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The Great Unconformity / Black Canyon of the Gunnison (Colorado)
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Photographer: Ron Wolf
ID: 0000 0000 1110 1813 (2010-11-26)Copyright © 2010 Ron Wolf
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INFORMATION PROVIDED WITH THE PHOTO
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date of photo Aug 24, 2010
location
Black Canyon of the Gunnison National Park (Gunnison County, Colorado, US)notes The Great Unconformity is displayed here at the Black Canyon of the Gunnison. The dark rock exposed in the sheer wall of the canyon is the Black Canyon Gneiss, a suite of quartzitic gneisses and mica schists formed in the middle Proterozoic, about 1.7 billion years ago. These deeply folded metamorphic rocks were subjected to several episodes of igneous intrusions beginning about 1.4 billion year ago, creating many lighter-colored dikes of pegmatite and granite. For more than a billion years, the area was subjected to two cycles of erosion, the invasion of shallow seas, deposition of sediments, uplift and complete erosion of those sediments, leaving a nearly flat plain on the black gneiss. The sedimentary layer on top of the gneiss here is the Entrada Sandstone, deposited in middle Jurassic time beginning about 190 million years ago. The contact between these two units represents a gap in earth history of about 1.2 billion years.keywords: geology, earth science, geomorphology, metamorphism, erosion, pediment, Proterozoic, pegmatite, gneiss, schist, unconformity, uplift
camera Canon 40D, 25mm, f/9, 1/200 sec.
photo category: Misc. - geology
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Using this photo The thumbnail photo (128x192 pixels) on this page may be freely used for personal or academic purposes without prior permission under the Fair Use provisions of US copyright law as long as the photo is clearly credited with © 2010 Ron Wolf.
For other uses, or if you have questions, contact Ron Wolf RonWolf[AT]EyeOnNature.com. (Replace the [AT] with the @ symbol before sending an email.) |
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