The Bliss 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 ...

that is exposed in southern

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 ...

, west

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 southeastern

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a U.S. state, state in the Southwestern United States. It is the list of U.S. states and territories by area, 6th largest and the list of U.S. states and territories by population, 14 ...

. 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 Cambrian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

early Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. Th ...

periods.

Description

The formation consists of ledge-forming brown to maroon medium- to coarse-grained

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 ...

; thinner beds of very fine-grained

glauconitic Glauconite is an iron potassium phyllosilicate (mica group) mineral of characteristic green color which is very friable and has very low weathering resistance. It crystallizes with a monoclinic geometry. Its name is derived from the Greek () me ...

sandstone; and fine-grained sandstone interbedded with

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 wh ...

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

. A

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** C ...

bed is often present at the base and there are rare beds of oolitic

ironstone Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron ore compound from which iron (Fe) can be smelted commercially. Not to be con ...

. The formation lies

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 ...

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of th ...

basement A basement or cellar is one or more Storey, floors of a building that are completely or partly below the storey, ground floor. It generally is used as a utility space for a building, where such items as the Furnace (house heating), furnace, ...

rock except in the

Florida Mountains The Florida Mountains are a small long, mountain range in New Mexico. The mountains lie in southern Luna County about southeast of Deming, and north of the state of Chihuahua, Mexico; the range lies in the north of the Chihuahuan Desert regi ...

, where it overlies

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...

syenite Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). Some syenites contain larger proport ...

and

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies und ...

. The formation fills paleovalleys in the basement rock, and in some locations (such as the central Franklin Mountains and the west-central Florida Mountains) it is absent. It grades into the overlying

El Paso Formation The El Paso Formation is a geologic formation that is exposed from the Permian Basin of New Mexico and Texas to southeastern Arizona. It preserves fossils dating back to the Ordovician period. Description The formation is composed of gray chert ...

, with the contact placed either at the top of uppermost red or brown sandstone bed of the Bliss Formation or the base of the carbonate cliff characteristic of the El Paso Formation. The formation straddles the Cambrian-Ordovician boundary, with the lower beds containing fossils of

Trempealeauan The Trempealeauan is the upper or latest stage of the Upper or Late Cambrian in North America, spanning about 4 million years from about 492.5 to 488.3 m.y.a., equivalent to the Fengshanian of China. The name comes from the Trempealeau Formation ...

age and the upper beds containing fossils of Skullrockian age. The formation is interpreted as marine sediments deposited on a

passive continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...

during a marine

transgression Transgression may refer to: Legal, religious and social *Sin, a violation of God's Ten Commandments or other elements of God's moral law *Crime, legal transgression, usually created by a violation of social or economic boundary **In civil law ju ...

advancing to the northeast.

Fossils

The formation is locally bioturbated and contains fossils of the

brachiopods 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, wh ...

Obolus The obol ( grc-gre, , ''obolos'', also ὀβελός (''obelós''), ὀβελλός (''obellós''), ὀδελός (''odelós''). "nail, metal spit"; la, obolus) was a form of ancient Greek currency and weight. Currency Obols were u ...

'', ''

Lingulella ''Lingulella'' is a genus of phosphatic-shelled brachiopod. It is known from the Middle Cambrian Burgess Shale (Canada) to the Upper Ordovician Bromide Formation (United States) in North America.Amsden, T.W. Catalogue of Fossils from the Middle ...

'', and ''

Lingulepis Obolidae is a family of extinct brachiopods. Species Obolidae species include:Emig C. C., Bitner M. A. & Álvarez F., 2019Linguliformea Brachiopoda database. Accessed 2020-09-27. *''Obolus apollinis The obol ( grc-gre, , ''obolos'', also ...

acuminata''. However, the formation has few macroscopic fossils useful for

biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of Bio ...

. The best dated section is in the Flordillo Canyon in the central

Caballo Mountains The Caballo Mountains, ( Spanish: "horse") are a mountain range located in Sierra Sierra (Spanish for "mountain range" and "saw", from Latin '' serra'') may refer to the following: Places Mountains and mountain ranges * Sierra de Juárez, a m ...

, which contains

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 ...

and

conodont Conodonts ( Greek ''kōnos'', " cone", + ''odont'', " tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, w ...

fossils that have helped determine its age. The lower beds are very scarce in fossils and difficult to date across the exposure area.

History of investigation

The formation was first named by G.B. Richardson in 1904 for exposures in the Franklin Mountains.

Footnotes

References

* * * * {{cite encyclopedia , last1=Taylor , first1=John F. , last2=Repetski , first2=John E. , year=1995 , title=High-Resolution trilobite and conodont biostratigraphy across the Cambrian-Ordovician boundary in south-central New Mexico , encyclopedia=Ordovician Odyssey: Seventh International Symposium on the Ordovician System , publisher=Pacific Section, Society for Sedimentary Geology , volume=77 , pages=133–136 , editor1-last=Cooper , editor1-first=J.D. , editor2-last=Droser , editor2-first=M.L. , editor3-last=Finney , editor3-first=S.C. Ordovician formations of New Mexico Ordovician geology of Texas Ordovician southern paleotropical deposits