Acquisition of a DGC Maceral Separation Laboratory: The Key to Maceral-Specific Isotopic and Geochemical Analysis

Recent work in our laboratory has shown that, using a novel combination of techniques (density-gradient centrifugation-DGC, organic petrography, and isotopic analysis) we can generate maceral-specific isotopic data for Devonian-Mississippian Type II kerogens, and Pennsylvanian and Cretaceous coals. This approach has significant potential for interpreting isotopic data beyond that provided by bulk or compound-specific isotopic analysis. One problem with bulk isotopic (and geochemical) analyses of organic matter is that it reflects the contribution of varying amounts of different constituents and their respective compositions. As a result, variations in bulk isotopic composition are difficult to interpret without detailed information on a) the relative amounts of each individual constituent (or maceral), and b) the isotopic or geochemical composition of these entities. The novel combination of DGC, organic petrography, and isotopic analyses allows us to provide these data. Density-gradient centrifugation (DGC), a technique initially developed for biological applications, has been used to separate individual macerals (the microscopically identifiable components of kerogen and coals) to allow detailed geochemical analysis of relatively pure (>95%) components. We have recently used this technique on both Type II kerogens and coals to determine maceral-specific isotopic compositions of end-member components that ultimately will allow more reasoned interpretation of bulk isotopic trends through sedimentary sequences. We propose to establish a DGC laboratory that will focus on kerogens and coal, with an emphasis on isotopic analysis. This would be a unique facility that will permit routine preparation of density separates (representing macerals at 95-99% purity levels) for subsequent isotopic and geochemical analysis. It will have immediate and significant impact on the research programs of the PI and both Co-PIs, collectively and individually, in projects that attempt to understand the isotopic and geochemical variability of ancient and modern sediments. It will also allow collaborations for these faculty members with researchers at other institutions who are interested in similar geochemical problems. Broader impacts include the continued inclusion of underrepresented groups in the research programs of the investigators. One of the key components of the PIs research program has been the inclusion of female students in her research lab, providing mentorship and a network of female colleagues at all levels. This facility will be utilized by both the investigators (all active collaborators in the department's newly established Biogeochemical Systems Group), but also by students (for both undergraduate and graduate research projects) within the group. An in-house facility will alleviate access and travel problems faced by students in earlier work, allowing us to broaden the scope of this line of investigation and actively involve more students in the hands-on preparation and analysis of samples.