Cochiti Formation
The Cochiti Formation is a geologic formation exposed near the southwest Jemez Mountains of northern New Mexico. Its age is estimated as 10 to 2.6 million years, corresponding to the middle Miocene to Pliocene.
| Cochiti Formation Stratigraphic range: Miocene to Pliocene, 10–2.6 Ma | |
|---|---|
 Cochiti Formation in road cut at Kasha-Katuwe Tent Rocks National Monument | |
| Type | Formation |
| Unit of | Santa Fe Group |
| Sub-units | Lookout Park Gravel Member |
| Overlies | Keres Group |
| Lithology | |
| Primary | Sandstone |
| Other | Conglomerate |
| Location | |
| Coordinates | 35.673°N 106.453°W |
| Region |  New Mexico |
| Country |  United States |
| Type section | |
| Named for | Cochiti Pueblo |
| Named by | Bailey, Smith, and Ross |
| Year defined | 1969 |
Description
The formation consists of volcanic sand and gravel eroded off the Keres Group of the southern Jemez Mountains. [1] The formation is restricted to sedimentary strata composed purely of volcaniclastic sediments that overlie Keres Group volcanic rocks and correlative volcanic sediments south of the Jemez Mountain and are in turn overlain by Pliocene and early Pleistocene gravels.
Members
The Lookout Park Gravel Member is a stratified cobble to boulder gravel composed almost entirely of Keres Group volcanic debris that underlies high level geomorphic surfaces sloping to the southeast. It is interbedded with basalt with an age of 2.5 million years.[2]
History of investigation
The formation was first defined by Bailey, Smith, and Ross in 1969 as part of their work establishing the stratigraphy of the Jemez Mountains. The formation was named for exposures near Cochiti Pueblo. [3]
Gary A. Smith and Alexis Lavine argued in 1996 that the original definition was inconsistent and that volcanic and sedimentary basin stratigraphers had worsened the problem by their different approaches to regional stratigraphy.[4] For example, Fraser Goff and his coinvestigators mapped volcaniclastic beds of the San Miguel Mountains as Cochiti Formation based on the original definition of the formation, while noting the inconsistency.[5] Smith and Lavine identified a mappable, distinct stratigraphic unit that included most of the original exposures mapped by R.L. Smith, R.A. Bailey, and C.S. Ross in 1970[6] and excluded most strata added by other investigators.[4]
R.M. Chamberlin and his coinvestigators tentatively assigned the Gravel of Lookout Park as a member of the Cochiti Formation in 1999.[2]
Footnotes
References
- Chamberlin, R.M.; Pazzaglia, F.J.; Wegmann, K.W.; Smith, G.A. (Jun 1999). "Geologic Map of the Loma Creston Quadrangle, Sandoval County, New Mexico" (PDF). New Mexico Bureau of Geology and Mineral Resources Open Map Series. 25. Retrieved 17 May 2020.
- Goff, Fraser; Gardner, Jamie N.; Reneau, Steven L. (2002). "Geology of the Frijoles quadrangle, Los Alamos, Sandoval, and Santa Fe Counties, New Mexico". New Mexico Burea of Geology and Mineral Resources Open File Geologic Map Series. 42. Retrieved 16 May 2020.
- Smith, Gary A.; Lavine, Alexis (1996). "What is the Cochiti Formation?" (PDF). New Mexico Geological Society Field Conference Series. 47: 219–224. Retrieved 17 May 2020.
- Smith, R.L.; Bailey, R.A.; Ross, C.S. (1969). "Stratigraphic Nomenclature of ' Volcanic Rocks in the Jemez Mountains, New Mexico" (PDF). Geological Survey Bulletin (1274-P). Retrieved 4 May 2020.
- Smith, R.L.; Bailey, R.A.; Ross, C.S. (1970). "Geologic map of the Jemez Mountains, New Mexico". U.S. Geological Survey Miscellaneous Investigations Map Series (I-571). Retrieved 16 May 2020.