Clinker breccia (Sentinel Butte Formation, Upper Paleocene; Coal Vein Trail, Roosevelt National Park, Little Missouri Badlands, North Dakota, USA) 2 : 無料・フリー素材/写真
Clinker breccia (Sentinel Butte Formation, Upper Paleocene; Coal Vein Trail, Roosevelt National Park, Little Missouri Badlands, North Dakota, USA) 2 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Clinker is a scarce, odd rock. It occurs adjacent to former coal bed horizons. Coal is combustible - that’s why coal is used as an energy source in human society. Coal beds can ignite accidentally or naturally. Accidental coal bed ignition often leads to environmental disaster areas (for example, Centralia, Pennsylvania, USA). Natural coal bed fires can be initiated by lightning strikes, grass fires, forest fires, or spontaneous combustion. Some ancient coal beds in the geologic record have burned away, leaving behind clinker beds. “Clinker” is the term for thermal metamorphic rocks (combustion metamorphic rocks) that have been significantly altered by the heat of burning coal. The appearance and color of clinker varies significantly. Scoriaceous to semivitreous clinker is called buchite, which formed by partial fusion/melting. Some sedimentary rocks adjacent to coal fires have melted to form paralava. Subsequent cooling and shrinking can form pseudocolumnar jointing in clinker horizons.Non-vesicular clinker that resembles unglazed porcelain is called porcellanite (a.k.a. porcelanite). Clinker having numerous, differently-oriented, angular clasts jumbled together is called clinker-bed breccia, which forms by shifting and collapse of beds overlying a burned-out coal horizon.Some early explorers of the American Great Plains, not knowing the non-volcanic origin of this material, called natural clinker “pumice” or “scoria”. Clinker is still called "scoria" today in Wyoming, Montana, and North Dakota, where clinker horizons are common and conspicuous; they frequently cap hilltops and buttes.The terms "buchite" and "porcellanite" are not restricted to clinker lithologies. To prevent confusion, these terms should always be combined with the term "clinker" to refer to rock types associated with coal fires (i.e., "buchite clinker" and "porcellanite clinker").-----------------------------From a park service trail guide:ChimneyWhat is unusual about this massive piece of clinker?Fires need oxygen, even when they are burning underground. As the coal fire burned deep into the hillside, cracks in the rock layers allowed air to be sucked down into the fire. Fire burned up the cracks and baked the rocks nearby, forming vertical "chimneys". Chimneys are the hottest part of the coal fire and bake the rock inside into a very hard clinker called porcellanite, which is especially resistant to erosion.This chimney was exposed when softer sediments around it eroded away.-----------------------------Stratigraphy: Sentinel Butte Formation, upper Fort Union Group, Upper PaleoceneLocality: outcrop along Coal Vein Trail, Little Missouri Badlands, South Unit of Roosevelt National Park, western North Dakota, USA |
| 撮影日 | 2008-08-28 15:21:39 |
| 撮影者 | James St. John |
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