ENVIRONMENTAL CONDITIONS AMIDST THE FRASNIAN-FAMMENIAN BIOTIC CRISIS: CLUES FROM NITROGEN ISOTOPES AND CHLOROPHYLL DERIVATIVES

The Frasnian-Fammenian(FF) biotic crisis is ranked among the top six mass extinctions in ecological severity, and was particularly devastating to shallow water tropical faunas and reef systems. The FF biotic crisis interval is expressed in Western New Yorks Java formation as two black shale beds known as the Upper and Lower Kellwasser intervals, and the FF boundary is preserved in Southern Indiana at the base of the Morgan Trail member of the New Albany shale. The organic matter preserved within these shales is in need of a broader characterization in order to investigate the climatic conditions present during its production/preservation. This will be achieved through nitrogen and carbon isotope analyses of the bulk rock, organic matter, and chlorophyll derived porphyrin fractions of the shales, as well as through porphyrin biomarker characterization.

Nitrogen isotope analyses were performed on bulk, powdered rocks and solvent extracted organic fractions. Extract and porphyrin nitrogen isotope data are produced using a cryo-trapping/capillary focusing procedure capable of analyzing nanomolar quantities of nitrogen. Porphyrin separation and characterization was performed using HPLC/LC-MSⁿ and diode array UV-Vis spectroscopy. Preliminary nitrogen isotope data show low to negative bulk sediment δ¹⁵N values (ranging from -2.3 to 0.5‰), which is consistent with many instances of black shale intervals during the Phanerozoic as well as during Ocean Anoxic Events. Also, the ε_por (δ¹⁵N_biomass - δ¹⁵N_{chloropigments}) values obtained from the organic extracts are consistent with the balance of sedimentary/extractable organic matter deriving from marine cyanobacteria (clustered around 0-1‰). The ε_por values were calculated using bulk organic extract δ¹⁵N measurements as there were insufficient porphyrin concentrations in these samples to run compound specific analyses. However, on the basis of ¹⁵N NMR characterization, this method is a potential proxy for δ¹⁵N of chloropigments in ε_por studies, as the majority of the nitrogen contained in the samples is likely pyrrolic and originating from chlorophylls.