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Iowa Coal Geology

Red ball iconIowa Coal Geology


Coals of past and future economic interest in Iowa occur in Pennsylvanian age rocks, or more specifically, in the Virgil and Des Moines Supergroups. These rocks cover about one-third of the state. The rank of Iowa's coals range from subbituminous to high-volatile B bituminous, but the majority are high-volatile C bituminous.

Coal Production, Resources

Historically, most of Iowa's coal production has been from coals in the Cherokee Group. Lesser production has come from the Marmaton Group, and other minor production from the Virgil Supergroup. Most coal produced in the state supplies electric utilities and industry.

Total original coal reserves of Iowa are estimated to have been 7,366.58 million tons, of which 3,510.60 million tons, or 48%, are classified as measured and indicated reserves in seams greater than 14 inches thick. An additional 3,855.98 million tons are classified as inferred reserves. Approximately 56% of the total coal reserves (4,118.49 million tons) occur in beds greater than 28 inches thick that underlie 12 counties: Appanoose, Jasper, Jefferson, Lucas, Mahaska, Marion, Monroe, Polk, Van Buren, Wapello, Warren, and Wright. Of this coal 73% is considered to be strippable.

Historic production from 10 counties having the highest total production (Monroe, Polk, Appanoose, Mahaska, Marion, Lucas, Boone, Dallas, Wapello, Jasper) is estimated to be 8% of the state's original reserves; in eight of these counties (Monroe, Polk, Appanoose, Mahaska, Marion, Lucas, Wapello, Jasper), historic production is estimated to be 20% of the original strippable reserves. Statewide, an estimated 95% of the original reserves remain in the ground.

Des Moines Supergroup
Cherokee Group

The strata of the Des Moines Supergroup, and particularly those of the Cherokee Group, are characterized by extremely complex lateral and vertical facies relationships, which have always presented serious correlation and nomenclature problems. In the past, various informal divisions have been used to separate the Upper and Lower Cherokee, primarily distinguishing the somewhat more regular and persistent strata of the Upper Cherokee and its dominantly marine lithologies from the irregular, discontinuous strata of the Lower Cherokee and its dominantly fluviodeltaic lithologies. The lack of laterally continuous beds in the lower Cherokee has resulted in a proliferation of informal names applied to coals and other distinctive lithologies. Unfortunately, most of the names assigned to coals in the past had only local significance.

A number of research projects in recent years has led to a more complete understanding of the stratigraphy of the Cherokee Group in southeast and south-central Iowa. Ten coal seams accorded member status are now recognized in the Cherokee Group by the Geological Survey Bureau, Iowa Department of Natural Resources, based upon biostratigraphic subdivisions. The resulting subdivision of the Cherokee Group made it necessary to review, formalize and, in some instances, replace or reject certain of the informal names previously applied to individual coal beds. Finally, lithostratigraphic division into four formations was established to record four major episodes of sedimentation.

The formational units that have been designated in the Cherokee Group are of somewhat larger scale than those established for overlying strata. Standard stratigraphic practice in the Upper Pennsylvania strata of the Western Interior Region has been to designate as separate formations each individual marine-deposited unit and each intervening nonmarine or marginally marine unit of a cyclic sedimentary phase. Similar cyclicity can be seen in Cherokee Group sediments, but it is often masked by the dominance of less regular deltaic and fluvial regimes, producing multiple, cyclic clastic units with few poorly developed marine units. This is particularly true of the lower portions of the Cherokee Group. Division of the Cherokee into individual units corresponding to each cycle would create an unwarranted proliferation of stratigraphic names, as well as lend a false impression of lateral traceability of horizons within the Cherokee Group. The present system reflects the broad depositional setting and history of the Cherokee Group, which can be applied to unstudied sections with moderate reliability.

(Previously applied coal names in Iowa were either derived locally, usually from mining operations or extended from the nomenclature of strata in neighboring states. Other names have been proposed in unpublished theses, too many of which exist to be reviewed here, but certain coal names have been used extensively in the literature discussing Cherokee Group coals. Certain names applied to mined beds, however, are not necessarily consistent with stratigraphic interpretations. Some coal seams may not have been named, while others may have more than one name. Conversely, a single name may apply to different seams.)

Kilbourn Formation

Coals of the Kilbourn Formation are thin, discontinuous, and have had no names applied to them. Although mined in small quantities they are of little economic importance. Biostratigraphically, they are of similar geologic age as the Tarter and Manly coals of the Atokan Series in the Illinois Basin. Some may possibly be as old as the Reynoldsburg coal (Early Atokan).

Kalo Formation

Blackoak Coal - The Blackoak coal is highly variable in thickness, and has been locally encountered in thicknesses exceeding 60 inches. The Blackoak Member consists of a single coal seam in its eastern-most occurrences. A thin parting appearing in the seam becomes thicker and more complex to the west and southwest. Additional splitting produces four thin coals in some locations. The Blackoak is the biostratigraphic equivalent of the Pope Creek coal of Illinois and is therefore assignable to the Atokan Series. The Blackoak has probably been mined in some areas. The names Manbeck and Hastie, formerly used in Polk County, may refer at least in part to this coal. Due, however, to the uncertainty in determining to which beds local names were applied, and the possibility that these two names may have been given to more than one coal bed, an estimate of the reserves of Blackoak coal is impractical at this time.

Cliffland Coal - The Cliffland coal commonly occurs as two discrete beds which, like the Blackoak, are separated by a thin shale which appears to thicken toward the southwest. The Cliffland seam is persistent and is often thick enough to be of economic interest. The Cliffland is probably the biostratigraphic equivalent of the Rock Island (No. 1) coal of Illinois. Although it is difficult to determine which names have been applied to this seam, portions of the Hastie and Hastie Plus coals may belong to the Cliffland Member. Original reserves for the Cliffland coal in four counties (Davis, Henry, Jefferson and Wapello) plus probable equivalents (i.e., Hastie Plus in Dallas, Polk and Story counties and Rock Island No. 1 in Scott and Muscatine counties) total 246.78 million tons.

Floris Formation

Laddsdale Coal - Most coals being mined in Iowa at the present time are in the Laddsdale Member. The Laddsdale is part of an extremely complex sedimentary unit consisting of up to five coal beds of varying thickness and separated by unnamed shale and marine sediments. The type section appears to represent the most complex development of the Laddsdale Member. It consists of five coal seams from one inch to 34 inches thick over a total thickness of about 30 feet. The individual coal beds in the Laddsdale are lensoidal and generally cannot be traced with reliability, except in areas of closely spaced exposures or by drill holes. Although these coals may sometimes achieve thicknesses of 72 inches or more in a few localities, their discontinuous nature demands careful exploration work.

Biostratigraphic evidence suggests that the coal called Lower Coal-Ford Coal in south-central Iowa is assignable to the Laddsdale Member. These informal names appear to have been applied to more than one coal bed, thus making reserve estimates of these beds difficult to determine. Original reserves for the Laddsdale coal in five counties (Davis, Henry, Jefferson, Van Buren, Wapello) and probable equivalents (Lower Coal-Ford Coal in Clarke, Dallas, Guthrie, Jasper, Lucas, Marion, Monroe, Polk, Poweshiek, and Warren counties and the Lower Coal in Mahaska County) total 2,902.67 million tons. This tonnage is about 39% of estimated reserves.

Most coals recently mined in Iowa are in the Laddsdale Member. This seam was being surface mined in Marion and Lucas counties.

Unnamed coal - Above the Laddsdale Member, as many as three thin coal seams have been observed. They are palynologically distinct from the overlying Carruthers coal and the underlying Laddsdale coal. The name Munterville has been historically applied to both a thin coal and a limestone in southern Iowa which probably occur stratigraphically in this position. Attempts to locate these units, however, have been unsuccessful. Thus the use of the name Munterville has been discontinued. Original reserves of probable equivalents (listed as "Munterville" in Dallas, Guthrie, Polk, Story, and Warren counties and "No. 5 Coal" in Lucas and Monroe counties) total 157.51 million tons.

Carruthers Coal - The Carruthers coal, a thin but relatively persistent coal that typically varies form 8 to 17 inches in thickness, was previously known in Iowa as the Wiley coal. The name Wiley was extended into Iowa on the basis of proposed correlation with the Wiley coal in Illinois. However, biostratigraphic analyses of coals originally believed to correlate with the Wiley of Illinois indicate that the probable Illinois equivalents are, instead, the Greenbush and DeKoven coals. The actual Wiley equivalent in Iowa is one of the unnamed coals lower in the Floris Formation. Although the Carruthers coal is probably too thin to be of economic significance, original reserves (listed as Wiley in Guthrie, Lucas, Marion, and Warren counties) totaling 43.62 million tons are estimated.

Swede Hollow Formation

Whitebreast Coal - The Whitebreast coal, together with the Oakley Shale and Ardmore Limestone, are the most persistent, easily recognized beds in the Cherokee Group. The Whitebreast Coal is remarkably uniform, commonly more than 12 inches thick. Although mostly considered uneconomic, it has been mined in some areas. The Whitebreast Coal is biostratigraphically equivalent to the Colchester (No. 2) of Illinois and the Croweburg Coal of Kansas. Original reserves of the Whitebreast Coal in Adair, Dallas, Decatur, Guthrie, Lucas, Monroe, Wapello, and Warren counties total 256.71 million tons.

Wheeler Coal and Bevier Coal - The Wheeler and Bevier coals are the lower and upper, respectively, of two related beds. The Bevier is a name carried into Iowa from Missouri and there is little doubt that they are equivalent. Wheeler, a locally-derived name from Lucas County, Iowa, has been applied to the lower of the two coals, which in that area is separated by about 20 feet of shale from the Bevier Coal. The split persists throughout the type area and appears to thicken towards the southwest. To the northeast, the separation between the two coals thins to a half-inch parting, possibly a reason that they were once considered synonymous in some areas.

In the same area of Lucas County, the Bevier Coal was called Bedford by others, further adding to the confusion among these coal names. Present nomenclature in northern Missouri recognizes the name Bevier for the upper coal seam and Wheeler for the lower. Although the two coal beds seldom exceed two feet in thickness individually, the potential for mining both coals together exists where separation is thin. Biostratigraphically, they are equivalent to the Lowell Coal of Illinois. Original reserves of the Wheeler Coal in Lucas, Polk, and Warren counties, the Bevier Coal in Decatur, Guthrie, Lucas, and Warren counties, and the Wheeler-Bevier coals together in Dallas and Monroe counties total 250.84 million tons.

Mulky Coal - The Mulky Coal in Iowa is a persistent thin coal which is readily recognized in core or outcrop. Although too thin to be of economic interest, it is a useful marker, being the uppermost bed of the Cherokee Group.

Marmaton Group

The strata of the Marmaton Group are both more persistent and laterally traceable than are those of the Cherokee Group, reflecting the greater influence of marine conditions on the deposition of these units. Several coal beds are present that are generally thin but traceable over large areas.

Mystic Coal - The Mystic Coal is probably the best known coal in Iowa. Averaging 30 inches in thickness, this coal has been mined extensively in Appanoose County. Original reserves of the Mystic Coal in Appanoose, Dallas, Lucas, Monroe, Warren, and Wayne counties total 1,043.38 million tons.

Virgil Supergroup
Wabaunsee Group

Nodaway Coal - The Nodaway coal is a persistent coal in southwestern Iowa, generally varying from 14 to 18 inches in thickness. Reserves of the Nodaway coal in Adams, Cass, Fremont, Montgomery, Page, and Taylor counties total 326.18 million tons.

Elmo and Nyman Coals - The Elmo and Nyman Coals are discontinuous and generally less than 14 inches thick. Consequently, no reserves have been estimated for these coals.

Remaining Coal Reserves

Remaining coal reserves were recently evaluated for three counties using computerized databases. Remaining resource calculations were prepared for categories of coal thickness, overburden thickness, data reliability, and geographic area (by township and county) for four named coal beds: Blackoak, Cliffland, Laddsdale, and Whitebreast. Calculations eliminated mined-out areas.

Results were not always directly comparable to previous estimates of total original reserves or strippable reserves because each estimate uses different techniques and category systems to analyze and report coal reserves. New geologic data, revised stratigraphic interpretations, computerized mapping capabilities including geographic information systems, and database manipulations were largely unavailable in past work.

In these three counties, there is a slight increase in reserves, even allowing for evaluation of fewer coals and remaining reserves versus original reserves. Strippable reserves are 36% higher in Wapello County and 187% higher in Monroe County even allowing for evaluation of fewer coals.

Present Mining Activity - None

Iowa coal production had been in a slowly declining state since about 1980. Iowa's last surface coal mine, which had been mining in Marion County, filed for bankruptcy in September 1994. Total 1994 production was 58,855 tons, including coal extraction incidental to landfill construction in Marion County.


Prepared by Paul VanDorpe, Iowa Department of Natural Resources, Geological Survey Bureau

References

Aubrey, W.D., 1970, Report for biennial period ending 12-31-1969. State Mine Inspector.

Aubrey, W.D., 1966, Report for biennial period ending 12-31-1965. State Mine Inspector.

Aubrey, W.D., 1968, Report for biennial period ending 12-31-1967. State Mine Inspector.

Aubrey, W.D., 1972, Report for biennial period ending 12-31-1971. State Mine Inspector.

Garvin, P.L., 1975, Strippable Coal Reserve Study in Selected Iowa Counties. Iowa Geological Survey Open-File Report, USBM Grant No. G0254008, 23 p.

Garvin, P.L. and Van Eck, O. J, 1976, Strippable Coal Reserve Study in Seven Iowa Counties. Iowa Geological Survey Open-File Report, USBM Grant No. G0264013, 29 p.

Hatch, J.R., Avcin, M.J., Van Dorpe, P.E., 1984, Element Geochemistry of Cherokee Group Coals (Middle Pennsylvanian) from south-central and southeastern Iowa. Iowa Geological Survey Technical Paper No. 5, 108 p.

Howes, M.R., 1988, Evaluation of Coal Resources in Wapello and Davis Counties, Iowa, Using Computerized Databases for Resource Estimates and Mapping. Iowa Department of Natural Resources Contract Completion Report, 71 p.

Howes, M.R., 1990, Development of a Coal Resource Database in the Iowa Natural Resources Geographic Information System for Monroe County, Iowa. Iowa Department of Natural Resources Open File Report 90-2, 70 p.

Landis, E.R. and Van Eck, O.J, 1965, Coal Resources of Iowa. Iowa Geological Survey Technical Paper No. 4, 141 p.

Ravn, R.L., Swade, J.W., Howes, M.R., Gregory, J.L., Anderson, R.R., and Van Dorpe, P.E., 1984, Stratigraphy of the Cherokee Group and revision of Pennsylvanian stratigraphic nomenclature in Iowa. Iowa Geological Survey Technical Information Series No. 12, 76 p.

Swade, J.W., 1985, Conodont Distribution, Paleocology and Preliminary Biostratigraphy of the Upper Cherokee and Marmaton Groups (Upper Desmoinsean, Middle Pennsylvanian) from Two Cores in South-Central Iowa. Iowa Geological Survey Technical Information Series No. 14, 71 p.

U.S. Department of the Interior, 1972, 1973, 1974, 1975, 1976, Minerals Yearbook, vol. I., Metals, Minerals, and Fuels.

U.S. Department of the Interior, 1977, Minerals Yearbook, vol. II., Area Reports: Domestic.

U.S. Department of the Interior, Office of Surface Mining, unpublished data.

Adapted from the KEYSTONE COAL INDUSTRY MANUAL Copyright 1995/1996 courtesy of Intertec Publishing Corp., Chicago, IL 60606. All rights reserved. The KEYSTONE MANUAL is published annually and contains approximately 880 pages of information, data and statistics on the U.S. and Canadian coal industries as well as on the buyers and users of coal. The KEYSTONE may be ordered by calling 1-800-247-8080. Ask for book No. M-558. For general information call 312-726-2802 and ask for the book department or Mining Information Services.