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The Dox Formation, also known as the Dox Sandstone, is a Mesoproterozoic rock formation that outcrops in the eastern Grand Canyon, Coconino County, Arizona. The strata of the Dox Formation, except for some more resistant sandstone beds, are relatively susceptible to erosion and weathering. The lower member of the Dox Formation consists of silty-sandstone and sandstone, and some interbedded argillaceous beds, that form stair-stepped, cliff-slope topography. The bulk of the Dox Formation typically forms rounded and sloping hill topography that occupies an unusually broad section of the canyon.〔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.〕 The Dox Formation comprises the bulk of the Unkar Group, the base section of the Grand Canyon Supergroup. The Unkar Group is about thick and composed of, in ascending order, the Bass Formation, Hakatai Shale, Shinumo Quartzite, Dox Formation, and Cardenas Basalt. The Unkar Group is overlain in ascending order by the Nankoweap Formation, about thick; the Chuar Group, about thick; and the Sixtymile Formation, about thick. The entire Grand Canyon Supergroup 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.〕 In general, the Dox Formation and associated strata of the Unkar Group rocks dip northeast (10°-30°) toward normal faults that dip 60+° 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). Within the central Grand Canyon, these strata occur in small, rotated, downfaulted blocks or slivers where they commonly are only partially exposed. Within this part of the Grand Canyon, the Unkar Group is incomplete because pre-Tapeats Sandstone erosion has removed strata above the level of the middle part of the Dox Formation. The missing part of the Dox Formation and overlying Cardenas Basalt and Chuar Group are preserved in a prominent syncline and fault block that is exposed in the eastern Grand Canyon. The Dox Formation contains thick basaltic sills and a number of small, dark dikes. In the area of Desert View and west of Palisades of the Desert, the basaltic sills form very prominent, dark gray cliffs.〔〔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.〕 The Dox Formation takes its name from frontier educator Virginia Dox, the first white woman to explore the Grand Canyon, for whom the Dox Castle butte was named. ==Description== West of 75-mile Creek in the central Grand Canyon, the strata of the Dox Formation occurs in small, rotated, downfaulted blocks or slivers, and commonly are only partially exposed. In these downfaulted blocks, only the lower two members, the Escalante Creek and Solomon Temple members, are preserved as the remainder of the Dox Formation and Unkar Group has been removed by pre-Tapeats Sandstone erosion. The only complete section of the Dox Formation is exposed in the eastern Grand Canyon. In that area, the Dox formation, which is the thickest unit of the Unkar Group, has been subdivided into four members. In ascending order, they are the Escalante Creek, Solomon Temple, Comanche Point, and Ochoa Point members. The contacts between members of the Dox Formation are gradational and are based mainly on topographic expression, the sedimentary depositional environment, and color changes.〔〔 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「Dox Formation」の詳細全文を読む スポンサード リンク
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