Precambrian-Cambrian nonconformity (Manitou Limetone over Peerless Formation over Sawatch Sandstone over Pikes Peak Granite; Manitou Avenue roadcut, Manitou Springs, Colorado, USA) 2 : 無料・フリー素材/写真
Precambrian-Cambrian nonconformity (Manitou Limetone over Peerless Formation over Sawatch Sandstone over Pikes Peak Granite; Manitou Avenue roadcut, Manitou Springs, Colorado, 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 | Great Unconformity in Colorado, USALight-colored rocks at top = Manitou LimestoneDark-colored sandstone = Peerless FormationLight-colored sandstone = Sawatch SandstonePinkish rocks just above road level = Pikes Peak GraniteThe rock record does not completely document Earth's history. In stratigraphic sections, missing time is represented by unconformities - surfaces of erosion and/or non-deposition of sediments. There are four types of unconformities: paraconformities, disconformities, nonconformities, and angular unconformities.Seen here is the Precambrian-Cambrian unconformity at Manitou Springs, Colorado. The slightly tilted layers in the upper part of the photo (click to zoom in) are Ordovician and Cambrian sedimentary rocks. The underlying, non-layered, pinkish-colored rocks just above road level are part of the Pikes Peak Granite. About one-half a billion years is missing at the contact. Erosion surfaces such as this that have sedimentary rocks over igneous rocks are called nonconformities.This contact is a megasequence boundary - the base of the Sauk Megasequence. Regionally recognizable packages of sedimentary rocks bounded by major unconformities are known as megasquences, or Sloss sequences (named after geologist L.L. Sloss, 1913-1996). The bounding unconformities were caused by erosion during regressions. Continental margins have more complete sedimentary successions, whereas craton interiors have more incomplete successions. The names for North America's megasequences are (from oldest to youngest): Sauk, Tippecanoe, Kaskaskia, Absaroka, Zuni, and Tejas.Stratigraphy: Manitou Limestone (Lower Ordovician) over Peerless Formation (Upper Cambrian) over Sawatch Sandstone (Upper Cambrian) over Pikes Peak Batholith (late Mesoproterozoic, 1.08 Ga)Locality: roadcut along the western side of Manitou Avenue (= Business Route 24), northwestern side of the town of Manitou Springs, west of Colorado Springs, western El Paso County, central Colorado, USA (38° 52’ 08.02” North latitude, 104° 55’ 31.83” West longitude) |
| 撮影日 | 2010-10-29 10:48:54 |
| 撮影者 | James St. John |
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