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

This paper presents information on pedogenic processes, weathering status and geochemical evolution of ultramafic soils at three areas in southwestern British Columbia characterized by climatic conditions ranging from relatively wet-cool to relatively dry-cool. The soils of the Coquihalla serpentine belt have Podzolic profiles that resulted from intense weathering in a moist environment. The Tulameen area has a moderately dry climate, and Brunisolic soils have developed in serpentinized peridotite and dunite. Brunisolic soils with composite profiles of tephra overlying serpenite developed in a dry environment at the Shulaps area. We investigated the weathering- status of five soils using a variety of chemical and mineralogical techniques. Chlorite arid mica weathering was indicated by XRD analysis of clay fractions for the Podzolic soils at the Coquihalla area. Serpentine dissolution was also indicated by geochemical analysis of these upland soil profiles. Weathering and leaching depleted Mg from B horizons relative to parent materials. 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 horizons in all but die driest environments. Redistribution of Mn also occurred, but to a lesser extent. The distribution patterns of Cr, Mn, Co, and Ni were useful indicators during the early stages of ultramafic pedogenesis.