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The Hakatai Shale is a Mesoproterozoic rock formation that outcrops in the Grand Canyon, Coconino County, Arizona. It consists of colorful strata that exhibit colors that vary from purple to red to brilliant orange on outcrop. The colors are the result of the oxidation of iron-bearing minerals in the Hakatai Shale. It consists of lower and middle members that consist of bright-red, slope-forming, highly fractured, argillaceous mudstones and shale and an upper member composed of purple and red, cliff-forming, medium-grained sandstone. Its thickness, which apparently increases eastwards, varies form . In general, the Hakatai Shale and associated strata of the Unkar Group rocks dip northeast (10°-30°) toward normal faults that dip 60° or more toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area (below East Rim). In addition, thick, prominent, and dark-colored basaltic sills and dikes cut across the purple to red to brilliant orange strata of the Hakatai Shale.〔Hendricks, JD, and GM Stevenson (2003) ''Grand Canyon Supergroup: Unkar Group.'' In SS Beus and M Morales, eds., pp. 39-52, Grand Canyon Geology, 2nd ed. Oxford University Press, New York.〕〔Billingsley, GH (2000) ''Geologic Map of the Grand Canyon 30 × 60 Quadrangle, Coconino and Mohave Counties, Northwestern Arizona, Pamphlet to accompany Geologic Investigations Series I–2688 Version 1.0.''U.S. Geological Survey, Reston, Virginia. 15 pp.〕〔Beus, SS, RR Rawson, RO Dalton, GM Stevenson, VS Reed, and TM Daneker (1974) ''Preliminary report on the Unkar Group (Precambrian) in Grand Canyon, Arizona.'' In TNV Karlstrom, GA Swann, and RL Eastwood, ed., pp. 34-53, Geology of northern Arizona, with notes on archaeology and paleoclimate; Part 1, Regional studies. Geological Society of America, Rocky Mountain Section, Boulder, Colorado. 407 pp.〕 The bright orange-red slopes of the Hakatai Shale contrasts sharply against the grayish outcrops of the Bass Formation. The outcrop of the Hakatai Shale also contrasts greatly with the steep cliffs formed by Shinumo Quartzite as seen at the base of Isis Temple. In the central Grand Canyon north of Grand Canyon Village and viewed from the south at the South Rim, the bright orange-red unit can be seen below the Isis Temple and Cheops Pyramid landforms at the intersection of Bright Angel Canyon and Granite Gorge; the Bright Angel Trail from the South Rim traverses through the geographic region to the north, the North Kaibab Trail in Bright Angel Canyon.〔〔 The Hakatai Shale is part of a conformable sequence of sedimentary strata that comprise the Unkar Group. The Unkar Group is about thick and composed, in ascending order, of the Bass Formation, Hakatai Shale, Shinumo Quartzite, Dox Formation, and Cardenas Basalt. In ascending order, the Unkar Group is overlain by the Nankoweap Formation, about thick; the Chuar Group, about thick; and the Sixtymile Formation, about thick. The Grand Canyon Supergroup, of which the Unkar Group is the lowermost part, overlies deeply eroded granites, gneisses, pegmatites, and schists that comprise Vishnu Basement Rocks.〔〔Elton, DP, and EH McKee (1982) ''Age and correlation of the late Proterozoic Grand Canyon disturbance, northern Arizona.'' Geological Society of America Bulletin. 93(8):681-699.〕〔Karlstrom, KE, BR Ilg, Bradley, D Hawkins, ML Williams, G Dumond, KK. Mahan, and SA Bowring, Samuel (2012) ''Vishnu Basement Rocks of the Upper Granite Gorge: Continent formation 1.84 to 1.66 billion years ago.'' In JM Timmons and KE Karlstrom, eds., pp. 7-24, Grand Canyon geology: Two billion years of earth's history. Special Paper no 294, Geological Society of America, Boulder, Colorado.〕 ==Description== Typically, the Hakatai Shale is subdivided into three informal members. In ascending order they are the Hance Rapids (lower), Cheops Pyramid (middle), and Stone Creek (upper) members. The total thickness of the Hakatai Shale varies from at Hance Rapids to nearly at the type section in Hakatai Canyon in the Shinumo Creek area.〔〔Timmons, JM, KE Karlstrom, MT Heizler, SA Bowring, GE Gehrels, and LJ Crossey, (2005) ''Tectonic inferences from the ca. 1254-1100 Ma Unkar Group and Nankoweap Formation, Grand Canyon: Intracratonic deformation and basin formation during protracted Grenville orogenesis.'' Geological Society of America Bulletin. 117(11-12):1573-1595.〕 First, the Hance Rapids (lower) member consists of purple to reddish-purple mudstone, interbedded sandy siltstone, and rare occurrences of thin-bedded subarkose- to quartz arenite. Beds of the lower member of the Hakatai Shale grade upward into the fine-grained middle member, with a boundary drawn at or very near their change in color. Second, the Cheops Pyramid (middle) member consists of mudstone, siltstone, and subordinate sandy siltstone that exhibit a striking reddish-orange color. These distinctively red-colored strata are commonly mottled with small to large (up to 10 cm and more across), non-red, spherical to spheroidal reduction spots. These mottles have a dark-gray to greenish-gray central nuclei that contain very dark gray to black central cores. Finally, the Stone Creek (upper) member of the Hakatai Shale consists of pale purple or lavender, fine- to coarse-grained, crossbedded coarse arkose.〔〔Reed VS (1976) ''Stratigraphy and depositional environment of the Hakatai Shale, Grand Canyon, Arizona.'' Unpublished Master's Thesis, Northern Arizona University, Flagstaff, Arizona. 163 pp.〕〔Elston, DP (1989) ''Middle and late Proterozoic Grand Canyon Supergroup, Arizona.'' In DP Elston, GH Billingsley, and RA Young, RA., eds., pp. 94-105, Geology of the Grand Canyon, Northern Arizona (with Colorado River Guides). American Geophysical Union Fieldtrip Guidebook T115/315 for International Geologic Congress, 28th. American Geophysical Union, Washington DC. 239 pp.〕 Basaltic sills and dikes intrude all of the Unkar Group below the Cardenas Basalt. Sills intruded only the Bass Formation and Hakatai Shale. Dikes intrude the Hakatai Shale, Shinumo Quartzite, and Dox Formation. The sills range in thickness from at Hance Rapids, eastern Grand Canyon, to in Hakatai Canyon in the Shinumo Creek area. The feeder dikes to these sills are not exposed. However, the feeder dikes for the Cardenas Basalt can be traced, discontinuously, to within a few meters of its base. Adjacent to the sills, the Hatakai Shale has been altered to knotted hornfels containing porphyroblasts of andalusite and cordierite that have been replaced by muscovite and green chlorite, respectively.〔 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「Hakatai Shale」の詳細全文を読む スポンサード リンク
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