November Meeting: Lateral Retreat and Quaternary Evolution of the Book Cliffs of Central Utah – Dr. Joel Pederson (Utah State University)
November 18 @ 5:30 pm - 8:00 pmFree – $20
Title – Lateral Retreat and Quaternary Evolution of the Book Cliffs of Central Utah
Geologists have long invoked escarpment retreat as a prevailing mode of erosion in the Colorado Plateau and other drylands. Yet, research on the evolution of desert escarpments and what controls their erosion is rare and limited by a lack of well dated and complete geomorphic records. We are addressing this research need through work on the Book Cliffs.
Prior investigations of escarpments in the Colorado Plateau and globally garner two end-member conceptual models of how they operate — one focused on bottom-up baselevel drivers and autogenic variations in erosion processes, the other focused on climate as a top-down control on sediment production and transport from cliffs. We test these conceptual models along a section of the Book Cliffs in central Utah, where four generations of talus flatirons and piedmont terraces are mapped and dated by optically stimulated luminescence and 10Be-exposure techniques.
Chronostratigraphic results indicate depositional ages cluster into distinct episodes over the late Quaternary, with sediment production and cliff retreat corresponding to times of climate change or disturbance, rather than to glacial epochs as long presumed. Thus, climate is a primary control driving pulses of mass wasting and sediment storage, with wetter climates of glacial epochs marked by greater piedmont erosion and sediment transport. Timing of sediment production/storage and erosion along the Book Cliffs does not correlate with similarly well-constrained records in Spain or the Negev, yet they all share the pattern of enhanced sediment production and cliff retreat corresponding to climate instability or disturbance.
Assuming that escarpments defined by layered strata maintain their relief and profile over geologic time, geometry dictates that the lateral component of erosion is faster than vertical incision, but has rarely been measured or tested. Terrain analysis on 46 remnant talus-flatiron landforms serves to quantify both escarpment retreat and stream incision over the late Quaternary. Results confirm that lateral cliff retreat proceeds several times faster than vertical incision of toeslopes (~2 m/ky vs. ~0.5 m/ky, respectively) and that retreat rates are similar to the estimates in the Colorado Plateau made by early workers without age control.
Dr. Joel Pederson received his bachelor’s degree in Geology from Gustavus Adolphus College near where he grew up in rural Minnesota. After gaining work experience in environmental remediation, he came to the Southwest for graduate school, earning a master’s degree in Geology from Northern Arizona University and a doctorate in Earth and Planetary Sciences from the University of New Mexico in 1999. Joel has been a faculty member at Utah State University his entire academic career, teaching geomorphology and other courses, mentoring a score of graduate students and many undergraduate researchers, and serving as the Department Head of Geosciences. His geomorphology and geoscience-education research are focused on the landscapes of the Colorado Plateau and the Intermountain West – how those landscapes have evolved by erosion over geologic time, how they respond to climate changes, and the context they provide for prehistoric cultures. Joel is a Fellow of the Geological Society of America and a recipient of GSA’s Biggs Earth Science Teaching Award.