Salina Group

Salina Group
Name	Salina Group
Type	Group
Age	Silurian–Devonian
Period	Silurian
Region	Appalachian Basin, Michigan Basin, Illinois Basin
Country	United States
Subunits	Salina A, Salina B, Salina C, Salina D, Salina E
Thickness	up to 1,000 ft (varies)

Salina Group is a Silurian to early Devonian evaporite-dominated stratigraphic group of the northeastern and midwestern United States notable for extensive halite and gypsum deposits. It crops out and subsurfaces across the Appalachian Basin, Michigan Basin, and Illinois Basin, influencing regional hydrogeology and petroleum geology and intersecting histories of mining in states such as New York, Pennsylvania, Ohio, Michigan, and Indiana. The unit records repeated episodes of restricted marine conditions and evaporitic concentration tied to Silurian eustatic and tectonic controls, and has been the subject of stratigraphic revision by researchers from institutions including the United States Geological Survey, Ohio Geological Survey, and New York State Museum.

Overview

The Salina Group comprises a succession of evaporites, carbonates, and siliciclastics widely recognized across the northeastern United States. Classic exposures and borehole intersections have been studied near localities such as the Erie area, the Niagara Falls region, and the Michigan subsurface. Lithostratigraphic subdivisions (commonly labeled Salina A–E or formations with local names) reflect lateral facies changes between halite-rich intervals and more argillaceous dolostones correlated with regional units like the Lockport Dolomite, Manlius Limestone, and Onondaga Limestone. The group is a key marker horizon for Silurian correlation across the Michigan Basin and the Ohio–Indiana subsurface.

Geology and Stratigraphy

Stratigraphically, the Salina Group overlies older Silurian carbonates and is overlain by younger Devonian units such as the Oriskany Sandstone and local shales. In the subsurface it reaches thicknesses up to approximately 300 meters where the basinal depocenters coincide with halokinetic provinces. The group is divided into multiple members and beds, including argillaceous dolostones, nodular anhydrite, bedded halite, and potash-bearing layers comparable to evaporite sequences in the Zechstein Group of Europe. Lateral equivalents and correlatives include the Wenlock–Ludlow interval in European successions and the Niagaran Series in parts of the Great Lakes region. Diagenetic fabrics, brecciation, and collapse breccias record post-depositional dissolution and salt tectonics that produced diapirism analogous to structures described in the Gulf Coast salt domes.

Paleontology and Fossil Content

Although dominated by evaporites, the Salina Group contains fossiliferous dolostone and shale horizons that preserve marine faunas characteristic of the Silurian. Fossils recovered include brachiopod assemblages similar to those recorded from the Niagara Escarpment, as well as crinoid fragments, ostracods, and benthic trilobites correlated with regional biostratigraphic zones used by paleontologists at institutions such as the American Museum of Natural History and the Smithsonian Institution. Microfossils and conodont elements from interbedded shales have been employed to refine age assignments and correlations with units like the Chazy Group and Eden Shale. Rare cherts and phosphatic lenses contain elements comparable to those studied in the Cincinnati Arch and Ontario exposures.

Depositional Environment and Paleoecology

The depositional model for the Salina Group invokes restricted epeiric seas on the Laurentia margin during Silurian highstands, with episodic marine incursions producing carbonate deposition followed by isolated evaporation and thick halite accumulation. Evaporitic rhythmicity reflects climatic oscillations and sea-level changes that can be compared to global Silurian events recorded in the Ireviken Event and other extinction/intervals. Facies belts transition from supratidal sabkha analogs to subtidal dolomitized platforms and deeper, anoxic basinal mudstones—paralleling depositional schemes documented for the Permian Basin evaporites at a process level. Paleoecological reconstructions suggest stressed benthic communities adapted to hypersaline and restricted oxygen conditions, with recolonization during transgressive phases by more diverse faunas.

Economic Resources and Uses

The Salina Group is economically important for evaporite commodities including bedded halite, anhydrite, and potash salts mined historically and in modern operations. Bedrock salt provided feedstock for chemical industries in Buffalo, New York, Cleveland, Ohio, and Detroit, Michigan. Bedded anhydrite and gypsum have been quarried for construction materials in multiple states while potash horizons were explored for fertilizer production and compared to Saskatchewan-type deposits. The group also influences subsurface fluid flow, serving as caprocks for hydrocarbons in the Appalachian Basin and creating subsurface hazards: subsidence, sinkholes, and salt dissolution issues documented near towns such as Youngstown, Ohio and Niagara-on-the-Lake, Ontario. Salt diapirs and related structures have been targets of geophysical surveys by the National Aeronautics and Space Administration and the USGS for resource and hazard assessment.

History of Study and Naming

Early descriptions of the evaporites date to 19th-century observers studying the Niagara Escarpment and regional saline springs. Nomenclature evolved through work by state survey geologists from the New York State Geological Survey, Ohio Department of Natural Resources, and 20th-century syntheses by the United States Geological Survey and academic stratigraphers. Key monographs and mapping campaigns in the mid-1900s refined the Salina stratigraphy, correlating borehole data from companies such as Standard Oil with academic studies at Cornell University and University of Michigan. Modern research integrates sequence stratigraphy, isotope geochemistry, and borehole geophysics conducted by university groups at Pennsylvania State University, University of Cincinnati, and international collaborators to resolve depositional and tectonic controls.

Category:Silurian geology of the United States