Popotosa Formation
The Popotosa Formation is a geologic formation in New Mexico. It preserves fossils dating back to the Neogene period.
| Popotosa Formation Stratigraphic range: Neogene | |
|---|---|
| Type | Formation |
| Unit of | Santa Fe Group |
| Underlies | Sierra Ladrones Formation |
| Thickness | 1,447 m (4,747 ft) |
| Lithology | |
| Primary | Volcaniclastics |
| Other | Tuff |
| Location | |
| Coordinates | 34.3282123°N 106.9916994°W |
| Region | New Mexico |
| Country | United States |
| Type section | |
| Named for | Canada Popotosa |
| Named by | C.S. Denny |
| Year defined | 1940 |
Description
The Popotosa Formation is a thick (up to 1,447 meters (4,747 feet)) sequence of volcanic debris beds with a few interspersed ash beds. It is exposed along the Rio Grande rift from the Socorro area. Radiometric dating of interbedded flows gives it an age of 26.4 to 7 Ma, corresponding to the late Oligocene to Miocene.[1]
The formation is interpreted as deposition of fanglomerates (mostly derived from the Datil-Mogollon volcanic field to the southwest) and playa sediments in a closed basin in the early stages of rifting along the Rio Grande rift. It is thus typical of the lower Santa Fe Group.[1]
History of investigation
The unit was first described by C.S. Denny in 1940, who named it for exposures near Canada Popotosa.[2] It was assigned to the lower Santa Fe Group by Machette in 1978.[3]
Footnotes
- Asher-Bolinder 1988
- Denny 1940
- Machette 1978
References
- Asher-Bolinder, Sigrid (1988). "Stratigraphy of reference sections in the Popotosa Formation, Socorro County, New Mexico" (PDF). U.S. Geological Survey Bulletin. 1800. doi:10.3133/b1800. Retrieved 10 June 2020.
- Denny, Charles S. (January 1940). "Tertiary Geology of the San Acacia Area New Mexico". The Journal of Geology. 48 (1): 73–106. doi:10.1086/624862.
- Machette, M.N. (1978). "Geologic map of the San Acacia quadrangle, Socorro County, New Mexico". U.S. Geological Survey Geologic Quadrangle Map. GQ-1415. Retrieved 10 June 2020.