Oronto Group

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

  1. ^ a b Bulletin, p. 48.
  2. ^ a b c Bulletin, p. 49.
  3. ^ 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
  4. ^ Bulletin, p. 100.
  5. ^ Bulletin, p. 105.
  6. ^ Bulletin, p. 50.

References