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.
Charles Collinson and Elwood Atherton
The Coggan Member of the Wapsipinicon Limestone (Norton, 1894, p. 23-24).
Named for Coggan, Linn County, Iowa.
The type section of the Coggan Member is at the Illinois Central Railroad crossing of the Buffalo River near Coggan, Linn County, Iowa.
The Coggan Member is at the base of the Wapsipinicon Limestone in Illinois.
Extent and thickness
The Coggan Member is not exposed in Illinois, but it occurs locally in subsurface and is as much as 20 feet thick in the area between Galesburg, Knox County, and Muscatine, Iowa.
The Coggan Member consists of massive, buff, cherty dolomite. It also contains a thin bentonite that has been correlated with the Tioga Bentonite Bed, which occurs near the top of the Grand Tower Formation southeast of the Sangamon Arch.
Well log characteristics
Age and correlation
Environments of deposition
NORTON, W. H., 1894, Notes on the lower strata of the Devonian Series in eastern Iowa: Iowa Academy of Science Proceedings 1, part 4, p. 22-24.
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