The Canutillo 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 the Franklin Mountains near

El Paso, Texas El Paso (; "the pass") is a city in and the seat of El Paso County in the western corner of the U.S. state of Texas. The 2020 population of the city from the U.S. Census Bureau was 678,815, making it the 23rd-largest city in the U.S., the ...

. The formation is

Middle Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...

in age.

Description

The Canutillo Formation consists of about of soft gray

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, ...

. It is

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 ...

overlain by the

Percha Formation The Percha Formation is a geologic formation in southern New Mexico. It preserves fossils dating back to the Famennian Age of the late Devonian period. Description The formation consists mostly of black to gray shale and minor limestone. I ...

. The Canutillo Formation likely correlates with the

Onate Formation The Onate Formation is a geologic formation that is exposed in most of the highlands of south-central New Mexico. It preserves fossils dating back to the middle Devonian period. Description At the type section, the Onate Formation consists ...

Fossils

The formation is fossiliferous, but few fossils are time diagnostic. Fossils include abundant ''

Leiorhynchus ''Leiorhynchus'' is an extinct genus of brachiopod belonging to the order Rhynchonellida and family Leiorhynchidae. Specimens have been found in South America, North America, and Russia in beds of middle Devonian to Mississippian Mississip ...

'' and other

brachiopod 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, ...

s and a few

pelecypod Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biva ...

History of investigation

The formation was first described in his dissertation by L.A. Nelson in 1937 for outcrops in the Franklin Mountains. Nelson assigned all beds between the

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago (Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozoi ...

Fusselman Formation and the

Mississippian Mississippian may refer to: * Mississippian (geology), a subperiod of the Carboniferous period in the geologic timescale, roughly 360 to 325 million years ago *Mississippian culture, a culture of Native American mound-builders from 900 to 1500 AD ...

Helms Formation to the Canutillo. Nelson formally published the definition in 1940 and extended the outcrop range to the

Hueco Mountains The Hueco Mountains are a range of mountains that rise in southern Otero County, New Mexico and extend south into Texas, generally along the El Paso– Hudspeth county line just east of the city of El Paso, Texas. The highest point of the range ...

. In 1945, F.V. Stevenson restricted the formation to the Franklin Mountains. In 1949, Lowell R. Laudon and Arthur L. Bowshwer restricted the formation to a sequence of just of soft gray siltstone.

Footnotes

{{Use mdy dates, date=May 2023 Devonian Texas Devonian southern paleotemperate deposits

Description

Fossils

History of investigation

See also

Footnotes