Stratigraphy of Middle and Upper Jurassic Rocks of the San Juan Basin: Historical Perspective, Current Ideas, and Remaining Problems
Published:January 01, 1986
Steven M. Condon, Fred Peterson, 1986. "Stratigraphy of Middle and Upper Jurassic Rocks of the San Juan Basin: Historical Perspective, Current Ideas, and Remaining Problems", A Basin Analysis Case Study: The Morrison Formation, Grants Uranium Region, New Mexico, Christine E. Turner-Peterson, Elmer S. Santos, Neil S. Fishman
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The Middle Jurassic San Rafael Group and Upper Jurassic Morrison Formation of the San Juan basin consist of complexly interrelated conglomerate, sandstone, silt- stone, mudstone, limestone, and gypsum. The San Rafael Group, consisting of the Entrada Sandstone, Wanakah Formation, Cow Springs Sandstone, and sandstone at Mesita, was deposited in eolian, sabkha, minor fluvial, and marine or possibly lacustrine environments. The Morrison Formation, consisting of the Salt Wash, Recapture, Westwater Canyon, and Brushy Basin Members, was deposited in widespread fluvial, lacustrine, and eolian environments.
The presence of eolian rocks in both the San Rafael Group and Morrison Formation led to mapping and correlation problems in the southern half of the basin. The chief problem was that a widespread eolian facies of the Recapture Member of the Morrison was considered a part of the eolian Cow Springs Sandstone by earlier workers. Recent work in the southern and western parts of the basin shows that eolian beds of the two units can be distinguished by lateral relationships and sedimentologic features including sorting, sedimentary structures, and crossbed dip-vector resultants. Separation of the two units yields an improved understanding of depositional processes and paleoenvironmental distributions. Problems in this interval still exist in the southeastern part of the basin where the relationship of the San Rafael Group to the Recapture Member of the Morrison remains unclear.
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A Basin Analysis Case Study: The Morrison Formation, Grants Uranium Region, New Mexico
This volume summarizes results of a U.S. Geological Survey multidisciplinary basin analysis research effort that encompasses all aspects of the geology of the Morrison Formation in the Grants uranium region, located in the San Juan basin of northwestern New Mexico, U.S.A. Tectonic, stratigraphic, sedimentologic, structural, petrographic, mineralogic, geochemical, and resource studies are drawn together to provide a geologic synthesis of the Jurassic Morrison Formation, the main uranium host rock in the region, and to provide background data for the formulation of genetic models for ore genesis. The result is a compendium of 21 papers that incorporates many recent and significant advances in our understanding of factors that favored uranium mineralization in the Morrison, and several new genetic models that incorporate these recent advances. The basin analysis approach used here has proved fruitful in that ore genesis can now be viewed in the context of the evolution of a sedimentary basin rather than as an isolated event. This approach to ore genesis has application not only to uranium deposits but also to all sediment-hosted ore deposits.