Detrital sanidine 40Ar/39Ar dating confirms <2 Ma age of Crooked Ridge paleoriver and subsequent deep denudation of the southwestern Colorado Plateau

• Published in: Geosphere (Boulder, Colo.) Colo.), 2021-04, Vol.17 (2), p.438-454
• Main Authors: Heizler, Matthew T, Karlstrom, Karl E, Albonico, Micael, Hereford, Richard, Beard, L. Sue, Cather, Steven M, Crossey, Laurie J, Sundell, Kurt E
• Format: Article
• Language: English
• Subjects: absolute age; alkali feldspar; alluvium; Apache County Arizona; Ar/Ar; Arizona; Bidahochi Formation; Cenozoic; Chuska Sandstone; clastic sediments; Coconino County Arizona; Colorado Plateau; Crooked Ridge River; denudation; feldspar group; fluvial environment; framework silicates; Geochronology; lithostratigraphy; lower Pleistocene; Miocene; Navajo County Arizona; Neogene; New Mexico; Oligocene; paleoenvironment; Paleogene; paleogeography; Pleistocene; Quaternary; Quaternary geology; San Juan County New Mexico; San Juan County Utah; sanidine; sediments; silicates; Tertiary; United States; Utah; White Mesa Alluvium
• ISSN: 1553-040X; 1553-040X
• DOI: 10.1130/GES02319.1

Crooked Ridge and White Mesa in northeastern Arizona (southwestern United States) preserve, as inverted topography, a 57-km-long abandoned alluvial system near the present drainage divide between the Colorado, San Juan, and Little Colorado Rivers. The pathway of this paleoriver, flowing southwest toward eastern Grand Canyon, has led to provocative alternative models for its potential importance in carving Grand Canyon. The ∼50-m-thick White Mesa alluvium is the only datable record of this paleoriver system. We present new 40Ar/39Ar sanidine dating that confirms a ca. 2 Ma maximum depositional age for White Mesa alluvium, supported by a large mode (n = 42) of dates from 2.06 to 1.76 Ma. Older grain modes show abundant 37-23 Ma grains mostly derived ultimately from the San Juan Mountains, as is also documented by rare volcanic and basement pebbles in the White Mesa alluvium. A tuff with an age of 1.07 ± 0.05 Ma is inset below, and hence provides a younger age bracket for the White Mesa alluvium. Newly dated remnant deposits on Black Mesa contain similar 37-23 Ma grains and exotic pebbles, plus a large mode (n = 71) of 9.052 ± 0.003 Ma sanidine. These deposits could be part of the White Mesa alluvium without any Pleistocene grains, but new detrital sanidine data from the upper Bidahochi Formation near Ganado, Arizona, have similar maximum depositional ages of 11.0-6.1 Ma and show similar 40-20 Ma San Juan Mountains-derived sanidine. Thus, we tentatively interpret the