Greenbush cyclical formation. [A name applied to a upper portion of Pottsville formation (Pennsylvanian) of central western Illinois, based upon the rhythmic-cycle theory of sedimentation. Origin of name not stated.]

Source: US geologic names lexicon (USGS Bull. 896, p. 867).

Pg. 1586 (fig. 1), 1589. Greenbush cyclothem. Above the marine shale of the Wiley cyclothem in some of the Iowa outcrops there is an embryonic cyclothem that because of stratigraphic position is correlated with the Greenbush cyclothem of Illinois. The unique and easily recognized fresh-water limestone of western Illinois [Greenbush limestone] is absent here, but a thin MARGINIFERA-bearing marine limestone has been observed at a few places, and locally about a foot of sandstone forms the base of the cyclothem. Underlies Abingdon cyclothem (new). Age is Pennsylvanian.

Source: Publication; supplemental information from US geologic names lexicon (USGS Bull. 1200, p. 1596).

Pg. 50 (fig. 22), 63, 81-82, 191, 197, 198, 200, 201, 202. Greenbush cyclothem in Tradewater group. Thickness of cyclothem as much as 14 feet; average 6 to 10 feet. Rests with apparent conformity on Wiley cyclothem; underlies Abingdon cyclothem; Isabel sandstone rests on Greenbush shale with an abrupt contact and truncates shale at some places. Greenbush limestone is discontinuous and is commonly 3 to 6 inches thick and is fine-grained, light-gray, and nearly lithographic. Cyclothem is present in western Kentucky where it includes the highest beds referred to the Tradewater group. Age is Pennsylvanian. Gives type exposure.
Type exposure: in ravine tributary to Swan Creek, in E/2 sec. 24, T. 8 N., R. 1 W., Greenbush Twp., Avon quadrangle, Warren Co., IL.

Source: US geologic names lexicon (USGS Bull. 1200, p. 1596).