Lower Cretaceous in Colorado Plateau

Abstract

Fossil collections consisting of non-marine microfossils, plants, and mollusks have recently been made from the Cedar Mountain and Burro Canyon formations of the Colorado Plateau. The containing sediments have previously been considered to be either Jurassic or Late Cretaceous but the fossil evidence indicates early Cretaceous age. The Morrison formation as previously understood should therefore be reduced in thickness and the so-called Dakota regarded as consisting, locally at least, of early Cretaceous sediments. Separation of the Lower Cretaceous beds is difficult if not impracticable in many areas but in others the base is marked by a thin conglomerate which may bridge the Jurassic-Cretaceous time plane.