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.

Abstract The Upper Triassic Chinle Formation and the Upper Jurassic Morrison Formation preserve a record of lacustrine deposition along the western margin of tropical Pangaea and post-Pangaean North America. The lake deposits in these formations contain archives of sedimentary and geochemical paleoclimatic indicators, paleoeco-logical data, and characteristic stratal architecture that provide glimpses into the evolution of basins linked to global- and continental-scale tectonic events and processes, and the establishment of a mosaic of continental paleoecosystems. This field trip highlights the lacustrine and associated fluvial deposits of the Monitor Butte Member of the Chinle Formation and the Tidwell and Brushy Basin Members of the Morrison Formation in the southern part of the Colorado Plateau region, with emphases on: (1) sedimentary facies analysis and paleogeography of the paleolakes; (2) stratal architecture and high-frequency sequence stratigraphy; (3) recognition of lake basin-fill types; and (4) paleontology and ichnology of lake strata and their paleoecologic, paleohydrological, and paleoclimatic interpretation .