Illinoian (stage)

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The Illinoian Stage is the name used by

penultimate glacial period
.

Definition

At its

Wisconsinan stage loess, called the Roxana Silt. A paleosol, called the Pike Soil, separates two of the till members within the Glasford Formation.[1]

Substages

The Illinoian Stage is further subdivided into:

Correlation

Since 1986, the Illinoian Stage has been interpreted as consisting of two glaciations, the early Illinoian (

Marine Isotope Stage 8) and late Illinoian glaciations (Marine Isotope Stage 6) and the intervening interglacial period (Marine Isotope stage 7). In this interpretation, the Pike Soil is proposed to an interglacial (Marine Isotope Stage 7) paleosol.[4][5] According to this interpretation, the Illinoian Stage started about 300,000 years ago and ended about 130,000 years ago.[6][7]

However, later studies of the

fluvial deposits of the Pearl Formation and Illinoian glacial tills of the Glasford Formation, which fill an ancient and buried Mississippi River valley in north-central Illinois, demonstrated that the Illinoian Stage in its type area consists of glaciations that occurred only during Marine Isotope Stage 6. The age of proglacial fluvial sediments underlying the oldest known glacial till (Kellerville Member) of the Glasford Formation yield optically stimulated luminescence (OSL) dates that averaged 160,000 BP. The oldest fluvial sediments, which overlay bedrock in the deepest part of the valley, were dated by OSL dating to around 190,000 BP.[8][9] These OSL dates demonstrate that the Illinoian Stage is temporarily equivalent only to Marine Isotope Stage 6, which ended at 130,000 BP and started at 191,000 BP.[6] If the Illinoian Stage is limited in duration to Marine Isotope Stage 6, the Yarmouth Soil (paleosol) spans a period of geologic time equivalent to Marine Isotope stages 7, 8, 9, 10, and 11.[4]

The Illinoian Stage in North America is not exactly equivalent to the Wolstonian Stage of the British Isles. The Wolstonian stage is equivalent to Marine Isotope stages 6, 7, 8, 9, and 10.[10][11] and, thus, started about 352,000 years ago and ended 130,000 years ago.[6][7] As a result, the Illinoian Stage is only temporally equivalent to either middle and late Wolstonian stage or late Wolstonian stage in the British Isles. In North America, the term "Wolstonian stage" is not used by geomorphologists and Quaternary geologists[1][5][12] to designate glacial deposits and paleosols lying between the Sangamon and Yarmouth soils (paleosols).

Extent

During the Illinoian Stage, the Laurentide Ice Sheet covered about 85 percent of Illinois. At its maximum extent during this stage, this ice sheet reached its southernmost extent in North America near Carbondale, Illinois. At their maximum extent, the edge of Illinoian ice sheet(s) lay further south than the southernmost extent, i.e. Douglas County, Kansas, of any of the Pre-Illinoian ice sheets.[12]

See also

References

  1. ^ a b c Willman, H.B., and J.C. Frye, 1970, Pleistocene Stratigraphy of Illinois. Bulletin no. 94, Illinois State Geological Survey, Champaign, Illinois.
  2. ^ In Illinois, there is accepted evidence for 3 glacial episodes (Liman, Monican, and Jubileean) separated by warmer non-glacial intervals, although recent work suggests that there were more glacial events. Mickelson, D. M. (2005) "Status of the Wisconsin and Illinoian Glaciations in their type area" Resúmenes del XVI Geológico Argentino, 20 al 23 de septiembre de 2005, La Plata
  3. ISBN 978-0-444-51592-6
  4. ^
    doi:10.1016/0277-3791(86)90170-8
    .
  5. ^
    doi:10.1016/0277-3791(86)90184-8
    .
  6. ^
    Lisiecki, L.E., 2005, Ages of MIS boundaries. LR04 Benthic Stack
    Boston University, Boston, MA
  7. ^
    doi:10.1594/PANGAEA.704257
    .
  8. ^ 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, 11 p.
  9. ^ McKay, E.D., and R.C. Berg, 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, Vol. 40, No. 5, p. 78 with Powerpoint presentation
  10. doi:10.1017/S0016774600022988
    .
  11. ^ Gibbard, P.L., S. Boreham, K.M. Cohen and A. Moscariello, 2007, Global chronostratigraphical correlation table for the last 2.7 million years v. 2007b, jpg version 844 KB. Subcommission on Quaternary Stratigraphy, Department of Geography, University of Cambridge, Cambridge, England
  12. ^
    ISBN 0-444-51462-7

Further reading

External links
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