Isabel Sandstone Member
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.
M. E. Hopkins and J. A. Simon
The Isabel Sandstone Member of the Spoon Formation (Wanless, 1931a, p. 192).
Named for Isabel Township, Fulton County.
Isabel Township includes the type section (NW NE 16, 4N-3E) (Wanless, 1956, p. 10; 1957, p. 83, 199).
Extent and thickness
The name is used in western Illinois for a sandstone that generally is relatively thin, fine-grained, micaceous, feldspathic, and cemented with various amounts of calcium carbonate.
The Isabel and younger sandstones differ from the stratigraphically lower sandstones in western Illinois in that they are less quartzose, contain much more mica and feldspar, are not as well sorted, and do not show the abundant quartz overgrowths that produce the "sparkling sandstones." A sandstone is present at this position essentially throughout Illinois.
Well log characteristics
Age and correlation
In southern Illinois it is called the Palzo Sandstone.
Environments of deposition
WANLESS, H. R., 1931a, Pennsylvanian cycles in western Illinois: Illinois State Geological Survey Bulletin 60, 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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