File:Polymict conglomerate (Ogishkemuncie Conglomerate, Neoarchean; Ogishkemuncie Lake, Boundary Waters, Minnesota, USA) 1 (22308698432).jpg
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Polymict conglomerate from the Precambrian of Minnesota, USA. (public display, Lake Superior Aquarium, Duluth, Minnesota, USA) This multicolored rock is a glacial erratic found near the town of Twig, northwest of Duluth, Minnesota. It was eroded from bedrock, transported, and deposited by a continental glacier during the Pleistocene Ice Age. The rock itself is a polymict conglomerate - a poorly sorted, coarse-grained, siliciclastic sedimentary rock having clasts of multiple lithologies (rock types). Some of the pebbles in this conglomerate are greenstone, a metamorphic rock. The most conspicuous pebbles are bright reddish-colored clasts of hematitic chert ("jasper"), originally eroded from a banded iron formation unit. The bedrock source of this rock is the Ogishkemuncie Conglomerate, which outcrops at Ogishkemuncie Lake in far-northeastern Minnesota. This stratigraphic unit is very old - over 2.5 billion years. The pebbles that make it up are even older, formed well into the Archean. Birkmeier et al. (2011) have identified clasts of the Saganaga Tonalite in this conglomerate unit. The Saganaga Tonalite dates to ~2.69 Ga. The Ogishkemuncie Conglomerate was deposited in ancient fluvial (river) and alluvial fan environments. Stratigraphy: Ogishkemuncie Conglomerate, Knife Lake Group, Neoarchean Provenance: Ogishkemuncie Lake, Boundary Waters, northeastern Minnesota, USA Reference cited: Birkmeier et al. (2011) - Geologic mapping of Neoarchean rocks near Ogishkemuncie Lake, by students of the Precambrian Research Center's 2010 field camp. 57th Annual Meeting, Institute on Lake Superior Geology, Ashland, Wisconsin, May 18-21, 2011, Programs and Abstracts, pp. 5-6. |
| Date | |
| Source | Polymict conglomerate (Ogishkemuncie Conglomerate, Neoarchean; Ogishkemuncie Lake, Boundary Waters, Minnesota, USA) 1 |
| 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@N05/22308698432 (archive). It was reviewed on 5 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 05:51, 5 December 2019 | | 3,612 × 2,574 (4.24 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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