Petrified Forest Member Research Articles

Termite (Insecta: Isoptera) nest ichnofossils from the upper triassic chinle formation, petrified forest national park, Arizona

A fossil nest (calie), including chambers and galleries (runaways), from the lower part of the Petrified Forest Member of the Upper Triassic Chinle Formation in Petrified Forest National Park, Arizona, is similar to nests constructed by modern primitive termites (Insecta: Isoptera), which reflect cooperation in nest construction typical of complex social behavior. A new ichnogenus and ichno‐species, Archeoentomichnus metapolypholeos, is proposed for the distinctive ichnofossil that may represent the efforts of a social caste system in primitive termites. The Late Triassic (Late Carnian) nest also may represent the earliest known fossil evidence of Isoptera (termites) and is suggestive of the antiquity of social behavior among insects. Social behavior in insects, including termites, was previously thought to have evolved in the Early Cretaceous in conjunction with the evolutionary radiation of angiosperms. Because the fossil and ichnofossil record of insects and organisms suggested to be insects dates back...

Preliminary palynological zonation of the Chinle formation, southwestern U.S.A., and its correlation to the Newark supergroup (eastern U.S.A.)

Three informal palynological assemblage zones can be distinguished in samples from Chinle Formation outcrops in Utah, Arizona and New Mexico. The oldest zone (zone I) is in the Temple Mountain Member in southeastern Utah; the middle zone (zone II) is in the Shinarump, Moss Back, Monitor Butte and (lower part of the) Petrified Forest Members (Utah, Arizona and New Mexico); the youngest zone (zone III) is in the upper Petrified Forest Member and silstone member in Arizona and Utah and the silstone member in northcentral New Mexico. Present palynological evidence suggests that Chinle deposition on the Colorado Plateau began locally in late Carnian time and continued at least into the early part of Norian time of the Late Triassic period. Because the upper boundary of the Chinle Formation is an unconformity and the overlying formations are palynologically barren, the length of time represented by this stratigraphic hiatus is not known with certainty. Current palynological evidence suggests, however, that the unconformity at the top of the Chinle cannot be older than early Norian nor younger than Hettangian. Zones I, II and III can now be recognized in the palynomorph assemblage sequences from the Eastern Mesozoic basins, which modifies earlier palynological zonations for the lower portions of the Newark Supergroup. This is based on our identification of palynomorphs not previously known from portions of the Newark Supergroup and the discovery that specific biomarker taxa combinations are the same for both the western and eastern palynomorph sequences. At present palynomorph assemblages from the Chinle Formation and Newark Supergroup compare more closely for zones II and III than they do for zone I, but research is still in progress.

Stratigraphy of the Upper Triassic Petrified Forest Member (Chinle Formation) in Petrified Forest National Park, Arizona, USA

The Petrified Forest Member of the Triassic Chinle Formation in Petrified Forest National Park, Arizona may be divided into a lower and upper unit by means of the Sonsela Sandstone Bed. Analysis of fossil vertebrates indicates that the Sonsela Sandstone Bed and upper Petrified Forest Member are characterized by a fauna distinct from that within the lower portion of the Petrified Forest Member. These faunas are believed to be of Norian and Carnian age respectively. Utilizing fossil vertebrates and certain lithostratigraphic units, especially the Sonsela Sandstone Bed and black forest tuff, exposures may be correlated within and between the Rainbow Forest, Blue Mesa, and Painted Desert areas of Petrified Forest National Park.

Fluvial Sandstone Beds in Petrified Forest Member of Upper Triassic Chinle Formation, Northwest New Mexico and Northeast Arizona: ABSTRACT

Distribution, lithology, and fluvial style of sandstone and conglomerate beds in the upper part of the Petrified Forest Member of the Chinle Formation provide new interpretations of Chinle stratigraphy and environments of deposition. Newly described sandstone beds near Taaiylone, Mitchell Draw, and Crazy Woman Canyon in the Grants-Gallup region, lie, respectively, 60, 110, and 180 m stratigraphically above the top of the widespread Sonsela Sandstone Bed. The Correo Sandstone Bed, exposed on the south flank of Mesa Gigante, 75 km east-southeast of Grants, has been miscorrelated with the sandstone at Mitchell Draw. Subsurface data indicate that the Correo occurs stratigraphically above the other sandstone beds, near the top of the Petrified Forest Member.

Vertebrate paleoecology of the Chinle formation (Late Triassic) of the Southwestern United States

The Late Triassic Chinle Formation is an extensive series of fluvial and lacustrine sediments exposed mostly in the Colorado Plateau region. Fossil vertebrates occur in local concentrations throughout the vertical and horizontal extent of the formation, although the most diverse accumulations occur within the Petrified Forest Member in Arizona and New Mexico. Successive faunas are known from the Lower and Upper Units of the Petrified Forest Member and can be subdivided into terrestrial and aquatic communities. Faunal turnover occurs among herbivores, phytosaurs, and metoposaurs between the Lower and Upper Units. No major change is observed in fish faunas throughout Chinle deposition. Mass accumulations of vertebrate fossils in the Chinle occurred on floodplains, in bogs and small ponds, and in or near fluvial channels. Paleontological and sedimentological evidence supports the interpretation of Chinle paleoclimates as having significant precipitation but being strongly seasonal. Vertebrate occurrences do not clearly reflect the gradual aridification at the end of Chinle deposition suggested by sedimentological study.

Correlation of Upper Triassic Strata Between Southern Colorado Plateau and Southern High Plains, New Mexico: ABSTRACT

Almost 600 m of Upper Triassic strata are exposed in the Hagan basin. They pertain to the basal Agua Zarca member of the Chinle Formation (as much as 80 m), overlain by about 500 m of mud-rock-dominated red beds of the Petrified Forest Member of the Chinle Formation. The top of the Triassic section here is the 5.5-24 m-thick Correo Sandstone Bed of Chinle Formation, which is disconformably overlain by the medial silty member of the Middle Jurassic Entrada Sandstone. At Lamy, approximately 370 m of Upper Triassic strata represent the westernmost outcrops of the Triassic section typical of the Tucumcari basin. This Triassic section consists of about 140 m of Santa Rosa Formation (divisible into three members) overlain by a mud-rock-dominated section (Chinle Formation) split by a medial sandy interval, the Cuervo member (Trujillo Formation of the Palo Duro basin). The youngest Triassic strata near Lamy are rhythmically bedded sediments of the Redonda Member. Based on lithologic similarity, stratigraphic position, and limited paleontological data, the central New Mexico Upper Triassic strata support for the following correlations (from west to east): (1) Shinarump = Agua Zarca = Santa Rosa; (2) lower Petrified Forest = lower shale member of the Chinlemore » = Tecovas; (3) Sonsela = Poleo = Cuervo = Trujillo; (4) upper Petrified Forest = upper shale member of the Chinle; and (5) Owl Rock = Redonda = Correo. These correlations reflect homotaxis of sedimentary cycles across a broad region of the southern Western Interior during the Late Triassic.« less