Facies Characterization and Architecture of a Muddy Shelf-Sandstone Complex: Mancos B Interval of Upper Cretaceous Mancos Shale, Northwest Colorado-Northeast Utah
Rex D. Cole, Robert G. Young, 1991. "Facies Characterization and Architecture of a Muddy Shelf-Sandstone Complex: Mancos B Interval of Upper Cretaceous Mancos Shale, Northwest Colorado-Northeast Utah", The Three-Dimensional Facies Architecture of Terrigenous Clastic Sediments and its Implications for Hydrocarbon Discovery and Recovery, Andrew D. Miall, Noel Tyler
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The Mancos B interval of the Upper Cretaceous Mancos Shale is represented by up to 372 m of thinly interstratified clays tone, siltstone, and very fine- to fine-grained sandstone deposited offshore, below storm-wave base, in the Western Interior Seaway. The Mancos B is best developed along Douglas Creek Arch in western Colorado and eastern Utah, where it is a major producer of natural gas and a minor producer of oil.
Combined stratigraphic and sedimentologic data suggest that the Mancos B is a regressive prodelta-plume complex genetically related to deltaic systems active along the western shoreline of the seaway. In outcrop and subsurface cores, the Mancos B is characterized by lenticular, cyclic, upward-coarsening parasequences, ranging in thickness from 2 to 32 m, and composed of five main lithofacies: silty claystone, sandstone-claystone, sandy siltstone, bioturbated muddy sandstone, and sandy dolomite (as beds and concretions). Sedimentary structures include horizontal lamination, wavy lamination, lenticular bedding, flaser bedding, ripple lamination, and horizontal lamination. Paleocurrent measurements indicate an average sediment-transport direction to the southeast (111°). Trace fossils are characteristic of the Cruziana ichnofacies. Lateral lithofacies variations in Mancos B parasequences are characterized by transitions from bioturbated muddy sandstone lithofacies into sandstone-claystone lithofacies then into sandy siltstone or silty claystone lithofacies. Horizons of sandy dolomite lithofacies cap most parasequences and represent periods of low sedimentation.
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The Three-Dimensional Facies Architecture of Terrigenous Clastic Sediments and its Implications for Hydrocarbon Discovery and Recovery
While there has been much interest in recent years in concepts of sequence stratigraphy, this book focuses on stratigraphic units that are, in general, an order of magnitude smaller than sequences. A knowledge of such architectural detail is of considerable significance in the development of detailed, scaled facies models for depositional environments, and is of paramount importance in the efficient design of advanced petroleum recovery projects. This book is the outcome of a SEPM Research Symposium held at the annual meeting of the Society in San Antonio, Texas, April 1989. The intent of the meeting was to bring together modern research on facies architecture, and to apply this research to the investigation of reservoir heterogeneities and production problems.