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Superb exposures of the Upper Cretaceous Ferron Sandstone Member of the Mancos Shale in southern Castle Valley, Utah, record rapid accumulation of clastic sediments in a suite of deltaic environments that existed along the western margin of the Interior Cretaceous seaway during late Turonian time. The Ferron consists of five major delta cycles. Each cycle records northeastward progradation of a high-constructive delta followed by phases of abandonment and destruction. A clear genetic relation exists between these deltaic cycles and the economically important coal beds of the Ferron, each cycle containing one thick bed of coal. Several of the coal beds contain one or more laterally continuous kaolinitic claystone partings that record falls of volcanic ash into the low-ener y swamp environment. These partings, viewed as time lines, permit detailed reconstructions of the histories of individual swamps. Two of the thickest claystone partings have been traced southwest beyond the landward limits of the peat-forming environment into noncarbonaceous facies and have been used to establish equivalency of facies. Further, it can be demonstrated that the thickest part of each of the coal beds is in a position just landward of the south-westward pinchout of its associated delta-front sandstone. This genetic relation forms the basis of a predictive model that can be used to guide exploratory drilling programs in Cretaceous coal-bearing rocks of the Western Interior.
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