The Helms 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 ...

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

and

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

. It preserves

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 ...

dating back to the Chesterian (

Serpukhovian The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from Ma to Ma. It is preceded by the Visean and is followed b ...

)

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 olde ...

of the Carboniferous

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

Description

At its type section in the

Hueco Mountains The Hueco Mountains are a range of mountains that rise in southern Otero County, New Mexico and extend south into Texas, generally along the El Paso– Hudspeth county line just east of the city of El Paso, Texas. The highest point of the range ...

, the formation consists of of olive-gray shale, shaly sandstone, and dirty limestone. It is

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

underlain by the Rancheria Formation and unconformably overlain by the La Tuna Formation. The formation also crops out in the

Organ Mountains The Organ Mountains (also known as La Sierra de los Órganos) are a rugged mountain range in southern New Mexico in the Southwestern United States. Organ Mountains–Desert Peaks National Monument was declared a national monument on May 21, 201 ...

of New Mexico. The formation is interpreted as having been deposited during a

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

(withdrawal of the sea from the continent) to the south.

Fossils

The formation contains fossils characteristic of the Chesterian (

)

of the Carboniferous

. These include abundant specimens of the

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, typic ...

Graphiadactyllis ''Graphiadactyllis'' is an extinct genus of ostracod (seed shrimp) belonging to the family Quasillitidae and order Podocopida. Specimens have been found in Mississippian to Permian The Permian ( ) is a geologic period and stratigraphic sys ...

arkansana'', as well as specimens of the bryozoan ''

Archimedes Archimedes of Syracuse (;; ) was a Greek mathematician, physicist, engineer, astronomer, and inventor from the ancient city of Syracuse in Sicily. Although few details of his life are known, he is regarded as one of the leading scienti ...

terebriformis'', the

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...

Pentremites ''Pentremites'' is an extinct genus of blastoid echinoderm belonging to the family Pentremitidae. Description These stalked echinoderms averaged a height of about but occasionally ranged up to about 3 times that size. They, like other blastoid ...

'', the

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, ...

s ''

Composita ''Composita'' is an extinct brachiopod genus that lived from the Late Devonian to the Late Permian.

subquadrata'', ''

Spiriferina ''Spiriferina'' is an extinct genus of brachiopods that lived from the Late Silurian to the Middle Jurassic in Asia, Europe, North America, South America, and New Zealand.Diaphragmus ''Diaphragmus'' is an extinct genus of brachiopod belonging to the order Productida and family Linoproductidae. Specimens have been found in Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 ...

elegans'', and several species of '' Dictyoclostus'', and the

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

Paladin The Paladins, also called the Twelve Peers, are twelve legendary knights, the foremost members of Charlemagne's court in the 8th century. They first appear in the medieval (12th century) ''chanson de geste'' cycle of the Matter of France, where ...

helmensis''.

History of investigation

The formation was first designated as the Helms Group by J.W. Beeded in 1920 for outcrops near Helms Well West near the Hueco Mountains. The original definition included the entire set of beds between

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago (Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozoi ...

and

Pennsylvanian Pennsylvanian may refer to: * A person or thing from Pennsylvania * Pennsylvanian (geology) The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the International Commission on Stratigraphy, ICS geologic timesca ...

in age. In 1949, L.R. Laudon and A.L. Bowsher restricted Helms Formation to only the uppermost beds of the original section.

References

Carboniferous formations of New Mexico Carboniferous Texas Carboniferous southern paleotropical deposits {{Carboniferous-stub

Description

Fossils

History of investigation

See also

References