Geomorphology and Geochronology of Sand Ramps Adjoining the Coral Pink Sand Dunes, Kane County, Utah

Projected climate change is expected to have widespread impacts on arid regions of the world. Inland, continental dune fields are sensitive to changes in climate and the surrounding environment and are an important source for understanding interactions between Earth’s surface, atmosphere, and biosphere in drylands. Reconstructing past periods of aeolian activity from dune fields can provide insights into how landscapes have responded to previous changes in climate. However, the nature of aeolian systems to recycle older deposits leads to a preservation bias towards only the youngest deposits. Targeting geomorphic settings that are conducive to preserving older records is critical to reconstructing longer and more complete records of landscape change. This MS thesis is divided into three chapters. Chapter One describes the geomorphology and geochronology of sand ramps adjacent to the lower dune field in the Coral Pink Sand Dunes, Utah. Chapter Two is written as a manuscript to be submitted as a Brief Research Report to Frontiers in Earth Science - Quaternary Science, Geomorphology and Paleoenvironment Section. Chapter Two discusses the results of the first chapter in the context of regional paleoclimate and geomorphic records to identify drivers of aeolian activity. Chapter Three is a summary of major findings and discusses suggestions for future work. Chapter One investigates sand ramps in the Coral Pink Sand Dunes (CPSD), Utah, a fault-bound dune field located on the northwestern Colorado Plateau. Sand ramps are topographically-controlled features composed of alluvial, fluvial, and aeolian sediments, and therefore have the potential to store long records of past landscape change. Sand ramp stratigraphy is described in the CPSD from natural exposures where ephemeral streams have incised through the sand ramps. Deposits are characterized as either aeolian, fluvial, or alluvial based on grain size, sorting, and primary bedding structures. Five aeolian units were sampled and analyzed using optically stimulated luminescence (OSL) to constrain timing of aeolian activity. Luminescence dating estimates the last time sediment was exposed to sunlight, providing a way to date past periods of aeolian activity. Stratigraphic positions of dated aeolian deposits are used to reconstruct the geomorphic history of the sand ramps. Results show that the CPSD sand ramps formed during the end of the last glacial (MIS 6) through MIS 5d/e (OSL ~149 ka to OSL ~114 ka) until at least the late Pleistocene-Holocene transition (OSL ~12.5 ka), filling the accommodation space at the base of the Sevier Normal Fault scarp. CPSD dune geochemistry is distinct from nearby dune fields, indicating that aeolian sediments are sourced locally, rather than transported long distances. Chapter 2 compares the CPSD aeolian chronology to other regional dune chronologies, geomorphic records, and paleoclimate reconstructions to identify possible climatic and environmental controls on aeolian activity. Topographic and structural (i.e., fault scarp) controls present in the CPSD sand ramp system have preserved the first evidence of aeolian activity during Marine Isotope Stages (MIS) 6 on the Colorado Plateau. Aeolian activity during the late Pleistocene-Holocene transition (MIS2/1; ~12.5 ka) occurred under conditions that were relatively wetter and cooler than present. Dune activity during the MIS 6 and MIS 5 (~149 to ~114 ka) spans a range of climate conditions during a period of rapid and abrupt change. Rather than a response to any specific climate regime, the late Pleistocene aeolian chronology may instead record changes in sediment supply under variable climate conditions