The Cutoff 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 , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

, US. 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 in ...

dating back to the

Permian The Permian ( ) is a geologic period and 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 period of the Paleoz ...

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

The Cutoff Formation consists of feet of thin

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

beds interbedded with dark

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

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) ...

. It grades northwards into the San Andres Formation and is likely

correlative In grammar, a correlative is a word that is paired with another word with which it functions to perform a single function but from which it is separated in the sentence. In English, examples of correlative pairs are ''both–and, either–or, nei ...

with the upper part of the Bone Spring Formation within the

Delaware Basin The Delaware Basin is a geologic depositional and structural basin in West Texas and southern New Mexico, famous for holding large oil fields and for a fossilized reef exposed at the surface. Guadalupe Mountains National Park and Carlsbad Cavern ...

. In age, the formation straddles the

Cisuralian The Cisuralian is the first Series (stratigraphy), series/Epoch (geology), epoch of the Permian. The Cisuralian was preceded by the Pennsylvanian (geology), Pennsylvanian and followed by the Guadalupian. The Cisuralian Epoch is named after the w ...

Guadalupian The Guadalupian is the second and middle series/epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± 0. ...

boundary. It lies atop the

Victorio Peak Victorio Peak is a high rocky outcropping in the Hembrillo Basin in southern New Mexico. This was one of Chief Victorio's hideouts, and was the site of a battle in 1880 between Victorio's Apaches and the U.S. Army Ninth Cavalry "Buffalo Sold ...

or Bone Spring Formation and is overlain by the Brushy Canyon Formation or

Cherry Canyon Formation The Cherry Canyon Formation is a geologic formation found in the Delaware Basin of southeastern New Mexico and western Texas. It contains fossils characteristic of the Guadalupian Age of the Permian Period.Kues and Giles 2004, p.100 Description ...

. Both these formations fill paleocanyons cut deeply in the Cutoff Formation, in some cases cutting clear through to the underlying Bone Springs or Victorio Peak beds. The formation is interpreted as a deep basin formation deposited on a drowned shelf to basin topography. It contains numerous

turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites were ...

sequences.

Fossils

Limestone beds of the formation contain chonetid brachiopods (''

Chonetes ''Chonetes'' is an extinct genus of brachiopods. It ranged from the Late Ordovician to the Middle Jurassic. Species The following species of ''Chonetes'' have been described: * ''C. (Paeckelmannia)'' * ''C. baragwanathi'' * ''C. billingsi' ...

'') and

gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. Ther ...

. The formation includes a few massive limestone beds that contain a diverse assemblage of fossils, including

fusulinids The Fusulinida is an extinct order within the Foraminifera in which the tests are traditionally considered to have been composed of microgranular calcite. Like all forams, they were single-celled organisms. In advanced forms the test wall was dif ...

corals Corals are marine invertebrates within the class (biology), class Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important C ...

, and

crinoids Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which are ...

. Other fossils include the shark ''

Helicoprion ''Helicoprion'' is an extinct genus of shark-like eugeneodont fish. Almost all fossil specimens are of spirally arranged clusters of the individuals' teeth, called "tooth whorls", which in life were embedded in the lower jaw. As with most extin ...

'', the

ammonoids Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

Pseudogastrioceras Pseudogastrioceratinae is one of two subfamilies of the Paragastrioceratidae family. They are an extinct group of ammonoid, which are shelled cephalopods related to squids, belemnites, octopuses, and cuttlefish, and more distantly to the ...

'' and '' Perrinites hilli'', the natiloid '' Foordiceras'', and the fusulinid ''

Parafusulina ''Parafusulina'' is a genus of foraminifera included in the fusulinacean family Schwagerinidae that were extant during the Permian. The shell, or test, of ''Parafusulina'' is elongate, up to 65 mm in length, fusiform to subcylindrical in sh ...

''.

History of investigation

The unit was first designated as the Cutoff shaly member of the Bone Spring Limestone by P.B. King in 1942, for exposures on the west face of Cutoff Mountain near the

border.

References

Permian geology of Texas Permian formations of New Mexico {{Permian-stub

Description

Fossils

History of investigation

See also

References