Roubidoux Formation

Roubidoux Formation
Name	Roubidoux Formation
Type	Formation
Period	Ordovician-Silurian
Primary lithology	Sandstone
Other lithology	Dolomite, Chert, Shale
Region	Ozark Plateaus
Country	United States
Namedby	unknown

Roubidoux Formation The Roubidoux Formation is a Cambrian–Ordovician to early Silurian stratigraphic unit exposed in the Ozark Plateaus of the central United States, notable for its siliciclastic and carbonate facies and for preserving a diverse assemblage of shallow‑marine fossils. It is a key unit for regional correlation across Missouri, Arkansas, Oklahoma, and Kansas, and has been cited in studies by institutions such as the U.S. Geological Survey, the Missouri Geological Survey, and university departments at University of Missouri and University of Oklahoma.

Overview and Stratigraphic Setting

The unit overlies units such as the Gasconade Dolomite and underlies the Jefferson City Formation and Eminence Dolomite in many localities, forming part of the lower Paleozoic succession within the Ozark Plateaus. Stratigraphic relationships have been compared with the St. Peter Sandstone, the Wonewoc Sandstone, and the Prairie du Chien Group of the Midcontinent. Correlation frameworks reference biostratigraphic markers used by workers associated with the Paleontological Society, the Geological Society of America, and regional geological surveys.

Lithology and Sedimentology

The lithology consists predominantly of well‑sorted quartzarenite sandstone interbedded with dolomitized carbonate layers, chert nodules, and minor shale; comparisons are often drawn to the St. Peter Sandstone and the Cambrian Sandstone successions studied in the Midcontinent Rift System. Sedimentological features include cross‑bedding, ripple marks, and bioturbation traces similar to those described from the Tremadocian shallow marine shelves documented in papers from the American Association of Petroleum Geologists and the Society for Sedimentary Geology (SEPM).

Paleontology and Fossil Content

Fossil content includes benthic marine faunas such as trilobites, brachiopods, gastropods, and trace fossils, with taxonomic comparisons to assemblages from the Bromide Formation, the Hessler Shale, and the Maquoketa Group. Studies by paleontologists affiliated with the Smithsonian Institution and regional museums report ichnofossils comparable to those in the Cambrian Explosion–age successions and hold importance for correlations used by the International Commission on Stratigraphy.

Geographic Distribution and Thickness

The Roubidoux is mapped across parts of Missouri, Arkansas, Oklahoma, and Kansas, with outcrops concentrated in the Ozark uplift and subsurface presence in the Ardmore Basin and Forest City Basin. Thickness varies regionally from a few meters in erosional windows to over a hundred meters in depocenters, analogous to thickness variations documented for the St. Peter Sandstone and the Decorah Formation across the Midcontinent. Borehole data used by the U.S. Geological Survey and state surveys inform these thickness estimates.

Age and Correlation

Biostratigraphic and lithostratigraphic data place the formation in the late Cambrian to early Ordovician with local extensions into the Silurian in some correlation schemes, paralleling chronostratigraphic frameworks established by the International Commission on Stratigraphy and regional syntheses by the Missouri Geological Survey and the Kansas Geological Survey. Correlative units cited in regional correlation charts include the Black River Group, the Trenton Group, and the Jordan Sandstone where facies and faunal elements provide tie points.

Economic Resources and Uses

The sandstone and dolomite of the Roubidoux serve as aquifers in parts of the Ozark Plateaus, being of interest to water resource managers in county governments and state agencies, and are evaluated in hydrogeologic reports by the U.S. Geological Survey. Locally, chert and dolomitic horizons have been studied for aggregate and dimension stone potential similar to assessments made for the Batesville Sandstone and the Cotter Dolomite, while petroleum exploration in adjacent basins has referenced the unit in basin analysis by firms and institutions such as the American Petroleum Institute and regional geoscience consulting companies.

History of Study and Nomenclature

Early descriptions and naming conventions for the unit were developed during bedrock mapping campaigns by state geological surveys in the late 19th and early 20th centuries, with subsequent refinement in regional stratigraphic syntheses published in journals of the Geological Society of America, the Journal of Paleontology, and bulletins from the U.S. Geological Survey. Key historical workers include survey geologists from the Missouri Geological Survey, researchers at the University of Missouri, and collaborators from the U.S. Geological Survey, whose field mapping, petrographic studies, and paleontological work established the modern concept of the formation.

Category:Ordovician geology of the United States Category:Geologic formations of Missouri