Espinaso Formation
The Espinaso Formation is a geologic formation in New Mexico. It has a radiometric age of 34.6 to 26.9 million years, corresponding to the late Eocene through Oligocene epochs.
| Espinaso Formation Stratigraphic range: Late Eocene to Early Oligocene | |
|---|---|
 Volcaniclastic beds of the Espinaso Formation at Arroyo del Tuerto | |
| Type | Formation |
| Underlies | Tanos Formation |
| Overlies | Galisteo Formation |
| Thickness | 430 m (1,410 ft) |
| Lithology | |
| Primary | Volcaniclastic |
| Location | |
| Coordinates | 35.4065805°N 106.3183249°W |
| Region | Central New Mexico |
| Country | United States |
| Type section | |
| Named for | Espinaso Ridge |
| Named by | K. Bryan and J.E. Upson |
  Espinaso Formation (the United States)  Espinaso Formation (New Mexico) | |
Description
The Espinaso Formation is principally debris flows and lahars from the Ortiz porphyry belt, with some interbedded lava flows and tuff beds. The upper part of the formation is dominated by upward-fining sequences, where sediments are coarser near the base of the sequence. This suggests waning volcanic activity and decreasing topographic relief.[1] The formation crops out in the Hagan and Galisteo Basins and the La Cienega area of New Mexico. The type section is at Arroyo del Tuerto (Arroyo Pinovetito) where it cuts a slot canyon through Espinaso Ridge. Espinaso Ridge is a hogback produced by the strongly cemented volcaniclastics of the Espinaso Formation, which contrast with the less resistant beds of the underlying Galisteo Formation and overlying Tanos Formation.[2]
Radiometric dating gives an age range of 34.3 +/-0.8 Ma near the base of the formation, 34.6 +/-0.7 Ma near the middle, and 26.9 +/-0.6 my near the top. A basalt flow at the base of the overlying Tanos Formation has an age of 25.1 +/-0.6 Ma.
The formation intertongues with the underlying Galisteo Formation but unconformably underlies the Tanos Formation of the Santa Fe Group.[2]
History of investigation
The formation was first described by C.E.Stearns in 1943, who credited the name "Espinaso Volcanics" to an unpublished manuscript by Kirk Bryan and J.E. Upson.[2] P.F. Kautz and coinvestigators recognized that it was primarily alluvial and designated it as the Espinaso Formation in 1981.[1]
Footnotes
References
- Kautz, P. F.; Ingersoll, R. V.; Baldridge, W. S.; Damon, P. E.; Shafiqullah, M. (December 1981). "Geology of the Espinaso Formation (Oligocene), North-Central New Mexico". GSA Bulletin. 92 (12_Part_II): 2318–2400. doi:10.1130/GSAB-P2-92-2318.
- Stearns, C.E. (June 1953). "Early Tertiary vulcanism in the Galisteo-Tongue area, north-central New Mexico". American Journal of Science. 251 (6): 415–452. doi:10.2475/ajs.251.6.415.
- Stearns, C.E. (1943). "The Galisteo formation of north-central New Mexico". Journal of Geology. 51 (5): 301–319. doi:10.1086/625156.