PEDOSEDIMENTARY HISTORY AND FLOODPLAIN DYNAMICS OF THE LOWER CRETACEOUS UPPER BLAIRMORE GROUP, SOUTHWESTERN ALBERTA, CANADA

Thick alluvial successions in the upper Blairmore Group in the Foothil ls of southwestern Alberta contain few well-developed paleosol profile s, but abundant evidence of pedogenic modification. The pedogenically modified successions are characterized by vertical root traces, compou nd 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 succ essions contain features similar to modern alluvial soils, Brunisols, and Luvisols. Vertical trends within individual paleosol successions p reserve the changing paleoenvironmental record at each site. The dynam ic nature of the floodplain topography is reflected in alternating dra inage conditions, represented by quasi-regular colour banding, compoun d clay coatings, and the type and degree of pedogenic development upwa rds within the paleosol successions. Overall, the paleosols indicate s oil development under a warm, temperate paleoclimate with seasonal pre cipitation. 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 att ributed to variations in sediment supply and water-table conditions re lated to the overall floodplain geomorphology.