Abstract A basin-scale pedostratigraphic model that focuses on paleosols and their pedostratigraphic relationships has been established for the Cenomanian Dunvegan Formation, a unit that represents a large delta complex. A detailed sequence stratigraphic and paleogeographic framework permits analysis of paleosol development with respect to distance from marine shorelines and coeval valleys. Paleosols that bracket sequence boundaries vary depending upon their paleo-landscape position. The sequence-bounding package of paleosols can be partitioned into three spatial zones based upon both the degree of development and the architecture of the paleosols. Zone 1 occurs in seaward localities near the maximum regressive shoreline and is characterized by hydromorphic, weakly developed paleosols typical of a poorly drained, progradational, and aggradational coastal plain. Zone 2 occurs in an intermediate location and is characterized by well-developed Alfisol-like welded paleosols that record a complex architecture indicating (i) an aggradational phase; (ii) a subsequent static and/or degradational phase related to valley incision, nondeposition, and soil thickening; and (iii) a final aggradational phase related to valley filling and renewed sedimentation across the coastal plain. Zone 3 occurs in more up-dip settings and is characterized by compound and complex Inceptisol-like paleosols that developed as the result of a reduced aggradation rate when valleys were being incised further down-dip. Because accommodation, sediment supply, and hydrological conditions vary in both dip and strike directions, the three zones represent lateral soil facies equivalents. The soil-forming interval bracketing the sequence boundary comprises a geosol composed of welded paleosols that subdivide both up-dip and down-dip into more weakly developed aggradational paleosol complexes. Above the sequence boundary, a high accommodation phase (equivalent to the Transgressive Systems Tract) is represented by widespread lacustrine and poorly drained floodplain facies and weakly developed hydromorphic paleosols. As accommodation rate decreases (late Highstand Systems Tract time) the alluvial succession becomes paleosol dominated, comprising floodplain pedocomplexes that record a regional decrease in the accommodation/sediment supply ratio. Up-dip variability along the sequence boundary and within sequences is controlled primarily by variations in the accommodation/sediment supply ratio, by hydrological variations associated with floodplain incision during valley formation, and by tectonic subsidence rates that vary in space and in time.

Abstract The Dunvegan Formation is a mid-Cretaceous alluvial plain-deltaic deposit exposed along the Rocky Mountain Foothills and Peace River Valley of Alberta and British Columbia, Canada. A multiproxy approach, combining paleosol micromorphology, geochemistry, and mineralogy with palynology, is used to reconstruct the climatic, pedogenic, and depositional history of this high-latitude setting during a greenhouse climate regime. Intrinsic features of paleosols within the Dunvegan Formation suggest a warm to cool temperate paleoclimate. These paleosols experienced multiple depositional phases superimposed on pedogenic phases that resulted in complicated compound, complex, and welded paleosol profiles. Well-preserved palynomorph assemblages within the paleosols are composed primarily of fern spores, with small percentages of gymnosperm pollen. The palynomorphs suggest a humid paleoclimate ranging from cool temperate to subtropical. The abundance of fern spores in all of the paleosol profiles suggests early successional colonization of the floodplain. Better-developed interfluve paleosols contain greater percentages of tree pollen, indicating the presence of nearby forests. Within interfluve paleosols, intervals barren of pollen coincide with sequence boundaries identified on the basis of micromorphology and geochemistry. Our combined paleopedological and palynological data sets, together with macrofloral and geochemical paleoclimate indicators, suggest that the Dunvegan alluvial-coastal plain complex probably formed under a humid, warm to cool temperate paleoclimate with a mean annual temperature (MAT) between 12 and 14° C and mean annual precipitation (MAP) between 1200 and 1300 mm yr -1 . These integrated data sets also provide a better understanding of the stratigraphic development of the coastal plains.