The Pajarito Formation 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 ...

in eastern New Mexico and west Texas. It preserves

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s dating back to the Albian

Age Age or AGE may refer to: Time and its effects * Age, the amount of time someone or something has been alive or has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

Period.

Description

Quay County, New Mexico Quay County () is a county in the state of New Mexico. As of the 2010 census, the population was 9,041. Its county seat is Tucumcari. The county was named for Pennsylvania senator Matthew Quay, who supported statehood for New Mexico. Its easter ...

, where the unit was first described, it consists of poorly cemented brown

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

and gray

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

and is thick. It overlies the Mesa Rica Formation and underlies the

Graneros Shale The Graneros Shale is a geologic formation in the United States identified in the Great Plains as well as New Mexico that dates to the Cenomanian Age of the Cretaceous Period. It is defined as the finely sandy argillaceous or clayey ''near-shore/ ...

, and is assigned to the Purgatoire Group. Further north, in the valley of the Dry Cimarron, the formation consists of medium gray shale and is thick. The formation was deposited in a shallow marine. or

delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D (NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also re ...

plain environment. This marked the onset of the Greenhorn marine cycle in northeastern New Mexico.

Fossils

The formation contains abundant fossil remains of the oyster '' Ostrea quadriplicata'', a fossil of

early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

age. Dinosaur trackways are preserved in the sandstone and silty sandstone horizons of the formation, which is part of the "dinosaur freeway" megatracksite of New Mexico, Colorado, and Oklahoma. Dinosaur tracks were discovered in the Pajarito Formation and underlying Mesa Rica Formation at the spillway of

Clayton Lake State Park Clayton Lake State Park is a state park of New Mexico, United States, featuring a recreational reservoir and a fossil trackway of dinosaur footprints. It is located north of Clayton, New Mexico, Clayton, close to New Mexico's border with Colora ...

in 1982. The Clayton Lake trackways are unusual in showing trail dragging traces. The trackways here are accessible by a trail with interpretive signage but are rapidly eroding in the lake spillway. Most of the tracks have been identified as ''

Caririchnium ''Caririchnium'' is an ichnogenus of ornithopod dinosaur footprint, belonging to either derived iguanodonts or basal hadrosauroids. It includes the species ''Caririchnium lotus'' from Lower Cretaceous Jiaguan Formation and ''C''. ''protohadrosau ...

leonardii''.

History of investigation

The formation was first named as the Pajarito shale member of the

Purgatoire Formation The Purgatoire Formation is an abandoned (1987) Cretaceous period geologic formation classification. The classification was used in Colorado, New Mexico, and Oklahoma, with mentions in older geologic literature in neighboring states.Griggs and Re ...

by Drobovolny ''et al.'' in 1947. They designated neither a type location nor an origin for the name, though it was originally mapped in Quay County, New Mexico. It was raised to formation rank by Griggs and Read in 1959, who also abandoned the use of the Purgatoire Formation in northeastern New Mexico. Kues and Lucas identified the formation in the valley of the Dry Cimarron in 1987 and concluded it was late Albian in age.

References

Bibliography

* * * * * * * {{cite journal , last1=Ziegler , first1=Kate E. , last2=Ramos , first2=Frank C. , last3=Zimmerer , first3=Matthew J. , title=Geology of Northeastern New Mexico, union and Colfax Counties, New Mexico: A Geologic Summary , journal=New Mexico Geological Society Field Conference Series , date=2019 , volume=70 , issue=4 , pages=47–54 , url=https://nmgs.nmt.edu/publications/guidebooks/downloads/70/70_p0047_p0054.pdf , accessdate=1 September 2020 Geologic formations of the United States Lower Cretaceous Series of North America Cretaceous Colorado Cretaceous formations of New Mexico Albian Stage Ichnofossiliferous formations

Description

Fossils

History of investigation

See also

References

Bibliography