Significance of New Ediacaran Fossils and U-Pb Zircon Ages from the Albemarle Group, Carolina Terrane of North Carolina

摘要

The Albemarle Group is one of the major defining stratigraphic units of the Carolina terrane, the best-known division of the southern Appalachian peri-Gondwanan block of Carolinia. As such, the group is a significant factor in the correlation of Carolinia with other peri-Gondwanan blocks both in the Appalachians and globally. The traditionally held Ediacaran age of the group has been in question for more than a decade because of a report of Late Cambrian and younger fossils from two quarries in the group. The fossil report led to a major revision of the stratigraphy and structural reinterpretation of the Carolina terrane. Our recent studies have focused on the stratigraphy, paleontology,and geochronology of the Cid Formation in the vicinity of one of the reported Paleozoic fossil locales. Contrary to the structural reinterpretation of the Albemarle Group, Cid mudstone is shown to be in conformable and gradational contact with Flat Swamp felsic volcanics of the Cid Formation; we have obtained a precise U-Pb zircon age of 547 ± 2 Ma for the volcanics at a nearby locality. We also recovered the Ediacaran fossil Aspidella from the Cid mudstone. In conjunction with the new stratigraphic and geochronological data, the new fossil find leads us to consider the Cid Formation to be Ediacaran. These new data support a mainly Neoproterozoic age for the lower half of the Albemarle Group, indicating that major stratigraphic and structural revisions of the Carolina terrane based on the supposed Paleozoic fossils are unwarranted. Confirmation of the stratigraphy of the Albemarle Group has a bearing on the correlation of Carolinia with other peri-Gondwanan crustal blocks in the Appalachian Orogen.