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

Abstract

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.