Genesis and Morphology of Soils Associated with Formation of Laramie Basin (Mima‐Like) Mounds in Wyoming

Abstract

AbstractSmall mounds of varied origin are a common microrelief feature over much of the western United States. In Wyoming's Laramie Basin, soil genesis and mound formation were studied in a 27.5 m long trench dug to expose intermound soils with strongly developed horizonation (Borollic Haplargids) and two mounds with weakly developed soils (Borollic Camborthids). Fossil permafrost sand wedges, common along the trench exposure, are believed to be evidence of a mid‐ to late‐ Wisconsin periglacial environment. The intermound soils date from pre‐ to early Wisconsin and were formed by a sequence of alluvial deposition, argillic horizon development, carbonate accumulation, sand wedge formation, and development of a second argillic horizon with weak carbonate accumulation. Mound formation occurred as a result of upwellings of gravelly substrata induced by cryostatic pressure. The gravelly pipes broke through large fossil sand wedges to the soil surface forming the mounds. Subsequent soil formation on the mounds has involved cambic horizon development, leaching of salts, and weak carbonate accumulation.