VARIABILITY OF INTERFLUVE PALEOSOLS WITH DISTANCE FROM PALEO-VALLEYS IN THE CENOMANIAN DUNVEGAN FORMATION, NE BRITISH COLUMBIA, CANADA

Five interfluve paleosols from the Cenomanian Dunvegan Formation have been studied in order to explore the relationships between interfluve paleosol variability and distance to the margins of coeval paleo-valleys. A detailed stratigraphic framework has been established for the Dunvegan Formation and a set of paleo-valley maps have been constructed that enables each interfluve paleosol to be placed in a precise paleogeographic context with respect to distance from coeval valley margins and shorelines. Pedosedimentary reconstructions of the five interfluve paleosols indicate that paleosols closest to valley margins have thicker sola and contain thicker Bt horizons with greater quantities of illuviated clay than those further from valley margins. All of the paleosols display hydromorphic features to some degree, although features indicating pervasively poorly-drained conditions are most common further from the valley margins. Molecular ratios and geochemcial mass-balance calculations for these interfluve paleosols suggest greater leaching and increased weathering closer to valley margins. Furthermore, interfluve paleosols closest to valley margins are most likely to contain geochemical evidence of a brackish water influence that may be attributed to marine hydromorphism during subsequent transgression.

During the initial stages of soil development, before valley incision, the water table was probably near the surface most of the time, and reducing conditions prevailed. As the valleys incised, the interfluves were starved of sediment and new paleosol development was superimposed upon the previously deposited alluvial materials to form complex or welded soils. Surface dissection probably resulted in soils with lower water tables near the dissected valley edges, whereas interfluve paleosols away from the dissected edge may have remained waterlogged, and therefore less well-developed, for several tens of thousands of years. Interfluve paleosol development is controlled by drainage characteristics that are influenced both by the nature of the underlying floodplain sediments and by distance to the dissected valley edge. This suggests that a regional understanding of interfluve paleosol variability is required in order to maximize their interpretive value and predictive capability.