Sandia Formation
Stratigraphic range: Bashkirian–Moscovian PreꞒ Ꞓ O S D C P T J K Pg N
Sandia Formation in the Sandia Mountains
Type	Formation
Underlies	Madera Group
Overlies	Osha Canyon Formation
Thickness	1,530 m (5,020 ft)
Lithology
Primary	Shale
Other	Sandstone
Location
Coordinates	35°58′35″N 105°17′00″W / 35.97639°N 105.28333°W / 35.97639; -105.28333
Region	New Mexico
Country	United States
Type section
Named for	Sandia Mountains
Named by	C.L. Herrick
Year defined	1900
Sandia Formation (the United States) Show map of the United States Sandia Formation (New Mexico) Show map of New Mexico

The Sandia Formation is a geologic formation in New Mexico, United States. Its fossil assemblage is characteristic of the early Pennsylvanian.^[1]

The Sandia Formation is mostly shale with some sandstone and conglomerate but only minor limestone beds, with the coarser sediments towards its base. Variations in thickness indicate deposition on an eroded Precambrian surface.^[1] The formation reaches its maximum thickness of 1,530 meters (5,020 feet) in the northern Sangre de Cristo Mountains, where its great inhomogeneity both laterally and vertically indicates a complex marine and nonmarine depositional environment.^[2][3] It is found in the Sandia, Jemez,^[4] Sangre de Cristo,^[3] and Manzano Mountains^[1] as well as the Las Vegas Basin.^[3]

The formation rests on Precambrian basement rock in the Sandia Mountains, but is underlain by Osha Canyon Formation in the southern Jemez Mountains or by formations of the Arroyo Penasco Group in the Sangre de Cristo Mountains and elsewhere.^[5] It transitions to the Madera Group in most locations, with the base of the Madera Group typically placed at the first massive limestone bed above the shales and sandstones of the Sandia Formation.

The Sandia Formation likely correlates with the Pinkerton Trail Formation of the Colorado Plateau.^[6]

Fossils found in the formation range from Morrowan brachiopods at its base to Atokan fusulinids at its top, making it a lower to middle Pennsylvanian formation. The uppermost beds contain abundant fossils of the fusulinid Fusulinella famula. However, the Morrowan section is missing in the Manzanos.^[1] The exposures at Priest Canyon in the southern Manzanos include Syringopora and the demosponge Chaetetes.^[7] The formation is bioturbated, with trace fossils of Zoophycos, in the southern Nacimiento Mountains.^[4]

The formation was first named by C.L. Herrick in 1900 for exposures in the Sandia Mountains of New Mexico. Herrick included the entire sequence of clastic beds resting on the Great Unconformity. Gordon identified the clastic beds between the Kelly Limestone and Madera Limestone in the Magdalena Mountains as Sandia Formation.^[4]

In 1946, Wood and Northrop divided the Sandia Formation as then defined into a Lower Limestone Member and an Upper Clastic Member in the Nacimiento Mountains. Armstrong discovered in 1951 that the Lower Limestone Member included Mississippian beds, which he broke out into the Arroyo Penasco Formation, separated by a clastic sequence (the Log Springs Formation) from early Pennsylvanian beds. Armstrong also noted that the zone immediately above the Log Springs Formation was characterized by fossils of the early Pennsylvanian brachiopod Schizophoria oklahomae and was separated from younger beds by an erosional discontinuity.^[8] These were broken out into the Osha Canyon Formation by H. DuChene in 1973^[5][9]

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

• Armstrong, Augustus K (1955). "Preliminary Observations of the Mississippian System of Northern New Mexico" (PDF). Circulars of the New Mexico Bureau of Mines and Mineral Resources. 39. Retrieved 21 May 2019.
• DuChene, H.; Kues, B. S.; Woodward, L. A. (1977). "Osha Canyon Formation (Pennsylvanian), new Morrowan unit in north-central New Mexico". American Association of Petroleum Geologists Bulletin. 61: 1513–1524.
• Baltz, Elmer H.; Myers, Donald A. (1984). "Porvenir Formation (New Name) and Other Revisions of Nomenclature of Mississippian, Pennsylvanian, and Lower Permian Rocks, Southeastern Sangre de Cristo Mountains, New Mexico" (PDF). Geoological Survey Bulletin 1537-B. Contributions to stratigraphy. U.S. Geological Survey: 14–19. Retrieved 11 May 2020.
• Baltz, E.H.; Myers, Donald A. (1999). "Stratigraphic framework of upper Paleozoic rocks, southeastern Sangre de Cristo Mountains, New Mexico". New Mexico Bureau of Mines and Mineral Resources Memoir Series. 48. Retrieved 23 May 2019.
• DuChene, Harvey R. (1974). "Pennsylvanian Rocks of North-Central New Mexico". New Mexico Geological Society Field Conference Series. 25: 159–165. CiteSeerX 10.1.1.578.7415.
• Huffman, A.C. Jr.; Condon, S.M. (1993). "Stratigraphy, structure, and paleogeography of Pennsylvanian and Permian rocks, San Juan basin and adjacent areas, Utah, Colorado, Arizona, and New Mexico". U.S. Geological Survey Bulletin. 1808-O: O1–O44. doi:10.3133/b1808O.
• Lucas, Spencer G.; Krainer, Karl; Vachard, Daniel (2016). "The Pennsylvanian section at Priest Canyon, southern Manzano Mountains, New Mexico" (PDF). New Mexico Geological Society Field Conference Series. 67. Retrieved 11 June 2020.
• Myers, Donald A. (1982). "Stratigraphic Summary of Pennsylvanian and Lower Permian Rocks, Manzano Mountains, New Mexico" (PDF). New Mexico Geological Society Field Conference Series. 33: 233–237. Retrieved 23 May 2019.