SIGNIFICANCE OF A NEW EDIACARAN FOSSIL FIND IN THE CAROLINA TERRANE OF NORTH CAROLINA

The Albemarle Group, one of the major defining units of the Carolina terrane, has long been considered to be mainly late Neoproterozoic in age by most workers. This age assignment has been in question for the past decade because of a report of Paleozoic fossils (Late Cambrian and younger) from two quarries sited in the unit. This report has not been confirmed; if true, it would demand major changes to our conception of the tectonic evolution of the Carolina terrane.

Recently, we recovered the Ediacaran fossil Aspidella from the Jacob's Creek quarry, a small quarry that purportedly hosts one of the Paleozoic fossil finds. Aspidella was found on bedding surfaces within typical bluish grey tuffaceous mudstone mapped as Cid Formation of the Albemarle Group. The fauna is preserved as elliptical impressions approximately 15 mm long by 10 mm wide; the best-preserved specimens exhibit a central dimple. Rocks in the quarry are stratigraphically ~ 200' below felsic volcanics of the Flat Swamp member of the Cid Fm. for which we have obtained a precise U-Pb zircon age of 547+2 Ma at a nearby locality.

Although members of the Ediacaran biota are not considered as index fossils for the Neoproterozoic, it is generally recognized that their age range is approximately c. 600-544 Ma and that "survivors" into the Cambrian are rare. The occurrence of Aspidella in the Jacob's Creek quarry combined with the new geochronological data lead us to suspect that the strata in the quarry are Neoproterozoic. In light of these new data, we are left with the following three possible interpretations: 1. the quarry contains rocks of both Neoproterozoic and Paleozoic age, but their interrelationship has not been recognized; any Paleozoic rocks would represent small outliers (stratigraphic or structural) on the Neoproterozoic strata, 2. Aspidella ranges well into the Paleozoic, or 3. reports of Paleozoic fossils from the quarry are erroneous. We favor interpretations 1. or 3., suggesting that major revision of our understanding of the tectonic history of the Carolina terrane based on the supposed Paleozoic fossils is unwarranted.