Historical:Moredock Member

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Handbook of Illinois Stratigraphy
Series Bulletin 95
Author H. B. Willman, Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, Jack A. Simon
Date 1975
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Lithostratigraphy: Ottawa Limestone Megagroup >>Galena Group >>Kimmswick Subgroup >>Dunleith Formation >>Moredock Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Trentonian Stage
Allostratigraphy: Tippecanoe Sequence


H. B. Willman and T. C. Buschbach

Name Origin

The Moredock Member of the Dunleith Formation is named for Moredock Lake, at Valmeyer, Monroe County, near the type section.

Type Section

The type section of the Moredock Member is in the Mississippi River bluff (cen. N line SW 3, 3S-11W), where the member is 58.4 feet thick.

Extent and Thickness

The Moredock is commonly 60-70 feet thick where overlain by the New London Member, but in many exposures in the southern outcrop area the Moredock is overlain unconformably by Maquoketa Group strata, as it is at the type section, or by the Cape Limestone, and the upper few feet of the member are missing.

Stratigraphic Position

The Moredock Member of the Dunleith Formation (Templeton and Willman, 1963, p. 124) occurs in the southern limestone facies, overlying the Eagle Point Member.


The Moredock is exceptionally pure, coarse-grained calcarenite that is massive, cross-bedded, crinoidal, nearly white, and banded with pink, buff, and gray beds. Although the member is generally noncherty, large chert nodules or lenses of chert occur locally. It is distinguishable from the Eagle Point Member, which is finer grained, has bands of chert nodules, and is less pure.


TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation