Absolute Time Constraints on the Silurian-Devonian Boundry D13C Excursion
Husson, Jon M.; Schoene, Blair; Maloof, Adam C.; Bluher, Sarah
Across the Pridoli-Lochovian (Silurian-Devonian) transition, carbon isotope analyses of bulk marine carbonates (d13Ccarb) from Euramerican (West Virginia, Nevada, and Oklahoma) and Gondwonan (Czech Republic, Austria, and Queensland Australia) successions reveal a positive d13Ccarb shift. Values reach +5.8 permil, making the Silurian-Devonian event one of the largest carbon isotope excursions in the Phanerozoic. Here we present a d13C chemostratigraphic dataset developed from the lower Devonian Helderberg Group of New York state, USA. Bulk carbonate analyses of the Manlius-Coeymans-Kalkberg formations of the Helderberg exhibit the very positive d13Ccarb values observed in other Silurian-Devonian carbonate basins. We have complemented this bulk record with fossil-specific d13Ccarb analyses from the same stratigraphic horizons, thus allowing us to quantify spatial heterogeneity in d13Ccarb within single horizons, decipher any facies dependence in d13Ccarb, and evaluate different models (e.g. vital effects, kinetic isotopic effects, differential diagenensis) that seek to explain such heterogeneity. Lastly, we present new, CA-ID-TIMS U/Pb zircon dates from numerous volcanic ashes that punctuate the lower Helderberg Group. By establishing an absolute chronostratigraphic framework for the Helderberg, we are able to constrain the timing and duration of d13C variability, and rigorously evaluate models which seek to explain the Silurian-Devonian boundary d13C excursion.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013