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Reevaluation of the Crooked Ridge River-early Pleistocene (ca. 2 Ma) age and origin of the White Mesa alluvium, northeastern Arizona

Richard Hereford, L. Sue Beard, William R. Dickinson, Karl E. Karlstrom, Matthew T. Heizler, Laura J. Crossey, Lee Amoroso, P. Kyle House and Mark Pecha
Reevaluation of the Crooked Ridge River-early Pleistocene (ca. 2 Ma) age and origin of the White Mesa alluvium, northeastern Arizona
Geosphere (Boulder, CO) (June 2016) 12 (3): 768-789

Abstract

Essential features of the previously named and described Miocene Crooked Ridge River in northeastern Arizona (USA) are reexamined using new geologic and geochronologic data. Previously it was proposed that Cenozoic alluvium at Crooked Ridge and southern White Mesa was pre-early Miocene, the product of a large, vigorous late Paleogene river draining the 35-23 Ma San Juan Mountains volcanic field of southwestern Colorado. The paleoriver probably breeched the Kaibab uplift and was considered important in the early evolution of the Colorado River and Grand Canyon. In this paper, we reexamine the character and age of these Cenozoic deposits. The alluvial record originally used to propose the hypothetical paleoriver is best exposed on White Mesa, providing the informal name White Mesa alluvium. The alluvium is 20-50 m thick and is in the bedrock-bound White Mesa paleovalley system, which comprises 5 tributary paleochannels. Gravel composition, detrital zircon data, and paleochannel orientation indicate that sediment originated mainly from local Cretaceous bedrock north, northeast, and south of White Mesa. Sedimentologic and fossil evidence imply alluviation in a low-energy suspended sediment fluvial system with abundant fine-grained overbank deposits, indicating a local channel system rather than a vigorous braided river with distant headwaters. The alluvium contains exotic gravel clasts of Proterozoic basement and rare Oligocene volcanic clasts as well as Oligocene-Miocene detrital sanidine related to multiple caldera eruptions of the San Juan Mountains and elsewhere. These exotic clasts and sanidine likely came from ancient rivers draining the San Juan Mountains. However, in this paper we show that the White Mesa alluvium is early Pleistocene (ca. 2 Ma) rather than pre-early Miocene. Combined (super 40) Ar/ (super 39) Ar dating of an interbedded tuff and detrital sanidine ages show that the basal White Mesa alluvium was deposited at 1.993 + or - 0.002 Ma, consistent with a detrital sanidine maximum depositional age of 2.02 + or - 0.02 Ma. Geomorphic relations show that the White Mesa alluvium is older than inset gravels that are interbedded with 1.2-0.8 Ma Bishop-Glass Mountain tuff. The new ca. 2 Ma age for the White Mesa alluvium refutes the hypothesis of a large regional Miocene(?) Crooked Ridge paleoriver that predated carving of the Grand Canyon. Instead, White Mesa paleodrainage was the northernmost extension of the ancestral Little Colorado River drainage basin. This finding is important for understanding Colorado River evolution because it provides a datum for quantifying rapid post-2 Ma regional denudation of the Grand Canyon region.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 12
Serial Issue: 3
Title: Reevaluation of the Crooked Ridge River-early Pleistocene (ca. 2 Ma) age and origin of the White Mesa alluvium, northeastern Arizona
Affiliation: U. S. Geological Survey, Flagstaff, AZ, United States
Pages: 768-789
Published: 201606
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 52
Accession Number: 2016-076725
Categories: Quaternary geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch maps
N36°15'00" - N36°40'00", W111°00'00" - W111°00'00"
Secondary Affiliation: University of Arizona, USA, United StatesUniversity of New Mexico, USA, United StatesNew Mexico Institute of Mining and Technology, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201637
Program Name: USGSOPNon-USGS publications with USGS authors
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