412 Gastropod Mollusks from the Brightseat Formation

The Brightseat Formation, exposed near the inner margin of the Salisbury Embayment in Maryland and Virginia, represents the earliest Paleocene sediments that crop out in this region of the northern Atlantic Coastal Plain. The formation is placed within the middle part of the Danian Stage. Although a number of studies have investigated the microfauna of the Brightseat, no similarly thorough evaluation has been afforded to the macrofauna. This study provides the first extensive taxonomic treatment of the gastropods, collected largely from now-inaccessible Brightseat localities near the original type section
in the lower Potomac River Valley, east of Washington, D. C.

The diverse gastropod fauna of the Brightseat Formation consists of 52 species or forms assigned to 41 genera distributed among 25 families. Twenty-five species or subspecies are described as new. The Brightseat gastropods include a mixture of genera indicative of both northern mild-temperate and southern warm-temperate affinities, and we compare the assemblage to faunas of similar age from elsewhere in the Coastal Plain of North America, from West Greenland, and from northwestern Europe. In overall composition, the Brightseat fauna more strongly resembles the Danian to Selandian shelf faunas of the
north-central and western margins of the North Atlantic Basin, than it does contemporaneous faunas to the southwest in the Gulf Coastal Plain (in Texas, Mississippi, and Alabama), on the northern margin of the Southern Warm-Temperate (SWT) Province. This mixture of elements of differing biogeographic affinities suggests that the Brightseat gastropods flourished on a portion of the eastern North American continental shelf situated within a zone of overlapping northern and southern influence that marked the boundary between the two Danian North Atlantic marine zoogeographic provinces.

David L. Govoni, Kiera D. Crowley, Thor A. Hansen, and Warren D. Allmon

Pages: 113

Issue: BAP 412

Year published: 2025