Paleopedology, Palynology and Paleoenvironmental Interpretation of Alluvial Paleosols, Cretaceous Dunvegan Formation, Western Canada Foreland Basin

Jacob R. Mongrain, Paul J. McCarthy, and Sarah J. Fowell
University of Alaska, Fairbanks, AK

Most paleoenvironmental studies examine either fossil soils or pollen, but rarely both. Alluvial paleosols in the Dunvegan Formation formed, at least partly, in environments which were conducive to the preservation of pollen. This provides an opportunity to examine both the paleosols and the fossil pollen assemblages in concert to formulate a multi-proxy paleoenvironmental interpretation. Micromorphological features from floodplain and interfluve paleosols, including illuvial clay coatings and infillings, Fe-oxide coatings, nodules and mottles, papules and pedorelicts, depletion residues, sphaerosiderite, bioturbation and strial matrix fabrics, indicate generally wet conditions alternating with periods of dryness that are probably attributable to local fluctuations in water table levels. Taken together these micromorphological features are consistent with those features formed in modern Inceptisols and Alfisols. The palynological assemblages are overwhelmingly dominated by trilete and monolete spores. Very little arboreal pollen is present, and angiosperm and gymnosperm palynomorphs are rare. This indicates that arboreal gymnosperms are located distal to the study sites. The paucity of arboreal pollen together with the diverse assemblages of well-preserved spores (from ferns and possibly lycopods) suggests moist conditions and poorly drained soils, and/or early successional colonization of these sites. Together, the pollen and paleosol data suggest that these paleosols formed in a cool temperate, humid to sub-humid paleoclimate. Our results support previous paleoenvironmental reconstructions for this area based upon macrofloral and stable isotopic data. Pollen stratigraphy tends to compliment microstratigraphic assemblages, clay mineralogy and geochemistry that are identified within paleosol profiles providing a high resolution environmental history of floodplain construction.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005