The Bar B 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 ...

found the

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 ...

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 ...

. 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 ...

showing it was deposited in the

middle Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek (d ...

to late Pennsylvanian.

Description

The Bar B formation is mostly cyclic beds of

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, especia ...

and

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 ...

, with shale making up about 80% of the formation and limestone the other 20%.

Chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...

is present in some of the limestone. The upper include reddish-brown

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, ...

, limestone conglomerate, and

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an a ...

siltstone. The total thickness is about . The formation rests on the

Nakaye Formation The Gray Mesa Formation is a geologic formation in New Mexico. Its fossil assemblage dates the formation to the Moscovian age of the Pennsylvanian. The formation as presently defined includes outcrops previously assigned to many local units, inc ...

and is unconformably overlain by the

Bursum Formation The Bursum Formation is a geologic formation in New Mexico. The formation likely correlates with the

Panther Seep Formation The Panther Seep Formation is a geologic formation found in the mountain ranges of south-central New Mexico. It preserves fossils dating back to the late Pennsylvanian to early Permian. Description The formation is highly variable in lithology, ...

in the

San Andres Mountains The San Andres Mountains are a mountain range in the southwestern U.S. state of New Mexico, in the counties of Socorro, Sierra, and Doña Ana. The range extends about 75 miles (120 km) north to south, but are only about 12 miles (19 ...

Fossils

The formation contains abundant bryozoan fossils.

History of investigation

The formation was first defined by V.C.Kelley and

Caswell Silver Caswell Silver (June 25, 1916 – October 18, 1988) was an American geologist and entrepreneur who was President of Sundance Oil Company from 1960 to 1984. In addition to the business of oil and gas exploration, he was active in the American Ass ...

in 1952. Bachman and Myers criticized its definition in 1975, but it is accepted by Kues and Giles, though they restrict it to the Caballo Mountains.

References

{{Reflist Carboniferous formations of New Mexico Carboniferous southern paleotropical deposits

Description

Fossils

History of investigation

See also

References