BEACH SAND RESTORATION PROJECT ON TOPSAIL ISLAND, NORTH CAROLINA, YIELDS OLIGOCENE FAUNA WITH UNUSUAL PRESERVATION, INCLUDING COLOR RETENTION

A beach sand restoration project in 2015 inadvertently dredged through a 30 MY old Oligocene River Bend Formation layer about a mile (1.6 km) offshore of Topsail Island, NC. The matrix was pumped through a large pipe as a slurry of rock, sand, and water for several miles/km, effectively sandblasting many of the fossils free of their matrix en route. Pumped onto the beach, the resulting mixture included a diverse assemblage of Oligocene fossils. This echinoderm-dominated fauna included echinoids, oysters, bivalves, gastropods, serpulids, bryozoans, barnacles, crustaceans, and brachiopods. Vertebrate material was much less common.

Several of the invertebrate genera appear to retain their original color markings. Visual comparison to related modern species supports this conclusion, although chemical analysis will be needed to prove this conclusively. Most significantly, many of the Pycnodonte oysters have radial patterns in gold and tan; many Balanus barnacles have red or rust coloration along growth lines; the majority of the Maretia echinoid tests have areas of mauve, purple, and lavender, especially on the ambulacra and areas of the adoral side; and nearly all Gagaria echinoids have tan-tipped spines, and some of their tests show trace color, especially on the adoral side. Color retention has been recorded in fossils of Holocene, Pleistocene, and Miocene age but is more unusual in older fossils, although similar color banding has been reported in Cretaceous Pycnodonte oysters. Prolonged exposure to sunlight causes these specimens to bleach white, tan, or grey.

Rapid, mass burial of this layer is suggested by larger chunks of sandy matrix that contain numerous echinoids densely packed in random orientation with their spines attached. In addition, most oysters are complete with both valves closed. The combination of rapid burial and the unorthodox way specimens were freed from the matrix (in contrast to a normal weathering process) may have contributed to the color retention. Although this set of circumstances may be unique, it suggests that the preservation of ancient color may not be uncommon; it is simply uncommon to retain it under normal weathering conditions.