Raccoon Creek Group
Nelson, W.J., 2020, Pennsylvanian Subsystem in Illinois: Illinois State Geological Survey Bulletin (in press).
Edited and figures drafted by Jennifer M. Obrad.
The term “Raccoon Creek Group” first appeared on a chart of Pennsylvanian stratigraphy in Indiana by Wier and Gray (1961). The first explicit description appeared in Shaver et al. (1970). In Indiana, the Raccoon Creek has always comprised, in ascending order, the Mansfield, Brazil, and Staunton Formations.
The name refers to Big Raccoon Creek, a tributary of the Wabash River in Parke County, west-central Indiana.
No other name refers to this specific interval of strata. The McCormick Group (Kosanke et al., 1960) comprised the Caseyville and Abbott (lower Tradewater) Formations, but not the Spoon (upper Tradewater) Formation.
Usage was confined to Indiana until the Tri-State Committee (2001) extended the Raccoon Creek Group into Illinois and western Kentucky, where it comprises the Caseyville and Tradewater Formations. The definition in Indiana remains unchanged, except that the upper boundary was moved from the top to the base of the Seelyville Coal Member (now in the Carbondale Formation or Group). “Raccoon Creek” replaced the former usage of “McCormick Group” in Illinois, the latter rendered obsolete by abandonment of the Abbott Formation (now part of the Tradewater Formation).
None was designated.
The Tri-State Committee (2001, p. 3) specified four continuous drill cores, on file at the Indiana Geological Survey, as the principal reference section.
The Raccoon Creek Group unites formations that are characterized by lenticular rock bodies and a lack of widely traceable marker beds. In these features, the Raccoon Creek contrasts with the overlying Carbondale Formation (which belongs to no group) and the younger McLeansboro Group, both of which contain many widely traceable members.
Extent and thickness
An isopach map (Droste and Horowitz, 1998) depicts the Raccoon Creek Group as ranging from less than 400 ft (120 m) in the northern part of the Illinois Basin to more than 1,200 ft (360 m) in the Evansville paleovalley in Union County, Kentucky (near the common border of Illinois, Indiana, and Kentucky). This small-scale map is probably based on widely spaced control points. Abrupt local thickness variations are chiefly the result of the deeply channelized sub-Pennsylvanian surface, although local tectonic activity probably plays a role. Isopach maps by Greb et al. (1992) of the Caseyville and Tradewater Formations in western Kentucky suggest similar combined thicknesses in Union County, Kentucky, near the common corner of the three states.
Overall, the Raccoon Creek is dominantly sandstone, siltstone, shale, and nonfissile mudstone, along with lenticular coal seams and occasional lenticular limestone. Coal, limestone, and black shale layers near the top of the group are more widely continuous. For further details, see discussions of constituent formations, members, and beds.
The lower contact is a major regional unconformity on rocks ranging in age from Middle Ordovician to Late Mississippian. By definition, the upper contact is the base of the Davis or Seelyville Coal Member of the Carbondale Formation.
Well log characteristics
Being lithologically diverse, the Raccoon Creek Group has widely varying well log characteristics. Atherton et al. (1960) outlined ways to differentiate Pennsylvanian from Mississippian rocks on resistivity logs and in well cuttings. For further details, see the Caseyville and Tradewater Formations and their constituent members.
Marine invertebrates occur in limestone and occasionally in shale. Fossil plants are locally abundant in shale units, especially those associated with coal seams. Casts of fossil stems and logs occur in sandstone. Trace fossils are widely distributed and are important environmental indicators (Devera 1989).
Age and correlation
The group spans the interval from middle, possibly early, Morrowan through early Desmoinesian.
Environments of deposition
The group represents an array of fluvial, coastal-plain, and shallow marine environments, including fluvial channel, overbank, swamp or marsh, delta, estuary, bay, and lagoon. The depositional surface was uneven because of ongoing tectonism and compaction over lenticular sand bodies and the sub-Pennsylvanian unconformity. By Desmoinesian time, low areas on the sub-Pennsylvanian surface had been largely infilled, allowing for more widespread continuity of rock units.
Coal has been mined from the group (mainly Tradewater and equivalents) extensively in Indiana and western Kentucky and to a lesser extent in southern and western Illinois. Substantial oil production has been achieved from Raccoon Creek sandstone reservoirs throughout the Illinois Basin, especially in Kentucky. The group also contains significant tar sands in western Kentucky. Sandstone has been quarried for building stone and flagstone, and in earlier times for millstones and grave markers. The production of bricks and ceramic products from Pennsylvanian shale and claystone formerly was an important industry. Scenic bluffs, glades, and glens with sandstone caves and alcoves provide the settings for numerous state parks that support tourism.
- Atherton, E., G.H. Emrich, H.D. Glass, P.E. Potter, and D.H. Swann, 1960, Differentiation of Caseyville (Pennsylvanian) and Chester (Mississippian) sediments in the Illinois Basin: Illinois State Geological Survey, Circular 306, 36 p.
- Devera, J.A., 1989, Ichnofossil assemblages and associated lithofacies of the Lower Pennsylvanian (Caseyville and Tradewater Formations), southern Illinois: Kentucky, Indiana, and Illinois Geological Surveys, Illinois Basin Studies 1, p. 57–83.
- Droste, J.B., and A.S. Horowitz, 1998, The Raccoon Creek Group (Pennsylvanian) in the subsurface of the Illinois Basin: Proceedings of the Indiana Academy of Science, v. 107, p. 71–78.
- Greb, S.F., D.A. Williams, and A.D. Williamson, 1992, Geology and stratigraphy of the Western Kentucky coal field: Kentucky Geological Survey, Ser. 11, Bulletin 2, 77 p.
- 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.
- Shaver, R.H., C. Ault, A. Burger, D. Carr, J. Droste, D. Eggert, H. Gray, D. Harper, N. Hasenmueller, W. Hasenmueller, A. Horowitz, H. Hutchison, B. Keith, S. Keller, J. Patton, C. Rexroad, and C. Wier, 1970, Compendium of rock-unit stratigraphy in Indiana: Indiana Geological Survey, Bulletin 43, 229 p., 1 pl.
- Tri-State Committee, 2001, Toward a more uniform stratigraphic nomenclature for rock units (formations and groups) of the Pennsylvanian System in the Illinois Basin: Illinois, Indiana, and Kentucky Geological Surveys, Illinois Basin Consortium Study 5, 26 p.
- Wier, C.E., and H.H. Gray, 1961, Geologic map of the 1° x 2° Indianapolis Quadrangle, Indiana and Illinois, showing bedrock and unconsolidated deposits: Indiana Geological Survey, Regional Geologic Map Ser., 1:250,000.
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