Caballero Formation
{{Short description|Geologic formation in New Mexico, US}}
{{Infobox rockunit
| name = Caballero Formation
| image =
| caption =
| type = Formation
| age = {{Geological range|Tournaisian}}
| period = Tournaisian
| prilithology = Limestone
| otherlithology = Shale
| namedfor =
| namedby = L.R. Laudon and A.L. Bowsher
| year_ts = 1941
| region = New Mexico
| country = United States
| coordinates = {{coord|32.8545|N|105.9043|W|display=inline}}
| unitof =
| subunits =
| underlies = Lake Valley Limestone
| overlies = Percha Shale
| thickness =
| extent =
| area =
| map ={{Location map+ | New Mexico
| AlternativeMap = Caballero Formation outcrop map.jpg
| relief = 1
| width = 250
| float = center
| places =
{{Location map~ | New Mexico
| lat_deg = 32.859
| lon_deg = -105.919
| mark = Green pog.svg
| marksize = 12
}}
}}
| map_caption =
}}
The Caballero Formation is a geologic formation found in the highlands flanking the southern Rio Grande River valley in New Mexico. It preserves fossils dating back to the Tournasian Age of the Carboniferous period.{{cite journal |last1=Laudon |first1=L.R. |last2=Bowsher |first2=A.L. |year=1941 |title=Stratigraphy of the Mississippian formations of the Sacramento Mountains, New Mexico |journal=Tulsa Geological Society Digest |volume=9 |pages=73–75 |url=http://archives.datapages.com/data/tgs/digest/data/009/009001/73_tgs090073.htm |access-date=29 July 2020}}
Description
The Caballero Formation consists of nodular gray argillaceous limestone, which grades upward into nodular gray marl with shale lenses. It rests conformably on the Percha Shale and is overlain unconformably by the Lake Valley Limestone. The formation likely correlates with the Chouteau Limestone of the upper Mississippi valley.
Fossils
The formation is locally abundant in fossils of Tournasian age, with more than 200 marine invertebrate species reported.{{cite journal |last1=Kues |first1=Barry S. |title=Paleontology of the Caballero and Lake Valley Formations (Lower Mississippian) west of the Rio Grande, south-central New Mexico |journal=New Mexico Geological Society Field Conference Series |date=1986 |volume=37 |pages=203-214 |url=https://nmgs.nmt.edu/publications/guidebooks/downloads/37/37_p0203_p0214.pdf |access-date=18 September 2020}} These include the ammonoids Pericyclus blairi, P. Cooperi P. costulatus, and Gattendorfia bransoni as well as Tournasian conodont and brachiopod faunas.{{cite journal |first1=Gordon Jr. |last1=Mackenzie |year=1986 |title=Late Kinderhookian (Early Mississippian) ammonoids of the western United States |journal=Paleontological Society Memoir |volume=19 |jstor=1315530}} The fauna changes significantly from the westernmost to easternmost exposures of the formation.
History of investigation
The beds forming this unit were originally included in the Devonian Percha Shale, but were separated into their own formation by Laudon and Bowsher in 1941, when it was recognized that they are Mississippian in age.
See also
{{Portal|Earth sciences|Paleontology}}