Английская Википедия:Gila Group
Шаблон:Use American English Шаблон:Short description Шаблон:Infobox rockunit
The Gila Group is a group of geologic formations found along the upper tributaries of the Gila River in Arizona and New Mexico.Шаблон:Sfn Radiometric dating of lava flows within the group yields an age of Miocene to Quaternary.Шаблон:SfnШаблон:Sfn
Description
The group is primarily conglomerate composed of clasts (rock fragments) weathered from nearby outcrops. There are also occasional thin sandstone and tuff beds and basalt flows. Total thickness is Шаблон:Convert.Шаблон:Sfn Radiometric ages of basalt flows within the group range from 12.1 million years (Ma)Шаблон:Sfn to 1 Ma.Шаблон:Sfn
The group is similar in age and character to the Santa Fe Group. Both are sedimentary fill of extensional basins. The two groups are separated by the Continental Divide, and the Gila Group is separated from formations of similar age to the north by the Rim Divide, which separates the San Francisco and Salt River drainage basins to the south from the Little Colorado River drainage basin to the north.Шаблон:Sfn
Fossils
The Gila Group has yielded a diversity of fossils at Pearson Mesa (Шаблон:Coord). These include four species of turtle, a heron, and fifteen mammal species. The latter includes the armadillo-like Glyptotherium arizonae, which is found in the southwestern United States only in beds of early Irvingtonian age.Шаблон:Sfn
History of investigation
The unit was first named as the Gila Conglomerate by G.K. Gilbert in 1875 from his participation in the Wheeler Survey. Only a type area was defined.Шаблон:Sfn By 1903 F.L. Ransome had mapped the unit into the Globe area.Шаблон:Sfn P.A. Wood divided the unit into the Bonita beds, Solomonsville beds, and Frye Mesa beds in 1960.Шаблон:Sfn In 1963, L.A. Heindl raised the unit to group rank and divided it into the San Manuel, Quiburis, and Sacaton Formations,Шаблон:Sfn but M.H. Krieger and coinvestigators removed the San Manuel and Quiburis Formations from the Gila and abandoned the Sacaton Formation, restoring the Gila to formation rank.Шаблон:Sfn J.C. Ratte and coinvestigators redesignated the unit as the Gila Formation based on its diverse lithology.Шаблон:Sfn
Cather and his coinvestigators redefined the extent of the Gila Group in 1994 as part of a sweeping revision of stratigraphy in western New Mexico and eastern Arizona. They retain it at group rank.Шаблон:Sfn
Footnotes
References
- Шаблон:Cite journal
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- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite journal
