| 词条 | Tapeats Sandstone | |||
| 释义 |
| image =Grand Canyon-Mather point.jpg | imagesize = 285px | caption = Muav Limestone-(greenish, slope-forming) and Bright Angel Shale, resting on Tapeats and the Tonto Platform, inner canyon, Granite Gorge (the two units are easily seen below the red-stained Redwall Limestone) (550 ft thick) | period = Cambrian | age = Early to Middle Cambrian[1][2] | type = Geological formation | prilithology = sandstone and conglomerate | otherlithology = conglomeratic sandstone | namedfor = Tapeats Creek[3] | namedby = Noble (1914)[3] | region = northern Arizona (Grand Canyon), central Arizona, southeast California, southern Nevada, and southeast Utah |country = United States of America | coordinates = | unitof = Tonto Group | subunits = | overlies = Vishnu Basement Rocks, Unkar Group, Nankoweap Formation, Chuar Group, and Sixtymile Formation | underlies = Bright Angel Shale | thickness = {{convert|230|ft|m|sp=us}} | extent = | area = | map = | map_caption = }} OverviewThe Cambrian Tapeats Sandstone is the lower geologic unit, about {{convert|230|ft|m|0}} thick,[4] at its maximum, of the 3-member Tonto Group. The Tapeats Sandstone is the highly erosion-resistant unit laid upon the Vishnu Basement Rocks in the central, parts of east, and parts of west Grand Canyon, Arizona. The unit comprises the 'base horizontal unit' of the platform around Granite Gorge (Inner Gorge) on the Colorado River, and because of its hardness, creates the Tonto Platform upon which the two slope-forming, highly erodable units, the Muav Limestone, and Bright Angel Shale lie. The Tapeats Sandstone and the Tonto Platform follow the Colorado River, and surrounding tributary canyons, creeks, watercourses, or washes, in a dendritic fashion, much like the branches of a tree. The Tapeats unit is the bottom member of the Tonto Group, a typical marine transgression series of sandstone-(conglomerate)-shale-limestone, all part of a paleo sea, initially adjacent to land, the source of the Tapeats rocks-(conglomerates) and sand; (a regressing sequence has the reverse order). The Tapeats Sea at the early Devonian ceased to deposit more Muav Limestone, and a period of erosion ensued, a deposition unconformity. The Tapeats Sandstone was laid upon the Vishnu Basement Rocks, after an unconformity of erosion, the Great Unconformity, of 1,000 million years (1.0 billion). Besides the erosion unconformity, the Unkar Group of the basement rocks are also at an angular unconformity, being an 8-member sequence tilted at 45 degrees. The horizontal Tonto Platform has hiking trails that cross it from the South Rim to North Rim, Grand Canyon for instance. The extensive Tonto Trail lies on parts of the Tapeats Sandstone, and the platform on the south side of Granite Gorge. Close-up of Tapeats Sandstone on the Great Unconformity{{clear}}Geologic sequenceThe units of the Tonto Group:
See also
References1. ^Rose, E (2006) "Nonmarine aspects of the Cambrian Tonto Group of the Grand Canyon, USA, and broader implications." Palaeoworld. 15:223–241. 2. ^Rose, E (2011) Modification of the nomenclature and a revised deposition model for the Cambrian Tonto Group of the Grand Canyon, Arizona. in JS Hollingsworth, FA Sundberg, and JR Foster, eds., pp 77-98, Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada: Museum of Northern Arizona Bulletin 67, 321 p. 3. ^1 Noble, LF (1914) The Shinumo quadrangle, Grand Canyon district, Arizona. Bulletin no. 549, US Geological Survey, Reston, Virginia. 4. ^Chronic, H (1983) Roadside Geology of Arizona. The Mountaineers Books, Seattle, Washington. (softcover, {{ISBN|978-0-87842-147-3}}) p. 179. 5. ^Chronic. Roadside Geology of Arizona, Ch. IV Scenic Wonderland – The Colorado Plateau, Graph, Stratigraphic section of Paleozoic formations of the Colorado Plateau, p. 179. Popular Publications
External links
Gallery--Tapeats Sandstone{{Commons category}}Examples of the deposition unconformity of time (550-800 million yrs), the Great Unconformity. The Tapeats approximately 200 ft thick. {{col-begin}}{{col-2}}Gallery—Great Unconformity and angular unconformityExamples of the angular unconformity below the Tapeats Sandstone, (approx. 15 degrees). {{col-begin}}{{col-2}} 7 : Sandstone formations of the United States|Natural history of the Grand Canyon|Geologic formations of Arizona|Geologic formations of Nevada|Cambrian Arizona|Cambrian Nevada|Cambrian System of North America |
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