| Sierra Ladrones Formation | |
|---|---|
| Stratigraphic range: Pleistocene to Pliocene 5–2 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓ | |
 Sierra Ladrones Formation northeast of Socorro, New Mexico, USA | |
| Type | Formation |
| Unit of | Santa Fe Group |
| Overlies | Popotosa Formation |
| Thickness | 470 m (1,540 ft) |
| Lithology | |
| Primary | Sandstone |
| Other | Siltstone, conglomerate |
| Location | |
| Coordinates | 34°23′38″N 107°00′03″W / 34.3939496°N 107.0007996°W / 34.3939496; -107.0007996 |
| Region | New Mexico |
| Country | United States |
| Type section | |
| Named for | Sierra Ladrones (mountain range) |
| Named by | M.N. Machette |
| Year defined | 1978; 47 years ago (1978) |
  Sierra Ladrones Formation (the United States)Show map of the United States Sierra Ladrones Formation (New Mexico)Show map of New Mexico | |
The Sierra Ladrones Formation is a geologic formation exposed near the Rio Grande Valley in New Mexico. It preserves fossils of Pliocene to Pleistocene age.
Description
The formation consists of three facies representing different depositional environments. These are piedmont slope and alluvial fan deposits, typically composed of light-brown to light-reddish-brown sandstone and fanglomerate; axial stream deposits, which are composed of light-gray to light-yellowish-brown fine- to medium-grained sand and sandstone with fluvial cross-bedding and cut-and-fill channels; and interbedded basalt flows with a K-Ar age of 4.5 +/-0.1 million years (Ma. The total thickness is in excess of 470 m (1,540 ft). The formation unconformably overlies or is in fault contact with the Popotosa Formation or older formations. Its age is early Pliocene to middle Pleistocene (2 Ma to 5 Ma.)
The formation is interpreted as fanglomerates shed from the flanking uplifts of the Rio Grande Rift and channel and floodplain deposits of the ancestral Rio Grande.
Fossils
The formation has yielded abundant fossils of Irvingtonian age at Tijeras Arroyo, south of Albuquerque International Airport. These include Hypolagus, Equus, Mammuthus, and Hesperotestudo.
History of investigation
The formation was defined by M.N. Machette in 1978 for exposures in the Sierra Ladrones, a range of low foothills of the Ladron Mountains, in the Sevilleta National Wildlife Refuge.
The formation was subsequently mapped into the lower Rio Puerco valley and as far north as the Santo Domingo basin.
Footnotes
- ^ Machette 1978.
- Osburn & Chapin 1983.
- Lucas 1997, p. 228.
- Love & Young 1983, p. 280.
- Smith & Kuhle 1998.
See also
References
- Love, David W.; Young, John D. (1983). "Progress report on the late Cenozoic geologic evolution of the lower Rio Puerco" (PDF). New Mexico Geological Society Field Conference Series. 34: 277–294. Retrieved 18 May 2020.
- Lucas, Spencer G. (1997). "New Mexico's Fossil Record 2". New Mexico Museum of Natural History and Science Bulletin. 16. Retrieved 18 May 2020.
- Machette, M.N. (1978). "Geologic map of the San Acacia quadrangle, Socorro County, New Mexico". U.S. Geological Survey Geologic Quadrangle Map Series. GQ-1415. Retrieved 18 May 2020.
- Osburn, G.R.; Chapin, C.E. (1983). "Nomenclature for Cenozoic rocks of northeast Mogollon-Datil volcanic field, New Mexico". New Mexico Bureau of Mines and Mineral Resources Stratigraphic Chart Series. 1. Retrieved 18 May 2020.
- Smith, G.A.; Kuhle, A.J. (1998). "Geology of the Santo Domingo Pueblo and Santo Domingo Pueblo SW 7.5-minute quadrangles, Sandoval County, New Mexico". New Mexico Bureau of Mines and Mineral Resources Open-File Map Series. OF-GM 15/26. Retrieved 18 May 2020.