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The Phosphoria Formation of the western United States is a geological formation of Early Permian age.〔Behnken, F.H., Wardlaw, B.R. and Stout, L.N., 1986, Conodont biostratigraphy of the Permian Meade Peak Phosphatic Shale Member, Phosphoria Formation, southeastern Idaho. University of Wyoming Contributions to Geology, v. 24, no. 2, p. 169-190.〕 It represents some 15 million years of sedimentation, reaches a thickness of and covers an area of .〔Blatt, Harvey and Robert J. Tracy, ''Petrology'', Freeman, 1996, 2nd ed. pp. 345-349 ISBN 0-7167-2438-3〕 The formation includes phosphorite beds that are an important source of phosphorus. They have been mined in southeastern Idaho, northern Utah, western Wyoming, and southwestern Montana. Low concentrations of uranium are present in the phosphorite beds,〔McKelvey, V.E., and L.D. Carswell, 1967. Uranium in the Phosphoria Formation. In: Anatomy of the Western Phosphate Field: A Guide to the Geologic Occurrence, Exploration Methods, Mining Engineering and Recovery Technology; AAPG Fifteenth Annual Field Conference, p. 119-123.〕 and a vanadium-enriched zone is present in western Wyoming and southeastern Idaho.〔McKelvey, V.E., Strobell Jr, J.D. and Slaughter, A.L., 1987. The vanadiferous zone of the Phosphoria Formation in western Wyoming and southeastern Idaho. In: The Thrust Belt Revisited; AAPG 38th Annual Field Conference Guidebook, p. 305-308.〕 Many of the Phosphoria shales are rich in organic matter and are petroleum source rocks,〔 and petroleum has been produced from some of the dolostones in the formation.〔Campbell, C.V. 1962. Depositional environments of Phosphoria Formation (Permian) in southeastern Bighorn basin, Wyoming. AAPG Bulletin 46(4): 478-503.〕 ==Stratigraphy and Lithology== The Phosphoria Formation was deposited under marine conditions in a foreland basin located between the Paleozoic continental margin and the North American cratonic shelf.〔Maughan, E.K. 1984. Geological setting and some geochemistry of petroleum source rocks in the Permian Phosphoria Formation. Rocky Mountain Association of Geologists.〕 The formation is commonly subdivided, from the top downward, as follows: * The Tosi chert member (chert with limestone at base). * The Retort phosphatic member (phosphorite, dolostone and siltstone). * The Rex chert member (gray limestone at base, black chert, and black cherty shale). * The Meade Peak phosphatic member (interbedded brown to black shale, gray dense limestone, dark brown oolitic phosphorite, and minor white calcareous sandstone). * The Lower Chert member (dark cherty shale). The Phosphoria is underlain by the Pennsylvanian-Permian Casper Formation〔 or, depending on the location, by the Park City Formation or the Tensleep Sandstone,〔 and it is overlain by the Triassic Dinwoody Formation.〔 The upper boundary is placed at the top of the uppermost phosphorite bed and below the tan calcareous siltstone of Dinwoody formation. The lower boundary is marked by a thin phosphorite that contains abundant fish scales and bones.〔 McKelvey, V.E., Cheney, T.M., Cressman, E.R., Sheldon, R.P., Swanson, R.W. and Williams, J. Steele, 1959. The Phosphoria, Park City, and Shedhorn formations in the western phosphate field. In: Geology of Permian rocks in the western phosphate field, U.S. Geological Survey Professional Paper 313-A, p. A1-A47.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Phosphoria Formation」の詳細全文を読む スポンサード リンク
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