Historical:New London 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 >>New London Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Trentonian Stage
Allostratigraphy: Tippecanoe Sequence


H. B. Willman and T. C. Buschbach

Name Origin

The New London Member of the Dunleith Formation is named for New London, Ralls County, Missouri, 2 miles south of the type section.

Type Section

The type section of New London Member is located in a roadcut and in the bluff east of U.S. 61 on the north side of Salt River (NE SW 25, 56N-5W), where it is 32.8 feet thick. The top of the member is not exposed in the type section, but it occurs in a roadcut and bluff half a mile south of Frankford, Ralls County, on the north side of Peno Creek (SE NE and NE SE 2, 54N-4W).

Extent and Thickness

The entire New London Member is exposed only in the extreme northern part of the southern outcrop area, where it is 35-45 feet thick. South of there it is generally overlapped by Cincinnatian strata, but the lower 3-5 feet, identified by the bentonite at its base, is present locally.

Stratigraphic Position

The New London Member of the Dunleith Formation (Templeton and Willman, 1963, p. 125) occurs in the southern limestone facies, overlying the Moredock Member and underlying the Wise Lake Formation.


The New London consists of fine-grained to lithographic, calcarenitic, cherty limestone that contains beds of fine- to medium-grained calcarenite and some thin argillaceous and slightly shaly beds. Red-brown shale partings occur locally. It is finer grained than the Moredock below, coarser than the Wise Lake above, and less pure and thinner bedded than either. A persistent bentonite, as much as 2 inches thick, commonly marks the base of the member. It is believed to be equivalent to the bentonite near the base of the Sherwood Member in the northern area.


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