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Book Chapter

Stratigraphic evidence for the role of lake spillover in the inception of the lower Colorado River in southern Nevada and western Arizona

By
P. Kyle House
P. Kyle House
Nevada Bureau of Mines and Geology, University of Nevada, Reno, Nevada 89557, USA
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Philip A. Pearthree
Philip A. Pearthree
Arizona Geological Survey, 416 W. Congress St. #100, Tucson, Arizona 85701, USA
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Michael E. Perkins
Michael E. Perkins
Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA
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Published:
January 2008

Late Miocene and early Pliocene sediments exposed along the lower Colorado River near Laughlin, Nevada, contain evidence that establishment of this reach of the river after 5.6 Ma involved flooding from lake spillover through a bedrock divide between Cottonwood Valley to the north and Mohave Valley to the south. Lacustrine marls interfingered with and conformably overlying a sequence of post–5.6 Ma fine-grained valley-fill deposits record an early phase of intermittent lacustrine inundation restricted to Cottonwood Valley. Limestone, mud, sand, and minor gravel of the Bouse Formation were subsequently deposited above an unconformity. At the north end of Mohave Valley, a coarse-grained, lithologically distinct fluvial conglomerate separates subaerial, locally derived fan deposits from subaqueous deposits of the Bouse Formation. We interpret this key unit as evidence for overtopping and catastrophic breaching of the paleodivide immediately before deep lacustrine inundation of both valleys. Exposures in both valleys reveal a substantial erosional unconformity that records drainage of the lake and predates the arrival of sediment of the through-going Colorado River. Subsequent river aggradation culminated in the Pliocene between 4.1 and 3.3 Ma. The stratigraphic associations and timing of this drainage transition are consistent with geochemical evidence linking lacustrine conditions to the early Colorado River, the timings of drainage integration and canyon incision on the Colorado Plateau, the arrival of Colorado River sand at its terminus in the Salton Trough, and a downstream-directed mode of river integration common in areas of crustal extension.

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Contents

GSA Special Papers

Late Cenozoic Drainage History of the Southwestern Great Basin and Lower Colorado River Region: Geologic and Biotic Perspectives

Edited by
Marith C. Reheis
Marith C. Reheis
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Robert Hershler
Robert Hershler
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David M. Miller
David M. Miller
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Geological Society of America
Volume
439
ISBN print:
9780813724393
Publication date:
2008

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