Canton Shale Member
Nelson, W.J., 2020, Pennsylvanian Subsystem in Illinois: Illinois State Geological Survey Bulletin (in press).
Edited and figures drafted by Jennifer M. Obrad.
Savage (1921, p. 240) wrote, “Overlying the calcareous shale above the limestone cap rock of the Springfield (No. 5) coal there is usually a bed of gray shale, which is exposed in several places along Big Creek and its tributaries south of Canton. This shale may be appropriately designated the ‘Canton shale’ as a matter of convenience for this report.”
Canton is the county seat of Fulton County, Illinois, presently a city of about 18,000. When Isaac Swan and Nathan Jones founded the town in 1825, Swan chose the name based on the mistaken belief that it was the direct antipode of Canton (now Guangzhou) in China.
No other names have been applied.
As listed by Kosanke et al. (1960) and subsequent authors, the type locality is the bank of Big Creek near the center of sec. 9, T 6 N, R 4 E, Fulton County.
Savage (1921, p. 241).
Unknown, but as described, this is a poor type section. Savage (p. 241) simply offered, “Shale, bluish gray, 22 feet thick,” with the upper contact eroded. ISGS field notes yield no further information.
Outcrops and cores in northern and western Illinois are poorly suited because the Briar Hill Coal, which defines the top of the Canton Member, is rarely present. A core from southern Illinois is hereby nominated. This is the ISGS #1 McCormick borehole, located in sec. 21, T 8 S, R 8 E, Gallatin County. In this core, the Canton Member extends from the base of the Briar Hill Coal at 325.0 ft (99.1 m) to the top of the St. David Limestone at 379.1 ft (115.5 m; Figure 4-61). The Canton is thus 54.1 ft (16.5 m) thick.
Logs from the McCormick borehole, including typed core descriptions and gamma-ray and resistivity logs, are on file at the Geological Records Unit of the ISGS and can be accessed via the ISGS website. Core is archived at the ISGS Geological Samples Library in Champaign under call number C-15339.
Defining the Canton Shale, Savage (1927) excluded fossiliferous shale less than 2 ft (60 cm) thick that commonly lies directly above the St. David Limestone (“cap rock”). Wanless (1957, 1958) did the same. Willman et al. (1975) overlooked this minor exclusion and considered the Canton to include all clastic strata between the St. David and the next younger named unit. The basal fossiliferous shale has never been named, and no reason exists to name it. Thus, it is considered here to be part of the Canton Member.
The Canton Member variably overlies the St. David Limestone, Turner Mine Shale, or Dykersburg Shale. Previous authors did not clearly define the upper contact. In this report, the top of the Canton is the base of the Briar Hill Coal, where present, or the base of the younger Antioch Limestone or Vermilionville Sandstone. However, in some cases, the Canton cannot be differentiated from the younger Big Creek Shale.
Extent and thickness
No isopach map is known, and published information is sparse. In northwestern Illinois, the maximum thickness seems to be about 30 to 35 ft (9.1 to 10.7 m). Based on a quick survey of core records and published quadrangle maps, the basin-wide maximum of 65 to 70 ft (19.8 to 21.3 m) is in southeastern Illinois (parts of Gallatin and White County) and adjacent Kentucky (Union and Webster Counties). Elsewhere in the Fairfield Basin of Illinois and adjacent western Indiana, the Canton seldom exceeds 33 ft (10.1 m) and in places is less than 10 ft (3 m) thick. Excluding areas where the Dykersburg Member is thick, the Briar Hill Coal generally is much closer to the Springfield than to the Herrin. Only in the Gallatin–White–Union–Webster area is the Briar Hill roughly midway between the Springfield and Herrin, and the total Springfield-to-Herrin interval can attain 150 ft (45.7 m).
Little has been published about the Canton beyond the outcrop-based reports of Willman and Payne (1942) and Wanless (1957, 1958) in northern and western Illinois, respectively. Core drilling and mine exposures, however, indicate that lithic properties are fairly consistent throughout the Illinois Basin. Like the Purington, Lagonda, and Delafield Members, the Canton is a clastic unit that coarsens upward. In places, a thin (≤ 2 ft, 0.6 m) basal unit of dark gray, laminated, fossiliferous shale is present. This transitions upward to dark gray, finely silty shale that contains numerous bands, nodules, and small concretions of siderite. Continuing upward, the shale becomes lighter gray, silt content increases, siderite nodules die out, and laminae of siltstone and sandstone appear. The upper Canton includes fine-grained sandstone that is laminated to thinly bedded. Bedding surfaces are thickly coated with mica and carbonaceous debris. Among other names, miners call this facies “stack rock.”
The lower contact to the St. David Limestone is sharp to rapidly gradational. The upper contact to the Briar Hill Coal is normally sharp. Channels filled with Vermilionville and younger sandstone units locally truncate the Canton. Where Briar Hill Coal is absent, as in most of northern and western Illinois, the upper contact (to Big Creek Shale) is difficult to determine.
Well log characteristics
Typical for an upward-coarsening clastic sequence.
Savage (1921) and Wanless (1957, 1958) listed an extensive marine invertebrate fauna from the basal calcareous portion of the Canton. Wanless (1958) logged 105 species, including foraminifera, bryozoans, brachiopods, pelecypods, gastropods, nautiloids, ostracods, and conodonts. Most conspicuous on the outcrop are brachiopods of genera Marginifera, Mesolobus, and Dictyoclostus. Above the basal zone, fossils are uncommon. Willman and Payne (1942) reported the gastropod Phanerotrema both in shale and in siderite concretions. Plant remains are largely fragmentary.
Age and correlation
The Canton corresponds, at least in part, to unnamed shale between the Houx (older) and Higginsville Limestone Members of the Stephens Forest Formation in Iowa (Ravn et al. 1984; Pope 2012). In Missouri, the same strata are assigned to the Blackwater Creek Member of the Little Osage Formation (Gentile and Thompson 2004).
Environments of deposition
Evidently, the Canton Member represents late highstand and regressive phases of a eustatic cycle. As the shoreline prograded into the basin, the setting progressed from fully marine, distal prodelta deposits to near-shore delta-front and delta-top deposits.
The “stack rock” laminated sandstone facies of the Canton is difficult to support in the mine roof and can bear water.
- Gentile, R.J., and T.L. Thompson, 2004, Paleozoic succession in Missouri, Part 5, Pennsylvanian Subsystem, Volume A, Morrowan strata through Cherokee Group: Missouri Geological Survey, Report of Investigations 70, 241 p. and correlation chart.
- 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. and 1 pl.
- Pope, J.P., 2012, Description of Pennsylvanian units, revision of stratigraphic nomenclature, and reclassification of the Morrowan, Atokan, Desmoinesian, Missourian, and Virgilian stages in Iowa: Iowa Geological and Water Survey, Special Report Series No. 5, 140 p.
- Ravn, R.L., J.W. Swade, M.R. Howes, J.L. Gregory, R.R. Anderson, and P.E. Van Dorpe, 1984, Stratigraphy of the Cherokee Group and revision of Pennsylvanian stratigraphic nomenclature in Iowa: Iowa Geological Survey, Technical Information Series No. 12, 76 p.
- Savage, T.E., 1921, Geology and mineral resources of the Avon and Canton Quadrangles: Illinois State Geological Survey, Bulletin 38, p. 209–271, 1 pl., 1:62,500.
- Savage, T.E., 1927, Significant breaks and overlaps in the Pennsylvanian rocks of Illinois: American Journal of Science, v. 14, p. 307–318.
- Wanless, H.R., 1957, Geology and mineral resources of the Beardstown, Glasford, Havana, and Vermont Quadrangles: Illinois State Geological Survey, Bulletin 82, 233 p.
- Wanless, H.R., 1958, Pennsylvanian faunas of the Beardstown, Glasford, Havana, and Vermont Quadrangles: Illinois State Geological Survey, Report of Investigations 205, 59 p.
- Willman, H.B., E. Atherton, T.C. Buschbach, C. Collinson, J.C. Frye, M.E. Hopkins, J.A. Lineback, and J.A. Simon, 1975, Handbook of Illinois stratigraphy: Illinois State Geological Survey, Bulletin 95, 261 p.
- Willman, H.B., and J.N. Payne, 1942, Geology and mineral resources of the Marseilles, Ottawa, and Streator Quadrangles: Illinois State Geological Survey, Bulletin 66, 388 p., 29 pls.
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