earth science

Illinoian (stage)

Illinoian (stage) is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Illinoian (stage) rather than just read about it. In short: The Illinoian Stage is the name used by Quaternary geologists in North America to designate the Penultimate Glacial Period c.191,000 to c.130,000 years ago, during the late Middle Pleistocene (Chibanian), when sediments comprising the Illinoian Glacial Lobe were deposited. It precedes the Sangamonian Stage (corresponding to the global Last Interglacial) and follows the Pre-Illinoian Stage in North America.

Key takeaways

Illinoian (stage) belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Illinoian (stage) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Illinoian (stage) from memory before moving on to harder problems.

Reference excerpt

The Illinoian Stage is the name used by Quaternary geologists in North America to designate the Penultimate Glacial Period c.191,000 to c.130,000 years ago, during the late Middle Pleistocene (Chibanian), when sediments comprising the Illinoian Glacial Lobe were deposited. It precedes the Sangamonian Stage (corresponding to the global Last Interglacial) 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.

Definition At its type exposure in Peoria County, Illinois, 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 Sangamon Soil (palesosol) has developed, is overlain by early Wisconsinan stage 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.

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. 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. 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 Wolstonian stage is equivalent to Marine Isotope stages 6, 7, 8, 9, and 10. 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 geologists 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.

See also Wolstonian Stage Bull Lake glaciation Ice age Glacial period Last glacial period Timeline of glaciation

References

Further reading Ehlers, J., and P.L. Gibbard, 2004a, Quaternary Glaciations: Extent and Chronology 2: Part II North America, Elsevier, Amsterdam. ISBN 0-444-51462-7 Gillespie, A.R., S.C. Porter, and B.F. Atwater, 2004, The Quaternary Period in the United States. Developments in Quaternary Science no. 1. Elsevier, Amsterdam. ISBN 978-0-444-51471-4 Mangerud, J., J. Ehlers, and P. Gibbard, 2004, Quaternary Glaciations: Extent and Chronology 1: Part I Europe, Elsevier, Amsterdam. ISBN 0-444-51462-7 Sibrava, V.; Bowen, D.Q; Richmond, G.M., eds. (1986). "Quaternary Glaciations in the Northern Hemisphere". Quaternary Science Reviews. 5: 1–514. doi:10.1016/S0277-3791(86)80002-6.

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.

Worked examples

Example 1 — a first encounter with Illinoian (stage)

Start with the simplest possible case. Write down what Illinoian (stage) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Illinoian (stage) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Illinoian (stage) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Illinoian (stage)

In research: Illinoian (stage) appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Illinoian (stage) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Illinoian (stage) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geology of Illinois, Glaciology of the United States, Ice ages, so understanding it makes those chapters shorter.
In everyday life: Look for Illinoian (stage) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Illinoian (stage)” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Illinoian (stage) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Illinoian (stage) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Illinoian (stage) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Illinoian (stage) in simple terms?

Why does Illinoian (stage) matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Illinoian (stage)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Illinoian (stage).