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| Hartshorne Sandstone | |
|---|---|
| Name | Hartshorne Sandstone |
| Type | Sedimentary rock |
| Age | Pennsylvanian (Desmoinesian) |
| Primary lithology | Sandstone |
| Other lithology | Shale, coal |
| Named for | Hartshorne, Oklahoma |
| Region | Arkansas, Oklahoma |
| Country | United States |
| Unit of | McAlester Group |
| Underlies | McAlester Shale |
| Overlies | Savanna Formation |
Hartshorne Sandstone The Hartshorne Sandstone is a Pennsylvanian-age sandstone unit recognized in the Ardmore Basin, Ouachita Mountains, and adjacent parts of Arkansas and Oklahoma, described for its coarse sand, conglomeratic lenses, and association with coal-bearing strata. It has been the subject of stratigraphic work linking it to regional correlations in the Midcontinent United States, sedimentologic studies connecting it to contemporaneous fluvial and deltaic systems, and economic assessments regarding coal mining and reservoir potential. Major geological surveys and academic researchers in institutions such as the United States Geological Survey, University of Oklahoma, and Arkansas Geological Survey have published mapping and petrologic analyses that inform its interpretation.
The Hartshorne Sandstone consists primarily of quartz-rich, medium- to coarse-grained sandstone with subordinate conglomerate, siltstone, shale, and coal seams, characteristics detailed in petrographic studies by investigators at the United States Geological Survey, University of Kansas, and Tulsa University. Thin sections and heavy-mineral analyses link its provenance to source areas exposed in the Ouachita Orogeny region and uplifted blocks tied to Atoka Formation provenance models, while sedimentary structures such as cross-bedding, planar lamination, and imbrication have been documented in fieldwork conducted by teams from the Oklahoma Geological Survey and the Arkansas Geological Commission. Diagenetic features including silica cementation, calcite overgrowths, and authigenic clays have been reported in publications by researchers affiliated with the Society for Sedimentary Geology and university departments at University of Arkansas.
The Hartshorne Sandstone is assigned to the Desmoinesian (middle Pennsylvanian) series and is formally placed within the McAlester Group in state stratigraphic nomenclature, as established by state surveys and stratigraphers from the American Association of Petroleum Geologists and the Geological Society of America. It conformably overlies the Savanna Formation and is overlain by McAlester Shale equivalents in mapped sections by the USGS and state geological surveys; regional correlations tie it to contemporaneous units such as the Atoka Formation and the Morrowan to Desmoinesian transition recognized in Midcontinent chronostratigraphy. Biostratigraphic and radiometric constraints discussed in papers from the University of Oklahoma and the Smithsonian Institution support a middle Pennsylvanian age assignment.
Sedimentological analyses interpret the Hartshorne Sandstone as deposited in fluvial to deltaic settings with episodes of high-energy channel flow, sheet floods, and estuarine reworking; these interpretations draw on comparisons with depositional models developed by researchers at the International Association of Sedimentologists, the Society for Sedimentary Geology, and academic groups at the University of Texas at Austin. Facies analysis and paleocurrent data from field studies by geologists of the USGS and the Oklahoma Geological Survey indicate braided to meandering fluvial systems draining uplifts related to the Ouachita belt, with periodic marine influence reflected in interbedded shale and coal interpreted in regional syntheses by the Geological Society of America.
Exposures and subsurface occurrences of the Hartshorne Sandstone are mapped across parts of eastern Oklahoma, western Arkansas, and marginal areas of the Ardmore Basin and McAlester coal field, as documented on state geologic maps produced by the Oklahoma Geological Survey, Arkansas Geological Survey, and the USGS. Key outcrop localities near towns such as Hartshorne, McAlester, and regional roadcuts studied by university field parties provide type sections and reference sections used in mapping by the American Association of State Geologists and regional petroleum geologists from companies historically active in the area like Continental Oil Company and later energy firms.
The Hartshorne Sandstone is economically significant primarily for its close association with Pennsylvanian coal seams exploited in the McAlester coal field, a focus of development by mining companies and state regulators including the Oklahoma Corporation Commission and firms historically such as Peabody Energy and regional operators. Its coarse-grained reservoirs have been evaluated for groundwater supply by municipal authorities and consultants affiliated with the United States Geological Survey and for hydrocarbon potential by petroleum geologists from the American Association of Petroleum Geologists; aggregate and construction uses have been documented by state transportation departments including the Oklahoma Department of Transportation.
Although predominantly clastic and often barren of abundant macrofossils, the Hartshorne Sandstone and its interbedded shales and coals yield plant fossils, palynomorphs, and fragments of marine invertebrates in transgressive intervals, with collections and identifications reported by paleobotanists and palynologists at the Smithsonian Institution, University of Kansas Natural History Museum, and the University of Arkansas Museum of Paleontology. Macrofloral assemblages and spores assist in biostratigraphic correlation with other Pennsylvanian floras cataloged by the Paleobotanical Society and used in regional chronostratigraphic frameworks.
The Hartshorne Sandstone was first named and mapped in the late 19th to early 20th centuries during regional surveys by geologists associated with the USGS and state geological surveys, with subsequent detailed stratigraphic and economic studies carried out by researchers at the University of Oklahoma, University of Arkansas, and industry geologists from firms documented in trade journals of the era. Key contributions include stratigraphic redefinitions and facies models published in bulletins and memoirs by the USGS, monographs by state surveys, and theses from departments at institutions such as Oklahoma State University and University of Tulsa, forming the foundation for ongoing research in sedimentology, coal geology, and regional tectonic synthesis.
Category:Sandstone formations