A NEW GENUS AND SPECIES OF TRIASSIC FRESHWATER BIVALVE FROM THE DURHAM SUB-BASIN NORTH CAROLINA

In eastern North America surface exposures of Triassic basins extend from Nova Scotia southwestward to South Carolina. This interrupted series of half grabens resulted from early Mesozoic rifting of the supercontinent Pangea. In south-central North Carolina the Deep River basin is comprised of the Durham sub-basin, the Colon cross-structure, the Sanford sub-basin, the Pekin cross-structure, and the Wadesboro sub-basin. Deposits within the Durham sub-basin are recognized as the Chatham Group, part of the Newark Supergroup and form part of a series informally designated as Lithofacies Association II. These strata are considered to be alternating fluvial and lacustrine sediments. Though there has been a lot of research on the vertebrate fauna from this lithofacies, considerably less research, particularly in North Carolina, has been done on the lacustrine invertebrate fauna.

On-going field work at a brick-clay quarry in the village of Genlee, Durham County, North Carolina has yielded a new genus and species of the order Unioniformes. Description of the specimens is ongoing, but these bivalves differ from those described from Massachusetts as Unio in that the Massachusetts Unio have hinge teeth and elevated umbos. The North Carolina specimens also differ from the six species of Antedipodon, Hyriidae described from Pennsylvania in that they do not show any evidence of radial umbonal sculpture or the thin, elongate shell shape of the species assigned to Mycetopoda, Mycetopodidae. All of the previously described freshwater bivalves from Pennsylvania and Massachusetts are much larger than this new species. This new genus and species is considered to be from the Cumnock Formation, based on conchostracan stratigraphy.

Non-unioniform bivalves, tentatively described as a mytiloid in shell outline and a sphaeriid in shell outline, are quite rare in these deposits. These and the unioniform bivalves are accompanied by ostracodes of the genus Darwinula, clam shrimp, genus Euestheria, represented by carbonized impressions of the shells, and fish and plant remains.