Charles Collinson and Elwood Atherton
The Wapsipinicon Limestone (Norton, 1895, p. 127, 155-166) is named for the Wapsipinicon River in Iowa.
The type section of the Wapsipinicon Limestone consists of exposures along the Wapsipinicon River between Troy Mills and Central City, Linn County, Iowa.
Extent and Thickness
The Wapsipinicon has a maximum thickness of about 60 feet near the Mississippi River and thins southeastward. It lenses out on the flanks of the Sangamon Arch, where it is overlapped by the Cedar Valley Limestone. The Wapsipinicon is exposed in Illinois only in the vicinity of Rock Island, and the principal exposures are in quarries and outcrops at Milan (fig. D-3C), Rock Island, and Andalusia in Rock Island County, and at Cleveland in Henry County (Savage, 1921b; Savage and Udden, 1921; Collinson et al., 1967b; Edmund and Anderson, 1967).
The Wapsipinicon Formation occurs in the basin northwest of the Sangamon Arch (fig. D-12), where it unconformably overlies Silurian and Ordovician strata (fig. D-7) and is overlain by the Cedar Valley Limestone.
The Wapsipinicon is dominantly fine-grained to lithographic, pure limestone, but some beds are argillaceous and dolomitic. Beds of anhydrite and gypsum occur locally in the subsurface in the westernmost part of the area, particularly in Hancock County. They are probably equivalent to the prominent brecciated beds that occur in the outcrop sections. Pods and lenses of sandstone occur in places, especially at and near the base. In the type region six members are differentiated, but in Illinois only the upper five are recognized (fig. D-11)-- the Coggan Member (cherty dolomite) at the base, the Otis Member (lithographic limestone), the Kenwood Member (argillaceous dolomitic limestone), the Spring Grove Member (dolomite and dolomitic limestone), and the Davenport Member (lithographic limestone) at the top.
The Wapsipinicon apparently was deposited in hypersaline waters and fossils are very rare.
COLLINSON, CHARLES, M. P. CARLSON, F. H. DORHEIM, and J. W. KOENIG, 1967b, Central Iowa Basin, in International symposium on the Devonian System: Alberta Society of Petroleum Geologists, v. 1, p. 963-971; Illinois State Geological Survey Reprint 1968-G.
EDMUND, R. W., and R. C. ANDERSON, 1967, Mississippi River Arch: 31st Annual Tri-State Field Conference Guidebook, Augustana College, Rock Island, Illinois, 64 p.
NORTON, W. H., 1895, Geology of Linn County: Iowa Geological Survey, v. 4, p. 121-195.
SAVAGE, T. E., 1921b, New species of Devonian fossils from western Illinois: Illinois Academy of Science Transactions, v. 14, p. 197-206.
SAVAGE, T. E., and J. A. UDDEN, 1921, Geology and mineral resources of the Edgington and Milan Quadrangles: Illinois State Geological Survey Bulletin 38, p. 115-208.
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