Rancheria Formation Explained

Rancheria Formation
Type:Formation
Period:Visean
Prilithology:Limestone
Otherlithology:Chert
Namedfor:Rancheria Peak
Namedby:Laudon and Bowsher
Year Ts:1949
Region:New Mexico
Texas
Country:United States
Coordinates:31.9551°N -106.5143°W
Underlies:Helms Formation
Overlies:Lake Valley Formation, Percha Formation
Thickness:255feet

The Rancheria Formation is a geologic formation in the Sacramento[1] and San Andres Mountains[2] of New Mexico, the Franklin Mountains of southern New Mexico and western Texas, and the Hueco Mountains of western Texas. It preserves fossils dating back to the Visean Age of the Mississippian.[1]

Description

The formation consists mostly of dense carboniferous silty limestone containing considerable chert. The base of the formation is a few inches of shale and carboniferous quartz sandstone, followed by a few feet of yellow to brown sandy siltstone and a few feet of carboniferous limestone composed almost entirely of crinoid fragments. The total thickness is up to 255feet.[3] The formation lies on the Percha Formation or Lake Valley Limestone or, where these are not present, the Caballero Formation. It is overlain by the Helms Formation or Gobbler Formation or Permian formations.[1]

The formation contains intraformational submarine erosional surfaces but relatively little slumping, indicating deposition on a deeply submerged stable basin floor.[4]

Fossils

The basal sandstone contains numerous plant fossils and the lower limestone is almost entirely crinoid fragments. The siltstone contains abundant brachiopods such as Leiorhynchus carboniferum.[3]

History of investigation

The Rancheria Formation was first described by Laudon and Bowsher in 1949.[3] In 1977, Yurewicz argued for abandoning their underlying Las Cruces Formation and placing its beds in the Rancheria Formation.[4]

See also

Notes and References

  1. Encyclopedia: Armstrong . Augustus K. . Mamet . Bernard L. . Repetski . John E. . 2004 . Mississippian System of New Mexico and adjacent areas . Mack . G.H. . Giles . K.A. . The geology of New Mexico. A geologic history (Special Volume 11) . New Mexico Geological Society . 77–93.
  2. Bachman . George O. . Myers . Donald A. . Geology of the Bear Peak area, Dona Ana County, New Mexico . U.S. Geological Survey Bulletin . 1969 . 1271-C . 10.3133/b1271C. free .
  3. Laudon . Lowell R. . Bowsher . Arthur L. . Mississippian formations of southwestern New Mexico . Geological Society of America Bulletin . 1949 . 60 . 1 . 1 . 10.1130/0016-7606(1949)60[1:MFOSNM]2.0.CO;2. 1949GSAB...60....1L .
  4. Yurewicz . Donald A. . Sedimentology of Mississippian basin-facies carbonates, New Mexico and west Texas -- The Rancheria Formation . SEPM Special Publication . 1977 . 25 . 203–219 . 18 September 2020.