overlies: | St. Peter Sandstone |
| Thickness: | 0 to 100+ feet in Arkansas[2] |
The Joachim Dolomite is a Middle Ordovician geologic formation in Arkansas, Illinois, and Missouri.[2] The name was first introduced in 1894 by Arthur Winslow in his study of the geology of Missouri.[1] Winslow designated a stratotype along Plattin Creek, which was misidentified as Joachim Creek, in Jefferson County.[3] The name was introduced into Arkansas in 1911, replacing part of the, now abandoned, Izard Limestone.[4]