Lytle Formation
The Lytle Formation/Lytle Sandstone is an Early Cretaceous geologic unit with its northern exposure running north and south within the Front Range foothills and the Dakota Hogback in northern Colorado and southern Wyoming where it is assigned formation rank within the Dakota Group. In south-central Colorado, the Lytle is a member of the Purgatoire Formation.
| Lytle Formation Lytle Sandstone Stratigraphic range: Early Cretaceous | |
|---|---|
 | |
| Type | Formation/Formation Member |
| Unit of | North-central CO:Dakota Group South-central CO:Purgatoire Formation[1] |
| Underlies | South Platte Formation (at Dinosaur Ridge) |
| Overlies | Morrison Formation (unconformably) |
| Lithology | |
| Primary | Sandstone |
| Other | conglomeratic sandstone (notably chert gravel), variegated claystone[1] |
| Location | |
| Region | central Colorado |
| Country | United States |
| Type section | |
| Named for | Lytle, sec 2, T17S, R67W, in valley of Turkey Creek, El Paso County, Colorado[1] |
The Lytle was the last (youngest) non-marine unit to form in the Denver Basin before the region was fully inundated by the Western Interior Seaway. It was formed above sea level from sediments carried by heavily laden rivers flowing from the eroding uplifts of the Sevier orogeny several tens of millions of years before the Rocky Mountains rose. It is particularly noted for abundant brown chert pebbles washed in from the uplifted Permian rock far to the west.[2][1]
Detrital zircon geochronology of the Lytle Formation in the Raton Basin suggests a late Jurassic age for this unit. However, it is possible that the lack of younger zircons reflects a hiatus in deposition of airfall material.[3]
Known fossils are fragments of petrified wood eroded from the west as well as nondescript animal burrows.[1]
References
- "Geologic Unit: Lytle". National Geologic Database. Geolex — Unit References. United States Geological Survey. Retrieved 2019-08-30.
- Jeremy McCreary. "Colorado Geology Photojournals - A Tribute to Colorado's Physical Past and Present - Colorado Geology Overview". cliffshade. Retrieved 2019-08-30.
- Bartnik, Samantha R.; Hampton, Brian A.; Mack, Greg H. (2019). "U-Pb Detrital Geochronology and Provenance Comparisons from the Nonmarine Strata of the Dakota Group, Lytle Sandstone, and Morrison Formation in Northeastern New Mexico" (PDF). New Mexico Geological Society Field Conference Series. 70: 55–65. Retrieved 19 May 2020.