| Sly Gap Formation | |
| Type: | Formation |
| Period: | late Devonian |
| Prilithology: | limestone |
| Otherlithology: | siltstone, shale |
| Namedby: | F.V. Stevenson |
| Year Ts: | 1945 |
| Region: | New Mexico |
| Country: | United States |
| Coordinates: | 33.3322°N -106.4574°W |
| Underlies: | Percha Formation, Contadero Formation |
| Overlies: | Onate Formation |
| Thickness: | 114feet |
The Sly Gap Formation is a geologic formation in south-central New Mexico. It preserves fossils dating back to the Frasnian Age of the late Devonian period.
The formation consists of about 114feet of brown, yellow, or gray limestone and siltstone and brown to greenish-gray shale. It disconformably overlies the Onate Formation and is overlain by the Percha Formation or the Contadero Formation. It pinches out in the west in the Basin and Range province.
The formation includes crinoidal siltstone beds and many other beds are fossiliferous, bearing crinoid, brachiopod, bryozoan, anthozoan, cephalopod, gastropod, fish, and coral remains.