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 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 ...

, west

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

, and southeastern

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

. 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 The Furongian is the fourth and final Epoch (geology), epoch and Series (stratigraphy), series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocia ...

early Ordovician The Early Ordovician is the first epoch (geology), epoch of the Ordovician period, corresponding to the Lower Ordovician series (stratigraphy), series of the Ordovician system. It began after the Cambrian Stage 10, Age 10 of the Furongian epoch o ...

periods.

Description

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

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 ...

; 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 () m ...

sandstone; and fine-grained sandstone interbedded with

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) ...

or dolomite. A conglomerate 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 c ...

. 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 pC, 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 t ...

basement A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...

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, New Mexico, Luna County about southeast of Deming, New Mexico, Deming, and north of the Chihuahua (state), state of Chihuahua, M ...

, where it overlies

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

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%). It is considered a granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, 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 coo ...

. 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 cher ...

, 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 age and the upper beds containing fossils of

Skullrockian Stage 10 of the Cambrian is the still unnamed third and final stage of the Furongian series. It follows the Jiangshanian and precedes the Ordovician Tremadocian Stage. The proposed lower boundary is the first appearance of the trilobite ''Lotagnost ...

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 margi ...

during a marine transgression advancing to the northeast.

Fossils

The formation is locally bioturbated and contains fossils of the

brachiopods Brachiopods (), 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 end, while the fron ...

Obolus The obol (, ''obolos'', also ὀβελός (''obelós''), ὀβελλός (''obellós''), ὀδελός (''odelós''). "nail, metal spit"; ) was a form of ancient Greek currency and weight. Currency Obols were used from early times. ...

'', ''

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 a ...

'', and '' Lingulepis 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 Biology ...

. 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 and Doña Ana Counties, New Mexico, United States. The range is located east of the Rio Grande and Caballo Lake, and west of the Jornada del Muerto; the south of ...

, which contains

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

and

conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...

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