Triassic notostracans in the Newark Supergroup, Culpeper Basin, northern Virginia

Abstract

Fossilized notostracan carapaces and abdominal fragments are present in the Upper Triassic (Rhaetian) Bull Run Formation in the Culpeper Basin near Manassas, Virginia. Over 250 notostracan carapaces and carapace fragments and three abdominal fragments with attached caudal rami were collected from light olive-gray, grayish-red, and brownish-gray shales in three on-strike localities. Carapace and abdomen are attached in one specimen. The Culpeper Basin notostracans have a rudimentary supra-anal plate and are identified asTriopscf.cancriformis. Their carapaces are indistinguishable from those of modern forms.Relatively few notostracan fossils are known and none have been reported previously from the Triassic of North America. Triassic notostracans, however, have been reported from Europe and Africa. Fossil notostracans have been reported from North America only once previously, from the Permian of Oklahoma.The notostracans are associated with conchostracans(Cyzicussp.), ostracodes(Darwinulasp.), fish scales, insects, plant fragments, and stromatolites.The notostracan-bearing beds are present at the top of a transgressive-regressive sequence, indicating that the notostracans inhabited shallow water near the edge of a perennial lake. Palynology indicates that these beds are most likely mid- to late-Rhaetian in age.