The Lake Valley Limestone 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 ...

widely exposed in southwestern

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

lower Lower may refer to: * ''Lower'' (album), 2025 album by Benjamin Booker *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is sit ...

to middle Mississippian.

Description

The Lake Valley Limestone consists of gray cherty

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) ...

with thin

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 ...

beds. It overlies the Caballero Formation and is overlain by Pennsylvanian beds. The total thickness is .

Members Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

of the formation, in ascending stratigraphic order, are the Andrecito, Alamogordo, Nunn, Tierra Blanca, Arcente, and Dona Ana Members.

Fossils

The formation contains abundant

crinoid Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...

s as well as

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

s and

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of 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 e ...

s. The Andrecito and Alamogordo Members contain

foraminifer Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of Rhizarian protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

s characteristic of the Kinderhookian (lower Tournasian) while the foraminifers of the Tierra Blanca Member are Osagean (upper Tournasian to lower Visean). The formation is notable for the presence of well-developed bioherms.

History of investigation

The formation was first named by E.D. Cope in 1882 for exposures at

Lake Valley, Sierra County, New Mexico Lake Valley was a silver-mining town in Sierra County, New Mexico, Sierra County, U.S. state of New Mexico. The 'heyday' of the town was from 1881 to 1893. The last resident departed in 1994. The present day ghost town is deserted. Access T ...

. In 1941, Laudon and Bowsher removed the lowermost beds into the Caballero Formation and divided the Lake Valley Limestone into the Alamgordo, Arcente, and Dona Ana Members. In 1949, they added the Andrecito, Nunn, and Tierra Blanca Members.

Economic geology

The formation hosted the rich

silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...

deposits at Lake Valley. These had produced some 5.8 million ounces (180 tonnes) of silver by 1931, but the richest lode was worked out by 1883, and by 1960 the mines had closed. The ore took the form of native silver,

argentite In mineralogy, argentite () is cubic silver sulfide (Ag2S), which can only exist at temperatures above , , or . When it cools to ordinary temperatures it turns into its monoclinic polymorph, acanthite. The International Mineralogical Associatio ...

chlorargyrite Chlorargyrite is the mineral form of silver chloride (AgCl). Chlorargyrite occurs as a secondary mineral phase in the oxidation of silver mineral deposits. It crystallizes in the isometric–hexoctahedral crystal class. Typically massive to column ...

, and

bromargyrite Bromyrite or bromargyrite is a natural mineral form of silver bromide found mainly in Mexico and Chile. Hardness is 1.5 to 2. Related are chlorargyrite and iodyrite. It was first described in 1859 for an occurrence in Plateros, Zacatecas, Mexico ...

, deposited in folds in impervious shale beds overlying intrusions of

monzonite Monzonite is an igneous intrusive rock, formed by slow cooling of underground magma that has a moderate silica content and is enriched in alkali metal oxides. Monzonite is composed mostly of plagioclase and alkali feldspar. Syenodiorite is an ...

porphyry of the Mogollon-Datil volcanic field.

References

{{Reflist Carboniferous formations of New Mexico Carboniferous southern paleotropical deposits Limestone formations of the United States

Description

Fossils

History of investigation

Economic geology

See also

References