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Abstract

The Cretaceous Lewis Shale of Southern Wyoming is an excellent outcrop example of a submarine fan deposited basinward of a coeval, prograding margin. A regional cross section constructed from outcrop and subsurface data reveal several large-scale attributes of the system. Regionally continuous, condensed sections in the Lewis Shale define southward-prograding clinoforms that are related to a shelf-slope-basin physiography during deposition. The condensed sections form the boundaries to fourth-order stratigraphic cycles/parasequences. The average height of the clinoforms is ~400 m (~1300 ft), which is interpreted to reflect the minimum water depth during deposition. Strata with 50% or more sandstone are located in fluvial-deltaic strata on the topset of the clinoforms and submarine-fan strata are located on the bottomset of the clinoforms. Slope strata on the foresets of clinoforms contain 15–20% sandstone. Although the sandiest strata are located in shelf and base-of-slope strata, the depocenter of each fourth-order cycle is consistently located in muddy slope strata.

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