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| Meramecian | |
|---|---|
| Name | Meramecian |
| Type | Stage/Series |
| Period | Mississippian |
| Region | Midwestern United States |
| Namedfor | Meramec River |
| Namedby | George H. Girty |
| Year | 1892 |
Meramecian is a regional stratigraphic stage of the Mississippian recognized primarily in the Midwestern United States and adjacent parts of the Interior Basin. It is used by regional stratigraphers and paleontologists to designate a suite of carbonate-dominated rock units that record middle Mississippian depositional systems and faunas. The Meramecian correlates with portions of international Mississippian chronostratigraphy and is employed in petroleum geology, stratigraphic correlation, and paleobiogeographic studies.
The Meramecian stage was originally defined in the late 19th century near the Meramec River by geologists working in the Missouri and Illinois region and later formalized in regional lexicons. Early workers such as George H. Girty and contemporaries of the United States Geological Survey applied the term to carbonate successions that overlie older Mississippian strata and underlie younger Mississippian units in the Midcontinent. Subsequent revisions by stratigraphers associated with the American Association of Petroleum Geologists and state geological surveys in Missouri, Illinois, Iowa, and Indiana refined the definition, integrating biostratigraphic markers and lithostratigraphic limits recognized in subsurface data from the Illinois Basin and the Southeastern Iowa Basin. Regional correlation projects tied Meramecian horizons to global frameworks developed by the International Commission on Stratigraphy and comparative sections in the Appalachian Basin.
The Meramecian represents a middle Mississippian temporal interval broadly equivalent to parts of the international Visean and possibly lower Serpukhovian depending on regional correlations and biostratigraphic control. It occupies depositional settings across the Midcontinent, including the Illinois Basin, Wabash Basin, and portions of the Ozark Plateaus and overlaps tectonically stable cratonic interior shelves influenced by eustatic sea-level fluctuations documented in global sea-level curves by workers at the U.S. Geological Survey and the British Geological Survey. Radiometric tie-points are sparse; age control relies heavily on conodont zonation developed by specialists associated with institutions such as the Smithsonian Institution and universities with active Mississippian research programs.
Meramecian lithologies are dominated by carbonate rocks—chiefly fossiliferous limestones, crinoidal-packstones, grainstones, and dolomitized equivalents—interbedded locally with shaly intervals and thin siliciclastic beds. Typical mineralogical components include calcite, dolomite, and accessory quartz and glauconite where siliciclastic influx occurred, as documented in cores from east-central Missouri and outcrops in the Ozarks. Petrographic analyses by researchers at Michigan State University and University of Missouri highlight allochem-rich micrites, micritic matrix fabrics, and diagenetic features including stylolites and neomorphic calcite, comparable to descriptions in regional monographs from the American Museum of Natural History. Karstic porosity and secondary dolomitization are common in basin-marginal exposures studied by field teams from the Kansas Geological Survey.
Regionally, Meramecian units overlie Kinderhookian and Osagean strata and are overlain by later Mississippian units such as those correlated with the Chesterian in parts of the eastern United States. Contacts are commonly conformable across broad shelf areas but may be unconformable adjacent to paleohighs and structural features mapped by the United States Geological Survey and state surveys. In the Illinois Basin and Southeastern Kansas, subsurface correlation uses well logs, core data, and biostratigraphic markers established by teams at the American Association of Petroleum Geologists and regional petroleum companies. Sequence stratigraphic interpretations link Meramecian transgressive–regressive cycles to global eustatic events discussed by authors associated with the Society for Sedimentary Geology (SEPM).
Fossil assemblages typical of Meramecian strata are richly preservable and include crinoids, brachiopods, bryozoans, corals, gastropods, and diverse conodont faunas used for biostratigraphic zonation. Notable taxa described from Meramecian exposures and cores have been cataloged by paleontologists affiliated with the Field Museum of Natural History, Illinois State Geological Survey, and the Paleontological Association. Crinoid genera and articulation patterns comparable to specimens in the Natural History Museum, London collections appear in Meramecian limestones, while bryozoan and rugose coral assemblages show affinities with coeval faunas reported from the Appalachian Basin and parts of Europe studied by researchers at the University of Cambridge. Conodont species identified by specialists at institutions such as the University of Iowa and Purdue University provide the primary zonal framework enabling correlation across the Midcontinent.
Interpretations of Meramecian depositional environments emphasize shallow, warm, epicontinental carbonate-platform settings with episodic siliciclastic input from nearby emergent areas. Facies analyses conducted by teams at the University of Kansas and the Missouri Geological Survey interpret tidal-flat to open-shelf gradients with carbonate shoals, back-reef lagoons, and localized patch reefs hosting diverse carbonate producers. Geochemical proxies examined by researchers at Ohio State University and the University of Tennessee—including stable isotope trends and elemental ratios—are used to reconstruct seawater chemistry, salinity variations, and diagenetic histories, linking Meramecian sequences to regional climatic and sea-level changes recorded in Mississippian global compilations by the International Commission on Stratigraphy.
Meramecian carbonates are of economic interest for hydrocarbon reservoirs, aggregate production, and potential karst-hosted groundwater resources. Porosity development through dolomitization and fracturing creates targets evaluated in exploration projects by companies registered with the American Association of Petroleum Geologists and analyzed in state publications by the Kansas Geological Survey and Missouri Department of Natural Resources. Quarrying of Meramecian limestones supplies crushed stone and dimension stone used by construction industries in Missouri and Illinois, with industry standards and reporting coordinated through organizations such as the National Stone Association. Groundwater studies by the United States Geological Survey document aquifer properties in karstified Meramecian exposures important for regional water supply planning.
Category:Mississippian geologic formations