POWRE: Carbon-13 Heterogeneity in Devonian-Mississippian Marine Shales: Integration of Density-Gradient Centrifugation (DGC) and Organic Petrography into Isotopic Studies

University Of Kentucky Research Foundation, Lexington KY

Investigators

Abstract

0074840 Rimmer Organic petrography allows the identification and quantification of organic components (macerals) in sedimentary rocks, and as such can indicate varying levels and types of terrestrial and marine inputs to basins. Understanding the carbon isotopic composition of Devonian-and Mississippian-age organic components is key to understanding cyclicity in the organic-rich shales units of central Kentucky that show variations on the order of dm, one-to-two-meter, and larger scales. Before arguments can be made to attribute variations in delta C-13 values to global changes in CO2, to changing redox conditions, or to variations in organic productivity levels, the impact of varying amounts and types of marine and terrestrial organic input must be evaluated. The research will address these issues as they relate to Upper Devonian/Lower Mississippian organic-rich shales of the Appalachian Basin. Consisting of Type II kerogen, these rocks contain a mixture of marine and terrestrial components (macerals), rather than purely marine organic matter. Specifically, carbon isotope analysis will be combined with petrographic analysis of both whole-rock and density-gradient fractions of kerogen concentrates for carbon-rich and carbon-poor intervals of these shales. Key to this work is the ability of density-gradient centrifugation to segregate kerogen into its component macerals. Kerogen in these shales contains at least two marine components (alginite and bituminite) and two terrestrial components (vitrinite and inertinite). The PI will identify amounts and variations in the type of macerals that exist in these rocks and their respective carbon isotopic compositions. Such data will be used to further elucidate cyclical changes observed in these sediments. This work also has important implications regarding the interpretation of long-term variations in the stable carbon isotope composition of organic matter in the Paleozoic, and inferences that may be made relative to CO2 in the atmosphere. Funding at this time from the POWRE program will allow this investigator to reinvigorate her research program, and establish/re-establish research collaborations after an extended time in administration (7 years). It also represents a natural progression and growth of the investigator's research into a new area (that of stable carbon isotopes). The research will also make an important contribution in the field of stable carbon isotope research.