Organic Carbon Accumulation in Paleozoic Black Shales: An Opportunity for Mentorship Teams

Paleozoic black shales represent important oil and gas source rocks throughout the U.S. and yet there is much about their formation that is still debated. We propose to study the geochemistry and petrography of two important groups of organic-rich, marine shales, those of Devonian age in the Appalachian Basin and those of Ordovician age in the Illinois Basin. These shales provide a unique opportunity to assess the different mechanisms that directly created and/or influenced water-column conditions, productivity, and sedimentation in what may have been (at times) anoxic basins. Preliminary petrographic and geochemical evidence from central Kentucky black shales supports the idea that Late Devonian-Early Mississippian time was a pivotal episode in Earth history, during which the enhanced influx of continentally derived nutrients energized biogeochemical cycling and carbon accumulation to new levels within the basin. Not only did this terrestrial expansion lead to enhanced productivity within the marine environment, but it also provided an enhanced flux of organic matter (OM) to the basin, in the form of refractory terrestrial OM associated with the evolution of higher plants. By contrast, Ordovician black shales from Iowa have little to no terrestrial OM, having accumulated at a time prior to the development of extensive and diverse land-plant communities. In addition, the absence of expansive terrestrial ecosystems limited the amount of terrestrial weathering and, thereby, the influx of terrestrially derived nutrients to the oceans. We will test the hypothesis that the rapid expansion of terrestrial higher plants in the Devonian played a significant role in altering the mode of organic carbon accumulation, providing additional complexities than existed during the Ordovician. By integrating petrographic and geochemical proxies, we propose to reconstruct Ordovician and Late Devonian-Early Mississippian conditions of biogeochemical cycling and compare the major controls on organic matter accumulation. Specifically, we will evaluate changes in the types and relative amounts of OM in these Devonian and Ordovician black shales using organic petrology, C/N ratios, and 013C and 015N values. Redox conditions during organic accumulation will be evaluated using abundances of redox sensitive metals (including Mo, U, V) and trace-metal ratios (including V/(V+Ni), NilCo, and V/Cr), and C-N-P relationships will be used to assess productivity during accumulation. Ultimately, these data will allow us to compare models of organic accumulation for these two groups of shales that formed at two distinctly different times in earth history relative to organic evolution. Broader impacts include the continued inclusion of underrepresented groups in the research programs of the investigators. Within the Department of Geological Sciences we have a group of faculty and students with research interests in biogeochemistry, with a special emphasis on carbon and nutrient cycling in ancient and modem sediments. We have developed a "mentorship-team approach" with graduate students working on independent but related projects, with undergraduates learning lab protocols as they assist the graduate students and develop their own projects, and with faculty working closely with both graduate and undergraduate students. Many of the students involved in the projects are female, an underrepresented group in our field, and we see exceptional synergy arising from this approach. The focus of these efforts has been to engage women in research early in their college careers, providing them with the qualifications and research skills necessary for successful graduate work, and we have had consistent success, with undergraduate students producing publishable data and continuing on to graduate programs both here at UK and elsewhere. The long-term goal is to increase the number of female undergraduates who continue on to graduate school and possibly contribute to our own recruitment of female graduate students here at UK. Funding at this time will allow us to collect preliminary data that will formulate the basis of a full proposal to NSF in January 2006, and will also expand the scope of work being performed on a related NSF grant on the Devonian. The new NSF proposal we plan to submit in January will support the graduate research project of one of the undergraduate women previously supported in the PI's mentorship program.