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PROGRADING DISTRIBUTIVE FLUVIAL SYSTEMS—GEOMORPHIC MODELS AND ANCIENT EXAMPLES G.S. WEISSMANN Department of Earth and Planetary Sciences, MSC03 2040, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA e-mail: weissman@unm.edu A.J. HARTLEY Department of Geology & Petroleum Geology, School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK L.A. SCUDERI Department of Earth and Planetary Sciences, MSC03 2040, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA G.J. NICHOLS Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK S.K. DAVIDSON Department of Geology & Petroleum Geology, School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK A. OWEN Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK S.C. ATCHLEY Baylor University, Department of Geology, One Bear Place #97354, Waco, Texas 76798, USA P. BHATTACHARYYA Department of Earth and Planetary Sciences, MSC03 2040, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA T. CHAKRABORTY AND P. GHOSH Geological Studies Unit, Indian Statistical Institute, 203 B.T. Road, Kolkata, 700108, India L.C. NORDT Baylor University, Department of Geology, One Bear Place #97354, Waco, Texas 76798, USA L. MICHEL AND N.J. TABOR Huffington Department of Earth Sciences, Southern Methodist University, P.O. Box 750394, Dallas, Texas 75275-0395, USA
ABSTRACT: Recent work indicates that most modern continental sedimentary basins are filled primarily by distributive fluvial systems (DFS). In this article we use depositional environment interpretations observed on Landsat imagery of DFS to infer the vertical succession of channel and overbank facies, including paleosols, from a hypothetical prograding DFS. We also present rock record examples that display successions that are consistent with this progradational model. Distal DFS facies commonly consist of wetland and hydromorphic floodplain deposits that encase single channels. Medial deposits show larger channel belt size and relatively well-drained soils, indicating a deeper water table. Proximal deposits of DFS display larger channel belts that are amalgamated with limited or no soil development across the apex of the DFS. The resulting vertical sedimentary succession from progradation will display a general coarsening-upward succession of facies. Depending on climate in the sedimentary basin, wetland and seasonally wet distal deposits may be overlain by well-drained medial DFS deposits, which in turn are overlain by amalgamated channel belt deposits. Channel belt size may increase upward in the section as the DFS fills its accommodation. Because the entry point of rivers into the sedimentary basin is relatively fixed as long as the sedimentary basin remains at a stable position, the facies tracts do not shift basinward wholesale. Instead, we hypothesize that as the DFS fills its accommodation, the accommodation/sediment supply (A/S) ratio decreases, resulting in coarser sediment upward in the section and a greater degree of channel belt amalgamation upward as a result of reworking of older deposits on the DFS. An exception to this succession may occur if the river incises into its DFS, where partial sediment bypass occurs with more proximal facies deposited basinward below an intersection point for some period of time. Three rock record examples appear to be consistent with the hypothesized prograding DFS signal. The Blue Mesa and Sonsela members of the Chinle Formation at Petrified Forest National Park, Arizona; the Tidwell and Salt Wash members of the Morrison Formation in southeastern Utah; and the Pennsylvanian–Permian Lodéve Basin deposits in southern France all display gleyed paleosols and wetland deposits covered by better-drained paleosols, ultimately capped by amalgamated channel belt sandstones. In the Morrison Formation succession, sediments that represent the medial deposits appear to have been partially reworked and removed by the amalgamated channel belts that show proximal facies, indicating that incomplete progradational successions may result from local A/S conditions. The prograding DFS succession provides an alternative hypothesis to climate change for the interpretation of paleosol distributions that show a drying upward succession.
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 16 and 17: SOIL DEVELOPMENT ON MODERN DISTRIBU
Page 18 and 19: A PEDOSTRATIGRAPHIC APPROACH TO NON
Page 20 and 21: oth higher temperatures and an inte
Page 22: EARLY CAMBRIAN HUMID, TROPICAL, COA

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