Soil toposequences in Carbon County, Wyoming: Pedogenic processes in a semi-arid region

The subject of this study is a set of four soil toposequences developed in late Tertiary sediments on the sagebrush steppe of south-central Wyoming. Most toposequence studies have been done in humid temperate climates, where soil morphological response to topographic and microclimatic variation is very distinctive. These soils, however, are developmentally quite young, and the climate of Carbon County is cold and dry. Thus, one purpose of this study was to determine the nature of topo-morphological relationships in a cool, dry climate; another was to evaluate the applicability of the toposequence as a framework for pedologic studies in such climates.; Another objective of this study was to evaluate interdisciplinary analytical methods for pedologic studies. These methods included petrographic examination of soils for determination of packing density, grain shape and surface morphology, and analysis of cumulative particle-size distribution plots both visually and by use of descriptive statistical parameters. More traditional pedologic methods were involved in sample selection, collection, description and classification of soils.; Emphasis on the nature of pedogenic process, rather than total absorption in the morphological product, was an important feature of this study. This focus enabled us to discern an inverse relationship between soil moisture and temperature and soil depth, and to attribute much of soil formation to freeze-thaw and wetting-drying cycles, and to vegetative activity. Some morphological features which indicate weathering in humid climates are invalid for these soils: clay production and illuviation, clay and Fe oxide relationships. Several descriptive systems were devised from petrographic and particle-size distribution data. Statistical interpretations of cumulative log-probability plots of these data are especially promising as semi-quantitative descriptors of parent material alteration.