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| Midway Group | |
|---|---|
| Name | Midway Group |
| Type | Geologic group |
| Period | Paleocene |
| Lithology | Sandstone, shale, marl, limestone |
| Namedfor | Midway (Texas) |
| Namedby | Plummer and Moore |
| Region | Gulf Coast, Southeastern United States |
| Country | United States |
| Subunits | Wilcox Formation; Tuscahoma Sand; Black Mingo Formation; Castle Hayne Formation |
| Underlies | Wilcox Group |
| Overlies | Cretaceous |
Midway Group The Midway Group is a Paleocene stratigraphic unit in the Gulf Coastal Plain of the United States, notable for its sedimentary facies, fossil assemblages, and role in early Paleogene chronostratigraphy. It crops out and is subsurface in states including Texas, Louisiana, Mississippi, Alabama, and Georgia, and it has been the subject of regional correlation, biostratigraphic analysis, and petroleum exploration by institutions such as the United States Geological Survey and university geology departments. The Group preserves records relevant to studies of the Paleocene–Eocene Thermal Maximum, Paleocene vertebrate turnover, and early Paleogene floras.
The Midway Group comprises a package of Paleocene siliciclastic and carbonate strata deposited in marginal marine, deltaic, and shallow shelf settings during the early Paleogene. Its lithofacies include fine- to coarse-grained sandstone, silty shale, calcareous marl, and localized limestone beds that record transgressive–regressive cycles associated with relative sea-level changes linked to eustatic events recognized in the Tertiary stratigraphic record. Correlations have been made with contemporaneous units such as the Willwood Formation, Fort Union Formation, Danian Stage-equivalent marine deposits, and with European Paleocene sequences like the London Clay for global paleoclimatic interpretations.
Stratigraphically, the Midway Group occupies the lowermost Paleogene above marine Upper Cretaceous strata such as the Catahoula Formation and regional equivalents. Lithostratigraphic subdivisions vary by state; widely used members include the Wilcox Formation, the Black Mingo Formation, and the Castle Hayne Formation, with local units like the Tuscahoma Sand recognized in Alabama. The Group demonstrates progradational packages, tidal-channel sandstones, estuarine shales, and carbonate shoal deposits that reflect influence from the proto-Gulf of Mexico basin and river systems comparable to those preserved in the Eocene Claiborne Group. Sequence stratigraphers correlate Midway transgressive surfaces with markers used in the Zincian and Danian chronostratigraphies, and magnetostratigraphic data have been integrated with biostratigraphic zonations based on foraminifera and palynomorphs.
The Midway Group yields a diverse Paleocene fossil record. Marine faunas include benthic and planktonic foraminifera, bivalves such as taxa comparable to Nucula and Glycymeris, and gastropods related to genera recorded in the London Clay and Paris Basin successions. Vertebrate remains comprise early Paleocene mammal teeth and isolated bones similar to faunas from the Willwood Formation and Puercan North American Land Mammal Age, as well as marine sharks represented by genera akin to Carcharocles and Odontaspis. Plant fossils and pollen assemblages include angiosperm palynomorphs related to modern families recorded in Green River Formation floras and dinoflagellate cysts used in biostratigraphic zonation comparable to schemes developed for the North Sea Basin and Gulf of Mexico cores.
The Midway Group has significance for hydrocarbon exploration in the Gulf Coastal Plain. Sandstone reservoirs within the group have been targeted in petroleum plays analogous to producing horizons in the Wilcox Trend and Tuscaloosa Marine Shale settings. Shale intervals serve as regional seals and source-rock analogs evaluated by energy companies and by the Energy Information Administration. In addition to hydrocarbons, certain calcareous horizons and marl beds have been investigated for use as agricultural lime and raw material in cement manufacture by companies operating near Houston, New Orleans, and Mobile, Alabama.
The Midway Group was named in early 20th-century North American stratigraphic work; early descriptions and formalization cite investigators such as A. C. Veatch and later refinements by A. C. Plummer and F. B. Plummer and colleagues who integrated lithologic and paleontologic data. Subsequent regional syntheses and monographs by the United States Geological Survey, state geological surveys of Texas, Louisiana and Alabama, and academic studies at institutions like Louisiana State University and the University of Texas at Austin refined subdivisions and correlations. Debates over nomenclatural priority and correlation with units such as the Wilcox Group and Tuscahoma Formation prompted revisions in successive bulletins and stratigraphic committees, reflecting evolving concepts in chronostratigraphy and sequence stratigraphy promoted by researchers affiliated with the Paleontological Society and the Geological Society of America.
Notable exposures and cores occur along river bluffs and coastal sections in eastern Texas near the city of Houston, across coastal Louisiana near Baton Rouge, in bluff exposures along the Mississippi River near Vicksburg, and in subsurface well logs throughout the Gulf Coast basin including offshore wells documented in industry archives. Outcrops at coastal localities provide sections that have been sampled for foraminiferal biostratigraphy and paleomagnetic study comparable to classic stratotypes used in Paleogene research such as the Clayton Formation and Tuscahoma Sand type sections.
Category:Paleogene stratigraphic units of North America