| Glencairn Formation | |
| Type: | Formation |
| Period: | Albian |
| Prilithology: | Shale |
| Otherlithology: | Sandstone |
| Namedfor: | Small tract of land north of Lytle, Colorado (sec 2, T17S, R68W) |
| Namedby: | G.I. Finlay |
| Year Ts: | 1916 |
| Region: | Colorado New Mexico |
| Country: | United States |
| Coordinates: | 38.517°N -104.972°W |
| Unitof: | Purgatoire Group |
| Underlies: | Dakota Group |
| Overlies: | Lytle Formation |
| Thickness: | NaNfeet |
The Glencairn Formation is a geologic formation found in Colorado[1] and New Mexico.[2] It preserves fossils characteristic of the Albian Age of the Cretaceous Period.[3]
The Glencairn Formation consists of dark gray shale and buff sandstone and siltstone. It disconformably overlies the Lytle Formation, underlies the Dakota Group, and varies in thickness from NaNfeet.[1] [3] The formation is present from central Colorado[1] to the valley of the Dry Cimarron in northeastern New Mexico.[3] The formation locally contains gypsum veins and gypsum-filled desiccation cracks.[1]
The exposures at the valley of the Dry Cimarron include a basal sandstone bed, the Long Canyon Sandstone Bed, that is up to 3meters thick, is heavily bioturbated, and contains an abundant late Albian invertebrate fossil fauna.[3] This is interpreted as infilling of a drainage system preceding the Kiowa-Skull Creek transgression.[4] It is likely the lateral equivalent of the Tucumcari Shale.[5]
The lower beds of the formation are heavily bioturbated and contain abundant fossils of the gryphaeid oyster Texigryphea.[6] The upper beds locally contain petrified plant material.[3] The formation also contains ammonoids, including Goodhallites, Idiohamites, and Engonoceras uddeni, and associated solitary corals, bivalves, and gastropods[7]
The formation was first named as the Glencairn shale member of the now abandoned Purgatoire Formation by G.I. Finlay in 1916, for exposures near Lytle, Colorado.[1] Waage subsequently traced the unit into northeastern New Mexico,[2] where it has been raised to formation rank.[8] [3]