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 of

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 ...

. 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

late Pennsylvanian The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, on the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period (or the upper of two subsystems of the Carboniferous System). It laste ...

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 (Urban Zakapa album), ''01'' (Urban Zakapa album), 2011 * ''01011 ...

.Otté 1959

Description

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

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

and

siliciclastic Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclastic rock types include mudrock, sandstone Sandstone is a Clastic ...

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

type section In geology, a stratotype or type section 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 ...

. 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.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York ...

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), dolomite rock (also kn ...

deposited on a narrow shelf lying between the Pedernal Uplift to the east and the Orogrande Basin to the west. Cycles are generally

transgressive Transgressive may mean: *Transgressive art, a name given to art forms that violate perceived boundaries *Transgressive fiction, a modern style in literature *Transgressive Records, a United Kingdom-based independent record label *Transgressive (l ...

(recording the advance of the sea), with basal conglomerate giving way to increasingly fine

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 ...

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. Although its permeabil ...

, and

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 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 d ...

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

bioherm A reef knoll is a landform that comprises an immense pile of calcareous material that had previously accumulated on an ancient sea floor. Reef knolls are geological remnants of reefs and other organic concentrations of calcareous organisms. Reef kn ...

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

cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

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. Specimens are also known from the Early Ordovician San Juan Formation, Argentin ...

'', calcivertellid

foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...

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; ) is a public research university in Albuquerque, New Mexico, United States. Founded in 1889 by the New Mexico Territorial Legislature, it is the state's second oldest university, a flagship university in th ...

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 Limestone formations of the United States Sandstone formations of the United States Shale formations of the United States Conglomerate formations of the United States

Description

Fossils

History of investigation

See also

Footnotes

References