Encrinite (crinoidal limestone) (Ft. Payne Limestone, Lower Mississippian; Lake Cumberland, Kentucky, USA) 24 : 無料・フリー素材/写真
Encrinite (crinoidal limestone) (Ft. Payne Limestone, Lower Mississippian; Lake Cumberland, Kentucky, USA) 24 / 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 | Encrinite (crinoidal packstone) from the Mississippian of Kentucky, USA.The Ft. 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 limestone shown above is almost entirely composed of crinoid columnals. Such crinoidal limestones are called "encrinites".Classification: Animalia, Echinodermata, CrinoideaStratigraphy: Ft. Payne Formation, Osagean Stage, upper Lower MississippianLocality: Cave Springs South outcrop - lakeside exposure just south of the westernmost tip of Cave Springs Ridge, north-central Lake Cumberland, southeastern Russell County, southern Kentucky, USA----------------See info. at:en.wikipedia.org/wiki/Encriniteanden.wikipedia.org/wiki/Crinoid |
| 撮影日 | 2017-05-26 14:51:58 |
| 撮影者 | James St. John |
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