Flechado Formation

Flechado Formation
Stratigraphic range: Moscovian PreꞒ Ꞓ O S D C P T J K Pg N
Flechado Formation at its type section, Rio Pueblo Valley, New Mexico.
Type	Formation
Underlies	Alamitos Formation
Overlies	Tererro Formation
Thickness	2,500 ft (760 m)
Lithology
Primary	Sandstone, shale
Other	Siltstone, limestone, conglomerate
Location
Coordinates	36°09′45″N105°34′43″W / 36.1623943°N 105.5786314°W / 36.1623943; -105.5786314
Region	New Mexico
Country	United States
Type section
Named for	Flechado Creek
Named by	P.K. Sutherland
Year defined	1963
Flechado Formation (the United States) Show map of the United States Flechado Formation (New Mexico) Show map of New Mexico

The Flechado Formation is a geologic formation in the northern Sangre de Cristo Mountains of New Mexico. It preserves fossils dating back to the early to middle Pennsylvanian. ^[1]

Description

The Flechado Formation consists of low-feldspar sandstone and shale alternating with thin beds of limestone. The total thickness is 2,500 feet (760 meters). ^[1] It overlies the Tererro Formation ^[2] and is overlain by the Alamitos Formation. ^[1] The formation is well to extremely well cemented in the type area, so that it can be difficult to distinguish from the Precambrian Ortega Formation. ^[3]

The formation grades laterally into the La Pasada Formation to the south of the Rio Pueblo, with the clastic beds of the Flechado abruptly thinning and transitioning to carbonate beds of the La Pasada over a distance of about 5 miles (8.0 kilometres). ^[1]

The terrigenous sediments of the Flechado Formation were likely derived from the southern part of Uncompahgre uplift during uplift on the west side of the Picuris-Pecos fault. ^[1]

• 
  Close view of Flechado Formation at its type section.

Fossils

Fossils are scarce in the upper portion of the Flechado Formation, but middle Desmoinesian (upper Moscovian) brachiopods are found about 800 feet (240 meters) below the top of the formation. Atokan (lower Moscovian) fusulinids and brachiopods are found in the lower part, which also contains broken crinoid, bryozoan, and algal remains. ^[1]

History of investigation

The formation was first described by P.K. Sutherland in 1963. ^[1]

See also

• Earth sciences portal
• Paleontology portal

• List of fossiliferous stratigraphic units in New Mexico
• Paleontology in New Mexico

Footnotes

1. Sutherland 1963.
2. Armstrong & Mamet 1974.
3. Aby & Hallet 2007.

References

• Aby, Scott; Hallet, Ben (May 2007). "Geologic Map of the Tres Ritos Quadrangle, Taos County, New Mexico" (PDF). New Mexico Bureau of Geology and Mineral Resources Open-file Digital Geologic Map. OF-GM 145. Retrieved 22 August 2020.
• Armstrong, A.K.; Mamet, B.L. (1974). "Biostratigraphy of the Arroyo Penasco Group, Lower Carboniferous (Mississippian), north-central New Mexico" (PDF). New Mexico Geological Society Field Conference Series }volume=25: 145–158. Retrieved 29 July 2020.
• Sutherland, P.K. (1963). "Paleozoic rocks" (PDF). In Miller, J.P.; Montgomery, Arthur; Sutherland, P.K. (eds.). Geology of part of the southern Sangre de Cristo Mountains, New Mexico: New Mexico Bureau of Mines and Mineral Resources Memoir 11. pp. 22–44. Retrieved 29 July 2020.