Historical:West Franklin Limestone Member
M. E. Hopkins and J. A. Simon
The West Franklin Limestone Member of the Modesto Formation (Collett, 1884, p. 61-62) is named for West Franklin, Posey County, Indiana.
The type section consists of outcrops near the town (24, 7S-12W) (Wanless, 1956, p. 11).
It is likely that the West Franklin Limestone is equivalent to the entire interval from the Piasa Limestone upward through the Lake Creek Coal in southern Illinois and through the Scottville Limestone in southwestern Illinois. The Piasa Limestone also may be equivalent to the lower bench of the West Franklin (Andresen, 1956). The West Franklin is probably also equivalent to the interval including the Lonsdale and Exline Limestones of western Illinois and to the Madisonville Limestone of western Kentucky.
Extent and Thickness
The member is recognized largely in southeastern Illinois. It is a fine-grained limestone generally less than 15 feet thick and occurs in one to three benches, each generally less than 10 feet thick and separated by a few feet of greenish gray to variegated claystone. The number of limestone benches decreases to the west as the underlying shale, probably the Farmington Shale, thins from east to west.
In the eastern part of its area the West Franklin is closely overlain by the Chapel (No. 8) Coal.
ANDRESEN, M. J., 1956, Subsurface stratigraphy and sedimentation of the West Franklin-Cutler limestone zones of southern Illinois: University of Illinois M.S. thesis.
COLLETT, JOHN, 1884, Geology of Posey County, Indiana: Indiana Department of Geology and Natural History, 13th Annual Report, p. 45-70.
WANLESS, H. R., 1956, Classification of the Pennsylvanian rocks of Illinois as of 1956: Illinois State Geological Survey Circular 217, 14 p.
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