TRIASSIC FRESHWATER BIVALVES OF THE RIFT LAKES IN CENTRAL 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 Sandford 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 three distinct forms of Triassic freshwater bivalves, one is considered here to be of the order Unionoida and the others tentatively a mytiloid in shell outline and a sphaeriid in shell outline. Descriptions of the specimens is ongoing, but will likely yield three new genera of uncertain family affinities. These new specimens are compared with those described from Massachusetts and Pennsylvania, specimens described as belonging to the unionoid families Unionidae, Hyriidae and Mycetopodidae. However, none of the North Carolina specimens exhibit the umbonal sculpture exhibited by the northeastern specimens. The North Carolina unionoid specimens lack any evidence of hinge development or umbonal sculpture.

The non-unionoid bivalves are quite rare in these deposits. They are accompanied by ostracodes of the genus Darwinula, clam shrimp, genus Howellisaura, represented by carbonized impressions of the shells, fish and plant remains. This freshwater environment is preserved in a mudstone or clayey siltstone.