STRATIGRAPHIC, FOSSIL AND GEOCHRONOLOGIC EVIDENCE FROM CENTRAL NORTH CAROLINA: IMPLICATIONS FOR THE AGE OF THE ALBEMARLE GROUP

The Albemarle Group extends from central North Carolina to the South Carolina border and is dominated by submarine epiclastic rocks with subordinate felsic and mafic volcanic rocks. It is a major defining unit of the Carolina terrane, and has been considered to be mainly Neoproterozoic by most workers. However, the discovery of Paleozoic fossils from two locales within the group has brought its age into question (Koeppen 1995). If true, these reports would require significant changes to our understanding of the tectonic evolution of the Carolina terrane; e..g, Offield (1999) has invoked significant thrust faults in the group in order to account for the presence of the Paleozoic fossils.

In order to determine the relationship between the purported fossil-bearing strata and the remainder of the group, we have initiated 1:24,000-scale mapping and detailed stratigraphic studies in the area around one of the fossil locales, the Jacob's Creek quarry, Denton, NC. Our field work completed at the quarry to date indicates a conformable sequence of bluish-grey, thickly laminated to very thinly bedded, silt to mud dominated argillite with local greywacke beds up to 30cm thick. Sedimentary structures are sparse, but include cross-bedding, hummocky cross-stratification and elliptical concretions. We are currently compiling a stratigraphic section from within the quarry to assist in the determination of depositional environment. Field mapping completed to date has not revealed evidence for significant thrust faulting.

In addition, we have discovered the Ediacaran fossil Aspidella in mudstone at the Jacob's Creek Quarry. Although not an index fossil, Aspidella has an accepted age range of Neoproterozoic to earliest Cambrian. The Aspidella fossils are located approximately 200' below the felsic volcanics which have precise U-Pb zircon ages of 541-547 Ma. The combined stratigraphic, fossil, and geochronologic evidence leads us to the interpretation that rocks in the quarry are an integral part of a conformable, Neoproterozoic sequence; thus, major changes to the stratigraphic-structural framework of the Albemarle Group are unwarranted.