Purington 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.
Wanless (1931) showed the “Purington shale” on three charts (p. 184, 188, 192). The earliest verbal descriptions of the shale are in Poor (1935) and Wanless (1957).
Wanless (1939, p. 99) mentioned that the shale was “used for brick manufacture at the Purington Paving Brick plant, East Galesburg, Knox County, W. Ill.” The North American Commission on Stratigraphic Nomenclature (2005, p. 1562) stipulates that names of rock units should be derived from “permanent natural or artificial features” shown on published maps. Thus, the name “Purington” may be considered to refer to Purington Lakes, which are shown on the Galesburg East 7.5' topographic map immediately north of the shale pits.
Brick manufacture commenced near Galesburg in 1849. D.V. and W.S. Purington founded the company that bore their name circa 1890. At its peak, the plant employed 800 workers and turned out more than 150,000 bricks a day. After World War II, the demand for paving bricks gradually declined, and the plant went out of business in 1974 (http://www.kville.org/kchistory/Pure.html).
Purington Paving Brick Company pit in SW¼ sec. 17, T 11 N, R 2 E, Knox County, Illinois.
Wanless (1956) and Kosanke et al. (1960) simply listed the location. No description has been published, and none has been found among the Survey’s extensive collection of field notes.
Abandoned for more than 40 years, the pit is heavily vegetated and slumped today. It is unlikely that any useful exposures remain.
The Audubon Oil & Gas #A-1 Green borehole drilled in sec. 30, T 2 S, R 10 E, Edwards County, southeastern Illinois (ISGS county no. 24519). The hole was cored continuously; core was described by W.J. Nelson of the ISGS and by company geologists. Electric, gamma ray, and density logs for #A-1 Green are on file. The Purington Member is 36.8 ft (11.2 m) thick and occupies the interval from 1,148.6 ft (350.1 m; base of Wheeler Coal) to 1,185.3 ft (361.3 m; top of Mecca Quarry Shale) (Figure 4-28). This log represents the situation in most of the Fairfield Basin, where the Wheeler and Bevier Coal Beds are present.
Logs of the #A-1 Green boring are filed at the ISGS Geological Records Unit and are available online at the ISGS website. Core is archived at the ISGS Geological Samples Library but presently lacks a call number.
The ISGS #1 Eric Miller borehole drilled in Section 2, T8N, R6E, Peoria County (ISGS county no. 35491). The hole was cored continuously and gamma-ray, spontaneous potential, and resistivity logs were run. The Purington Member is 56.3 ft (17.2 m) thick and extends from the base of the Houchin Creek Coal at 247.6 ft (75.5 m) to the top of the Oak Grove Member at 303.9 ft (92.6 m). This log exemplifies the situation in most of western Illinois, where the Wheeler and Bevier Coals are absent. The log is shown graphically in Figure 4-29.
Logs of the Eric Miller boring are filed at the ISGS Geological Records Unit and are available online at the ISGS website. Core is archived at the ISGS Geological Samples Library but presently lacks a call number.
The base of the Purington Member originally was defined as the top of the Oak Grove Member (Wanless 1931). That definition is accepted here, with the amendment that the lower contact steps down to the top of the Mecca Quarry Shale where the Oak Grove is absent. Kosanke et al. (1960) indicated that the Purington Member overlies the Oak Grove Limestone and variously underlies the Pleasantview Sandstone, Kerton Creek Coal, or Summum (now Houchin Creek) Coal. Smith et al. (1970, p. 2) showed the Purington overlying the Lowell Coal, which is now correlated with the Survant Coal. Willman et al. (1975) carried that definition forward. Part of the problem is that the Survant Coal Member and its constituent Wheeler (older) and Bevier Coal Beds are not developed in most of western Illinois, including the Purington type area. As a further complication, Wanless (1964) suggested that the Wheeler and Bevier Coal horizons, and their overlying marine limestone and shale units, merge into the Oak Grove Member. However, the Wheeler and Bevier and their underclays merge not with the Oak Grove, but with the underclay of the Houchin Creek Coal on the shelf northwest of the Illinois Basin. Thus, the Wheeler Coal position overlies the Purington Shale. Moreover (as Wanless 1957 detailed), the Roodhouse and Kerton Creek coals occupy the upper parts of incised valley deposits that are filled mainly with Pleasantview Sandstone and incised through the Purington Shale and older strata. The Roodhouse and Kerton Creek Coals are interpreted here to be overthickened Bevier Coal that was deposited within abandoned channels of Pleasantview age.
In summary, the Purington Shale Member occupies the interval between the top of the Oak Grove Member (or the top of the Mecca Quarry Shale where the Oak Grove is missing) and the base of the Wheeler Coal, or its correlative horizon. Where the Wheeler position cannot be identified, the top of the Purington steps up to the base of the Bevier Coal Bed. Where both Wheeler and Bevier (Survant) Coals are absent, the Purington cannot be differentiated from the overlying Lagonda Member.
Extent and thickness
No isopach maps of the Purington are known. Regional subsurface cross sections and selected core data show that the Purington extends throughout the Illinois Basin, except where truncated by younger channels. The member maintains a thickness between 33 and 66 ft (10 to 20 m) across large areas of the Fairfield Basin and Western Shelf in Illinois. A core near the northern margin of the basin in LaSalle County shows a thickness of 11.6 ft (3.54 m), which may be a depositional minimum. The greatest known thickness, nearly 100 ft (30 m), is near Martinsville in Clark County, east-central Illinois. Curiously, this thick shale occurs near the crest of an anticline. The Purington is 70 ft (21 m) thick in a core from Tazewell County, east of Peoria on the Western Shelf. The Purington averages close to 50 ft (15 m) thick west of the Illinois River (Wanless 1957; Reinertsen 1964). David A. Williams (Kentucky Geological Survey, written communication, 2017) has observed that the Purington thins markedly in the southeastern part of the western Kentucky coalfield.
The Purington Shale is a typical fine-grained, upward-coarsening deltaic clastic succession. The lower part consists of dark gray, silt-free to slightly silty shale that has common siderite bands and nodules; some bear fossils. Upward, silt-free shale gives way to silty or sandy shale, siltstone, and fine-grained sandstone. The uniformity of the Purington across the basin is striking. Wright (1965) depicted the member as “prodelta shale” throughout the Illinois Basin, as well as most of Iowa and Missouri. No channels or incised valleys of Purington–Wheeler Coal age are known to exist. The younger Pleasantview Sandstone fills valleys that were eroded during development of the underclay of the Bevier Coal.
The base of the Purington Member is the top of the Oak Grove Member, or the top of the Mecca Quarry Shale where the Oak Grove is absent. This contact is generally conformable and sharp or gradational through a few inches (centimeters). The top of the Purington is the base of the Wheeler Coal or, in parts of northern and western Illinois, the younger Bevier or Houchin Creek Coal. These contacts are sharp to rapidly gradational and conformable or slightly disconformable. Paleosols underlying the coal seams are considered part of the Purington Member. Locally, incised valleys (channels) filled with Pleasantview Sandstone or younger units truncate part or all of the Purington.
Well log characteristics
The Purington exhibits log profiles typical for fine-grained, upward- coarsening sequences. From low readings near the base, electrical resistivity gradually increases upward. Gamma-ray, density, and neutron readings are fairly uniform throughout the member.
The lower part of the Purington contains a brackish to marine invertebrate fauna in western Illinois. Wanless (1958) listed a fauna largely of gastropods and pelecypods, but also including foraminifera, the inarticulate brachiopods Lingula and Trigonoglossa, the articulate brachiopods Crurythyris and Mesolobus, ostracods, crinoid fragments, holothurian plates and spicules, and fish remains. In addition, fossil land plants occur in siderite concretions and as compressions in shale. Pfefferkorn (1979, p. 131) referred to the “Galesburg flora” that was “collected by Jelliff from the Purington Shale near Galesburg, Illinois” and archived at Knox College in Galesburg. Pfefferkorn (1979, table, p. 132) listed 27 species and 15 genera of fossil plants. Pfefferkorn et al. (1975) further quantified the collection, comprising lycopods (2%), sphenopsids (12%), “ferns” (17%), pteridosperms (64%), and cordaitaleans (4%). He noted, “It was a typical pteridosperm flora of that time interval, without any rare elements, i.e., what I called a Mazon Creek type I flora” (H.W. Pfefferkorn, written communication, August 19, 2014). The collector evidently was Fred Reuben Jelliff (1854–1902), a newspaper editor, historian, and amateur geologist in Galesburg (https://www.knox.edu/about-knox/our-history/honorary-degrees/honorary-degrees-1900-1999.html).
Age and correlation
Invertebrate and plant fossils from the Purington Shale are long-ranging taxa that are not useful for detailed biostratigraphic zonation. On the basis of the enclosing and correlative units, the Purington resides near the top of the Beedeina novamexicana–Wedekindellina euthysepta fusulinid zone (Wahlman 2013) and the upper part of the conodont zone of Idiognathodus rectus/Idiognathodus iowaensis (Barrick et al. 2013). These data place the Purington near the middle of the Desmoinesian Stage. In Missouri, the Purington is equivalent to the lower part of the Wheeler Member of the Verdigris Formation (Gentile and Thompson 2004). In Iowa, the Purington equivalent resides in unnamed strata at the base of the Swede Hollow Formation. No exact Appalachian equivalent is known, but the Purington is believed to lie between the Lower and Middle Kittanning coal beds in the middle part of the Allegheny Formation (Peppers 1996).
Environments of deposition
The relatively uniform thickness and lithology of the Purington throughout the Illinois Basin implies that the shale accumulated as offshore mud during a major highstand to early regression. This event began with a rapid and deep transgression, drowning the Colchester peat and depositing in turn thick Francis Creek Shale near the northern landward margin, followed by basin-wide black phosphatic Mecca Quarry Shale during early highstand. Later highstand carbonates of the Oak Grove Member developed mainly on the relatively shallow northern and western margins of the basin. The only indication of a nearby landmass during Purington sedimentation is the presence of diverse, well-preserved fossil land plants in Knox County, near the northwestern outcrop limit. Presumably, portions of the Transcontinental Arch, and perhaps the Wisconsin and Kankakee Arches, lay above sea level.
Evidently, parts of the Fairfield Basin subsided rapidly enough that the sea bottom was not exposed during the minor Wheeler regression. Thus, neither coal nor underclay is developed in some parts of the deep basin, where only a break between two upward-coarsening sequences marks the horizon of the Wheeler. A minor regression is consistent with the absence of known incised valleys of Purington–Wheeler age.
Shale of the Purington formerly was mined for the manufacture of clay products such as brick and tile.
- Barrick, J.E., L.L. Lambert, P.H. Heckel, S.J. Rosscoe, and D.R. Boardman, 2013, Midcontinent Pennsylvanian conodont zonation: Stratigraphy, v., 10, no. 1–2, p. 55–72.
- 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.
- North American Commission on Stratigraphic Nomenclature, 2005, North American stratigraphic code: American Association of Petroleum Geologists Bulletin, v. 89, no. 11, p. 1547–1591.
- Peppers, R.A., 1996, Palynological correlation of major Pennsylvanian (Middle and Upper Carboniferous) chronostratigraphic boundaries in the Illinois and other coal basins: Geological Society of America, Memoir 188, 111 p. and correlation chart.
- Pfefferkorn, H.W., 1979, High diversity and stratigraphic age of the Mazon Creek flora: in M.H. Nitecki (ed.), Mazon Creek Fossils: New York, Academic Press, p. 129–142.
- Pfefferkorn, H.W., H. Mustafa and H. Hass, 1975, Quantitative Charakterisierung ober-karboner Abdruckfloren: Neues Jahrbuch für Geologie und Paläontologie Abhandlungen (Stuttgart, Germany), v. 150, no. 3, p. 253–269 (in German).
- Poor, R.S., 1935, Geology and mineral resources of the Galesburg Quadrangle: Illinois State Geological Survey, https://isgs.illinois.edu/publications/manuscripts/ms-poor-rs-4.
- Reinertsen, D.L., 1964, Strippable coal reserves of Illinois, part 4, Adams, Brown, Calhoun, Hancock, McDonough, Pike, Schuyler, and the southern parts of Henderson and Warren Counties: Illinois State Geological Survey, Circular 374, 32 p., 1 pl.
- Smith, W.H., R.B. Nance, M.E. Hopkins, R.G. Johnson, and C.W. Shabica, eds., 1970, Depositional environments in parts of the Carbondale Formation—western and northern Illinois: Francis Creek Shale and associated strata and Mazon Creek biota: Illinois State Geological Survey, Guidebook Series No. 8, 125 p.
- Wahlman, G.P., 2013, Pennsylvanian to Lower Permian (Desmoinesian-Wolfcampian) fusulinid biostratigraphy of Midcontinent North America: Stratigraphy, v. 10, no. 1–2, p. 73–104.
- Wanless, H.R., 1931, Pennsylvanian cycles in western Illinois: Illinois State Geological Survey, Bulletin 60, p. 179–193.
- Wanless, H.R., 1939, Pennsylvanian correlations in the Eastern Interior and Appalachian coal fields: Geological Society of America, Special Paper 17, 130 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.
- Wanless, H.R., 1958, Pennsylvanian faunas of the Beardstown, Glasford, Havana, and Vermont Quadrangles: Illinois State Geological Survey, Report of Investigations 205, 59 p.
- Wanless, H.R., 1964, Local and regional factors in Pennsylvanian cyclic sedimentation, in D.F. Merriam, ed., Symposium on cyclic sedimentation: Kansas Geological Survey, Bulletin 169, v. 2, p. 593–605.
- 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.
- Wright, C.R., 1965, Environmental mapping of the beds of the Liverpool cyclothem in the Illinois Basin and equivalent strata of the northern mid-continent region: Urbana, University of Illinois, Ph.D. thesis, 100 p.
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