Date of Award:

8-2022

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Geosciences

Committee Chair(s)

Tammy Rittenour

Committee

Tammy Rittenour

Committee

Patrick Belmont

Committee

Joel Pederson

Committee

Paul Grossl

Committee

Dennis Newell

Abstract

The southwestern United States is characterized by dry climate, and droughts are common. The region is currently in an extreme drought that began in 2000 CE and has lasted longer than any previous drought in at least 500 years. Models predict greater future climate extremes under human-caused climate change. Understanding of the natural range of climate variability is important to put these changes in context. Sedimentary archives of past sand dune activity can help extend the available instrumental observations (last century) and tree-ring records (last millennium).

Sand dunes are landforms that are sensitive to aridity and decreased vegetation cover. They can reactivate and migrate downwind during periods of aridity leaving behind a sediment record of past dune field activity. Research goals were to reconstruct past dune activity the Kanab and San Rafael dune fields in southern Utah. This was accomplished by mapping the dune forms and sampling for age control and sediment character. Modern wind data were compared to the orientation of the older dune forms to determine if wind directions have changed.

The Kanab dune field, in southwestern Utah, was found to have been active five times over the last 10,000 yr. The data indicate 1000 yr-long periods of activity separated by similar duration periods of stability. The San Rafael dune field, in east central Utah contained records of seven episodes of eolian activity from late Pleistocene (~17,000 years ago) to the present. Dunes are active today in this dune field with thinner dune deposits and sparser vegetation suggesting greater wind erosion than in the Kanab dune field. Comparing records between the two dune fields indicates three time periods when they were both actively migrating, suggesting regional aridity ~9,500-7,500, 2000-1500 and 1000-500 years ago. Expanding this comparison to existing sand dune records across the Colorado Plateau suggests at least these three periods, and as many as five periods of regional aridity, may have occurred in the last 10,000 years. Wind and geochemical data indicate similar wind and source sediments have been active over the history of the dune fields.

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