Arundel Formation

Arundel Formation Stratigraphic range: Lower Cretaceous
Type	sedimentary
Unit of	Potomac Group
Underlies	Patapsco Formation
Overlies	Patuxent Formation
Thickness	up to 125 feet
Lithology
Primary	clay
Location
Region	Maryland, Washington D. C.
Country	United States
Type section
Named by	W. B. Clark, 1897

The Arundel Formation, also known as the Arundel Clay, is a clay-rich sedimentary rock formation, within the Potomac Group, found in Maryland of the United States of America. It is of Aptian age (Lower Cretaceous). This rock unit had been economically important as a source of iron ore, but is now more notable for its dinosaur fossils. Although often considered a formation, it may be only oxbow swamp facies within the Potomac Group.

Dinosaurs present include cf. Acrocanthosaurus, the poorly known theropods "Allosaurus" medius, "Creosaurus" potens, and "Coelurus" gracilis, the ornithomimosaurian "Dryosaurus" grandis, as well as other indeterminate ornithomimosauria, the sauropods Astrodon and Pleurocoelus, the nodosaurid Priconodon, a possible basal ceratopsian, and potentially the ornithopod Tenontosaurus. Other vertebrates are not as well-known from the formation, but include a freshwater shark, a lungfish., at least three genera of turtles, and at least one crocodilian.