Charles Collinson and Elwood Atherton
The Saverton Shale (Keyes, 1912, p. 149) is named for Saverton, Ralls County, Missouri.
No type section was designated for the Saverton Shale by Keyes, but Mehl (1960) named an exposure in the Mississippi River bluff at Louisiana, Pike County, Missouri, as the type section, the same exposure named as the type for the Grassy Creek Shale (a section in the Mississippi bluffs several hundred feet north of the Champ Clark Bridge at Louisiana, Pike County, Missouri, (SW NW NE 18, 54N-1W)).
Extent and Thickness
The Saverton is well exposed in western Illinois in and near the Mississippi and Illinois River bluffs in Pike, Calhoun, and Jersey Counties. It is 5-110 feet thick in western Illinois, but is generally less than 10 feet thick where overlain by the Louisiana Limestone. In eastern and southern Illinois, it is commonly not differentiated and is included in the Hannibal Formation.
The Saverton Shale is a gray shale overlying the black Grassy Creek Shale and underlying the Louisiana Limestone. Because the Louisiana Limestone is limited to a small area in Illinois (fig. D-20), the Saverton is more commonly overlain by the Mississippian "Glen Park" or Hannibal Formations.
The Saverton is a bluish to greenish gray, silty shale that contains both thin sandy beds and calcareous beds and grades to calcareous siltstone in the upper part. It grades into the overlying Louisiana Limestone, the lower part of which in places grades laterally into the uppermost Saverton.
The few macrofossils present in the Saverton include Spirifer marionensis and Orbinaria puxidata. Conodonts are abundant, especially in the siltstone at the top, and Palmatolepis minuta, P. gracilis, P. glabra, and P. quadratinodosa marginifera indicate an Upper Devonian age (Scott and Collinson, 1961; Collinson et al., 1967a).
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.
KEYES, C. R., 1912, Some provincial and local phases of the general geologic section of Iowa: Iowa Academy of Science Proceedings, v. 19, p. 147-151.
MEHL, M. G., 1960, Relationships of the base of the Mississippian System in Missouri: Denison University Journal of Scientific Laboratories, v. 45, p. 57-107.
SCOTT, A. J., and CHARLES COLLINSON, 1961, Conodont faunas from the Louisiana and McCraney Formations of Illinois, Iowa, and Missouri, in Kansas Geological Society Guidebook, 26th Field Conference, northeastern Missouri and west central Illinois: Missouri Geological Survey Report of Investigations 27, p. 110-141; Illinois State Geological Survey Reprint 1961-V.
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