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
TypeFormation
UnderliesTanos Formation
OverliesGalisteo Formation
Thickness430 m (1,410 ft)
Lithology
PrimaryVolcaniclastic
Location
Coordinates35.4065805°N 106.3183249°W / 35.4065805; -106.3183249
RegionCentral New Mexico
CountryUnited States
Type section
Named forEspinaso Ridge
Named byK. Bryan and J.E. Upson
Espinaso Formation (the United States)
Espinaso Formation (New Mexico)

Description

Espinaso Ridge near Arroyo del Tuerto

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The formation was first described by C.E.Stearns in 1943, who credited the name "Espinaso Volcanics" to an unpublished manuscript by Kirk Bryan and J.E. Upson.[2] P.F. Kautz and coinvestigators recognized that it was primarily alluvial and designated it as the Espinaso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.
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