The Petrified Forest Member is a
stratigraphic unit of the
Chinle Formation
The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In Ne ...
in
Arizona,
Colorado,
New Mexico,
Nevada, and
Utah. 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
Triassic period.
Subunits
Beds (are in alphabetical order, asterisks (*) indicate usage by the U.S. Geological Survey, other usages by state geological surveys):
* Capitol Reef Bed (UT*)
* Correo Sandstone Bed (NM*)
* Sonsela Sandstone Bed (AZ*,NM*)
In the Chama Basin of New Mexico, the Chinle Formation is promoted to group status and the Petrified Forest Formation has the following members:
* Painted Desert Member
* Mesa Montoso Member
The Mesa Montosa Member is up to thick and is mostly composed of
sandstone (44%) and
mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
(35%), with a lesser proportion of
siltstone
Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...
(20%). The color is reddish brown to brown and the sandstone is thinly bedded and ripple laminated.
The Painted Desert Member is up to thick and is primarily reddish brown
bentonitic
Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-mon ...
mudstone. The name was originally applied to the beds above the Sonsela Sandstone Bed in
Petrified Forest National Park
Petrified Forest National Park is an American national park in Navajo County, Arizona, Navajo and Apache County, Arizona, Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about , encompassin ...
in eastern Arizona. Correlative beds of similar lithology are found throughout west-central and central New Mexico and the
Four Corners
The Four Corners is a region of the Southwestern United States consisting of the southwestern corner of Colorado, southeastern corner of Utah, northeastern corner of Arizona, and northwestern corner of New Mexico. The Four Corners area ...
. The Black Forest Bed within this member has a maximum age of 213 ± 1.7
Ma based on
detrital zircon geochronology
Detrital zircon geochronology is the science of analyzing the age of zircons deposited within a specific sedimentary unit by examining their inherent radioisotopes, most commonly the uranium–lead ratio. Zircon is a common accessory or trace ...
, with an actual age estimated as 209 Ma. This places the upper part of the Painted Desert Member in the latest
Norian
The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.
Stratigraphic defi ...
age
Age or AGE may refer to:
Time and its effects
* Age, the amount of time someone or something has been alive or has existed
** East Asian age reckoning, an Asian system of marking age starting at 1
* Ageing or aging, the process of becoming older ...
.
Fossils
The Snyder quarry, discovered by amateur fossil hunter Mark Snyder near the town of
Abiquiu, New Mexico, in 1998, is an unusually productive and diverse bone bed in the Petrified Forest Formation. Abundant charcoal suggests a mass kill due to a paleowildfire. Fossils include
archosaur
Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
s,
procolophonids,
metoposaurid amphibians,
semionotid fish, a
decapod, a
conchostracan, and
unionid bivalves.
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 column. ...
Footnotes
References
*
*
*
*
* {{cite journal , last1=Zeigler , first1=Kate E. , last2=Heckert , first2=Andrew B. , last3=Lucas , first3=Spencer G. , title=Taphonomic analysis of a fire-related Upper Triassic vertebrate fossilassemblage from north-central New Mexico , journal=New Mexico Geological Society Field Conference Series , date=2005 , volume=56 , pages=341-354 , url=https://nmgs.nmt.edu/publications/guidebooks/downloads/56/56_p0341_p0354.pdf , accessdate=25 May 2020
Triassic formations of New Mexico
Chinle Formation