File:Mudcracks in argillite (Snowslip Formation, Mesoproterozoic; Glacier National Park, Montana, USA).jpg
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| Description |
English: Mudcracks in argillite from the Precambrian of Montana, USA. (public display, Museum of the Rockies, Bozeman, Montana, USA)
Mudcracks are diagnostic sedimentary structures indicating subaerial exposure of sediment surfaces, with alternating wet & dry conditions. They are much more common that raindrop imprints, which indicate the same environmental setting. Mudcracks are most likely to occur in fine-grained siliciclastic rocks, fine-grained carbonate sediments, and in some evaporitic successions. Mudcracks are distinctive and easy to identify, but they do vary in appearance. The cracks themselves vary in width, depth, and areal density. Mudcrack polygons also vary in size & shape. The sample shown above has mudcracks preserved in argillite, a very low grade metamorphic rock formed by slight metamorphic alteration of shale/mudstone. The dark reddish color is from hematite (Fe2O3 - iron oxide). Reddish-colored siliciclastic sedimentary rocks (sandstones, siltstones, shales) are called "redbeds". Stratigraphy: Snowslip Formation, Belt Supergroup, Mesoproterozoic, ~1.44 Ga Locality: unrecorded/undisclosed site in Glacier National Park, northwestern Montana, USA |
| Date | |
| Source | https://www.flickr.com/photos/47445767@N05/29651822854/ |
| 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@N05/29651822854 (archive). It was reviewed on 2 March 2020 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 22:41, 2 March 2020 | | 2,368 × 1,971 (3.05 MB) | Ser Amantio di Nicolao (talk | contribs) | User created page with UploadWizard |
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