Application of Relative-Age Dating Techniques on Rock Glaciers of the La Sal Mountains, Utah: An Interpretation of Holocene Paleoclimates

Abstract

This paper applies a variety of relative-age dating techniques on rock glaciers of the La Sal Mountains, Utah to interpret the area's Holocene paleoclimates. Relative ages of rock glaciers and talus of the La Sal Mountains, Utah, were determined using several techniques: lichenometry, Schmidt-hammer rebound value, clast roundness, clast surface roughness, and weathering rind thickness. The techniques were compared against one another and evaluated as to their effectiveness. Lichenometry can be used to differentiate among depositional episodes of the past 2–3000 yrs, but lichens are sometimes adversely affected by environmental factors such as prolonged snowcover, which can periodically reduce or eliminate thalli. Rock hardness, as measured by the Schmidt hammer, and roundness did not prove to be particularly useful in differentiating sites. Weathering rind development is less subject to variations in rate, and its measurement is less subjective than most of the other methods. Weathering rinds were therefore used in conjunction with lichenometry to establish a Holocene paleoclimatic chronology. The combination of methods permits some potential disadvantages of lichenometry to be exploited to advantage and used for paleoenvironmental interpretation.Data support a threefold sequence of deposition during the late Holocene. Weathering rind data indicate deposition in early Holocene-late Pleistocene as well, but precise relative-dating of this older material is beyond the resolving abilities of these techniques. Our conclusions are in general agreement with radiometrically-based Holocene chronologies of the Colorado Front Range.