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The stratigraphy of the Upper Cretaceous rocks north of the Arkansas River in eastern Colorado

1937; United States Government Publishing Office; Linguagem: Inglês

10.3133/pp186k

2330-7102

C. H. Dane, William Gamewell Pierce, John B. Reeside,

Geological formations and processes

A comparison of the _ stratigraphic sections of the rocks of Benton age in western Kansas and the southern foothill region of eastern Colorado indicates the probability that the lower "11.embers of the Greenhorn of Kansas merge westward into the nnper part of the Graneros shale of the foothills, the Green-!rn of the type locality being much thinner than that of western Kansas and the Graneros of the type locality being much thicker than the Graneros of western Kansas.The Greenhorn of Prowers County, Colo., north of • the Arkansas River, has, however, the thickness of the Kansas Greenhorn, and the member subdivisions of the Greenhorn made in Kansas can also be recognized in Prowers County.'J'he Carlile shale, which overlies the Greenhorn, contains at the top the persistent but variable Codell sandstone member.This member, which contains the Carlile fauna, is believed to have been deposited.in shallow water under conditions that were maintained fori ~onsiderable period of time.The faunal discontinuity between the Carlile and the overlying Niobrara formation •is believed to represent a time lapse, although no evi~ence was seen to indicate subaerial erosion of the Carlile.In the foothill region of Colorado the Niobrara consists of the Timpas limestone member and the overlying Apishapa shale member.The Timpas includes in its upper part limy shales and thin limestone beds which, in Kansas, have been excluded from the basal Hays limestone member.The Hays limestone member appears to be a more satisfactory lithologic and faunal unit, and the name is therefore extended into that part of Colorado east of the foothills and north of the Arkansas River.Similarly, the name "Smoky Hill" is extended from the chalk member of that name in Kansas .to the marl member overlying the• Hays limestone in eastern Colorado.The basal portion of the overlying Pierre shale consists of black shale nearly devoid of fossils, to which the name "Sharon Springs member" is extended from the type locality in Wallace County, Kans.The overlying portion of the Pierre shale was not sufficiently studied to warrant the establishment of member names, although the "rusty zone", ''tepee zone", and "transition zone" of previous authors are recognized.The known invertebrate faunas of the several formations are briefly described, and the fauna of the overlying Fox Hills sandstone is also discussed beca.use of its close relationship to the fauna of the "transition zone" of the Pierre shale.