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Anatomy of an Arkansas River Sand Bar: Abstract
Detailed relationships between cross-bed measurements and shifting channel patterns will be demonstrated, and grain size analyses showing a wide variety of distributions will be presented.
The sand bar is located in the Arkansas River valley approximately 10 miles upstream from Tulsa, Oklahoma. From aerial photo sequences, plus discharge and river stage records, it was determined that the entire sand bar (600,000 cubic yards) was deposited in 156 hours. Deposition occurred during two floods, May 19 to 22, 1957 (60 hours) and October 3 through 6, 1959 (96 hours).
The sand bar was studied in detail along a natural cubank (500 feet long) parallel to the valley axis and in a trench (700 feet long by 15 feet deep) dug perpendicular to the cutbank. Sand peels and box cores were taken, and cross-bed types were recorded. Closely spaced cross-bed measurements (N = 210) recorded at 12 vertical sections, and grain size analyses were performed on 210 samples from the same sections.
Results show that the highly variable patterns of cross-bed dips match the erratic and changing flow directions prevalent during flood stages. In some of the vertical sections, cross-bed dip directions are at all angles to the overall east-west orientation of the Arkansas River valley. Mean grain size ranges from 0.07φ (0.95 mm) to 4.44φ (0.05 mm), and standard deviation ranges from 0.26φ to 1.48φ At most of the vertical sections, grain size distributions show no systematic change from bottom to top.
Acknowledgments and Associated Footnotes
1 Amoco Production Company, P.O. Box 591, Tulsa, Oklahoma 74102 U.S.A.
Copyright © 2009 by the Canadian Society of Petroleum Geologists