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 (; ; or ) is a city in and the county seat of El Paso County, Texas, United States. The 2020 United States census, 2020 population of the city from the United States Census Bureau, U.S. Census Bureau was 678,815, making it the List of ...

. The formation is

Middle Devonian In the geological timescale, the Middle Devonian epoch (from 393.3 ± 1.2 million years ago to 382.7 ± 1.6 million years ago) occurred during the Devonian period, after the end of the Emsian age. The Middle Devonian epoch is subdivided into two ...

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. Although its permeabil ...

. 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 Canutillo Formation likely correlates with the Onate Formation.

Fossils

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

brachiopod Brachiopods (), phylum (biology), 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 e ...

s and a few

pelecypod Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

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 23.5 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 third and shortest period of t ...

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 cultures, a network of precontact cultures across the midwest and Easte ...

Helms Formation to the Canutillo. Nelson formally published the definition in 1940 and extended the outcrop range to the Hueco Mountains. 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 Shale formations of the United States Siltstone formations of the United States

Description

Fossils

History of investigation

See also

Footnotes