Arsenal Member

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Lithostratigraphy: Knox Dolomite Megagroup >>Prairie du Chien Group >>Oneota Dolomite >>Arsenal Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Canadian Series >>Trempealeauan Stage
Allostratigraphy: Sauk Sequence

Primary source

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)

H. B. Willman and T. C. Buschbach


Original description

The Arsenal Member of the Oneota Dolomite (Buschbach, 1964, p. 45).


Named for the Joliet Arsenal, Will County.

Other names


Type section

Type location

The type section for the Arsenal Member is located near Joliet Arsenal, where the type section is represented in a boring (NE NE SW 25, 34N-9E) by samples (sample set 6199) from 980-1085 feet deep.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The Arsenal Member of the Oneota Dolomite is the lower, very cherty member.

Extent and thickness

The Arsenal Member is recognized in the northeastern quarter of the state, where it varies from 90 to almost 200 feet thick.


It is a cherty to very cherty dolomite that is light gray with some brown or pink tinting. The dolomite is medium grained but has some coarsely crystalline zones. The chert is white or light gray, partly banded, and only rarely oolitic. Sand grains are rare, but thin shale partings are common near the base.




Well log characteristics


Age and correlation

Environments of deposition

Economic importance



BUSCHBACH, T. C., 1964, Cambrian and Ordovician strata of northeastern Illinois: Illinois State Geological Survey Report of Investigations 218, 90 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation