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| Chester Series (geology) | |
|---|---|
| Name | Chester Series |
| Type | Geologic series |
| Period | Pennsylvanian |
| Primary lithology | Limestone, dolomite, shale |
| Other lithology | Sandstone, coal |
| Region | Midcontinent United States |
| Country | United States |
| Named for | Chester, Illinois |
| Named by | Niles Eldredge |
| Year defined | 19th century |
Chester Series (geology)
The Chester Series is a late Paleozoic stratigraphic interval of the Pennsylvanian subperiod notable across the Midcontinent United States and parts of the Illinois Basin, Midcontinent Shelf, and Appalachian Basin. It is recognized for its cyclic carbonate and siliciclastic alternations, diverse marine fossils, and economic deposits that have influenced industrial development in regions associated with the Illinois, Ohio, and Mississippi rivers. Its nomenclature and subdivisions have been incorporated into regional stratigraphic charts used by agencies such as the United States Geological Survey, State geological surveys, and university departments.
The name derives from the city of Chester, Illinois, where exposures and borehole logs first illustrated the unit’s characteristic lithologies. Early geologists and surveyors from institutions including the Illinois State Geological Survey, United States Geological Survey, and university field parties contributed to naming and correlating the series. Prominent historical figures in North American stratigraphy, such as James Dwight Dana, Charles D. Walcott, and regional workers at Harvard University and the University of Illinois Urbana–Champaign refined its usage. The term has seen different applications in state-level stratigraphic schemes in Illinois, Missouri, Indiana, and Kentucky and has been cross-referenced with lithostratigraphic units recognized by the American Association of Petroleum Geologists.
The Chester Series occupies an interval near the top of the Mississippian–Pennsylvanian transition in some sections and within the Pennsylvanian in others, with local equivalence to stages defined by chronostratigraphers at organizations such as the International Commission on Stratigraphy and regional committees. It comprises cyclic successions of fossiliferous limestones, dolomites, calcareous shales, black shales, and subordinate sandstones and coal seams. Key formations within the series in different basins include carbonate-dominated units correlated with the St. Louis Limestone, siliciclastic interbeds linked to the Carbondale Formation, and marker beds used in sequence stratigraphy by petroleum geologists at Shell and ExxonMobil. Lithofacies mapping by state surveys has identified buildups, grainstone shoals, and basinal marls that exhibit diagenetic features such as dolomitization and stylolitization documented in cores held by the American Association of Petroleum Geologists Datapages.
Fossil assemblages in the Chester Series include diverse marine invertebrates such as brachiopods, crinoids, bryozoans, rugose and tabulate corals, and mollusks that have been studied by paleontologists affiliated with museums like the Smithsonian Institution, Field Museum of Natural History, and American Museum of Natural History. Microfossils including foraminifera and conodonts have been used for biostratigraphic correlation by specialists at institutions such as Purdue University and Ohio State University. Trace fossils and benthic ichnofabrics have been analyzed in comparative studies involving collections at the Peabody Museum of Natural History and regional universities, while occasional vertebrate remains and plant debris link the series to paleobotanical research at Yale University and University of Chicago. Taxonomic revisions in journals and monographs by researchers associated with the Geological Society of America have refined species-level identifications within these assemblages.
Sedimentological and facies analyses place Chester Series deposition on a tropical to subtropical shallow epicontinental sea influenced by eustatic sea-level oscillations recognized in global curves by researchers working with the International Commission on Stratigraphy and proponents of sequence stratigraphy like Vail, Hardenbol, and Todd. Intertidal to subtidal carbonate platforms, lagoonal mudflats, tidal channels, and deeper basinal settings are reconstructed from core, outcrop, and seismic data acquired by regional surveys and energy companies including BP and ConocoPhillips. Paleogeographic reconstructions situate the Midcontinent region near equatorial latitudes during the Pennsylvanian, a position consistent with paleomagnetic studies conducted at Columbia University and University of Michigan.
The Chester Series hosts economically important resources such as building stone, crushed aggregate, lead–zinc mineralization in some carbonate facies, and hydrocarbon reservoirs in porous carbonates and sandstones evaluated by firms like Chevron and Schlumberger. Coal-bearing intervals correlated with adjacent Pennsylvanian formations have historically supported regional mining, with production records maintained by the Energy Information Administration and state agencies. Quarrying for dimension stone in Chester-type limestones supplies construction materials in municipalities overseen by state departments of transportation and urban planners. Groundwater aquifers developed in porous Chester carbonates serve municipal and agricultural needs under management frameworks at county and state water authorities.
Systematic study began in the 19th century with fieldwork by surveyors from the Illinois State Geological Survey and academic expeditions from Indiana University and University of Kentucky. Type sections and reference exposures were designated in roadcuts, river bluffs along the Mississippi River and Ohio River, and outcrops near Chester, Illinois, where early stratigraphic descriptions were published in bulletins of state surveys and proceedings of the American Association of Stratigraphic Palynologists. Modern lithostratigraphic and biostratigraphic frameworks have been refined through collaborative projects involving the United States Geological Survey, university research groups, and industry partners conducting core studies and regional correlation panels.
Category:Pennsylvanian geology Category:Geologic series of the United States