CARBON ISOTOPES AS A TOOL FOR HIGH RESOLUTION STRATIGRAPHY OF UPPER CAMBRIAN STRATA

This study evaluates the potential of using well constrained stratigraphic trends in isotope variations as correlation tools for rock successions that lack prominent biomarkers. A large, positive carbon-isotope excursion is recorded within the Steptoean (Upper Cambrian) strata of the southern Appalachians. Similar excursions have been reported for the western United States (the Great Basin area), China, Kazakhstan, and Australia, indicating that this is a global phenomenon. The anatomy of this excursion was determined through extensive sampling of homogenous micrite and dolomicrite from strata at the Thorn Hill locality in northeastern Tennessee. The d¹³C values show an increase from the upper Nolichucky Shale into the overlying Maynardville Formation (Conasauga Group). The most positive d¹³C values (4 to 5 ‰ VPDB) correspond to the transition between the Maynardville and the Copper Ridge Dolomite (Knox Group). The d¹³C values decline in the lower part of the Copper Ridge. This characteristic carbon-isotope record is compared with the d¹³C record from the Lee Valley locality. The Lee Valley and Thorn Hill outcrops are about 30 km apart and contain coeval stratigraphic successions of strata that represent similar depositional environments. A comparison of the d¹³C records shows a remarkable similarity and provides the means for a detailed correlation of these two stratigraphic successions. The results of this study encourage further application of similar approaches in correlation of Steptoean strata at more widely spaced outcrops within and beyond the Appalachian basin.