The Illinois Basin holds a wealth of resources, including groundwater, coal, oil and gas, industrial minerals, and metals and also has become increasingly valuable as a resource to mitigate climate change by storing carbon dioxide deep underground. It is truly a geological gift that keeps on giving!
What is the Illinois Basin?
The Illinois Basin is an archive of our geologic history and the resources that helped power our past. It began forming during the late Precambrian to Early Cambrian as the crust was pulling apart (rifting) along the southern margin of the proto-North American continent. However, when rifting ended, thermal cooling in the crust caused the region to continue subsiding, while also filling with sediment.
This massive oval depression underlies roughly 70% of Illinois, extending about 110,000 square miles. It contains sedimentary rocks that accumulated from about 540 million to 250 million years ago, during the Cambrian through Permian periods. At its center in southeastern Illinois the Illinois Basin is approximately 15,000 feet deep.
The Illinois Basin contains many geological structures. One of the most significant is the New Madrid Rift System, which underlies its southern portion. This rift system has been a region of highest earthquake activity, including the severe New Madrid seismic events of 1811-12.
Resources provided by the Illinois Basin
Coal was one of the first economic resources recognized within the Illinois Basin in the 1670s, and coal mining has played a vital role in the Illinois economy since the 1820s. These coal resources formed from plant debris in swamps and peat bogs during the Mississippian and Pennsylvanian Periods (360 million to 300 million years ago). Illinois has some of the largest reserves of bituminous coal in the United States, with energy amounts equivalent to the oil reserves of Saudi Arabia.
The Illinois Basin also has long been a source for oil, as evidenced by the more than 30,000 oil and gas wells found in Illinois. There has been relatively steady production of more than 9 million barrels of oil and gas per year in Illinois for the past 20 or so years.
Finally, the Illinois Basin contains the Illinois-Kentucky Fluorspar Mining District in southeastern Illinois. Here, Permian aged volcanic intrusions brought igneous rocks and mineral-bearing fluids from deep in the earth to the surface, where they are valuable sources of critical minerals for industrial applications. Renewed interest in fluorite and associated minerals, plus the tantalizing discovery of rare earth elements (REEs), makes this region poised for revitalization as demand for critical minerals increases. The oncoming renewable energy and electric vehicle revolution will require extensive quantities of REEs as well as lithium, barite, zinc, and others.
The Illinois Basin may also hold untapped and extensive supplies of many critical minerals in coal waste piles and coal seams. REEs from coal ash ponds and waste piles, and critical substances like graphite from coal feed stocks, are used in large amounts in electric vehicle batteries.
Storage in the Illinois Basin
Since the early 2000s, there has been strong interest in using the unique geology of the Illinois Basin to permanently store, or sequester, carbon dioxide from power production and industrial activities. Capturing and storing this greenhouse gas is an important strategy to mitigate climate change.
The Mt. Simon Sandstone, at a depth of 6,000 to 7,000 feet, was among the first strata used to store CO2, and the focus of the United States’ first commercial-scale carbon sequestration project, the Illinois Basin - Decatur Project. The basin continues to be a focus for carbon sequestration as many other projects also are evaluating storage potential at numerous sites.
Most recently, there are new technologies looking at the Illinois Basin for storing compressed air and releasing it to generate electricity. There is similar potential for geologically storing hydrogen, as the energy transition may force the need for a reliable hydrogen supply for transportation fuel.
The Illinois Basin also has considerable potential for geothermal resources used for heating/cooling via heat exchangers.
