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Characterization of Cretaceous Age Lewis Shale Deepwater Lobe Sands: Sanger Ranch, Washakie Basin, Wyoming

Boyce, Matthew D. 1, Roger M. Slatt1, David Pyles2 (1) University of Oklahoma, Norman, OK (2) Bureau of Economic Geology, Austin, TX


The Dad Sandstone Member of the Maastrichtian Age Lewis Shale on Sanger Ranch (Section 31, T18N, R90W, Sulphur Springs Quad, WY) provides an exceptional km+ continuous depositional dip oriented exposure of base-of-slope submarine lobe sands; thus, the sands are a good outcrop analog for similarly deposited sands (e.g., GOM & offshore Nigeria). Prograding Dad Member Sandstones were 10 to 30 km in length and were dominated by upper fine to lower medium grained structureless sands and silty to fine grained turbidites. Paleocurrent direction was largely to the south at Sanger Ranch, in accord with regional data from past studies. Herein, hydrodynamic facies were used to classify flow. Parallel laminated, ripple formset, flamed, and clast conglomerate facies are associated due to rapid deposition on a partially lithified substrate; local soft sediment deformation was common, due to the depositional rate, even though lateral continuity was maintained at outcrop scale.


AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana