Английская Википедия:Bell Ranch Formation

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Шаблон:Short description Шаблон:Infobox rockunit The Bell Ranch Formation is a Late Jurassic (Kimmeridgian) geologic formation in eastern and northeastern New Mexico and the western Oklahoma panhandle. Fossil theropod tracks have been reported from the formation.Шаблон:SfnШаблон:Sfn

Description

At the type section near Tucumcari, the formation consists of alternating beds of light gray sandstone and brownish red siltstone. Bed thicknesses vary from Шаблон:Convert, distinguishing the unit from the massive sandstone of the underlying Exeter Sandstone and poorly bedded sediments of the overlying Morrison Formation. Small gypsum nodules are present in the upper beds. Thickness is up to Шаблон:Convert.Шаблон:Sfn Further north, in the valley of the Dry Cimarron, the facies changes to dark mudstone with no cycles and more abundant gypsum. Here the thickness is no more than Шаблон:Convert.Шаблон:Sfn

Fossil content

The formation contains sandy track beds which are "mud-cracked" with finer brownish silty interbeds and an overlying conglomeratic sandstone which fills the mudcracks of the upper bed.Шаблон:Sfn Three trackways of large dinosaurs are present.Шаблон:Sfn

Ichnofossils

History of investigation

The beds making up the unit were originally assigned to the Wanakah Formation, but were renamed by Griggs and Read in 1959 for exposures at Carpenter's Point, Шаблон:Convert northwest of Tucumcari.Шаблон:Sfn The correlation with the Wanakah is uncertain.Шаблон:Sfn In 1987, Conrad et al. correlated the "brown-silt member" assigned by Baldwin and Muehlberger to the Morrison Formation in the valley of the Dry CimarronШаблон:Sfn to the Bell Ranch Formation.Шаблон:Sfn

In 1992, Anderson and Lucas advocated abandoning the Bell Ranch Formation in favor of the Summerville Formation.Шаблон:Sfn However, this has not be universally accepted.Шаблон:Sfn

See also

References

Шаблон:Reflist

Bibliography

Further reading