Discovery of beach sand, beachrock, and capping tufa on Balakai Mesa: Implications of the Bidahochi Formation and the overflow origin of the Grand Canyon

Douglass, John; Gootee, Brian F.

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Author

Douglass, John
Gootee, Brian F.

Affiliation

Paradise Valley Community College
Arizona Geological Survey

Issue Date

2024

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Citation

Douglass, J. and Gootee, B.F., 2024. Discovery of beach sand, beachrock, and capping tufa on Balakai Mesa: Implications for the Bidahochi Formation and the overflow origin of the Grand Canyon: University of Arizona, Arizona Geological Survey, Open-File Report 24-02, 9 p.

Publisher

Arizona Geological Survey (Tucson, AZ)

Description

During the transition from Miocene to Pliocene, an enormous lake existed in the Bidahochi basin. The lake sat upstream of the Kaibab Plateau was fed by the Colorado River. The lake dates from ~8 to <6 Ma, which predates the Grand Canyon. In the literature, various sources estimated the lake highstand elevation to be about 2,000 m. The highstand of the lake needed to be roughly 2,300 m to have spilled across the Kaibab Plateau. We assumed that erosion and removal of even higher high-stand lake deposits could account for the present absence of lake deposits above 2,000 m. Therefore, we searched for higher, unidentified lake deposits using geologic maps and Google Earth. We then visited numerous outcrops during multiple field trips to test our results. We found two separate facies: south of the town of Greasewood, AZ subaerial deposits dominate with minor lenses of lacustrine sediments. North of Greasewood, however, subaerial deposits are absent and lacustrine deposits dominate. We interpret the lack of subaerial deposits north of Greasewood and on Balakai Mesa to result from the capture of one or more streams that had previously drained from the Chuska Mountains into the Bidahochi basin. The stream capture shut off most of the sediment supply. The reduced sediment input allowed for the deposition and preservation of three units on Balakai Mesa: beach sand, followed by beachrock and capping tufa. Beachrock formed during periods of higher sand input and the capping tufa as the sand input decreased. The carbonate precipitation necessary for beachrock and capping tufa resulted from three different mechanisms: 1. Evidence for a biologic origin of the tufa includes individual algae filament sheaths and coarse concentrations of algal filaments. Further evidence includes sand grains, ooids, and peloids deposited within massive to structured micrite and laminated cements that built microbialites within the tufa. 2. Piping structures at the contact between the beach sand and the capping tufa are consistent with a groundwater or lake water recirculation origin. Differences in water chemistry between lake and groundwater or recycled lake water could drive carbonate deposition. 3. Wave agitation also likely played a role in carbonate production. The lake would have had a long fetch of 150 km, allowing wind driven waves to form over long distances. The agitation of waves promoted degassing of CO2 and precipitation of CaCO3. The newly identified beach sand, beachrock, and capping tufa deposits are exposed at nearly 2,250 m, just 50 m below the 2,300 m elevation needed for a lake to spill over the Kaibab Plateau. Deposits between 2,250 and 2,300 are likely eroded, not yet identified or mapped, or poorly preserved due to rapid expansion near the maximum depositional highstand. These discoveries support the hypothesis that the Colorado River drained into and filled Lake Bidahochi to the point where the lake overflowed the Kaibab Plateau and cut the Grand Canyon.

URI

http://hdl.handle.net/10150/673799

Additional Links

https://library.azgs.arizona.edu/

Language

Series/Report no.

Arizona Geological Survey Open File Report

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Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact azgs-info@email.arizona.edu.

North Bounding Coordinate

37.18

South Bounding Coordinate

34.47

West Bounding Coordinate

-112.12

East Bounding Coordinate

-108.77

Collections

AZGS Document Repository