The Illinoian Stage is the name used by

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

geologists in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

to designate the Penultimate Glacial Period c.191,000 to c.130,000 years ago, during the late

Middle Pleistocene The Chibanian, more widely known as the Middle Pleistocene (its previous informal name), is an Age (geology), age in the international geologic timescale or a Stage (stratigraphy), stage in chronostratigraphy, being a division of the Pleistocen ...

(Chibanian), when sediments comprising the Illinoian Glacial Lobe were deposited. It precedes the Sangamonian Stage (corresponding to the global

Last Interglacial The Last Interglacial, also known as the Eemian, was the interglacial period which began about 130,000 years ago at the end of the Penultimate Glacial Period and ended about 115,000 years ago at the beginning of the Last Glacial Period. It cor ...

) and follows the Pre-Illinoian Stage in North America. The Illinoian Stage is defined as the period of geologic time during which the

glacial A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

s and

outwash An outwash plain, also called a sandur (plural: ''sandurs''), sandr or sandar, is a plain formed of glaciofluvial deposits due to meltwater outwash at the terminus of a glacier. As it flows, the glacier grinds the underlying rock surface and c ...

, 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.

Definition

At its type exposure in Peoria County,

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

, the Illinoian deposits consist of three

members of the Glasford Formation. They overlay Pre-Illinoian tills of the Banner Formation, in which the Yarmouth Soil (

paleosol In Earth science, geoscience, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The definition of the term in geology and paleontology is slightly different from its use in soil science. In geo ...

) 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 i ...

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

loess A loess (, ; from ) is a clastic rock, clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loesses or similar deposition (geology), deposits. A loess ...

, called the Roxana Silt. 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 Marine isotope stages (MIS), marine oxygen-isotope stages, or oxygen isotope stages (OIS), are alternating warm and cool periods in the Earth's paleoclimate, deduced from Oxygen isotope ratio cycle, oxygen isotope data derived from deep sea core ...

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 A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

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 main stem, primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri River, Missouri. From its traditional source of Lake Ita ...

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 pot ...

(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 The Wolstonian Stage is a middle Pleistocene stage of the geological history of Earth from approximately 374,000 until 130,000 years ago. It precedes the Last Interglacial (also called the Eemian Stage) and follows the Hoxnian Stage in the Briti ...

of the

British Isles The British Isles are an archipelago in the Atlantic Ocean, 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 Hebrides, Inner and Outer Hebr ...

. 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 (

s).

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 Carbondale is a city in Jackson County, Illinois, United States, within the Southern Illinois region informally known as "Little Egypt". As of the 2020 United States census, 2020 census, the city had a population of 25,083, making it the most po ...

. 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 is a county located in the U.S. state of Kansas. Its county seat and most populous city is Lawrence. As of the 2020 census, the county population was 118,785, making it the fifth-most populous county in Kansas. The county ...

, 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