Onate Formation

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Onate Formation
Stratigraphic range: Givetian
387.7–382.7  Ma
O
S
D
C
P
T
J
K
Pg
N
Type Formation
Underlies Sly Gap Formation
Overlies Fusselman Formation, Montoya Group
Thickness85–95 feet (26–29 m)
Lithology
Primary Siltstone
Other Shale, sandstone
Location
Coordinates 32°44′31″N106°34′19″W / 32.742°N 106.572°W / 32.742; -106.572
Region New Mexico
Country United States
Type section
Named forOnate Mountain
Named byF.V. Stevenson
Year defined1945
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Onate Formation (the United States)
USA New Mexico relief location map.svg
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Onate Formation (New Mexico)

The Onate Formation is a geologic formation that is exposed in most of the highlands of south-central New Mexico. [1] It preserves fossils dating back to the middle Devonian period. [2] [3] [4]

Contents

Description

At the type section, the Onate Formation consists of about 85–95 feet (26–29 m) of orange yellow-weathering dolomitic siltstone with shales and sandstone. [2] Elsewhere the thickness is more typically 15 to 32 ft (4.6 to 9.8 m). [5] The base of the formation is a profound regional unconformity, so that the formation rest on either the Fusselman Formation or the Montoya Group. It is overlain by the Sly Gap Formation and thins to the north and south. [3]

The formation is interpreted as having been deposited on a shallow shelf environment deepening to a euxenic basin to the south. [6]

Fossils

The formation contains the fossil brachiopod Spirifer acuminatu, as well as crinoids and bryozoans. [2] The brachiopod assemblage includes 34 genera and 41 species. Conodonts are rare but a few tabulate corals, ichnofossils, and the receptaculid Sphaerospongia is present. The receptaculids provided a solid substrate for colonization by the rugose coral Tabulophyllum traversensis. [4] The fossil assemblage gives an age of late Givetian. The formation is highly bioturbated. [3]

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. [7] In 1985, G.A. Cooper and J.T. Dutro, Jr., conducted the first thorough study of the fossil assemblage of the formation. [3] The fossils were further characterized by James E. Souraf in 1987. [4]

See also

Footnotes

Related Research Articles

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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 plates, and some early taxonomists placed it among the echinoderms. It is found in close association with the horn coral Tabulophyllum traversensis in the Onate Formation of New Mexico, US, where it provides a substrate for the coral.

The Canutillo Formation is a geologic formation that is exposed in the Franklin Mountains near El Paso, Texas. The formation is Middle Devonian in age.

References