Holocene chemostratigraphy of spring sediments in Range Creek Canyon, Utah, USA

Abstract

This study builds off the paleoclimatic reconstruction created by Hart et al. that used a multiproxy study to examine the role of moisture in the exodus of the Fremont from Range Creek Canyon in the 12th century. For this research, elemental ratios, weathering indices, and pollen data from two wetland spring sediment cores were used to compare with the existing Hart et al. paleoclimatic reconstruction (Objective 1). Elemental ratios and pollen data proved to be effective proxies for precipitation fluctuation, with the ratio of Pinus to Juniperus pollen representing effective moisture and increasing with the intensity of chemical weathering. Elemental data were additionally used to identify crypto tephra in the cores to validate Range Creek Canyon’s existing chronology (Objective 2). The XRF analysis of the sediment cores constrained the chronology of environmental change in the canyon by identifying the elemental signature of the Mazama eruption (7627 ± 150 cal. year BP). The concentration of Al, Y, and Ti were 50 times higher in this layer than elsewhere in the core, indicating a sudden depositional event, such as a volcanic eruption. Based on the multiproxy data and confirmed chronology, the Fremont entered the canyon during a period of elevated precipitation lasting until 600 AD. Precipitation levels remained steady until 1200 AD, after which precipitation levels decreased, causing drought conditions that coincide with the Fremont’s departure from Range Creek Canyon.