CHEMOSTRATIGRAPHY OF THE HELDERBERG (SILURO-DEVONIAN) MIXED CARBONATE-CLASTIC SUCCESSION FROM THE NORTHERN TO CENTRAL APPALACHIANS

Appalachian limestones of Helderberg (Silurian-Devonian) age contain a sizeable (> +4‰) carbon isotope (δ¹³C) excursion that is also traceable through the southern mid-continent and Great Basin areas of North America. We have used the excursion to establish time lines in thick, well-exposed successions in the central part of the Appalachian basin in West Virginia (Smoke Hole and Oak Flat), and Pennsylvania (Altoona Bible Church) as well as in the thinner, more proximal facies in New York (Cherry Valley). Used in conjunction with existing conodont data that reveal the presence of the cosmopolitan species Icriodus woschmidti, the excursion provides an independent constraint on the position of the Silurian-Devonian boundary. These time lines have enabled us to evaluate previous sequence stratigraphic interpretations of Helderberg succession, including the application of Punctuated Aggradational Cycles (PACs). In addition, we are evaluating the paleoceanographic significance of the S-D boundary carbonate carbon excursion by developing parallel records of organic carbon isotopes and total organic carbon (TOC) trends throughout the Helderberg Basin. A shallowing event in the basin may have restricted circulation and led to widespread dysoxia in some regions. Enhanced nutrient fluxes also contributed to enhanced burial of organic carbon that played an important role in the carbon isotope (δ¹³C) excursion.