Caseyville Formation

Lithostratigraphy: Raccoon Creek Group >>Caseyville Formation
Chronostratigraphy: Paleozoic Erathem >>Pennsylvanian Subsystem >>Morrowan Series
Allostratigraphy: Absaroka Sequence

Primary source

Nelson, W.J., P.H. Heckel and J.M. Obrad, 2022, Pennsylvanian Subsystem in Illinois: Illinois State Geological Survey, Bulletin (in press).

Contributing author(s)

W.J. Nelson

Name

Original description

Referring to outcrops of quartz-pebble conglomerate and pebbly sandstone near Caseyville, Owen (1856, p. 48, 49, 56) introduced the name in the form “Caseyville conglomerate.”

Derivation

Caseyville is an unincorporated community on the Ohio River in Union County, Kentucky. According to The Political Graveyard website (http://politicalgraveyard.com/geo/KY/UN-buried.html), Caseyville was founded prior to 1821 and later named for Samuel L. Casey, U.S. Representative from the 1st District of Kentucky. Casey was born here in 1821; he died in 1902 and is buried in the Caseyville cemetery.

Other names

Some early authors used “Millstone Grit,” a name borrowed from early usage for rocks of similar age and lithology in northern England. Others used generic terms such as “conglomerate.” Early authors, such as Shaw and Savage (1912) and Lamar (1925), applied the Pennsylvania name “Pottsville Formation” to the Caseyville and much of the Tradewater Formation in southern Illinois. The name “Mansfield Sandstone” (Hopkins 1896) became established in Indiana before widespread acceptance of Caseyville elsewhere and evolved into the current Mansfield Formation, which includes strata younger than the Caseyville.

History/background

Glenn (1912) was the first to use the name “Caseyville” in a formational sense. Lee (1916) described the type section, along with that of the overlying Tradewater Formation. The first geologist to map the Caseyville in Illinois was Butts (1925); however, Illinois State Geological Survey (ISGS) publications continued to use “Pottsville formation” for the lower part of the Pennsylvanian into the late 1930s. As cyclothemic classification took hold, the ISGS adopted the Caseyville as a group (e.g., Weller 1940). With their thorough overhaul of Pennsylvanian classification, Kosanke et al. (1960) essentially established the present usage. The name Caseyville Formation is currently used in Illinois and Kentucky, but not in Indiana (Greb et al. 1992, 2002; Tri-State Committee 2001).

Type section

Figure 2-1. Map showing the type area of the Caseyville Formation and several of its members. Base is a U.S. Geological Survey Dekoven 7.5-minute topographic map. Base map courtesy of the U.S. Geological Survey. Map drafted by Alan Myers. © University of Illinois Board of Trustees.

Type location

The type section was “measured from outcrops on the Illinois shore of the Ohio River between the mouth of the Saline River and Gentry’s Landing below Battery Rock” in Hardin County, Illinois (Lee 1916, p. 15; Figure 2-1).

Type author(s)

Lee (1916, p. 15–16) created the original description (Figure 2-2). Kosanke et al. (1960) and Nelson (1989) reproduced the section. Geologic maps by Baxter et al. (1963), Kehn (1974), Denny et al. (2012), and Seid et al. (2013) cover the area.

Type status

Like other natural exposures of the Caseyville, the type section comprises prominent cliffs and ledges of sandstone, separated by poorly exposed or covered intervals of shaly strata.

Reference section (1)

Figure 2-2. Graphic columns of the Caseyville type section and three reference sections. Column 1 after Lee (1916). Used courtesy of the Kentucky Geological Survey. Columns 2 to 4 from Kosanke et al. (1960); Palmer and Dutcher (1979) and unpublished field notes by W.J. Nelson and J.T. Popp; and Nelson and Weibel (1996) and unpublished field notes by W.J. Nelson, respectively. Copyright © 1960, 1979, and 1996 University of Illinois Board of Trustees.

Reference location

Railroad cuts on the Canadian National (formerly Illinois Central Gulf) Railroad from the NW¼ SW¼ SE¼, sec. 31, T11S, R5E to NE¼ SE¼ NE¼, sec. 18, T12S, R5E, Pope County, Illinois.

Reference author(s)

Kosanke et al. (1960, p. 28, 61–62) created the original description (Figure 2-2), although Potter (1957) described some features of the exposures. Geologic maps by Nelson and Lumm (1990) and Devera (1991) cover the site.

Reference status

The cuts and adjacent natural outcrops remain in good condition. The surrounding land is Shawnee National Forest. Train traffic along the line at the type section is heavy.

Reference section (2)

Reference location

Roadcuts on Interstate 24 just south of Exit 7, in secs. 8, 9, 16, and 17, T12S, R3E, Johnson County, Illinois.

Reference author(s)

Published descriptions appear in Palmer and Dutcher (1979, p. 89–91), Cecil and Eble (1989, p. 33–37), and a thesis by Koeninger (1978). Devera (1989) described trace fossils from the upper part of the roadcut. The site is on the geologic map by Nelson et al. (2004). A graphic column is presented in Figure 2-2.

Reference status

Exposures in separate box cuts along northbound and southbound lanes remain mostly in good condition, although the shaly interval between the Pounds and Battery Rock Sandstones is largely grassed over. The Pounds Sandstone at this locality contains anomalous amounts of clay and dark mineral grains.

Reference section (3)

Reference location

Roadcuts on Interstate 57 beginning just south of Exit 36, in secs. 24 and 25, T11S, R1E, Johnson County, Illinois.

Reference author(s)

Published descriptions appear in Ethridge et al. (1973, Stops 4 and 5, p. 63–78), Koeninger (1978), Palmer and Dutcher (1979, Stop 8, p. 84–88), Cecil and Eble (1989, p. 30–32), and Nelson and Weibel (1996, p. 18, 24). Devera (1989) described trace fossils from the upper part of the roadcut. This site is on the geologic map of Weibel and Nelson (1993). A graphic column is presented in Figure 2-2.

Reference status

Exposures on both sides of the highway remain in good condition, although the shaly interval between the Pounds and Battery Rock Sandstones was never visible.

Reference section (4)

Figure 2-3. Graphic log based on continuous core from Illinois State Geological Survey #1 Berry test hole in Sec. 8, T9S, R3W, Jackson County, Illinois. This is a reference section for the Caseyville Formation. QA = quartz arenite. © University of Illinois Board of Trustees.

Reference location

A core that represents the entire Caseyville Formation is ISGS #1 Berry, drilled in sec. 8, T9S, R3W, Jackson County, Illinois (ISGS county #26246). The Caseyville is 285.2 ft (86.9 m) thick in the Berry core, extending through a depth range from 105.1 to 390.3 ft (32 to 119 m; Figure 2-3). The upper contact is an abrupt change from clay- and iron-rich sublitharenite above to white, pure quartz arenite below. The lower contact is unconformable between conglomerate of the Caseyville and the Mississippian Kinkaid Limestone below.

Reference author(s)

This report.

Reference status

Records of the Berry test hole, including the core description and electric and gamma-ray logs, are on file at the Geologic Records Unit of the ISGS and are accessible via the ISGS website. Core is archived at the ISGS Samples Library in Champaign under call number C-15356.

Stratigraphic relationships

Resting with major unconformity on older rocks, the Caseyville is the oldest Pennsylvanian formation in the Illinois Basin. It is also the only Pennsylvanian formation that sometimes can be recognized on purely lithologic grounds, without identifying specific named members. Nearly pure quartz sandstone (quartz arenite or orthoquartzite) characterizes the Caseyville, whereas the sandstone in younger Pennsylvanian formations is subarkose and sublitharenite.

A number of beds and members in the Caseyville Formation have been named. Most of the names were originally used informally and then formalized by Kosanke et al. (1960). Formalizing these units may have impeded more than helped understanding of the Caseyville. Formalizing gave the impression that the Caseyville comprises two major sandstone members, Pounds and Battery Rock, bounded by shaly units. In reality, many sections of the Caseyville contain five or more sandstone units (e.g., Figure 2-3). In my own mapping experience, the existence of named sandstone members created a bias toward connecting isolated sandstone outcrops in the field. None of the named members of the Caseyville can be traced more than a few miles into the subsurface.

Extent and thickness

Figure 2-4. Isopach map of Morrowan Stage, which essentially corresponds to the Caseyville Formation in the Illinois Basin. From Nelson et al. (2013), after McKee and Crosby (1975), Gray et al. (1987), Greb et al. (1992), Droste and Furer (1995), and Droste and Horowitz (1998). Copyright permission granted by Micropress, 2020.

Owing to the difficulty of identifying the top of the Caseyville Formation in the subsurface, the thickness and lithofacies of the formation have not been mapped in detail from well data. Small-scale maps that depict the thickness of roughly the Caseyville interval appear in McKee and Crosby (1975, Plate 3A), Greb et al. (1992, Figure 15), Droste and Furer (1995, Figure 4), and Droste and Horowitz (1998, Figure 4). Compiled from these sources, the map shown here (Figure 2-4) is essentially an isopach map of the Caseyville.

These maps indicate that the Caseyville Formation and equivalent strata lie largely southeast of a line that runs from Vigo County in west-central Indiana to Randolph County in southwestern Illinois. Northwest of this line, Caseyville rocks are largely confined to paleovalleys on the sub-Pennsylvanian surface. A sizeable outlier of the Caseyville occurs in the Quad Cities area in northwestern Illinois and adjacent Iowa.

Along its outcrop, the exposed Caseyville shows in map view as multiple semicircular arcs extending southeast and east from Randolph County, Illinois, into western Kentucky. Resistant Caseyville sandstone forms scenic bluffs at many localities, including Pounds Hollow, Garden of the Gods, Dixon Springs, and Ferne Clyffe State Parks, Lusk Creek Canyon, Bell Smith Springs, and Burden Falls. Caseyville outcrops continue southeastward to Muhlenberg County, Kentucky. Farther southeast in Kentucky, geologic mappers did not differentiate Caseyville and Tradewater Formations in areas where quartzose sandstones are thin or absent above paleo-uplands on the sub-Pennsylvanian surface. In Indiana, the lower part of the Mansfield contains thick units of massive and cross-bedded quartz arenite that contains abundant rounded granules and small pebbles of quartz. These outcrops are identical in lithology and inferred age to typical Caseyville Formation in southern Illinois.

The Quad Cities outlier is called Caseyville Formation because its lithology and age are similar to the type Caseyville (Ravn et al. 1984; Ravn 1986; Isbell 1985). Outcrops occur within and west of the Quad Cities in Mercer and Rock Island Counties, Illinois, and Muscatine and Scott Counties, Iowa. As in the southern part of the basin, Caseyville sandstones of the northwestern outlier are quartz arenites; however, quartz granules are rare. Shale, siltstone, and at least three coal layers make up the rest of the formation. These rocks have a maximum observed thickness of 100 ft (30 m) and are overlain unconformably by lower Desmoinesian rocks of the upper Tradewater Formation. The Caseyville of the Quad Cities area has been established as Morrowan age via palynology of its coal beds (Ravn and Fitzgerald 1982; Ravn et al. 1984).

Figure 2-5. Map showing where the Caseyville Formation crops out in Illinois and where the formation has been identified in the subsurface. Map drafted by Alan Myers. © University of Illinois Board of Trustees.

A few authors have described Caseyville strata in the subsurface of Illinois. Lowenstam (1951, p. 45–46) reported Caseyville sandstone and quartz-pebble conglomerate occupying what is now known to be a paleochannel cut into the Mississippian surface in the Bible Grove area of Clay County (Figure 2-5). Winslow (1959) identified Caseyville-age fossil spores in drill cores from the Allendale oil field in northern Wabash County (Figure 2-5). Although not identified as “Caseyville,” the quartz-rich sandstone serving as an oil reservoir in the Hardinville field of Crawford County (Figure 2-5) probably represents this formation. Sealed by overlying shale, the productive sandstone lies at the bottom of a sub-Pennsylvanian paleovalley (Howard and Whitaker 1988). Using limited palynological control, Droste et al. (2000) published a series of generalized maps and cross sections showing Morrowan (Caseyville age) depositional patterns in part of the Illinois Basin.

Lithology

The Caseyville Formation is primarily sandstone, siltstone, and shale, with lenticular coal beds and rare limestone. The sandstones are dominantly composed of quartz and contain very few lithic fragments and very little feldspar, clay, or mica. Caseyville sandstone is consistently classified as orthoquartzite or quartz arenite (Potter and Siever 1956b; Potter and Glass 1958; Potter and Pryor 1961; Morrow 1979; Bohm 1981). Quartz granules and pebbles, mostly less than half an inch (12 mm) in diameter, commonly occur either scattered throughout the sandstone or concentrated in beds of conglomerate. The coarser sandstones reach about 100 ft (30.5 m) thick and show relatively uniform cross-bedding, with dip directions to the west, south, or southwest (Potter and Olsen 1954; Potter 1962, 1963; Greb 1989a) parallel to the direction of elongation of the sandstone bodies. In the finer grained sandstone units, which are usually less than 25 ft (7.6 m) thick, the most prevalent sedimentary structure is ripple bedding. Shale or siltstone interbeds are common.

The shales and siltstones are not as widely exposed. The thicker shale units are sandy and contain several beds of sandstone, some relatively coarse grained. A few shales associated with coals are dark, relatively fine, and uniform, and their clay mineral content is high. Most of the Caseyville in northwestern Illinois is composed of medium gray to dark gray brittle shales interbedded with silty shales and a few clean quartz sandstones.

Several coal seams, most of them somewhat lenticular, are found in the Caseyville Formation, although only one—the Gentry Coal Bed in southeastern Illinois—is named. In Rock Island and Mercer Counties, as many as seven impure coals up to 2 ft (0.6 m) thick occur in the Caseyville (Searight and Smith 1969). Limestone is rare, and marine body fossils have been reported from only a few localities.

Contacts

The Caseyville rests unconformably on Mississippian and older rocks throughout the Illinois Basin. In outcrops and in wells where samples are available, the upper contact can be placed at the highest occurrence of quartz arenite, in contrast to overlying sandstones that are less mature. This contact is locally sharp, commonly gradational, and partly intertonguing. In parts of western Kentucky, the contact has been mapped at the base of the Bell or Hawesville coal beds. When subsurface geophysical logs are used, the top of the Caseyville is generally at the top of a thick, upward-fining sequence, but correlating such sequences among wells can be problematic. In many outcrops and well records, the top of the Caseyville cannot be identified with confidence.