Skip to Main Content
GEOREF RECORD

Dating of Pliocene Colorado River sediments; implications for cosmogenic burial dating and the evolution of the lower Colorado River

Ari Matmon, Greg M. Stock, Darryl E. Granger and Keith A. Howard
Dating of Pliocene Colorado River sediments; implications for cosmogenic burial dating and the evolution of the lower Colorado River
Geological Society of America Bulletin (October 2011) 124 (3-4): 626-640

Abstract

We applied cosmogenic (super 26) Al/ (super 10) Be burial dating to sedimentary deposits of the ancestral Colorado River. We compared cosmogenic burial ages of sediments to the age of an independently well-dated overlying basalt flow at one site, and also applied cosmogenic burial dating to sediments with less precise independent age constraints. All dated gravels yielded old ages that suggest several episodes of sediment burial over the past approximately 5.3 m.y. Comparison of burial ages to the overlying 4.4 Ma basalt yielded good agreement and suggests that under the most favorable conditions, cosmogenic burial dating can extend back 4-5 m.y. In contrast, results from other sites with more broadly independent age constraints highlight the complexities inherent in burial dating; these complexities arise from unknown and complicated burial histories, insufficient shielding, postburial production of cosmogenic isotopes by muons, and unknown initial (super 26) Al/ (super 10) Be ratios. Nevertheless, and in spite of the large range of burial ages and large uncertainties, we identify samples that provide reasonable burial age constraints on the depositional history of sediment along the lower ancestral Colorado River. These samples suggest possible sediment deposition and burial at ca. 5.3, 4.7, and 3.6 Ma. Our calculated basinwide erosion rate for sediment transported by the modern Colorado River ( approximately 187 mm k.y. (super -1) ) is higher than the modern erosion rates inferred from the historic sediment load (80-100 mm k.y. (super -1) ). In contrast, basinwide paleo-erosion rates calculated from Pliocene sediments are all under 40 mm k.y. (super -1) The comparatively lower denudation rates calculated for the Pliocene sediment samples are surprising given that the sampled time intervals include significant Pliocene aggradation and may include much incision of the Grand Canyon and its tributaries. This conflict may arise from extensive storage of sediment along the route of the Colorado River, slower paleobedrock erosion, or the inclusion of sediments that were derived preferentially from higher elevations in the watershed.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 124
Serial Issue: 3-4
Title: Dating of Pliocene Colorado River sediments; implications for cosmogenic burial dating and the evolution of the lower Colorado River
Affiliation: Hebrew University of Jerusalem Givat-Ram, Institute of Earth Sciences, Jerusalem, Israel
Pages: 626-640
Published: 20111014
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 85
Accession Number: 2012-012559
Categories: GeochronologyGeomorphology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch map
N35°00'00" - N36°30'00", W115°00'00" - W114°00'00"
Secondary Affiliation: Yosemite National Park, USA, United StatesPurdue University, USA, United StatesU. S. Geological Survey, 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: 201207
Program Name: USGSOPNon-USGS publications with USGS authors
Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal