The Patuxent Formation is an Early Cretaceous (Aptian)-aged geologic formation of the Atlantic coastal plain. It is part of the Potomac Group.
The Patuxent formation was first described by William Bullock Clark in 1897. The formation is primarily unconsolidated white-grey or orange-brown sand and gravel, with minor clay and silt. The sand often contains kaolinized feldspar, making it an arkose. Clay lumps are common, and sand beds gradually transition to clay. Sandy beds may be crossbedded, which is evidence of shallow water origin.The Patuxent is the basal unit of the Coastal Plain sedimentary formations and unconformably overlies the crystalline basement rocks. This underlying unconformity is the subsurface equivalent of the Atlantic Seaboard Fall Line.
The type locality is the upper and lower valleys of the Little Patuxent River and Big Patuxent River in Maryland.
The Patuxent is a notable aquifer in southern Maryland.
Biostratigraphic dating by Dorf (1952) confirmed Early Cretaceous (Neocomian) age.
A diverse ichnofauna is known from the formation, comprising the trackways of dinosaurs, pterosaurs, mammals, turtles, and amphibians. Notably, a high proportion of these dinosaur prints appear to be from hatchlings, suggesting nesting sites were located nearby. The preservation of hatchling-sized dinosaur tracks is otherwise very rare in Cretaceous formations. A frog trackway from this formation provides the earliest known evidence of frogs moving by hopping. A particularly diverse trackway series deposited in a former wetland environment is known from the vicinity of Goddard Space Flight Center.
Very few vertebrate body fossils are known from this formation, which is thought to be an artifact of preservation. Propanoplosaurus, a nodosaurid known from a single natural cast and mold of a hatchling, was found recovered from rocks belonging to the Patuxent Formation in Maryland. A single partial impression is known of a bony fish (potential affinities to Paraelops). Isolated nodosaurid scutes are also known.
E. Dorf (1952) compared the flora identified in the Patuxent to that of the Wealden Flora in England studied by Albert Seward. Pollen spores have been identified in the formation by G. J. Brenner (1963). Based on the Paleobiology Database and Weems (2021):
Based partially on Weems (2021):
Along with an assemblage from Angola, the Patuxent comprises the world's largest known assemblage of Mesozoic mammal footprints.