Historical:Geneva Dolomite Member
Charles Collinson and Elwood Atherton
The Geneva Dolomite Member of the Grand Tower Limestone (Collett, 1882, p. 63, 81-82), is named for Geneva, Shelby County, Indiana.
The type locality of the Geneva Dolomite Member is located in Geneva, Shelby County, Indiana.
Extent and Thickness
The Geneva Dolomite Member is continuous from its type locality westward into eastern and central Illinois, where it is as much as 50 feet thick but is not exposed.
In Illinois the Geneva Dolomite Member is the basal member of the Grand Tower Limestone, wherever the patchy Dutch Creek Sandstone Member is not present, but in Indiana it is classified as a formation (Shaver et al., 1970). The member grades laterally into the lower part of the Grand Tower (Meents and Swann, 1965; North, 1969).
The Geneva is dark brown, crystalline, porous, pure dolomite. It contains finely disseminated organic material and produces oil in several fields (Schwalb, 1955). In some localities floating grains of rounded, coarse to fine quartz sand occur in the Geneva, particularly in its lower part.
The Geneva is essentially nonfossiliferous but contains a few chitinozoans and scolecodonts (Collinson et al., 1967a).
COLLETT, JOHN, 1882, Eleventh annual report: Indiana Department of Geology and Natural History, 414 p.
COLLINSON, CHARLES, L. E. BECKER, G. W. JAMES, J. W. KOENIG, and D. H. SWANN, 1967a, Illinois Basin, in International symposium on the Devonian System: Alberta Society of Petroleum Geologists, v. 1, p. 940-962; Illinois State Geological Survey Reprint 1968-G.
MEENTS, W. F., and D. H. SWANN, 1965, Grand Tower Limestone (Devonian) of southern Illinois: Illinois State Geological Survey Circular 389, 34 p.
NORTH, W. G., 1969, Middle Devonian strata of southern Illinois: Illinois State Geological Survey Circular 441, 45p.
SCHWALB, H. R., 1955, Geneva (Middle Devonian) Dolomite in Illinois: Illinois State Geological Survey Circular 204, 7 p.
SHAVER, R. H., et al., 1970, Compendium of rock-unit stratigraphy in Indiana: Indiana Geological Survey Bulletin 43, 229 p.
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