The Menefee Formation is an upper

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya ( million years ago) and 83.6 ± 0.7 m ...

to lower

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

geologic

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

found in

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 ...

, United States.

Description

The Menefee Formation consists of

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

, and

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

. Based on

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...

, the age of the Menefee Formation can be constrained to 84.2-79 million years ( Ma), based on the presence of '' Baculites perplexus'' in the overlying

Cliff House Sandstone The Cliff House Sandstone is a late Campanian stratigraphic unit comprising sandstones in the western United States. Description The Cliff House Sandstone consists of fine grained white to orange calcareous sandstone. It intertongues with the ...

, and ammonites from the late

in the underlying

Point Lookout Sandstone The Point Lookout Sandstone is a Cretaceous bedrock formation occurring in New Mexico and Colorado. Description The formation consists of two informal members. The lower is a sequence of thinly bedded sandstone and shale, while the upper is a ...

. Named members include a lower Cleary Coal Member and an upper Allison Member. The

Mesaverde Group History The Mesaverde Formation was first described by W.H.Holmes in 1877 during the Hayden Survey. Holmes described the formation in the northern San Juan Basin as consisting of three units, which were a "Lower Escarpment" consisting of 40 m ...

in the

San Juan Basin The San Juan Basin is a geologic structural basin located near the Four Corners region of the Southwestern United States. The basin covers 7,500 square miles and resides in northwestern New Mexico, southwestern Colorado, and parts of Utah a ...

records a

marine regression A marine regression is a geological process occurring when areas of submerged seafloor are exposed during a drop in sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously-exposed land. Descript ...

- transgression sequence of the western margin of 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 ...

. The Menefee Formation was deposited at the peak of the regression as coastal

river delta A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creat ...

and swamp sediments, and includes numerous coal beds. The formation is exposed at Chaco Canyon National Park, where many of the coal beds have been burned to produce distinctive red cinder outcrops. San Juan Basin Upper Cretaceous stratigraphy PeerJ e5435 fig 1

San Juan Basin Upper Cretaceous stratigraphy PeerJ e5435 fig 1

Fossils

The Menefee Formation includes

fossils 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 ...

of turtles, fish and crocodiles and fragmentary evidence of

hadrosaurs Hadrosaurids (), also hadrosaurs or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod fami ...

ankylosaurs Ankylosauria is a group of herbivorous dinosaurs of the clade Ornithischia. It includes the great majority of dinosaurs with Armour (zoology), armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short ...

, and

ceratopsian Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Asia and Europe, during the Cretaceous Period, although ancestral forms lived earlier, in the Late Ju ...

dinosaurs. Plant fossils include leaf impressions of palms, conifers, laurels, witchhazel, and camellia. The flora are suggestive of a moist subtropical environment.

Vertebrate fauna

Several vertebrates have been recovered from the Menefee Formation, including intermediate remains of baenids, trionychids, and

dromaeosaurids Dromaeosauridae () is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Gree ...

Economic geology

The Menefee Formation has been extensively mined for coal since the early 20th century. The Monero field in

Rio Arriba County, New Mexico Rio Arriba County () is a List of counties in New Mexico, county in the U.S. state of New Mexico. As of the 2020 United States census, 2020 census, the population was 40,363. Its county seat is Tierra Amarilla, New Mexico, Tierra Amarilla. Its ...

, was mined from the 1880s into the early 1920s to support the

Denver and Rio Grande Western Railroad The Denver and Rio Grande Western Railroad , often shortened to ''Rio Grande'', D&RG or D&RGW, formerly the Denver & Rio Grande Railroad, was an American Class I railroad company. The railroad started as a narrow-gauge line running south fr ...

, but while the coal is of good quality, the coal beds are relatively thin and the terrain is rugged. Remaining reserves are around 13.5 million tons, inadequate for economic exploitation in the 21st century.

History of investigation

The Menefee Formation was first described by W.H.Holmes in 1877 during the

Hayden Survey Ferdinand Vandeveer Hayden (September 7, 1829 – December 22, 1887) was an American geologist noted for his pioneering surveying expeditions of the Rocky Mountains in the late 19th century. He was also a physician who served with the Union A ...

as the "Middle Coal Group" of the Mesaverde Formation. A.J. Collier redesignated this unit in 1919 as the Menefee Formation and raised the Mesaverde Formation to group rank.

References

Bibliography

* * * * * * * * * * * * * * * {{Chronostratigraphy of Colorado, Mesozoic state=expanded Geologic formations of the United States Cretaceous formations of New Mexico Campanian Stage Sandstone formations of the United States Shale formations of the United States Coal formations