Pedogenesis on talus slopes, the Buckskin range, Nevada, USA

Abstract

Soil development on steep mountainous topography generally leads to thin and undifferentiated pedons. On talus slopes of the Buckskin Mountains, a fault-blocked range of west-central Nevada, USA, thick, differentiated pedons occur. Talus occurs on the western front where block rotation has formed very steep slopes and consists of angular dacite cobbles and boulders. The study area is arid, averaging less than 20 cm of precipitation per year. Typical pedons consist of surface talus filled with vesicular, non-structured, sandy loam to loam material. This material overlies clay-textured, prismatic- and blocky-structured horizons, mostly rock-free that, in places, are over 1 m thick. Pedons are classified as fine, mixed, mesic Xeralfic Paleargids. Soil macro- and micromorphological features, soil mineralogy, and soil chemical and physical attributes suggest the following developmental sequence which began sometime before the middle Pleistocene. The talus serves as a baffle to collect eolian dust. Once eolian dust accumulates to a threshold thickness, primary minerals are transformed, in situ, mostly to a smectitic clay. As clay content increases, a second threshold level is reached at which time the horizon of clay enrichment has sufficient strength and shrink-swell potential to support and raft the talus upward. The exposed talus can then continue to trap eolian dust, the soil profile thickens, and the pedon is protected from erosion. A variation of this soil cumulation process may be partially responsible for textural-B horizon formation in avid and semiarid climates.