PEDOGENIC AND GEOCHEMICAL PROCESSES OF ULTRAMAFIC SOILS ALONG A CLIMATIC GRADIENT IN SOUTHWESTERN BRITISH-COLUMBIA

This paper presents information on pedogenic processes, weathering sta tus and geochemical evolution of ultramafic soils at three areas in so uthwestern British Columbia characterized by climatic conditions rangi ng from relatively wet-cool to relatively dry-cool. The soils of the C oquihalla serpentine belt have Podzolic profiles that resulted from in tense weathering in a moist environment. The Tulameen area has a moder ately dry climate, and Brunisolic soils have developed in serpentinize d peridotite and dunite. Brunisolic soils with composite profiles of t ephra overlying serpenite developed in a dry environment at the Shulap s area. We investigated the weathering- status of five soils using a v ariety of chemical and mineralogical techniques. Chlorite arid mica we athering was indicated by XRD analysis of clay fractions for the Podzo lic soils at the Coquihalla area. Serpentine dissolution was also indi cated by geochemical analysis of these upland soil profiles. Weatherin g and leaching depleted Mg from B horizons relative to parent material s. Chromium accumulated in B horizons of the soils, and was associated with high levels of Fe(d). The distribution of total and extractable Ni and Co indicated that these elements were transported to the C hori zons in all but die driest environments. Redistribution of Mn also occ urred, but to a lesser extent. The distribution patterns of Cr, Mn, Co , and Ni were useful indicators during the early stages of ultramafic pedogenesis.