Earth and Planetary Sciences ETDs

Publication Date

9-10-2010

Abstract

The Hualapai Limestone, at the western edge of the Colorado Plateau, provides the best sedimentary record available for 12 to 6 Ma at the mouth of the Grand Canyon. Because it directly underlies the first Colorado River gravels, this unit is a key element for understanding the integration of the Colorado River from the Colorado Plateau to the Basin and Range province, and the early paleogeography of the Grand Canyon region. This study combines a tectonic investigation with a stratigraphic and sedimentologic analysis that includes new geochemistry, tephrochronology, and detrital zircon analysis to examine variations of the sedimentary and tectonic records from the Hualapai Limestone basins. Thickness variations, with progressively thicker deposits towards the east in two of the four basins, indicate syntectonic deposition of the unit in half grabens formed above listric faults with 5-11 km depth to detachments. A sedimentary facies analysis highlights that the Hualapai Limestone was deposited in spring-fed lake and marsh systems fed by groundwater similar in composition to modern Havasu Creek and western Colorado Plateau groundwater. Stable isotope analysis of carbon and oxygen suggests gradual increase in meteoric water input through time. Sr isotopes, though variable, show an up-section decrease in 87Sr/86Sr and confirm a freshwater origin for the Hualapai Limestone. These data, plus facies analysis, suggest that waters that fed the Hualapai Limestone contained a significant component of endogenic spring inputs. Detrital zircon data for the Grand Wash trough indicate that red siltstones that underlie and interfinger with the Hualapai Limestone, from 13 to 6 Ma, were not derived from the Colorado Plateau, but likely from the Kingman Arch to the south. Western basins contain a more diverse suite of detrital zircons, suggesting possible connections to a northern Paleo Virgin River source. Tephrochronologic analyses show a 12 Ma ash near the base of the unit, extending the basal Hualapai date. We propose that the Hualapai Limestone was a long-lived (12-6 Ma) groundwater-fed series of lake and marsh systems that were deposited in syntectonic half grabens via spring vents along faults and discharge along the dissected aquifer of the Grand Wash Cliffs.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Karlstrom, Karl

Second Committee Member

Allen, Bruce

Project Sponsors

Geological Society of America National Science Foundation United States Geological Survey

Language

English

Keywords

Hualapai Limestone, Colorado River, Grand Canyon, geochemistry, detrital zircon

Document Type

Thesis

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