The Shannon Shelf-Ridge Sandstone Complex, Salt Creek Anticline Area, Powder River Basin, Wyoming
R. W. Tillman, R. S. Martinsen, 1985. "The Shannon Shelf-Ridge Sandstone Complex, Salt Creek Anticline Area, Powder River Basin, Wyoming", Shelf Sands and Sandstone Reservoirs, R. W. Tillman, D. J. P. Swift, R. G. Walker
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Two vertically stacked shelf-ridge (bar) complexes in the Shannon Sandstone member of the Cody Shale (designated upper and lower sandstones) crop out in the Salt Creek anticline of the Powder River Basin, Wyoming. The shelf-ridge complexes are composed primarily of moderately to highly glauconitic, fine-to medium-grained lithic sandstone and attain thicknesses of over 70 feet. The shelf-ridge complexes were deposited at least 70 miles from shore at middle to inner shelf depths by south to southwest-flowing shore-parallel currents intensified periodically and frequently by storms. Ridges in each sequence trend north-south, slightly oblique to current flow. A possible source of sediments for the shelf ridges was the Eagle Sandstone shoreline and deltaic deposits of southern Montana 200 miles to the northwest.
Eleven facies were defined in outcrop on the basis of physical and biologic sedimentary structures and lithology. Vertical and lateral changes in facies are relatively abrupt where observed in closely spaced outcrop sections, and, in general, facies are stacked in coarsening-upward sequences with Central Bar Facies commonly immediately overlying Interbar Sandstone Facies. Porous and permeable potential reservoir facies include: Central Bar Facies, a clean, cross-bedded sandstone; Bar Margin Facies (Type 1), a highly glauconitic, cross-bedded sandstone containing abundant shale and limonite (after siderite) rip-up clasts and lenses; and Bar Margin Facies (Type 2), a cross-bedded to rippled sandstone. These facies were formed by sediment transported and deposited in the form of medium- to large-scale troughs and sand waves on and across the tops of ridges by moderate to high energy
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Shelf sandstone reservoirs are becoming a more and more common exploration target. What they are, how they may be characterized, and how they differ from shoreline and deep-water deposits in the subject of this publication. Shelf sands and sandstone reservoirs are among the more poorly understood types of sandstones. Continental, shoreline and deep water sandstones have all been studied in much more depth than have shelf sands and sandstones. However, during the last fifteen years significant progress has been made in understanding shelf sands and sandstones. Studies of modern sediments have allowed us to understand many of the depositional processes active on the shelf. This book is intended to be an up-to-date summary of shelf processes and products. The papers are intended for those new to shelf sands and sandstones as well as the shelf specialist.