- Oronto Group
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The Oronto group is a thick group of arkose sandstone and shale located beneath the Bayfield Group in northern Wisconsin,[1] and believed to extend into Minnesota.[2] Because it is almost entirely red in color and highly tilted, it is considered separate from the Bayfield Group.[1] The Oronto group is divided into the Copper Harbor Conglomerate, Freda Sandstone, and Nonesuch Shale.[3] As the group is devoid of fossils, its age is difficult to ascertain,[4] though it may be of Keweenawan Age (about 1100 Mya).[5]
The group is composed of conglomerate, sandstone and shale. It is typically red, with bands, streaks, and spots of greenish-white no more than a few inches thick.[2] The total thickness of the group is unknown, but may be as much as 21,000 ft (6,400 m) deep.[6]
The Oronto group has a higher proportion of undecomposed minerals, feldspars, micas, ferromagnesian compounds, magnetite and calcium carbonate than the Bayfield Group.[2]
Notes
- ^ a b Bulletin, p. 48.
- ^ a b c Bulletin, p. 49.
- ^ Scott W. Imbus and others, "Organic geochemistry and sedimentology of middle Proterozoic Nonesuch Formation - hydrocarbon source rock assessment of a lacustrine rift deposit," in Lacustrine Basin Exploration, Tulsa, Okla.: American Association of Petroleum Geologists, p.197-208
- ^ Bulletin, p. 100.
- ^ Bulletin, p. 105.
- ^ Bulletin, p. 50.
References
- Bulletin, Issue 25. Wisconsin Geological and Natural History Survey. 1912. http://books.google.com/books?id=wJTPAAAAMAAJ.
Categories:- Geology of Wisconsin
- Sedimentary rocks
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