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A PEDOSTRATIGRAPHIC APPROACH TO NONMARINE SEQUENCE STRATIGRAPHY: A THREE-DIMENSIONAL PALEOSOL-LANDSCAPE MODEL FROM THE CRETACEOUS (CENOMANIAN) DUNVEGAN FORMATION, ALBERTA AND BRITISH COLUMBIA, CANADA PAUL J. MCCARTHY Department of Geology & Geophysics and Geophysical Institute, University of Alaska, Fairbanks, Alaska 99775-5780 e-mail: pjmccarthy@alaska.edu AND A. GUY PLINT Department of Earth Sciences, The University of Western Ontario, London, Ontario, N6A 5B7, Canada 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.
ANATOMY, EVOLUTION, AND PALEOENVIRONMENTAL INTERPRETATION OF AN ANCIENT ARCTIC COASTAL PLAIN: INTEGRATED PALEOPEDOLOGY AND PALYNOLOGY FROM THE UPPER CRETACEOUS (MAASTRICHTIAN) PRINCE CREEK FORMATION, NORTH SLOPE, ALASKA, USA PETER P. FLAIG The University of Texas at Austin, Bureau of Economic Geology, Jackson School of Geosciences, 10100 Burnett Road, Austin, Texas 78758, USA e-mail: peter.flaig@beg.utexas.edu PAUL J. MCCARTHY Department of Geology and Geophysics, and Geophysical Institute, University of Alaska, P.O. Box 755780, Fairbanks, Alaska 99775, USA AND ANTHONY R. FIORILLO Perot Museum of Nature and Science, 2201 N. Field St., Dallas, Texas 75201, USA ABSTRACT: The Cretaceous (Early Maastrichtian), dinosaur-bearing Prince Creek Formation (Fm.) exposed along the Colville River in northern Alaska records high-latitude, alluvial sedimentation and soil formation on a low-gradient, muddy coastal plain during a greenhouse phase in Earth history. We combine sedimentology, paleopedology, palynology, and paleontology in order to reconstruct detailed local paleoenvironments of an ancient Arctic coastal plain. The Prince Creek Fm. contains quartz- and chert-rich sandstone and mudstone-filled trunk and distributary channels and floodplains composed of organic-rich siltstone and mudstone, carbonaceous shale, coal, and ash-fall deposits. Compound and cumulative, weakly developed soils formed on levees, point bars, crevasse splays, and along the margins of floodplain lakes, ponds, and swamps. Abundant organic matter, carbonaceous root traces, Fe-oxide depletion coatings, and zoned peds (soil aggregates with an outermost Fe-depleted zone, darker-colored Fe-rich matrix, and lighter-colored Fe-poor center) indicate periodic waterlogging, anoxia, and gleying, consistent with a high water table. In contrast, Fe-oxide mottles, ferruginous and manganiferous segregations, bioturbation, and rare illuvial clay coatings indicate recurring oxidation and periodic drying of some soils. Trampling of sediments by dinosaurs is common. A marine influence on pedogenesis in distal coastal plain settings is indicated by jarosite mottles and halos surrounding rhizoliths and the presence of pyrite and secondary gypsum. Floodplains were dynamic, and soil-forming processes were repeatedly interrupted by alluviation, resulting in weakly developed soils similar tomodern aquic subgroups of Entisols and Inceptisols and, in more distal locations, potential acid sulfate soils. Biota, including peridinioid dinocysts, brackish and freshwater algae, fungal hyphae, fern and moss spores, projectates, age-diagnostic Wodehouseia edmontonicola, hinterland bisaccate pollen, and pollen from lowland trees, shrubs, and herbs record a diverse flora and indicate an Early Maastrichtian age for all sediments in the study area. The assemblage also demonstrates that although all sediments are Early Maastrichtian, strata become progressively younger from south to north. A paleoenvironmental reconstruction integrating pedogenic processes and biota indicates that polar woodlands with an angiosperm understory and dinosaurs flourished on this ancient Arctic coastal plain that was influenced by seasonally(?) fluctuating water table levels and floods. In contrast to modern polar environments, there is no evidence for periglacial conditions on the Cretaceous Arctic coastal plain, and
Page 2 and 3: New Frontiers in Paleopedology and
Page 4 and 5: A SHORT HISTORY AND LONG FUTURE FOR
Page 6 and 7: CO 2 CONCENTRATIONS IN VERTISOLS: S
Page 8 and 9: SOIL AND LANDSCAPE MEMORY OF CLIMAT
Page 10 and 11: PALEOCLIMATIC APPLICATIONS AND MODE
Page 12 and 13: ALLUVIAL STACKING PATTERN ANALYSIS
Page 14 and 15: PROGRADING DISTRIBUTIVE FLUVIAL SYS
Page 16 and 17: SOIL DEVELOPMENT ON MODERN DISTRIBU
Page 20 and 21: oth higher temperatures and an inte
Page 22: EARLY CAMBRIAN HUMID, TROPICAL, COA

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