The Culpeper Basin is one of the Newark Supergroup's Late TriassicâÂÂEarly Jurassic rift basins, exposed in Northern Virginia and Maryland. Its development is tied to the initial rifting of the supercontinent Pangea (~201 Ma, across the Triassic-Jurassic boundary). Volcanism associated with the Culpeper Basin was part of a much larger event known as the Central Atlantic magmatic province (CAMP), one of the largest flood basalt eruptions in Earth's history.
The Culpeper Basin lies just east of the Appalachian Mountains and extends from the Madison CountyâÂÂOrange County line in Virginia to Frederick, Maryland. A diverse group of sedimentary rocks including siltstone, sandstone, and conglomerate within the basin were intruded by igneous rocks (primarily diabase), which caused thermal metamorphism at the contact with sedimentary rock.
The Culpeper Basin is nearly continuous with the Gettysburg Basin to the north and with the Barboursville Basin to the south. The Groveton Member of the Bull Run Formation is exposed there. The formation has produced disarticulated fish remains including isolated bones and scales.
The Culpeper Basin preserves a series of both sedimentary formations and large basaltic lava flows associated with the initial rifting of Pangea. From oldest to youngest, these subunits are:
A large body of diabase in central Montgomery County, Maryland, is known as the Boyds Sill, named after the town of Boyds. Today, the Culpeper Basin is covered by up 12,800 feet of sediment, mainly composed of fluvial siltstones and sandstones.
In the upland Bull Run Formation, gastroliths (swallowed stomach stones) have been reported. They have been found in four different locations within the Bull Run Formation. These stones are interpreted as being eaten by herbivorous sauropodomorph dinosaurs to help them digest their food.
Footprints are among the most common fossils in the Culpeper Basin. Footprints of theropod dinosaurs: Grallator and Kayentapus, Eubrontes, the small ornithischian Anomoepus, pseudosuchian/Aetosaur type reptiles like Brachychirotherium and Chirotherium, and crocodilian Batrachopus tracks have all been found. Many marine fossils can also be found in the Culpeper Basin. Ostracodes, clam shrimp, Cyzicus sp. and Cornia sp.), fish, and plant fragments all show that saline lakes once existed in the basin. These lakes gave rise to their own ecosystems.