SILURIAN-DEVONIAN CARBONATES OF PENNSYLVANIA AND NEW YORK AND THE ROLE OF ENHANCED ORGANIC CARBON BURIAL IN A CARBON ISOTOPIC EXCURSION

The previous work of Saltzman (2002) has identified a carbon isotope excursion at the Silurian-Devonian boundary in the Appalachians (West Virginia), southern mid-continent (Oklahoma) and Great Basin (Nevada) in North America. Recent work has shown that the excursion is further traceable into the Appalachians of Pennsylvania (Altoona Bible Church) and New York (Cherry Valley), where it can aid in identification of the Silurian-Devonian boundary. Correlated with the data of Denkler and Harris (1988), this study enables definition of the S-D boundary to be expanded to sections throughout the Appalachian Basin where the I. woschmidti conodont and M. uniformis graptolite zones have not be identified. At Bible Church, the S-D boundary is approximately 18m above the Keyser-Tonoloway contact. From a base level of +1-1.5‰, the excursion reaches its peak at over +4‰ approximately 16m from the Keyser-Tonoloway, where stromatoporids are prevalent in large meter scale rip up beds. The ripped up stromatoporids underlying dessicated mudrocks imply a shallowing upwards sequence at Bible Church. This suggests a restriction of the Appalachian Basin, perhaps causing dysoxic bottom waters in deeper parts of the basin. The data support a mechanism for this excursion related to increased nutrient delivery that resulted in the burial of organic carbon.