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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.