Angular unconformity - Flagstaff Formation over Twist Gulch Formation (Salina Canyon, central Utah, USA) 14 : 無料・フリー素材/写真
Angular unconformity - Flagstaff Formation over Twist Gulch Formation (Salina Canyon, central Utah, USA) 14 / 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 | One of the world's most impressive angular unconformities is located along Interstate 70 in Salina Canyon, central Utah. Angular unconformities are formed by structural tilting or folding of flat-lying sedimentary rocks, followed by erosion, followed by deposition of more flat-lying sedimentary rocks. The Salina Canyon angular unconformity can't get more angular than it is already, with flat-lying beds atop vertical beds, separated by an erosion surface having small-scale irregular topography. The overlying beds are basal Flagstaff Formation (mid-Paleocene). The underlying reddish-colored beds are tilted Twist Gulch Formation (Middle Jurassic) (also known as the Twist Gulch Member of the Arapien Formation). The angular unconformity is exposed throughout the lower parts of Salina Canyon (Salina Creek valley), east of the town of Salina, on both sides of Interstate 70 (but better seen on the northern side of the highway). Eastward, the underlying rocks become less vertical, and eventually have a disconformable relationship with the overlying rocks.The structural tilting of the Twist Gulch Formation has been attributed to local salt dome tectonics. Evaporites occur in underlying Middle Jurassic strata. Some of the rock salt intervals have domed upward as salt diapirs, resulting in tilting of overlying beds. The Salina Canyon angular unconformity provides information about the timing of rock salt diapirism (i.e., post-Jurassic & pre-Paleocene - in other words, during the Cretaceous).The rocks just above the unconformity are sandstones, with some conglomerate lenses (basal lags). |
| 撮影日 | 2007-09-07 13:50:17 |
| 撮影者 | James St. John |
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