Lusk Shale Member (abandoned)
Nelson, W.J., 2020, Pennsylvanian Subsystem in Illinois: Illinois State Geological Survey Bulletin (in press).
Edited and figures drafted by Jennifer M. Obrad.
Weller (1940, p. 35–36) introduced the unit as the Lusk formation (of the Caseyville group).
The unit was named for Lusk Creek in Pope County, far southern Illinois.
Wayside Member (Lamar 1925) has priority over Lusk Member.
In early usage, the Lusk was classified both as a formation and as a cyclothem, the two being considered equivalent. Wanless (1956) listed the Lusk Formation containing the Wayside marine zone. When Kosanke et al. (1960) revised the Caseyville from a group to a formation and abandoned cyclothem-based formations, they changed the Lusk Formation to Lusk Shale Member in southeastern Illinois. Assigning the name Wayside Sandstone Member to equivalent strata in southwestern Illinois, these authors wrote (p. 29), “Like the Lusk Shale Member to the east, the Wayside Sandstone Member is a complex unit consisting of several beds of massive sandstone separated by silty shale. It probably includes strata equivalent to the Lusk Shale.”
Describing strata of the Caseyville Formation in parts of Johnson and Pope Counties, Nelson et al. (1991, p. 18) wrote, “Mapping in progress demonstrates that the type Wayside and the type Lusk are lithologically similar units of interbedded shale and sandstone and are stratigraphically equivalent. The name Lusk is therefore abandoned in favor of Wayside, which has priority [Lamar 1925].” This statement mirrors the passage from Kosanke et al. (1960) cited previously.
Weller (1940) did not designate a type section. Wanless (1956) listed outcrops in T12S, R5E and R6E and T13S, R6E, but no description has been published.
- Kosanke, R.M., J.A. Simon, H.R. Wanless, and H.B. Willman, 1960, Classification of the Pennsylvanian strata of Illinois: Illinois State Geological Survey, Report of Investigations 214, 84 p., 1 pl.
- Lamar, J.E., 1925, Geology and mineral resources of the Carbondale Quadrangle: Illinois State Geological Survey, Bulletin 48, 173 p., 3 pls.
- Nelson, W.J., J.A. Devera, R.J. Jacobson, D.K. Lumm, R.A. Peppers, B. Trask, C.P. Weibel, L.R. Follmer, M.H. Riggs, S.P. Esling, E.D. Henderson, and M.S. Lannon, 1991, Geology of the Eddyville, Stonefort, and Creal Springs Quadrangles, southern Illinois: Illinois State Geological Survey, Bulletin 96, 85 p., 1 pl.
- Wanless, H.R., 1956, Classification of the Pennsylvanian rocks of Illinois as of 1956: Illinois State Geological Survey, Circular 217, 14 p.
- Weller, J.M., 1940, Geology and oil possibilities of extreme southern Illinois: Illinois State Geological Survey, Report of Investigations 71, 71 p.
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