Английская Википедия:Bisbee Group

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The Bisbee Group is a geologic group in Arizona,Шаблон:Sfn Mexico, and New Mexico.Шаблон:Sfn It preserves fossils dating back to the early Cretaceous period.Шаблон:Sfn

Description

The group consists of sandstone, claystone, limestone, and conglomerate,Шаблон:Sfn with a maximum thickness of Шаблон:Convert in the Chiricahua Mountains.Шаблон:Sfn In the Tombstone, Arizona, area, it overlies the Naco Formation.Шаблон:Sfn In the Bisbee area, the group is divided into four formations, which in ascending stratigraphic order are the Glance Conglomerate, the Morita Formation, the Mural Limestone, and the Cintura Formation.Шаблон:Sfn These extend into northern Sonora.Шаблон:Sfn The group is overlain by the Bronco Volcanics,Шаблон:Sfn the Nipper Formation, or the Faraway Ranch Formation.Шаблон:SfnШаблон:Sfn

In the Chiricahua Mountains, where the thickest section is found, the Crystal Cave Formation and Onion Saddle Formation are found between the Glance Conglomerate and the Morita Formation. A thrust fault has placed the lower Jurassic beds over the Cretaceous beds.Шаблон:Sfn

In southwestern New Mexico, the group thickens to Шаблон:Convert and is divided into the Glance Conglomerate, the Hell-to-Finish Formation, the U-Bar Formation, and the Mojado Formation.Шаблон:SfnШаблон:SfnШаблон:SfnШаблон:Sfn

In northwestern Sonora, in addition to the Glance Conglomerate, the Morita Formation, the Mural Limestone, and the Cintura Formation, the group includes the Cerro de Oro Formation and Arroyo Sásabe Formation.Шаблон:Sfn

The group was deposited in the Bisbee basin, which was the central basin of the Jurassic-Cretaceous border rift belt. This rift belt was located between the Mogollon Highlands of central Arizona and New Mexico, which formed the northern shoulder of the belt, and Cordilleran (or Alisitos) volcanic arc along what is now the western side of the Gulf of California.Шаблон:Sfn Deposition began in the late Jurassic with the Glance Conglomerate. This was followed by at least three additional marine transgressions. The second of these was restricted to western Sonora and deposited the Cerro de Oro Formation. This was followed by deposition of typical fluvial, tidal flat, and delta deposits of the Morita Formation to the west and marine beds to the east. The third and largest incursion formed the lagoon belt of the Arroyo Sásabe Formation and the marine Mural Limestone. This was followed by delta deposits of the Cintura Formation. A final small fourth incursion affected only northeastern Sonora.Шаблон:Sfn

Fossils

The group contains fossils such as the mollusc Exogyra and the clam Trigonia characteristic of the Cretaceous.Шаблон:Sfn The limestone formations contain fossils of scleractinian corals from a diversity of genera, including several species not found elsewhere.Шаблон:Sfn

History of investigation

The Bisbee beds were first named by E.T. Dumble in 1902 for exposures around Bisbee, Arizona.Шаблон:Sfn In 1904, Frederick Leslie Ransome divided the Bisbee Group into formations in the Bisbee area.Шаблон:Sfn By 1938, the group had been mapped into the Tombstone, Arizona areaШаблон:Sfn and into southwestern New Mexico.Шаблон:Sfn Samuel G. Lasky defined several new formations within the group, but some of these were synonyms for each other due to fault doubling.Шаблон:Sfn

See also

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References

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External links

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