| Petrified Forest Member | |
| Type: | member |
| Age: | late Triassic, |
| Period: | Norian |
| Prilithology: | Mudstone |
| Otherlithology: | Sandstone, siltstone |
| Namedfor: | Petrified Forest, Navajo and Apache Counties, AZ |
| Namedby: | Herbert E. Gregory |
| Year Ts: | 1947 |
| Region: | New Mexico |
| Country: | United States |
| Coordinates: | 35.074°N -109.78°W |
| Unitof: | Chinle Formation |
| Underlies: | Rock Point Formation |
| Overlies: | Poleo Formation |
The Petrified Forest Member is a stratigraphic unit of the Chinle Formation in Arizona, Colorado, New Mexico, Nevada, and Utah. It preserves fossils dating back to the Triassic period.
Beds (are in alphabetical order, asterisks (*) indicate usage by the U.S. Geological Survey, other usages by state geological surveys):
In the Chama Basin of New Mexico, the Chinle Formation is promoted to group status and the Petrified Forest Formation has the following members:
The Mesa Montosa Member is up to 22meters thick and is mostly composed of sandstone (44%) and mudstone (35%), with a lesser proportion of siltstone (20%). The color is reddish brown to brown and the sandstone is thinly bedded and ripple laminated.
The Painted Desert Member is up to 176meter thick and is primarily reddish brown bentonitic mudstone. The name was originally applied to the beds above the Sonsela Sandstone Bed in Petrified Forest National Park in eastern Arizona. Correlative beds of similar lithology are found throughout west-central and central New Mexico and the Four Corners. The Black Forest Bed within this member has a maximum age of 213 ± 1.7 Ma based on detrital zircon geochronology, with an actual age estimated as 209 Ma. This places the upper part of the Painted Desert Member in the latest Norian age.
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 archosaurs, procolophonids, metoposaurid amphibians, semionotid fish, a decapod, a conchostracan, and unionid bivalves.