Fossils of the Blue Ridge and Piedmont

Mesozoic fossils

Triassic and Jurassic

The Triassic to Jurassic rift basin rocks of the Piedmont formed after the Paleozoic orogenies had ended and the Atlantic Ocean began to widen. Lakes were common in these basins. Sediments deposited in and around the lakes—part of what geologists call the Newark Supergroup—contain fossils that record freshwater environments and terrestrial habitats along lake margins. The most common fossils are fishes, plant remains, and the footprints (trace fossils) of reptiles and amphibians.

Plant remains can be particularly abundant in these rift valley sediments and include a variety of foliage (leaf) types, such as ferns, cycadeoids, ginkgoes, and conifers.

Trace fossils are marks left by the behavior of organisms on sediment or other substrate. Traces include burrows, footprints, toothmarks, holes drilled in shells by predators, and the tunnels left by plant roots. Because paleontologists can almost never be sure of exactly which kind of organism made a particular trace, there is a completely separate system of naming trace fossils that does not refer to organisms represented by body fossils. Despite this difficulty, trace fossils are widely used to help reconstruct ancient environments.

The Triassic-Jurassic rift basins of the East Coast have been renowned for their dinosaur trackways since the early nineteenth century, and the basins of North Carolina and Virginia do not disappoint in this respect (see examples here of Triassic dinosaur footprints at the Luck Stone quarry in Culpepper, Virginia). The tracks and skeletal fossils of crocodilians and the small reptile Tanytrachelos are also well documented from other sites, including the famous Solite Quarry near the Virginia-North Carolina state line (see images of fossils from the Solite Quarry on Flickr).

The aetosaurs Coahomasuchus chathamensis and Gorgetosuchus pekinensis are known from the Pekin Formation in North Carolina. (Aetosaurs are a group of armored reptiles that are distantly related to modern crocodiles.) The predatory archosaur Postosuchus alisonae has also been found in the Deep River Basin.

The rift valley lakes contained fish, which are found as fossils in rocks that formed from lake bottom sediments. Many of these fossils are from an extinct group armored with thick, bony scales.

Fossil invertebrates in the Newark Supergroup rocks include clams, crustaceans, and abundant insects. Many invertebrate fossils preserved remains of soft tissue and delicate features like wings and antennae. A few factors may account for the extraordinary preservation of these fragile organisms. Lake-bottom waters may have been poorly oxygenated, which would have slowed decomposition. Alternatively, saline and alkaline water chemistry may have discouraged predators and bioturbation (burrowing) that otherwise would have contributed to breakdown of body parts.

Cretaceous

A small band of Cretaceous rocks is exposed in northeastern Virginia. Petrified wood is found in Prince William Forest Park, located southwest of Washington, DC. This wood is thought to belong to bald cypress (Taxodium), a type of conifer that is still found in the coastal plain of the southeastern United States today.