The Illinois Basin is a Paleozoic

Paleozoic

The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...

 depositional

Sedimentary basin

The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification...

 and structural basin in the United States, centered in and underlying most of the state of Illinois

Illinois

Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...

, and extending into southwestern Indiana

Indiana

Indiana is a US state, admitted to the United States as the 19th on December 11, 1816. It is located in the Midwestern United States and Great Lakes Region. With 6,483,802 residents, the state is ranked 15th in population and 16th in population density. Indiana is ranked 38th in land area and is...

 and western Kentucky

Kentucky

The Commonwealth of Kentucky is a state located in the East Central United States of America. As classified by the United States Census Bureau, Kentucky is a Southern state, more specifically in the East South Central region. Kentucky is one of four U.S. states constituted as a commonwealth...

. The basin is elongate, extending approximately 400 miles northwest-southeast, and 200 miles southwest-northeast.

Boundaries and sedimentary rocks

The basin is bordered on the northeast by the Kankakee Arch, on the southeast by the Cincinnati Arch

Cincinnati Arch

The Cincinnati Arch is a broad structural uplift between the Illinois Basin to the west, the Michigan Basin to the northwest and the Appalachian Basin and Black Warrior Basin to the east and southeast. It existed as a positive topographic area during Late Ordovician through the Devonian Period...

, on the south by the Pascola Arch, on the southwest by the Ozark Dome, on the northwest by the Mississippi River Arch, and on the north by the Wisconsin Arch. The New Madrid Seismic Zone

New Madrid Seismic Zone

The New Madrid Seismic Zone , sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes in the southern and midwestern United States, stretching to the southwest from New Madrid, Missouri.The New Madrid fault system was responsible for the...

 and the Wabash Valley Seismic Zone

Wabash Valley Seismic Zone

The Wabash Valley Seismic Zone is a tectonic region located in the Midwest of the United States, centered on the valley of the Lower Wabash River, along the state line between southeastern Illinois and southwestern Indiana.-Geology:The Wabash Valley Seismic Zone consists largely of...

 intersect the southern portion of the basin.

At its center beneath southern Illinois, the basin contains a thickness of about 15,000 feet of Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

 through Pennsylvanian

Pennsylvanian

The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...

 sedimentary rock

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

s, predominantly marine, and mostly dolomite

Dolomite

Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....

, limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

, shale

Shale

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

, and sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

.

The basement rock

Basement Rock

Basement or Basement Rock music was a sub-genre coined in 2006 in an article by music magazine TGR. This was first in relation to the existence of underground record label Criminal Records but more for the independent bands they represent. The roots of the sub-genre are noted to be as far back as...

s deep below the sedimentary rocks of the basin are Proterozoic

Proterozoic

The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...

 granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

s and rhyolite

Rhyolite

This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...

 of the Eastern Granite–Rhyolite Province which dates to around 1.55 Ga.

Mineral resources

The rocks of the Illinois Basin are sources of coal

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, petroleum

Petroleum

Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

, and minerals.

Coal

Bituminous coal is present in Pennsylvanian rocks in the basin, deposited in freshwater swamp environments. Over the years, the Illinois Basin has produced more than eight billion tons of coal in Southern Illinois, particularly in the Harrisburg Coal Field

Harrisburg, Illinois

Harrisburg is a city and township in Saline County, Illinois, United States. It is located about southwest of Evansville, Indiana, southeast of St. Louis, Missouri. The 2010 population was 9,017, with a township population of 10,790. It is the county seat of Saline County...

, and the Western Coal Fields

Western Coal Fields

thumb|right|Regions of Kentucky, with the Western Coal Fields shown in brownThe Western Coal Fields of Kentucky compose an area in the west-central part of the state, bounded by the Dripping Springs Escarpment. This area is bordered on three sides by the Pennyroyal Plateau and to the north by the...

 of Kentucky. Coal production was 99 million short tons in 2008, roughly equally divided between Illinois, Indiana, and western Kentucky. The basin provided 8% of US coal production in 2008.

Petroleum

The Illinois Basin has produced more than four billion barrels of petroleum. Major oil production began in 1905, and from 1907 through 1912, the basin was the third-most oil productive area in the United States. Oil production peaked in 1908 at 34 million barrels per year, and declined steadily to 5 million barrels in 1933. A new wave of exploration brought oil production to a new high of 140 million barrels in 1940, after which production again declined. Waterflooding of old reservoirs caused a third peak of oil production in the 1950s.

Much recent drilling activity has targeted shale gas

Shale gas

Shale gas is natural gas produced from shale. Shale gas has become an increasingly important source of natural gas in the United States over the past decade, and interest has spread to potential gas shales in the rest of the world...

 in the Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

-Mississippian New Albany Shale

New Albany Shale

The New Albany Shale is an organic-rich geologic formation of Devonian and Mississippian age in the Illinois Basin of the United States. It is a major source of hydrocarbons. -Stratigraphy:...

.

Nonfuel minerals

The rocks of the Illinois Basin are thought to be the source of metals in Mississippi Valley-Type lead-zinc

Zinc

Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 deposits, both within the basin and in surrounding areas, such as the Lead Belt

Lead Belt

The Southeast Missouri Lead District, commonly called the Lead Belt, is a lead mining district in the southeastern part of Missouri. Counties in the Lead Belt include Saint Francois; Crawford; Dent; Iron; Madison: Reynolds; and Washington...

 of southeast Missouri

Missouri

Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...

.

Within the basin, deposits valuable for lead, zinc, coal balls and fluorite

Fluorite

Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...

 are mined in Hardin and Pope counties, Illinois, and Crittenden

Crittenden County, Kentucky

Crittenden County is a county located in the U.S. state of Kentucky.It was formed in 1842. As of 2000, the population was 9,384. Its county seat is Marion. The county is named for John J. Crittenden who was Governor of Kentucky 1848-1850...

 and Livingston

Livingston County, Kentucky

Livingston County is a county located in the U.S. state of Kentucky. As of 2000, the population was 9,804. Its county seat is Smithland. The county is named for Robert R. Livingston...

 counties, Kentucky. the deposits are in the form of veins and limestone replacement deposits in Mississippian sedimentary rocks. Ore minerals are fluorite, galena

Galena

Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...

, and sphalerite

Sphalerite

Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...

. Gangue minerals include common quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 and calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

, and minor barite

Barite

Baryte, or barite, is a mineral consisting of barium sulfate. The baryte group consists of baryte, celestine, anglesite and anhydrite. Baryte itself is generally white or colorless, and is the main source of barium...

 and chalcopyrite

Chalcopyrite

Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS2. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green tinged black.On exposure to air, chalcopyrite...

.

Carbon sequestration

Some geologic formations in the Illinois Basin are considered to have potential for carbon sequestration, as a permanent disposeal site for carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 that would otherwise be released into the atmosphere. In 2009, Archer Daniels Midland

Archer Daniels Midland

The Archer Daniels Midland Company is a conglomerate headquartered in Decatur, Illinois. ADM operates more than 270 plants worldwide, where cereal grains and oilseeds are processed into products used in food, beverage, nutraceutical, industrial and animal feed markets worldwide.ADM was named the...

Corp. began pilot testing the carbon sequestration potential of the Mt. Simon formation beneath its ethanol manufacturing facility in Illinois.