Chertified encrinite (Fort Payne Formation, Lower Mississippian; Rt. 61 roadcut, north of Burkesville, Kentucky, USA) 6 : 無料・フリー素材/写真
Chertified encrinite (Fort Payne Formation, Lower Mississippian; Rt. 61 roadcut, north of Burkesville, Kentucky, USA) 6 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
|---|---|
| 説明 | Chertified encrinite in the Mississippian of Kentucky, USA.The Fort Payne Formation of southern Kentucky is richly fossiliferous and is dominated by crinoids. Crinoids ("sea lilies") are sessile, benthic, filter-feeding, marine invertebrates that were abundant in Paleozoic oceans. The group nearly went extinct at the Permian-Triassic mass extinction 251 million years ago. Crinoids are not common in modern oceans - they are usually deep-water forms now, but some shallow-water forms also exist today. A crinoid is essentially a starfish on a stick. The stick, or stem, lifts the organism to a moderately high tier above the seafloor, which is conducive to non-competitive filter feeding. The flower-like "head" of the crinoid consists of numerous cemented calcite plates that surround the digestive system and other soft parts. The arms are feather-like and are the structures that engage in filter-feeding. In the fossil record, crinoid stems are common, whereas crinoid heads are uncommon to rare, because they disaggregate quickly after death. Individual pieces of a crinoid stem are called columnals - they are usually somewhat shaped like poker chips. Each columnal is composed of a single crystal of calcite (CaCO3 - calcium carbonate).The rock shown above is almost entirely composed of crinoid pieces - it was originally a fossiliferous limestone, but has since been mostly chertified (replaced by cryptocrystalline quartz). Crinoidal limestones are called "encrinites".Classification: Animalia, Echinodermata, CrinoideaStratigraphy: Fort Payne Formation, Osagean Stage/Series, upper Lower MississippianLocality: Burkesville North Outcrop - Route 61 roadcut at milepost 23, way north of Burkesville, Kentucky, USA. (36° 54’ 08.08” North latitude, 85° 25’ 56.19” West longitude)----------------See info. at:en.wikipedia.org/wiki/Encriniteanden.wikipedia.org/wiki/Crinoid |
| 撮影日 | 2018-03-14 11:17:28 |
| 撮影者 | James St. John |
| タグ | |
| 撮影地 |