File:Folded dolostones and argillaceous beds (Tymochtee Dolomite, Upper Silurian; South Bass Island, Lake Erie, Ohio, USA) 2 (48632920151).jpg
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Folded dolostone and argillaceous beds in the Silurian of Ohio, USA. Dolostone is a common lithology in the Silurian of America's Midwest. Dolostone is a chemical sedimentary rock composed of the mineral dolomite (CaMg(CO3)2 - calcium magnesium carbonate). Dolomite and dolostone are usually gray in color and readily bubble in acid only when powdered. Seen here are thin-bedded dolostones and shaly/muddy intervals in the upper Tymochtee Dolomite (pronounced "Tie-mock") on South Bass Island in Lake Erie, Ohio. Description of unit from Herdendorf (1993): Tymochtee - 170 feet thick. Dolomite, dark, bluish-gray to brown, thin-bedded to shaly; calcareous shale partings in upper beds; containing gypsum and anhydrite; uppermost 5 meters exposed on South Bass Island, Catawba Island, and West Sister Island. Notice the beds are folded into an anticline - an uparched fold. Unlike folded rocks in mountain belts, the folds on South Bass Island are not structural in origin - they formed by anhydrite-to-gypsum conversion in the subsurface. The Tymochtee Dolomite has anhydrite intervals and lenses. Anhydrite is an uncommon calcium sulfate mineral - CaSO4. With the addition of water, anhydrite converts to gypsum - CaSO4·2H2O. Historically, gypsum masses were recovered from the floor of Lake Erie. Possible sources of water for the conversion include: 1) rain (meteoric water) seeping downward through joints and fractures; 2) pre-glacial rivers (fluvial water); or 3) modern lake water (lacustrine water) - see Verber & Stansbery (1953). Anhydrite-to-gypsum conversion involves a significant volume increase, which results in folding of overlying beds. Stratigraphy: Tymochtee Dolomite, upper Salina Group, Ludlovian Series, lower Upper Silurian Locality: lakeshore cliff, South Bass Island State Park, western South Bass Island, western Lake Erie, far-northern Ohio, USA References cited: Herdendorf (1993) - Lake Erie islands. pp. 37-41 in: Lake Erie and Lake St. Clair Handbook. Verber & Stansbery (1953) - Caves in the Lake Erie islands. Ohio Journal of Science 53: 358-362. |
| Date | |
| Source | Folded dolostones and argillaceous beds (Tymochtee Dolomite, Upper Silurian; South Bass Island, Lake Erie, Ohio, USA) 2 |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/48632920151 (archive). It was reviewed on 10 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 00:31, 10 October 2019 | | 3,008 × 2,000 (5.53 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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