Overview of the Cenozoic geomorphic evolution of the Colorado River through Glen Canyon and Upper Colorado River Corridor and how it relates to the age and origin of Grand Canyon, Colorado Plateau, USA

Abstract

The overall purpose of this paper is to integrate the geomorphic evolution of Glen Canyon and Upper Colorado River Corridor with that of Grand Canyon in order to address two key enigmas: why did the Colorado River not arrive at the mouth of Grand Canyon until 5.5 Ma, and how did the Colorado River cross the Kaibab arch high? This evolution was approached from three different perspectives: (1) by reviewing geologic investigations in the Glen Canyon area from the late 1800s to the present; (2) by explaining how a paleo-Colorado River constrained within a lake or a chain of lakes on the Colorado Plateau is necessary for the Colorado River to have arrived at the mouth of Grand Canyon ca. 5.5 Ma; and (3) by proposing how the incision rates in Marble Canyon, Glen Canyon, and central Colorado Plateau may be related to a prolonged base-level fall at the Confluence of the Colorado-Little Colorado rivers starting at ~5.5 Ma, to a karst-connection model of a Colorado River crossing under the Kaibab arch, or to a lake-overflow model. An attempt was made to find field and analytic evidence for a pre-5.5 Ma Miocene lake along the north to west sides of Navajo Mountain, Utah, where high pediment surfaces still remain along the Colorado River, but from field investigations, 26Al10Be cosmogenic dating, and SEM analysis, no direct evidence for a past lake was substantiated. However, a number of lines of indirect evidence are discussed supporting the possible existence of a Miocene lake or chain of lakes along Glen Canyon and Upper Colorado River Corridor. A lake-overflow model is compared with a karst-connection model as to how the Colorado River might have crossed the Kaibab arch.