The Lytle Formation or Lytle Sandstone is a geologic formation found in

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

, and

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

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 or the Glencairn Formation. The formation is likely an

early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

geologic unit, with its northern exposure running north and south in the Front Range foothills and the Dakota Hogback in northern

and southern

where it is assigned formation rank within the Dakota Group. 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 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, or the Western Interior Sea) was a large inland sea (geology), inland sea that existed roughly over the present-day Great Plains of ...

. 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 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 great-circle distance, straight-line distance from the northernmost part of Western Can ...

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 251.902 Mya. It is the s ...

rock far to the west. Detrital zircon geochronology of the Lytle Formation in the Raton Basin suggests a

late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

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 (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 plant, terrestrial vegetation. ''Petrifaction ...

eroded from the west as well as undistinguished animal burrows, possibly '' Skolithos'' and '' Arenicolites''. Body fossils are extremely rare, but a few

ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...

and

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

fossils are consistent with an

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

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

in age. Waage subsequently traced the unit into northeastern New Mexico and northern Colorado.

References

{{reflist, 30em Cretaceous Colorado Cretaceous formations of New Mexico Sandstone formations of the United States