Percha Formation
{{Short description|Geologic formation in New Mexico, US}}
{{Infobox rockunit
| name = Percha Formation
| image =
| caption =
| type = Formation
| age = {{fossilrange|Famennian}}
| period = Famennian
| prilithology = Shale
| otherlithology = Limestone
| namedfor = Percha Creek
| namedby = G.H. Gordon
| year_ts = 1907
| region = New Mexico
| country = United States
| coordinates = {{coord|32.9159|N|107.5267|W|display=inline}}
| unitof =
| subunits = Ready Pay Member, Box Member
| underlies = Lake Valley Limestone, Caballero Formation, Escabrosa Limestone
| overlies = Fusselman Formation, Sly Gap Formation, Onate Formation
| thickness = {{convert|132|feet|meters}}
| extent =
| area =
| map = {{Location map+ | New Mexico
| AlternativeMap = Percha outcrop map.jpg
| relief = 1
| width = 250
| float = center
| places =
{{Location map~ | New Mexico
| lat_deg = 32.910
| lon_deg = -107.530
| mark = Brown pog.svg
| marksize = 12
}}
}}
| map_caption =
}}
The Percha Formation is a geologic formation in southern New Mexico. It preserves fossils dating back to the Famennian Age of the late Devonian period.{{sfn|Kues|2004|pp=65-67}}
Description
The formation consists mostly of black to gray shale and minor limestone.{{sfn|Gordon|1907}}{{sfn|Kues|2004|pp=65-67}} It rests on a regional unconformity, so that the underlying formation may be the Fusselman Formation,{{sfn|Stevenson|1945}} the Sly Gap Formation, or the Onate Formation.{{sfn|Kues|2004|pp=65-67}} It underlies the Lake Valley Limestone,{{sfn|Stevenson|1945}} Caballero Formation, Escabrosa Limestone, or other Mississippian formations.{{sfn|Kues|2004|pp=65-67}} Total thickness is about {{convert|132|feet|meters}}.{{sfn|Stevenson|1945}}
The formation is divided into two members.{{sfn|Stevenson|1945}} The Ready Pay Member (formerly lower Percha) is mostly black fissile shale nearly devoid of fossils and with a total thickness of about {{convert|132|feet|meters}}.{{sfn|Kues|2004|pp=65-67}} The Box Member (formerly upper Percha), which is much less limited in areal extent,{{sfn|Stevenson|1945}} is about {{convert|47|feet|meters}} of gray to green calcareous shale with limestone nodules and beds. It is highly fossiliferous.{{sfn|Kues|2004|pp=65-67}}
Fossils
The base of the formation contains fossils of arthrodiran fish, shark teeth, late Fammenian conodonts, brachiopods, and corals. The Box Member contains fossils of brachiopods, crinoids, bryozoans, sponges, corals, and late Fammenian conodonts.{{sfn|Schumacher|Witter|Meader|Keith|1976}}
History of investigation
The formation was first named as the Percha Shale by C.H. Gordon in 1907 for exposures at Percha Creek.{{sfn|Gordon|1907}} However, a type section was not designated until 1945, by F.V. Stevenson. Stevenson also divided the formation into the lower Ready Pay Member and the upper Box Member.{{sfn|Stevenson|1945}}{{sfn|Kues|2004|p=65}} D. Schumacher and coinvestigators mapped the formation into southeastern Arizona and renamed it the Percha Formation in 1976.{{sfn|Schumacher|Witter|Meader|Keith|1976}}
See also
{{Portal|Earth sciences|Paleontology}}
Footnotes
{{Reflist}}
References
- {{cite journal |last1=Gordon |first1=C.H. |year=1907 |title=Mississippian (Lower Carboniferous) Formations in the Rio Grande Valley, New Mexico.
|journal=American Journal of Science |volume=24 |number=139 |url=https://www.proquest.com/openview/d46587c91489d66a28a88bf9494d3b87/1?pq-origsite=gscholar&cbl=42176 |access-date=20 February 2021}}
- {{cite encyclopedia |last1=Kues |first1=B.S. |year=2004 |title=Devonian of New Mexico |editor1-last=Mack |editor1-first=G.H. |editor2-last=Giles |editor2-first=K.A. |encyclopedia=The geology of New Mexico. A geologic history: New Mexico Geological Society Special Volume 11 |pages=59–75 |isbn=9781585460106}}
- {{cite journal |last1=Schumacher |first1=D. |last2=Witter |first2=D.P. |last3=Meader |first3=S.J. |last4=Keith |first4=S.B. |year=1976 |title=Late Devonian tectonism in southeastern Arizona |journal=Arizona Geological Society Digest |volume=10 |pages=59–70 |url=http://www.nativefishlab.net/library/textpdf/11282.pdf |accessdate=5 August 2020}}
- {{cite journal |last1=Stevenson |first1=Frank V. |title=Devonian of New Mexico |journal=The Journal of Geology |date=July 1945 |volume=53 |issue=4 |pages=217–245 |doi=10.1086/625283}}
Category:Devonian formations of New Mexico