The Illinoian Stage is the name used by Quaternary geologists in North America to designate the period c.191,000 to c.130,000 years ago, during the middle

Pleistocene The Pleistocene ( , often referred to as the '' Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed ...

, when sediments comprising the Illinoian Glacial Lobe were deposited. It precedes the Sangamonian Stage and follows the Pre-Illinoian Stage in North America. The Illinoian Stage is defined as the period of geologic time during which the glacial tills and outwash, which comprise the bulk of the Glasford Formation, accumulated to create the Illinoian Glacial Lobe.Willman, H.B., and J.C. Frye, 1970, ''Pleistocene Stratigraphy of Illinois.'' Bulletin no. 94, Illinois State Geological Survey, Champaign, Illinois. It occurs at about the same time as the penultimate glacial period.

Definition

At its type exposure in Peoria County,

Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Roc ...

, the Illinoian deposits consist of three till members of the Glasford Formation. They overlay Pre-Illinoian tills of the Banner Formation, in which the Yarmouth Soil ( paleosol) has developed. In this exposure, the Illinoian Glasford Formation, in which the

interglacial An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene ...

Sangamon Soil (palesosol) has developed, is overlain by early Wisconsinan stage loess, called the

Roxana Silt Roxana (c. 340 BC – 310 BC, grc, Ῥωξάνη; Iranian languages#Old Iranian, Old Iranian: ''*Raṷxšnā-'' "shining, radiant, brilliant"; sometimes Roxanne, Roxanna, Rukhsana, Roxandra and Roxane) was a Sogdian or a Bactrian princess whom ...

. A paleosol, called the Pike Soil, separates two of the till members within the Glasford Formation.

Substages

The Illinoian Stage is further subdivided into: * the Liman Substage, * the Monican Substage, and * the Jubileean Substage.Ehlers, Jürgen and Gibbard, Philip Leonard (2004) ''Quaternary glaciations: extent and chronology, Part 2: North America'' Elsevier, Amsterdam
page 77

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. According to this interpretation, the Illinoian Stage started about 300,000 years ago and ended about 130,000 years ago. Lisiecki, L.E., 2005
''Ages of MIS boundaries.''
Boston University, Boston, MA

data: . However, later studies of the

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluv ...

deposits of the Pearl Formation and Illinoian glacial tills of the Glasford Formation, which fill an ancient and buried

Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it ...

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 In physics, optically stimulated luminescence (OSL) is a method for measuring doses from ionizing radiation. It is used in at least two applications: * Luminescence dating of ancient materials: mainly geological sediments and sometimes fired po ...

(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.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.McKay, E.D., and R.C. Berg, 2008

Geological Society of America Abstracts with Programs, Vol. 40, No. 5, p. 78 wit
Powerpoint presentation
/ref> 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. 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. The Illinoian Stage in North America is not exactly equivalent to the Wolstonian Stage of the

British Isles The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles (O ...

. The Wolstonian stage is equivalent to Marine Isotope stages 6, 7, 8, 9, and 10.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 and, thus, started about 352,000 years ago and ended 130,000 years ago. 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 geologistsStiff, B. J., and A.K. Hansel, 2004, ''Quaternary glaciations in Illinois.'' in Ehlers, J., and P.L. Gibbard, eds., pp. 71-82, ''Quaternary Glaciations: Extent and Chronology 2: Part II North America'', Elsevier, Amsterdam. to designate glacial deposits and paleosols lying between the Sangamon and Yarmouth soils ( paleosols).

Extent

During the Illinoian Stage, the

Laurentide Ice Sheet The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glacial epochs, from 2.58 million year ...

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 Carbondale is a city in Jackson and Williamson Counties, Illinois, United States, within the Southern Illinois region informally known as "Little Egypt". The city developed from 1853 because of the stimulation of railroad construction into the ...

. At their maximum extent, the edge of Illinoian ice sheet(s) lay further south than the southernmost extent, i.e.

Douglas County, Kansas Douglas County (county code DG) is located in the U.S. state of Kansas. As of the 2020 census, the county population was 118,785, making it the fifth-most populous county in Kansas. Its county seat and most populous city is Lawrence. Hist ...

, of any of the Pre-Illinoian ice sheets.

References

External links

*anonymous, 2007
''Global correlation tables for the Quaternary''
Subcommission on Quaternary Stratigraphy, Department of Geography, University of Cambridge, Cambridge, England *Hallberg, G.R., ed., 1980a
''Pleistocene stratigraphy in east-central Iowa''
PDF version 15.6 MB. Technical information Series. no. 10. Iowa Geological Survey Bureau, Ames, IA. *Hallberg, G. R., ed., 1980b
''Illinoian and Pre-Illinoian stratigraphy of southeast Iowa and adjacent Illinois''
PDF version 19.3 MB. Technical information Series. no. 11. Iowa Geological Survey Bureau, Ames, IA. *Hallberg, G. R., T. E. Fenton, T. J. Kemmis, and G. A. Miller, 1980
''Yarmouth Revisited: Midwest Friends of the Pleistocene 27th Field Conference''
PDF version 4.6 MB. Guidebook no. 3. Iowa Geological Survey Bureau, Ames, IA. {{DEFAULTSORT:Illinoian (Stage) Glaciology of the United States Ice ages Middle Pleistocene Pleistocene geochronology Pleistocene North America Pleistocene United States Geology of Illinois