Sandia Formation
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| Sandia Formation | |
|---|---|
| Stratigraphic range: | |
 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 |
| 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)  Sandia Formation (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]
Fossil content
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]