Tanos Formation

The Tanos Formation is a geologic formation in New Mexico. It is estimated to be about 25 million years in age, corresponding to the Oligocene epoch.

Tanos Formation
Stratigraphic range: Oligocene
Tanos Formation outcrop near Espinaso Ridge, New Mexico, USA
TypeFormation
Unit ofSanta Fe Group
UnderliesBlackshare Formation
OverliesEspinaso Formation
Thickness279 m (915 ft)
Lithology
PrimaryMudstone, sandstone
Otherconglomerate
Location
Coordinates35.414°N 106.311°W / 35.414; -106.311
RegionNew Mexico
Country United States
Type section
Named forArroyo de la Vega de los Tanos
Named byConnell et al.
Year defined2002
Tanos Formation (the United States)
Tanos Formation (New Mexico)

Description

The Tanos Formation consists of a very pale brown basal conglomerate overlain by reddish-yellow to reddish-brown sandstone and reddish-brown and olive-gray mudstone. It is exposed in a small belt along the east flank of Espinaso Ridge in the Hagen basin of central New Mexico, where it is truncated to the northwest by the San Francisco Fault and disappears to the southeast in the subsurface. The formation is 279 m (915 ft) thick at the type section on Arroyo de la Vega de los Tanos east of Espinaso Ridge. The age is constrained by an interbedded basalt flow at the bottom of the formation that has a radiometric age of 25.41 ± 0.32 Ma.[1] The upper age range is poorly controlled but may extend into the Miocene.

The formation lies discontinuously on the Espinaso Formation and interfingers with the overlying Blackshare Formation, with the boundary placed at the highest thickly bedded tabular sandstone below the lenticular conglomerate of the Blackshare Formation. The Tanos Formation dips 20 to 32 degrees to the northeast.[1]

It is interpreted as sediments deposited in a closed basin during early rifting along the Rio Grande rift, and is the oldest exposed Santa Fe Group formation near the Albuquerque Basin.[1]

History

The beds were first studied in detail by Searns in 1953, who tentatively assigned them to the Abiquiu Formation.[2] However, no clasts of Amalia Tuff, pervasive in the Abiquiu Formation further north, are present.[1] The beds were reassigned to the Zia Formation by Kelley in 1977[3] and finally designated as the Tanos Formation by Connell et al. in 2002.[1]

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References
  1. Connell et al. 2002
  2. Stearns 1953
  3. Kelley 1977

Bibliography
  • Connell, Sean D.; Cather, Steven M.; Dunbar, Nelia W.; McIntosh, William C.; Peters, Lisa (November 2002). "Stratigraphy of the Tanos and Blackshare Formations (lower Santa Fe Group), Hagan embayment, Rio Grande rift, New Mexico" (PDF). New Mexico Geology. 24 (4). Retrieved 9 June 2020.
  • Kelley, V. C. (1977). "Geology of Albuquerque Basin, New Mexico" (PDF). New Mexico Bureau of Mines and Mineral Resources Memoir. 33. Retrieved 10 June 2020.
  • Stearns, Charles E. (1953). "Tertiary geology of the Galisteo-Tonque area, New Mexico". Geological Society of America Bulletin. 64 (4): 459. doi:10.1130/0016-7606(1953)64[459:TGOTGA]2.0.CO;2.
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