Poleo Formation | |
---|---|
Stratigraphic range: | |
Type | Formation |
Unit of | Chinle Group |
Underlies | Petrified Forest Formation |
Overlies | Salitral Formation |
Thickness | 30 m (98 ft) |
Lithology | |
Primary | Sandstone |
Other | Conglomerate |
Location | |
Coordinates | 36°10′25″N106°39′13″W / 36.173563°N 106.6534824°W |
Region | New Mexico |
Country | United States |
Type section | |
Named for | Poleo Mesa (now known as Mesa Montoso) |
Named by | Huene |
Year defined | 1911 |
The Poleo Formation is a geologic formation in northern New Mexico. Its stratigraphic position corresponds to the late Triassic epoch.
The Poleo Formation is a cliff-forming formation composed mostly of yellowish-gray fine to medium sandstone, but with up to 20% conglomerate. The sandstone shows cross bedding and cuspate ripples. It resembles the Shinarump Conglomerate, and the two formations can be difficult to distinguish where they are not separated by the Salitral Formation. However, the Poleo Formation is finer grained and shows other distinguishing lithological features. [1] The lower contact with the Salitral Formation is sharp and scoured, while the upper contact with the Petrified Forest Formation is gradational. The Poleo Formation has an inverse thickness relationship with the Salitral that suggests the thick sections fill valleys cut into the Salitral. [2]
The formation is exposed throughout the Chama Basin, the Nacimiento Mountains, and Jemez Mountains of New Mexico. It divides the lower and upper Chinle Group where present, but rapidly pinches out to the south, where the underlying Salitral Formation becomes indistinguishable from the overlying Petrified Forest Formation. [3] [1] [2]
The Poleo Formation is at the same stratigraphic position as the Trujillo Formation of West Texas and eastern New Mexico, the Sonsela Member of the Petrified Forest Formation in west-central New Mexico and northeastern Arizona, and the Moss Back Member of southern Utah and southwestern Colorado. All are extensive sandstone sheets, but the Poleo Formation is distinguished by its great local thickness, grayish-yellow color, and lithology of micaceous litharenite and mixed-clast conglomerate. [2]
The formation is almost devoid of fossils, yielding only oxidized fragments of petrified wood and indeterminate vertebrate bone that are unusable for biostratigraphy. [2]
Huene described the unit in 1911, giving it the name "Poleo-top-sandstone" as the caprock of Mesa Montosa (which he knew as "Mesa Poleo"). [2] During their petroleum survey in 1946, Wood and Northrop formally named it the Poleo sandstone lentil of the Chinle Formation. [3] Lucas and Hunt renamed the unit the Poleo Formation in the same 1992 study in which they raised the Chinle Formation to group rank. [4]
The exposed geology of the Capitol Reef area presents a record of mostly Mesozoic-aged sedimentation in an area of North America in and around Capitol Reef National Park, on the Colorado Plateau in southeastern Utah.
The Cutler Formation or Cutler Group is a rock unit that is exposed across the U.S. states of Arizona, northwest New Mexico, southeast Utah and southwest Colorado. It was laid down in the Early Permian during the Wolfcampian epoch.
The Moenkopi Formation is a geological formation that is spread across the U.S. states of New Mexico, northern Arizona, Nevada, southeastern California, eastern Utah and western Colorado. This unit is considered to be a group in Arizona. Part of the Colorado Plateau and Basin and Range, this red sandstone was laid down in the Lower Triassic and possibly part of the Middle Triassic, around 240 million years ago.
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 New Mexico, it is often raised to the status of a geological group, the Chinle Group. Some authors have controversially considered the Chinle to be synonymous to the Dockum Group of eastern Colorado and New Mexico, western Texas, the Oklahoma panhandle, and southwestern Kansas. The Chinle Formation is part of the Colorado Plateau, Basin and Range, and the southern section of the Interior Plains. A probable separate depositional basin within the Chinle is found in northwestern Colorado and northeastern Utah. The southern portion of the Chinle reaches a maximum thickness of a little over 520 meters (1,710 ft). Typically, the Chinle rests unconformably on the Moenkopi Formation.
The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much thinner. The Dockum rests on an unconformity over the Anisian aged Anton Chico Formation.
Redondasaurus is an extinct genus or subgenus of phytosaur from the Late Triassic of the southwestern United States. It was named by Hunt & Lucas in 1993, and contains two species, R. gregorii and R. bermani. It is the youngest and most evolutionarily-advanced of the phytosaurs.
The Garita Creek Formation is a geologic formation in New Mexico that contains vertebrate fossils characteristic of the Carnian Age of the late Triassic.
The Santa Rosa Formation is a geologic formation exposed in New Mexico that was deposited in the Carnian Age of the late Triassic Period.
The Shinarump Conglomerate is a geologic formation found in the Four Corners region of the United States. It was deposited in the early part of the Late Triassic period.
The Trujillo Formation is a geologic formation in Texas and New Mexico. It preserves fossils dating back to the upper Triassic period. It is also known as the Trujillo Sandstone.
The Sandia Formation is a geologic formation in New Mexico, United States. Its fossil assemblage is characteristic of the early Pennsylvanian.
The El Cobre Canyon Formation is a geologic formation in New Mexico. It preserves fossils dating back to the late Pennsylvanian to early Permian periods.
The Galisteo Formation is a geologic formation in New Mexico. It contains fossils characteristic of the Bartonian stage of the Eocene epoch, Duchesnean in the NALMA classification.
The Bluewater Creek Formation is a geologic formation in west-central New Mexico. It preserves fossils dating back to the late Triassic period.
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.
The Salitral Formation is a Late Triassic geologic formation found in north-central New Mexico, primarily the northwestern Jemez Mountains. It is an older subunit of the Chinle Group, overlying the Shinarump Conglomerate and underlying the Poleo Formation.
The San Pedro Arroyo Formation is a geologic formation in south-central New Mexico. It preserves fossils dating back to the late Triassic period.
The Rock Point Formation is a geologic formation in New Mexico, Arizona, and Utah. It preserves fossils dating back to the late Triassic.
The Arroyo del Agua Formation is a geologic formation in New Mexico. It preserves fossils dating back to the early Permian period.
The Chama Basin is a geologic structural basin located in northern New Mexico. The basin closely corresponds to the drainage basin of the Rio Chama and is located between the eastern margin of the San Juan Basin and the western margin of the Rio Grande Rift. Exposed in the basin is a thick and nearly level section of sedimentary rock of Permian to Cretaceous age, with some younger overlying volcanic rock. The basin has an area of about 3,144 square miles (8,140 km2).