The Percha Formation is a
geologic formation in southern
New Mexico. It preserves
fossils
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...
dating back to the
Famennian Age of the
late Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...
period.
Description
The formation consists mostly of black to gray
shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
and minor
limestone. It rests on a regional
unconformity, so that the underlying formation may be the
Fusselman Formation
The Fusselman Formation is a geologic formation in westernmost Texas and southern New Mexico. It preserves fossils dating back to the early Silurian period.
Description
The formation consists mostly of medium to dark gray massive dolomite. ...
, the
Sly Gap Formation, or the
Onate Formation
The Onate Formation is a geologic formation that is exposed in most of the highlands of south-central New Mexico. It preserves fossils dating back to the middle Devonian period.
Description
At the type section, the Onate Formation consists ...
. It underlies the
Lake Valley Limestone
The Lake Valley Limestone is a geologic formation widely exposed in southwestern New Mexico. It preserves fossils dating back to the lower to middle Mississippian.
Description
The Lake Valley Limestone consists of gray cherty limestone with ...
,
Caballero Formation,
Escabrosa Limestone, or other
Mississippian
Mississippian may refer to:
* Mississippian (geology), a subperiod of the Carboniferous period in the geologic timescale, roughly 360 to 325 million years ago
*Mississippian culture, a culture of Native American mound-builders from 900 to 1500 AD ...
formations. Total thickness is about .
The formation is divided into two
members. The Ready Pay Member (formerly lower Percha) is mostly black fissile shale nearly devoid of fossils and with a total thickness of about . The Box Member (formerly upper Percha), which is much less limited in areal extent, is about of gray to green calcareous shale with limestone nodules and beds. It is highly fossiliferous.
Fossils
The base of the formation contains fossils of
arthrodiran fish, shark teeth, late Fammenian
conodont
Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which ...
s,
brachiopods, and
corals. The Box Member contains fossils of brachiopods,
crinoids,
bryozoans,
sponges, corals, and late Fammenian conodonts.
History of investigation
The formation was first named as the Percha Shale by C.H. Gordon in 1907 for exposures at
Percha Creek
The Percha Creek Bridge near Hillsboro, New Mexico formerly brought New Mexico State Road 90 NM 90 over Percha Creek.
It was built in 1927. It was bypassed in 1995 but preserved by the NMSHTD, and it was listed on the National Register of Hist ...
. 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. D. Schumacher and coinvestigators mapped the formation into southeastern Arizona and renamed it the Percha Formation in 1976.
See also
*
List of fossiliferous stratigraphic units in New Mexico
*
Paleontology in New Mexico
Paleontology in New Mexico refers to paleontological research occurring within or conducted by people from the U.S. state of New Mexico. The fossil record of New Mexico is exceptionally complete and spans almost the entire stratigraphic colu ...
Footnotes
References
*
*
*
* {{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
Devonian formations of New Mexico