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Lithostratigraphy
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Chronostratigraphy
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Allostratigraphy
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Hydrostratigraphy
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Primary source[edit]

Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.

Contributing author(s)[edit]

H. B. Willman and T. C. Buschbach

Name[edit]

Original description[edit]

The Forreston Member of the Grand Detour Formation (Templeton and Willman, 1963, p. 87).

Derivation[edit]

Named for Forreston, Ogle County, which is 7 miles northeast of the type section.

Other names[edit]

History/background[edit]

Type section[edit]

Type location[edit]

The type section of the Forreston Member is located in a quarry in Carroll County on the north side of a ravine 1 mile northwest of Brookville (NE SE NW 21, 24N-7E), where it is 17.9 feet thick.

Type author(s)[edit]

Type status[edit]

Reference section[edit]

Reference location[edit]

Reference author(s)[edit]

Reference status[edit]

Stratigraphic relationships[edit]

Extent and thickness[edit]

The Forreston Member is commonly 5-25 feet thick in the northern outcrop area and in the northern part of the southern outcrop area, but it thickens southward to 40 feet at Cape Girardeau.

Lithology[edit]

The Forreston Member consists largely of dolomite-mottled lithographic limestone or fine-grained dolomite. It is commonly fossiliferous. In many exposures it can be differentiated into three cyclical units, each consisting of a thin-bedded, shaly unit at the base and a thicker bedded, purer unit at the top. The shaly units generally contain the thickest red-brown shale partings in the Grand Detour. The member contains some chert, and thin beds of calcarenite are common. In subsurface in west-central Illinois, a sandy zone about 5 feet thick is present at or near the base.

Core(s)[edit]

Photograph(s)[edit]

Contacts[edit]

Well log characteristics[edit]

Fossils[edit]

Age and correlation[edit]

Environments of deposition[edit]

Economic importance[edit]

Remarks[edit]

Reference(s)[edit]

place a <pre><br></pre>at the end of a line to get a line return TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.

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