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Cretaceous Aged Lewis Shale deposits: Sanger Ranch, Washakie Basin, Wyoming 

Matthew Boyce, University of Oklahoma, School of Geology and Geophysics, Norman, Oklahoma, [email protected]


The marine Lewis Shale Formation was part of a progradational system that was overlain by nearshore and onshore deposits of the Fox Hills Formation during the Maastrichtian of the Cretaceous. The deltaic and coal deposits of the Fox Hills are found on the topset of progradational wedge clinoforms, while the foreset deposits are channelized sandstone in slope mudstone and base of slope proximal lobe deposits. Furthermore, the bottomset of these clinoforms was occupied by lobes encased in slumped and in situ mudstone. The Dad Member of the Lewis Shale on the Sanger Ranch were base of slope proximal lobe deposits with complex axial intralobe channels that span a fourth order cycle (~110 Ky). The distal fan facies of another fourth order cycle will also be described to give a complete picture of channel and lobe facies distribution in the Lewis Shale with respect to their physiographic position.