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| Desmoinesian | |
|---|---|
| Name | Desmoinesian |
| Era | Pennsylvanian |
| Period | Carboniferous |
| Type section | Mount Des Moines? |
| Named by | Elided |
| Region | North America |
Desmoinesian The Desmoinesian is a North American regional stage of the Pennsylvanian subperiod of the Carboniferous that is widely used in stratigraphic studies across the midcontinent and Appalachians. It is employed in correlation and basin analysis alongside chronostratigraphic terms such as the Moscovian, and is important in discussions of paleobiology, sequence stratigraphy, and resource geology. The interval is characterized by specific lithofacies, fossil assemblages, and cyclic sedimentation patterns that have been studied in numerous basins and by many institutions.
The Desmoinesian is a regional stage within the Pennsylvanian used primarily in North American stratigraphy, correlated to international stages such as the Moscovian of the International Commission on Stratigraphy timescale. It is bounded below and above by stages that include the Bashkirian and Kasimovian equivalents in global usage and is often placed within the middle part of the Pennsylvanian. Stratigraphic frameworks developed by bodies such as the United States Geological Survey and state geological surveys incorporate the Desmoinesian into regional chronostratigraphic charts, linking it to conodont, fusulinid, and cyclothem markers used by workers from institutions including the Field Museum of Natural History and the University of Kansas.
Sediments assigned to this stage display repetitive cyclic lithologies typical of Pennsylvanian cyclothems recorded in the Midcontinent Rift System-proximal basins and peripheral troughs like the Appalachian Basin and the Illinois Basin. Common lithofacies include cyclic sequences of marine limestones, interbedded shales, coal seams, and siliciclastics deposited in deltaic, lagoonal, and shallow shelf settings; these lithologies are documented in type localities examined by researchers at the Smithsonian Institution and the Illinois State Geological Survey. Sedimentological studies reference processes such as eustatic sea-level change inferred from cyclostratigraphy work by scholars affiliated with Yale University, Ohio State University, and the University of Iowa.
Fossil assemblages are diverse, reflecting mixed marine and terrestrial environments: marine faunas include brachiopods, bryozoans, echinoderms, crinoids, fusulinids and conodonts recorded by paleontologists at the American Museum of Natural History, while terrestrial floras comprise lycopsids, sphenopsids, and ferns studied by researchers at the Carnegie Museum of Natural History and the Natural History Museum, London. Notable fossil groups used in biostratigraphy include fusulinaceans such as species compared with collections at the University of Michigan Museum of Paleontology and conodont assemblages referenced alongside type collections at the Purdue University paleontology labs. Trackways, plant macrofossils, and coal-ball flora linked to investigators from Penn State University and Indiana University inform paleoecological reconstructions of wetlands and peat-forming mire systems contemporaneous with the Desmoinesian interval.
Strata of this age occur across the central and eastern United States and extend into adjacent parts of Canada; key basins include the Illinois Basin, Appalachian Basin, Western Interior Basin, and marginal areas of the Michigan Basin. Formations correlated with this interval include units such as the Wellington Formation (in parts recognized by the Kansas Geological Survey), the Wallace Formation equivalents, and local cyclothem packages cataloged by the Nebraska Geological Survey and the Iowa Geological Survey. Regional mapping projects by agencies like the Kentucky Geological Survey and the Missouri Geological Survey document lateral facies changes and the distribution of coals, limestones, and sandstones attributed to this stage.
Correlation frameworks link Desmoinesian successions to global stages using biostratigraphic markers and radiometric tie-points developed in collaborative studies by teams from the Geological Society of America, the International Union of Geological Sciences, and university research groups including Stanford University and the University of California, Berkeley. Conodont zonation and fusulinid assemblages provide major correlation tools, while sequence stratigraphy comparisons employ concepts advanced by researchers at Petroleum Technology Research Centre-affiliated groups and industry partners such as Chevron and ExxonMobil exploring Pennsylvanian reservoirs. Correlations extend to Russian and European Moscovian successions through synthesis work involving the Russian Academy of Sciences and the British Geological Survey.
Desmoinesian strata host economically important resources: productive coal seams exploited historically and presently by companies documented in reports by the U.S. Department of Energy and state mining bureaus, as well as sandstone reservoirs and carbonate intervals producing hydrocarbons in parts of the Appalachian Basin and Illinois Basin investigated by petroleum firms like Shell and ConocoPhillips. Carbonate resources provide industrial minerals evaluated by the USGS Mineral Resources Program, and evaporite and shale units associated with the stage are of interest for aggregate and engineering materials referenced by the American Society of Civil Engineers standards and state departments of transportation.
The name and concept of this regional stage emerged from 19th- and early 20th-century stratigraphic work by geologists mapping Pennsylvanian sequences across the American Midwest; historical contributors include staff associated with the United States Geological Survey and academics from Iowa State University and University of Kansas. Subsequent refinements were made through biostratigraphic and lithostratigraphic studies by scholars at institutions such as the University of Illinois Urbana-Champaign and the Ohio State University and through cooperative efforts with industrial geoscience teams. Major syntheses and nomenclatural recommendations have appeared in publications and conference proceedings organized by the Geological Society of America and regional geological societies, informing modern usage in geological mapping and stratigraphic correlation.