The Lytle Formation or Lytle Sandstone is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

found in

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the s ...

Colorado Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

, and

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ke ...

Description

The Lytle Formation consists of white to light gray gravels and conglomerates. It is variable in thickness but is about at the type location. It is separated from the underlying Morrison Formation by a significant regional unconformity. It is overlain by the

South Platte Formation The South Platte Formation is a Mesozoic geologic formation found in the U.S. state of Colorado. Fossil ankylosaur tracks have been reported from the formation.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607. See also * List o ...

or the Glencairn Formation. The formation is likely an early Cretaceous geologic unit, with its northern exposure running north and south within the Front Range foothills and the

Dakota Hogback : North terminus: : South terminus: The Dakota Hogback is a long hogback ridge at the eastern fringe of the Rocky Mountains that extends north-south from southern Wyoming through Colorado and into northern New Mexico in the United St ...

in northern

and southern

where it is assigned formation rank within the

Dakota Group The Dakota is a sedimentary geologic unit name of formation and group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and shales deposited in the Mid-Cretaceous opening of the Western ...

. In south-central Colorado, the Lytle is an unassigned formation. The formation is also mapped in the valley of the Dry Cimarron in northeastern

, where it forms a prominent band in the lower parts of the cliffs. The Lytle was the last (youngest) non-marine unit to form in the

Denver Basin The Denver Basin, variously referred to as the Julesburg Basin, Denver-Julesburg Basin (after Julesburg, Colorado), or the D-J Basin, is a geologic structural basin centered in eastern Colorado in the United States, but extending into southeast W ...

before the region was fully inundated by the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea ...

. It was formed above sea level from sediments carried by heavily laden rivers flowing from the eroding uplifts of the

Sevier orogeny The Sevier orogeny was a mountain-building event that affected western North America from northern Canada to the north to Mexico to the south. The Sevier orogeny was the result of convergent boundary tectonic activity, and deformation occurred f ...

several tens of millions of years before the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico ...

rose. It is particularly noted for abundant brown chert pebbles washed in from the uplifted

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...

rock far to the west.

Detrital zircon geochronology Detrital zircon geochronology is the science of analyzing the age of zircons deposited within a specific sedimentary unit by examining their inherent radioisotopes, most commonly the uranium–lead ratio. Zircon is a common accessory or trace ...

of the Lytle Formation in the

Raton Basin Raton or Ratón (Spanish for "mouse") may refer to: Places: * Raton Basin, a geologic structural basin in southern Colorado and northern New Mexico * Raton, New Mexico, the county seat of Colfax County, New Mexico ** Raton Downtown Historic ...

suggests a

late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

age for this unit. However, it is possible that the lack of younger zircons reflects a hiatus in deposition of airfall material.

Fossils

Known fossils are fragments of

petrified wood Petrified wood, also known as petrified tree (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of '' fossilized wood'', the fossilized remains of terrestrial vegetation. ' ...

eroded from the west as well as nondescript animal burrows, possibly ''

Skolithos ''Skolithos'' (formerly spelled ''Scolithus'' or ''Skolithus'') is a common trace fossil ichnogenus that is, or was originally, an approximately vertical cylindrical burrow. It is produced by a variety of organisms in shallow marine environmen ...

'' and '' Arenicolites''. Body fossils are extremely rare, but a few

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typi ...

and bivalve fossils are consistent with an Aptian to

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

age for the formation.

History of investigation

The formation was first named as the Lytle sandstone member of the Purgatoire Formation by G.I. Finlay in 1916, for exposures near Lytle, Colorado. Finlay found no fossils in the unit, but regarded it as likely early Cretaceous in age. Waage subsequently traced the unit into northeastern New Mexico and northern Colorado.

References

{{reflist, 30em Cretaceous Colorado Cretaceous formations of New Mexico