Eolian deposition in the alpine zone of the Uinta Mountains, Utah, USA

Field and laboratory investigations were conducted to determine the origin of a ubiquitous layer of silt that caps soil profiles in the alpine zone of the Uinta Mountains, Utah, USA. Fine sediment isolated from snowbanks was studied to constrain the fraction of this material derived from allochthonous eolian additions. Lake sediments representing deposition over the past few centuries were analyzed to determine whether dust deposition in the Uintas has been a long-term process, and if properties of the modern dust differ from dust which accumulated prior to European settlement. Results indicate that alpine soils have been strongly influenced by long-term eolian deposition. The loess cap in these soil profiles averages 18 cm thick, and physical and chemical properties of soil horizons derived from the eolian parent material are significantly different than those of the subsurface horizons derived from in situ produced congelifractate. Fine sediment observed at the surface of snowbanks in the early summer is a mixture of silty exotic eolian material and sandy locally derived sediment. Snowbanks on ridgecrests and on slopes of blocky scree tend to accumulate the maximum amount of exotic dust with the minimum amount of local material. The grain-size distribution, mineralogy, and geochemistry of lake sediments indicate that dust has been accumulating in the Uintas for at least the last few centuries. Modern lake sediments are significantly enriched in elements indicative of upwind mining and agricultural activity, recording an anthropogenic change in dust composition following settlement of the surrounding lowland basins.