Tornoceras uniangulare aldenense (fossil goniatite) (Alden Pyrite Bed, Ludlowville Formation, Middle Devonian; Alden, New York State, USA) 5 : 無料・フリー素材/写真
Tornoceras uniangulare aldenense (fossil goniatite) (Alden Pyrite Bed, Ludlowville Formation, Middle Devonian; Alden, New York State, USA) 5 / 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 | Tornoceras uniangulare aldenense House, 1965 - pyritized fossil goniatite in a pyrite concretion from the Devonian of New York State, USA. (lateral view, 2.7 centimeters across)The original hard parts of many fossils of shelly organisms (e.g., bivalves, gastropods, brachiopods, cephalopods) have dissolved away through geologic time. In such cases of dissolution, the fossil itself is an impression of the outside of the shell (external mold) or an impression of the inside of the shell (internal mold).Seen here is a pyritized mold of a Devonian-aged goniatite from the famous Alden Pyrite Bed of New York State. Goniatites are a group of ammonoid cephalopods with relatively simple suture patterns. Sutures are the lines formed by the intersection of the outer shell wall and the internal walls (septa) that separate chambers. Nautiloid cephalopods (e.g., the modern pearly nautilus; see: www.flickr.com/photos/25562347@N00/51950635384/in/photost...) generally have curvilinear suture patterns. Ammonoid cephalopods have goniatitic, ceratitic, or ammonitic suture patterns (see: higheredbcs.wiley.com/legacy/college/levin/0471697435/cha...). Goniatitic sutures are characterized by having several broad lobes & saddles. Goniatitic sutures are seen in the earliest ammonoids.Pyritization is a type of replacement, a fossil preservation style involving the crystal structure and the mineral of an organism's hard parts being changed. The most common replacement mineral is quartz (silica) (SiO2) - fossils that have been replaced by quartz are said to be silicified (silicification). Many silicified fossils have rounded to pustulose structures covering their surfaces. These are called beekite rings, but they're composed of ordinary quartz. Other common replacment materials include the mineral pyrite (FeS2 - iron sulfide) and apatite (calcium phosphate). Those replacement styles are called pyritization and phosphatization.Many other minerals have been found replacing fossils - many of them are quite rare. Reported examples include: anglesite, apatite, barite, calamine, calcite, cassiterite, celestite, cerargyrite, cerussite, chalcocite, cinnabar, copper, dolomite, fluorite, galena, garnet, glauconite, gumbelite, gypsum, hematite, kaolinite, limonite, magnesite, malachite, marcasite, margarite, opal, pyrite, romanechite/psilomelane, siderite, silica/quartz, silver, smithsonite, specular hematite, sphalerite, sulfur, uranium minerals, and vivianite. [List mostly from info. in Hartzell, 1906 and Klein & Hurlbut, 1985.]Classification: Animalia, Mollusca, Cephalopoda, Ammonoidea, Goniatitida, TornoceratidaeStratigraphy: Alden Pyrite Bed, Ledyard Shale Member, Ludlowville Formation, Middle DevonianLocality: Spring Creek, Alden, western New York State, USA |
| 撮影日 | 2023-10-09 15:52:59 |
| 撮影者 | James St. John |
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