Pre-Illinoian

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Pre-Illinoian
~2.5 – 0.2 Ma
↓
Usage information
Celestial body
Age
Stratigraphic unitStage

The Pre-Illinoian Stage is used by Quaternary geologists for the early and middle

geologic time in North America from ~2.5–0.2 Ma (million years ago).[1]

North America

As the oldest stage in the North American regional subdivision of the Quaternary, the Pre-Illinoian precedes the Illinoian Stage.[2][3] Researchers have identified 11 distinct glacial stages during the Pre-Illinoian Stage.

The Pleistocene prior to the Illinoian stage had previously been subdivided into the Nebraskan, Aftonian, Kansan, and Yarmouthian stages (ages).[4] However, detailed studies of these stages revealed that the assumptions and criteria on which they were defined proved to be wrong to such a point that these stages became meaningless in terms of the actual glacial–interglacial record.[5][6][7]

For example, instead of two glaciations having occurred prior to the Illinoian Stage, researchers found that 11 distinct glaciations had occurred. In addition, what was presumed to have been a single volcanic ash bed, which was used to correlate and differentiate between Kansan and Nebraskan glacial deposits, was found to be three volcanic ash beds of greatly differing ages. Similarly, paleosols used in the definition of the stages were found to have been greatly miscorrelated, as they consisted of paleosols of greatly differing ages. Because of these and other major problems, the concepts on which the Nebraskan, Aftonian, Kansan, and Yarmouthian (Yarmouth) stages are defined were discredited. North American geologists discarded these stages as unusable and merged them into the Pre-Illinoian Stage.[2][8]

Great Britain

The Pre-Illinoian stage is contemporary with the

Marine Isotope Stage 6 at 191,000 BP.[10][12][13][14]

See also

References

  1. ISBN 0-8137-2337-X
    .
  2. ^
    doi:10.1016/0277-3791(86)90169-1
    .
  3. ^
    doi:10.1016/0277-3791(86)90184-8
    .
  4. ISBN 978-1-4437-2173-8
    .
  5. S2CID 2258822
    .
  6. ^ Boellstorff, J (1978). "Chronology of some Late Cenozoic deposits from the central United States and the Ice Ages" (pdf). Transactions of the Nebraska Academy of Science. 6: 35–49. Retrieved 2012-04-04.
  7. S2CID 12724466
    .
  8. doi:10.1130/B25325.1. Archived from the original
    (PDF) on 2018-09-28. Retrieved 2012-04-04.
  9. ^ Cohen KM, Gibbard PL (2011). "Global chronostratigraphical correlation table for the last 2.7 million years". University of Cambridge. Retrieved 2012-04-04.
  10. ^
    Lisiecki, L.E., 2005, Ages of MIS boundaries. LR04 Benthic Stack
    Boston University, Boston, MA
  11. doi:10.1029/2004PA001071
  12. ^ McKay, E.D. (2007). "Six Rivers, Five Glaciers, and an Outburst Flood: the Considerable Legacy of the Illinois River". Proceedings of the 2007 Governor's Conference on the Management of the Illinois River System: Our continuing Commitment 11th Biennial Conference, Oct. 2-4, 2007 (PDF). p. 11. Retrieved 2012-04-04.
  13. ^ McKay, E.D.; Berg R.C. (2008). "Optical ages spanning two glacial-interglacial cycles from deposits of the ancient Mississippi River, north-central Illinois". Geological Society of America Abstracts with Programs. 40: 78. Retrieved 2012-04-04.
  14. ISBN 978-0-615-41739-4
    .

Further reading

External links
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