Clastic dike in nonmarine siliciclastic sedimentary rocks (White River Group, Tertiary; White River Badlands, South Dakota, USA) 3 : 無料・フリー素材/写真
Clastic dike in nonmarine siliciclastic sedimentary rocks (White River Group, Tertiary; White River Badlands, South Dakota, USA) 3 / 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 | The White River Badlands of South Dakota consist of a scenic landscape of differentially weathered and eroded, nonmarine sedimentary rocks of Tertiary age. The most visually-striking areas have been set aside as an American national park (Badlands).The simplified stratigraphic succession in Badlands National Park is:Sharps Formation (Oligocene)Brule Formation (Oligocene)Chadron Formation (Eocene)Chamberlain Pass Formation (Eocene)Fox Hills Formation (Cretaceous-Paleocene?)Pierre Shale (Cretaceous)The Brule and Chadron Formations make up the White River Group, which along with the overlying Sharps Formation, are the principal scenery-making units in the White River Badlands. Light-colored volcanic ash beds are present in the succession, as are numerous reddish-colored paleosol ("fossil soil") horizons. The Pierre Shale at the base of the exposed succession is a marine unit.The White River Group weathers and erodes relatively quickly into a rugged landscape with steep slopes, little to no soil, and little to no vegetation. These are the characteristics of badlands topography - "bad" referring to its unsuitability for farming.Nonmarine fossils are relatively common in the White River Group - principally fossil mammals and other vertebrates. Fossils in the Chadron Formation indicate a swampy, near-sea level environment. The overling Brule Formation produces fossils consistent with a grassy prairie environment. The transition from low-elevation swamp to higher-elevation prairie in this area coincides with the uplift of the Rocky Mountains during the late stages of the Laramide Orogeny.Erosion rates in the White River Badlands indicate that the landscape started to appear about half-a-million years ago and will disappear about half-a-million years from now. The landscape has about a one million year lifespan.The zig-zag structure near the center of this picture is a clastic dike. Dikes are planar igneous intrusions that cut across country rocks. (See: www.flickr.com/photos/jsjgeology/albums/72157632467411234) Common lithologies in igneous dikes include granite and basalt/diabase. Some dikes are composed of sedimentary material - such clastic dikes form when loose material fills in fractures in other rocks from below or above. (See: www.flickr.com/photos/jsjgeology/albums/72157711855111128)----------------------------------Online pub. covering the geology of Badlands National Park:pubs.usgs.gov/of/2003/0035/pdf/of03-35.pdf |
| 撮影日 | 2023-06-23 17:40:03 |
| 撮影者 | James St. John |
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