Redwall Limestone

Redwall Limestone
Name	Redwall Limestone
Period	Mississippian
Type	Formation
Primary lithology	Limestone, dolomite
Other lithology	Chert, siltstone
Named for	Redwall Canyon
Named by	G. K. Gilbert
Region	Arizona, Utah, Nevada
Country	United States

Redwall Limestone The Redwall Limestone is a conspicuous Mississippian carbonate formation exposed in the Grand Canyon National Park, Coconino County, Arizona, Mohave County, Arizona and adjacent parts of Utah and Nevada. It forms vertical cliffs and prominent platforms that influence Colorado River canyon morphology and attract study by geologists from institutions such as the United States Geological Survey, Arizona Geological Survey, and university departments at University of Arizona, Northern Arizona University, and Arizona State University. The unit records marine carbonate deposition during the Early to Middle Mississippian and is a key marker in regional stratigraphic correlations used by researchers involved with the Geological Society of America and the Society for Sedimentary Geology.

Description and lithology

The formation consists predominantly of thick-bedded, fossiliferous limestone and locally dolomitized carbonate, with interbeds of chert and minor siltstone and shale; these lithologies have been described in field studies by G. K. Gilbert and mapped by the U.S. Geological Survey. Outcrops form sheer reddish-brown to gray cliffs, where iron-stained faces weather into the characteristic red talus and ledges that name exposures near Redwall Canyon and other canyons of the Grand Canyon. Petrographic analyses conducted by researchers affiliated with the Smithsonian Institution and the University of Colorado Boulder report predominantly micrite and spar matrix, bioclastic debris, and nodular chert; diagenetic dolomitization and stylolite development are common where sampled by teams from Stanford University and University of California, Los Angeles.

Stratigraphy and age

Biostratigraphic work using conodonts and brachiopod assemblages ties the unit to the Mississippian (Tournaisian to Visean) interval; stratigraphers from Princeton University and the Texas Bureau of Economic Geology have refined its age using regional correlations with the Chesterian and adjacent carbonate units. The Redwall records a succession above the Temple Butte Formation in many sections and is overlain by Pennsylvanian or later Paleozoic strata such as the Supai Group and locally by Permian limestones; stratigraphic frameworks developed in collaboration with the Arizona Geological Survey and the Nevada Bureau of Mines and Geology enable cross-basin correlation across the Colorado Plateau and the Mojave Desert margin.

Geographic distribution and extent

Exposures extend along the Colorado Plateau province, notably throughout the Grand Canyon, the Paria Plateau, and into the western Kaibab Plateau, with outliers in western Arizona and southeastern Nevada. Mapping by the U.S. Geological Survey and state geological surveys delineates its lateral continuity and thickness variations, which can exceed several hundred meters in the Grand Canyon region but thin toward the basin margins near the Basin and Range Province. The formation is part of broader regional frameworks used by researchers at Columbia University and Yale University when reconstructing paleogeography across western North America during the Mississippian.

Fossils and paleoenvironments

Fossil content includes diverse marine invertebrates—brachiopods, crinoids, bryozoans, pelecypods, gastropods—and abundant rugose corals; notable collections are curated at the Smithsonian Institution National Museum of Natural History and university museums at Arizona State University and Northern Arizona University. Conodont biostratigraphy has been applied by paleontologists from Iowa State University and University of Kansas to refine temporal placement. Sedimentary structures, fossil assemblages, and isotopic work undertaken by investigators at Massachusetts Institute of Technology and the University of Michigan indicate deposition in warm, shallow, open marine carbonate platforms and ramp settings, punctuated by episodes of relative sea-level change and minor siliciclastic input from nearby terranes such as the Antler Orogeny-affected regions.

Economic resources and uses

The Redwall provides dimension stone and riprap in local construction and park infrastructure projects managed by the National Park Service and has been quarried historically for building stone in towns like Flagstaff, Arizona. Limestone and dolomite from the formation are of interest for aggregate, lime, and soil amendment, activities regulated by state agencies including the Arizona Department of Environmental Quality and overseen for cultural-resource impacts by the National Park Service and Bureau of Land Management. Its cliffs constrain groundwater flow and influence aquifer behavior studied by hydrologists at the U.S. Geological Survey and Arizona Department of Water Resources for regional water-resource planning.

History of research and naming

The name originates from early geological surveys in the late 19th century, with pioneering field descriptions by G. K. Gilbert during investigations of the Grand Canyon; subsequent revisions and formal stratigraphic definitions were advanced by workers affiliated with the U.S. Geological Survey, Arizona Geological Survey, and academic researchers at Harvard University and University of California, Berkeley. Classic monographs and mapping projects published through the Geological Society of America and technical reports by the U.S. Geological Survey and state surveys have documented its lithology, paleontology, and regional correlations, forming the basis for ongoing research on Mississippian paleoenvironments and western North American stratigraphy.

Category:Geologic formations of Arizona Category:Mississippian geology of the United States