Soils and soil-forming processes in a cool-dry environment: The upper Green River Basin, western Wyoming, United States

This study documents the effects of periglacial and eolian processes on the development of a calcic soil chronosequence in the upper Green River Basin in western Wyoming. The soils are formed on a flight of ten fluvial terraces ranging in height from 3 to 207 meters above the modern Green River channel. The upper Green River Basin is a cool, semi-arid sagebrush steppe. This study represents the first detailed investigation of soils on this landscape.; The soils on the upper eight terraces are morphologically similar. The soils on the T-3 through T-10 surfaces have a similar sequence of horizonation (A-Bt-Btk-Bk-BCk-Ck), and all classify as Ustic Calciargids. Calcic horizons on T-3 through T-10 have pedogenic ooids, carbonate nodules, and fragments of petrocalcic material embedded within non-cemented, friable, carbonate-rich matrix. However, none of the soils reach Stage IV carbonate morphology.; There is a dichotomous relationship between the calcic horizons and the overlying A and Bt horizons. The calcic horizons indicate progressive development with time. Also, thickness of the desert dust layer increases on the higher terraces. Conversely, the overlying A and Bt horizons show minimal changes with increasing terrace height. There is a trend of overall textural fining with increasing terrace height, especially evident in the sand fractions of the surface horizons. However, I interpret the textural fining as an eolian sorting effect.; I propose a model of pedogenesis, the Cryo-Calcic Theshold Model, which explains these trends in three stages. In Stage 1 (interglacial climate), the overall trend in soil development includes the slow accumulation of desert dust, translocation and redistribution of silicate clay, carbonates and other soluble salts, and the development of incipient petrocalcic horizons. In Stage 2 (full glacial climate), the soils experience periglacial conditions. The surface horizons are stripped by strong periglacial winds, and the upper portions of the calcic (and any incipient petrocalcic) horizons are disrupted by thermal cracking and cryoturbation. These processes lead to sand wedges, involutions, injections, dissolution by cold melt water, and many other permafrost features in the soils. Finally, in Stage 3 (return to interglacial climate) the soils resume the accumulation of desert dust, and the permafrost features are slowly buried and masked by pedogenesis. This model fits and may explain many of the trends observed by workers in other parts of Wyoming and adjacent areas. (Abstract shortened by UMI.)...