Culpeper Basin
The Culpeper Basin is one of the Newark Supergroup's Late Triassic–Early Jurassic rift basins, exposed in Northern Virginia and Maryland. Its development is tied to the initial rifting of the supercontinent Pangea. Volcanism associated with the Culpeper Basin was part of a much larger event known as the Central [Atlantic magmatic province], one of the largest flood basalt eruptions in Earth's history.
Geography
The Culpeper Basin lies just east of the Appalachian Mountains and extends from the Madison County—Orange 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, 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.
Geology
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:- Manassas Sandstone: Alluvial and stream sandstone and conglomerate, including the Poolesville, Tuscarora Creek, Reston, and Rapidan members. Footprints and fish are occasional found in these layers.
- Bull Run Formation: Alluvial, stream, and playa lake sediments, including the Groveton, Balls Bluff, Haudricks Mountain, Mountain Run, and Leesburg members. Footprints are common in the Groveton Member, while body fossils sometimes occur in the Balls Bluff Member.
- Catharpin Creek Formation: Alluvial sandstone and conglomerate, including the Goose Creek Member.
- Mount [Zion Church Basalt]: This was the first eruption during CAMP volcanism, near the end of the Triassic.
- Midland Formation: Stream and lake sandstone and siltstone, equivalent in age to the Triassic-Jurassic boundary. Footprints and fish are occasional found in these layers.
- Hickory Grove Basalt: This was the second outpouring of basaltic lava during the CAMP eruptions, near the start of the Jurassic.
- Turkey Run Formation: River, lake, and delta sediments
- Sander Basalt: This was the final pulse of CAMP-related volcanic activity in the Culpeper Basin.
- Waterfall Formation: Lake sediments, including the Millbrook Quarry Member.
Fossils
In the upland Bull Run Formation, gastroliths 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.