Laborcita Canyon - Flickr - aspidoscelis

The Laborcita 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 the

Sacramento Mountains The Sacramento Mountains are a mountain range in the south-central part of the U.S. state of New Mexico, lying just east of Alamogordo in Otero County (small portions of the range lie in Lincoln County and Chaves County). From north to south, ...

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 ...

. 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

late Pennsylvanian The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the ICS geologic timescale, the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. It lasted from roughly . As with most ot ...

early Permian 01 or '01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * '01 (Richard Müller album), 01'' (Richard Müller album), 2001 * 01 (Son of Dave album), ''01'' (Son of Dave album), 2000 * 01 (Urban ...

.Otté 1959

Description

The formation is composed mostly of marine beds consisting of alternating cycles of

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 ...

and

siliciclastic Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclasic rock types include mudrock, sandstone, and conglomerate Conglomera ...

sedimentary bedsKrainer ''et al.'' 2003 with a thickness of about at the

type section A stratotype or type section in geology is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the stan ...

. It is exposed only in a small area of the northernmost Sacramento Mountains, and transitions to mostly continental red

mudstones Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' ...

some thick before abruptly pinching out to the southeast. The formation lies on the

Holder Formation The Holder Formation is a geologic formation in the Sacramento Mountains of New Mexico. It preserves fossils dating back to the late Pennsylvanian. Description The Holder Formation consists of limestone, red and gray calcareous shale, sandstone, ...

and is overlain by the

Abo Formation The Abo Formation is a geologic formation in New Mexico. It contains fossils characteristic of the Cisuralian epoch of the Permian period. Description The Abo Formation consists of fluvial redbed mudstones and sandstones, including river channel ...

. The formation is interpreted as cyclic sequences of terrestrial and shallow marine

carbonate rocks Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3), and dolomite rock (also known as doloston ...

deposited on a narrow shelf lying between the Pedernal Uplift to the east and the

Orogrande Basin The Orogrande Basin is a geologic province in southern New Mexico and western Texas. It includes Doña Ana, Sierra, Socorro, Lincoln, and Otero Counties in New Mexico and El Paso County, Texas. The province takes its name from the community o ...

to the west. Cycles are generally transgressive (recording the advance of the sea), with basal conglomerate giving way to increasingly fine

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) ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

, and

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 finally

. Corresponding regressive sequences (recording the retreat of the sea) are very poorly developed.

Fossils

The limestone beds of the formation are highly fossiliferous, containing bioclastic remains from all the main late Paleozoic shallow marine biotic groups.

Fusulinid 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 di ...

s are present that are characteristic of the latest Pennsylvanian and earliest Permian. The uppermost beds contain algal

bioherm A reef knoll is a land-based landform that comprises an immense pile of calcareous material that accumulated on a previously existing ancient sea floor. At the time of its accumulation it may have had enough structure from organisms such as sponges ...

s thick.Cross and Klosterman 1981Bowsher 1987 Microfossils of the formation include the

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

such as ''

Girvanella ''Girvanella'' is a fossil thought to represent the calcified sheath of a filamentous cyanobacterium known from the Burgess Shale and other Cambrian fossil deposits. ''Girvanella'' was originally described as a foraminifera. It was later assign ...

'', calcivertellid

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular Ectoplasm (cell biology), ectoplasm for catching food and ot ...

ns, and phylloid (leaflike) algae such as '' Eugonophyllum''.

History of investigation

The formation was first named by Otté in 1959 as part of his dissertation at the

University of New Mexico The University of New Mexico (UNM; es, Universidad de Nuevo México) is a public research university in Albuquerque, New Mexico. Founded in 1889, it is the state's flagship academic institution and the largest by enrollment, with over 25,400 ...

Footnotes

References

* * * * {{cite journal , last1=Otté , first1=C. Jr. , year=1959 , title=Late Pennsylvanian and Early Permian stratigraphy of the northern Sacramento Mountains, Otero County. New Mexico. , journal=New Mexico Bureau of Mines and Mineral Resources Bulletin , volume=5Q , number=1 Permian formations of New Mexico Carboniferous southern paleotropical deposits

Description

Fossils

History of investigation

See also

Footnotes

References