Historical:Francis Creek Shale Member
M. E. Hopkins and J. A. Simon
The Francis Creek Shale Member of the Carbondale Formation (Savage, 1927, p. 309) is named for Francis Creek in Fulton County.
The type locality is along the creek (NE SW 22, 5N-1E) (Wanless, 1929, p. 89; 1956, p. 10; 1957, p. 88, 203).
Extent and Thickness
The shale is more than 80 feet thick in northeastern Illinois. It forms a large clastic wedge that extends across the northern part of the area of Pennsylvanian rocks and thins out to the west and south (Smith, 1970). It has not been recognized in southern Illinois.
The shale is medium gray and silty. It is best known for the famous Mazon Creek sideritic concretions that are found in the Kankakee-Will-Grundy Counties area and have yielded what is probably the best known Pennsylvanian flora in the United States (Noé, 1925). In Will County and at one place in Fulton County, concretions in the shale have a diverse fauna (Johnson and Richardson, 1970). The upper part of the Francis Creek commonly contains a few sandstone beds, probably equivalent to the Jake Creek Sandstone.
JOHNSON, R. G., and E. S. RICHARDSON, JR., 1970, Fauna of the Francis Creek Shale in the Wilmington area: Illinois State Geological Survey Guidebook Series 8, p. 53-60.
NOÉ, A. C., 1925, Pennsylvanian flora of northern Illinois: Illinois State Geological Survey Bulletin 52, 113 p.
SAVAGE, T. E., 1927, Significant breaks and overlaps in the Pennsylvanian rocks of Illinois: American Journal of Science, v. 14, p. 307-316.
SMITH, W. H., 1970, Lithology and distribution of the Francis Creek Shale in Illinois: Illinois State Geological Survey Guidebook Series 8, p. 34.
WANLESS, H. R., 1929, Geology and mineral resources of the Alexis Quadrangle: Illinois State Geological Survey Bulletin 57, 230 p.
WANLESS, H. R., 1956, Classification of the Pennsylvanian rocks of Illinois as of 1956: Illinois State Geological Survey Circular 217, 14 p.
WANLESS, H. R., 1957, Geology and mineral resources of the Beardstown, Glasford, Havana, and Vermont Quadrangles: Illinois State Geological Survey Bulletin 82, 233 p.
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