Rancheria Formation
{{Short description|Geologic formation in New Mexico and Texas, US}}
{{Infobox rockunit
| name = Rancheria Formation
| image =
| caption =
| type = Formation
| age = {{Geological range|Visean}}
| period = Visean
| prilithology = Limestone
| otherlithology = Chert
| namedfor = Rancheria Peak
| namedby = Laudon and Bowsher
| year_ts = 1949
| region = New Mexico
Texas
| country = United States
| coordinates = {{coord|31.9551|N|106.5143|W|display=inline}}
| unitof =
| subunits =
| underlies = Helms Formation
| overlies = Lake Valley Formation, Percha Formation
| thickness = {{convert|255|feet|meter|abbr=on}}
| extent =
| area =
| map = {{Location map+ | United States#Texas
| relief = 1
| width = 250
| float = center
| places =
{{Location map~ | United States#Texas
| lat_deg = 31.9551
| lon_deg = -106.5143
| mark = Lightgreen pog.svg
| marksize = 12
}}
}}
| map_caption =
}}
The Rancheria Formation is a geologic formation in the Sacramento{{cite encyclopedia |last1=Armstrong |first1=Augustus K. |last2=Mamet |first2=Bernard L. |last3=Repetski |first3=John E. |year=2004 |title=Mississippian System of New Mexico and adjacent areas |editor1-last=Mack |editor1-first=G.H. |editor2-last=Giles |editor2-first=K.A. |encyclopedia=The geology of New Mexico. A geologic history (Special Volume 11) |publisher=New Mexico Geological Society |pages=77–93}} and San Andres Mountains{{cite journal |last1=Bachman |first1=George O. |last2=Myers |first2=Donald A. |title=Geology of the Bear Peak area, Dona Ana County, New Mexico |journal=U.S. Geological Survey Bulletin |date=1969 |volume=1271-C |doi=10.3133/b1271C|doi-access=free }} 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.
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 {{convert|255|feet|meters|sp=us}}.{{cite journal |last1=Laudon |first1=Lowell R. |last2=Bowsher |first2=Arthur L. |title=Mississippian formations of southwestern New Mexico |journal=Geological Society of America Bulletin |date=1949 |volume=60 |issue=1 |pages=1 |doi=10.1130/0016-7606(1949)60[1:MFOSNM]2.0.CO;2|bibcode=1949GSAB...60....1L }} 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.
The formation contains intraformational submarine erosional surfaces but relatively little slumping, indicating deposition on a deeply submerged stable basin floor.{{cite journal |last1=Yurewicz |first1=Donald A. |title=Sedimentology of Mississippian basin-facies carbonates, New Mexico and west Texas -- The Rancheria Formation |journal=SEPM Special Publication |date=1977 |volume=25 |pages=203–219 |url=http://archives.datapages.com/data/sepm_sp/SP25/Sedimentology_of_Mississippian.htm |accessdate=18 September 2020}}
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.
History of investigation
See also
{{Portal |Earth sciences|Paleontology}}