CARBON ISOTOPE VARIABILITY IN KEROGEN FROM DEVONIAN-MISSISSIPPIAN MARINE BLACK SHALES
Preliminary data from black shales in Kentucky indicate that not only does the mix of terrestrial versus marine components affect the carbon isotopic composition, but the type of marine organic components may as well. For example, whole-rock analysis of samples that contain abundant well-preserved algal matter have d13C values of -27 to 29 per mil; whereas, samples with an abundance of bacterially degraded bituminite have d13C values of 29 to 30 per mil. Terrestrial organic material in these sediments has a d13C value of around -27 per mil. Thus, variations in carbon isotopic composition appear to be related to alginite/bituminite ratios in addition to terrestrial/marine ratios.
Organic petrology and density gradient centrifugation were used to assess carbon isotope variability in kerogen from the Sunbury, Cleveland, and Huron shales. Analysis of whole kerogen samples and kerogen separates include petrography, C-H-N, Rock Eval pyrolysis, and carbon isotopes. These analyses show the effects of variations in organic components on overall carbon isotope composition, and may provide insights for studies that utilize carbon isotopes in paleoenvironmental reconstructions.