The Onate Formation is a geologic formation that is exposed in most of the highlands of south-central New Mexico. 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 in ...

dating back to the middle Devonian period.

Description

At the type section, the Onate Formation consists of about of orange yellow-weathering dolomitic

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, p ...

with

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, especial ...

s and sandstone. Elsewhere the thickness is more typically . The base of the formation is a profound regional unconformity, so that the formation rest on either the

Fusselman Formation The Fusselman Formation is a geologic formation in westernmost Texas and southern New Mexico. It preserves fossils dating back to the early Silurian period. Description The formation consists mostly of medium to dark gray massive dolomite. ...

or the

Montoya Group The Montoya Group is a group of geologic formations in westernmost Texas and southern New Mexico. It preserves fossils dating back to the late Ordovician period.Richardson 2008Pope 2004 Description The group consists mostly of dolomitePray ...

. It is overlain by the Sly Gap Formation and thins to the north and south. The formation is interpreted as having been deposited on a shallow

shelf Shelf ( : shelves) may refer to: * Shelf (storage), a flat horizontal surface used for display and storage Geology * Continental shelf, the extended perimeter of a continent, usually covered by shallow seas * Ice shelf, a thick platform of ice f ...

environment deepening to a euxenic basin to the south.

Fossils

The formation contains the fossil brachiopod ''

Spirifer ''Spirifer'' is a genus of marine brachiopods belonging to the order Spiriferida and family Spiriferidae. Species belonging to the genus lived from the Middle Ordovician (Sandbian) through to the Middle Triassic (Carnian) with a global distribu ...

acuminatu'', as well as crinoids and bryozoans. The brachiopod assemblage includes 34 genera and 41 species. Conodonts are rare but a few tabulate corals, ichnofossils, and the receptaculid ''

Sphaerospongia ''Sphaerospongia'' is an extinct genus of organism found in marine beds of Devonian age. Its classification is enigmatic, but it is typically placed among the sponges or the receptaculites. The organism has a surface covered with hexagonal plat ...

'' is present. The receptaculids provided a solid substrate for colonization by the rugose coral ''

Tabulophyllum ''Tabulophyllum'' is an extinct genus of horn coral belonging to the order Stariidae and family Kyphophyllidae. Specimens have been found in Devonian beds in Australia North America, and most other major areas of Devonian outcrops. The genus ...

traversensis''. The fossil assemblage gives an age of late Givetian. The formation is highly bioturbated.

History of investigation

The beds assigned to the formation were previously correlated with the Canutillo Formation of west Texas. However, F.V. Stevenson questioned the correlation, and designated a new Onate Formation including the beds in 1945. In 1985, G.A. Cooper and J.T. Dutro, Jr., conducted the first thorough study of the fossil assemblage of the formation. The fossils were further characterized by James E. Souraf in 1987.

Footnotes

References

* * * * * * {{Use dmy dates, date=April 2017 Devonian formations of New Mexico Devonian southern paleotemperate deposits

Description

Fossils

History of investigation

See also

Footnotes

References