AN EMPIRICAL PALEOSOL-LANDSCAPE MODEL OF A DISSECTED COASTAL PLAIN, CENOMANIAN DUNVEGAN FORMATION, ALBERTA AND BRITISH COLUMBIA, CANADA

Detailed paleopedological analyses have been completed on more than 20 paleosols along a transect from a single interfluve surface in the Cenomanian Dunvegan Formation exposed in Alberta and British Columbia, Canada. A detailed stratigraphic framework has been established previously that permits analysis of paleosol development along this transect with respect to spatial position relative to adjacent valleys and the marine shoreline. The coastal plain can be partitioned into three zones along an updip transect based upon both paleosol development and architecture. Zone 1 occurs in distal locations near the maximum regressive shoreline and is characterized by hydromorphic, cumulative paleosol development typical of poorly drained, progradational coastal plains. Zone 2 occurs in an intermediate location and is characterized by well-developed Alfisol-like paleosols that record a complex architecture indicating: (i) an aggradational phase; (ii) a subsequent static and/or degradational phase related to valley incision, non-deposition and soil thickening, and (iii) a final aggradational phase related to valley filling and renewed sedimentation across the coastal plain. Zone 3 occurs in the more proximal, updip settings and is characterized by compound and complex Inceptisol development. Paleosols in each of the three zones vary to some degree on the basis of local hydrology and parent materials. Variability in basin-scale paleosol architecture indicates that the most well-developed paleosols occur in intermediate locations along the interfluve transect (Zone 2), where valley incision occurred first and where interfluves were isolated from new additions of sediment for the longest periods of time. Relatively weak paleosol development both updip and downdip from this intermediate location suggests that valley incision began initially at the shoreline, progressing updip by knick-point migration, while downdip paleosols developed at the same time on a coastal plain that prograded in response to relative sea level fall. The similarity of soil processes in all three zones suggests that regional paleoclimate was similar and that basin-scale soil development was controlled primarily by hydrological variations that were ultimately controlled by valley incision and shoreline position.