Abstract

Thick alluvial successions in the upper Blairmore Group in the Foothills of southwestern Alberta contain few well-developed paleosol profiles, but abundant evidence of pedogenic modification. The pedogenically modified successions are characterized by vertical root traces, compound illuvial clay coatings, and ferruginous coatings and nodules. Five representative paleosol successions, composed of nine microfacies, are analyzed. The paleosol successions indicate soil development on more or less continuously aggrading floodplains; however, locally, rates of sedimentation and pedogenesis were highly variable. The paleosol successions contain features similar to modern alluvial soils, Brunisols, and Luvisols. Vertical trends within individual paleosol successions preserve the changing paleoenvironmental record at each site. The dynamic nature of the floodplain topography is reflected in alternating drainage conditions, represented by quasi-regular colour banding, compound clay coatings, and the type and degree of pedogenic development upwards within the paleosol successions. Overall, the paleosols indicate soil development under a warm, temperate paleoclimate with seasonal precipitation. Although representing minor diastems, the paleosols formed contemporaneously with sedimentation and are an integral part of the alluvial successions. Local variations in paleosol development are attributed to variations in sediment supply and water-table conditions related to the overall floodplain geomorphology.

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