File:Pseudocolumnar jointing in clinker bed (Sentinel Butte Formation, Upper Paleocene; Coal Vein Trail, Roosevelt National Park, Little Missouri Badlands, North Dakota, USA) 26.jpg
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English: The fracture pattern in the outcrop seen here is "pseudocolumnar jointing", a rare type of fracturing. The Tertiary-aged nonmarine bedrock in this area of North Dakota includes lignite coal beds. Lignite sometimes ignites from lightning strikes or grass fires or spontaneous combustion. Burning coal horizons will thermally metamorphose subjacent and superjacent rocks, leaving behind "clinker beds". Clinker horizons consist of many specific lithologies that range in texture from clastic to near-glassy to vesicular to frothy. Like true columnar jointing, pseudocolumnar jointing forms as very hot rocks cool, shrink, and crack. True columnar jointing occurs in some lava flows (for example, Devils Postpile in California: www.flickr.com/photos/jsjgeology/albums/72157689404468185).
This North Dakota clinker horizon is likely Quaternary in age. Clinker beds in the Powder River Basin of Wyoming and Montana date to the Pleistocene and Holocene. Stratigraphy: Sentinel Butte Formation, upper Fort Union Group, Upper Paleocene Locality: outcrop along Coal Vein Trail, Little Missouri Badlands, South Unit of Roosevelt National Park, western North Dakota, USA |
| Date | |
| Source | https://www.flickr.com/photos/47445767@N05/52057152668/ |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/52057152668. It was reviewed on 8 May 2022 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
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| current | 03:38, 8 May 2022 | | 3,008 × 2,000 (4.42 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/52057152668/ with UploadWizard |
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