Recent research
Our research currently focuses on:
1) coal maturation and the role of heating rate (contact metamorphism vs. burial maturation) 2) maceral separation (through density-gradient centrifugation, DGC) and geochemistry 3) biogeochemical cycles in organic-rich sediments 4) trace element redox indicators in black shales including the New Albany and Ohio shales 5) controls on stable isotope composition of organic matter (OM) and interpretation of C and N isotope records in organic-rich sediments and coals 6) linkages between OM and past atmospheric composition 7) maceral response to the Oxidative Hydrothermal Dissolution (OHD) process |
Some recent projects:
Devonian charcoal:
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In Devonian-Mississippian marine black shales of the Appalachian Basin, fossil charcoal (inertinite) steadily increases up-section suggesting a rise in widespread fire systems. The occurrence and relative abundance of fossil charcoal in marine black shales are significant in that these shales may provide a more continuous record of fire than is preserved in terrestrial environments. Our data support the idea that major fires are not seen in the fossil record until there is both sufficient and connected fuel and a high enough atmospheric oxygen content for it to burn. The rise in fire activity also had important feedbacks in the carbon cycle.
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Intrusion of coals: impact on the ancient atmosphere |
It has been suggested that the emplacement of large igneous provinces (LIP's) altered vast amounts of coal and carbon-rich shales, releasing large amounts of methane (a greenhouse gas) into the atmosphere, resulting in global warming and large-scale extinction events. Do we see evidence for this in the remaining coal or shale? Our data suggest that there is no isotopic evidence for this - it would be expected that the carbon isotopic composition of the evolved gas would be depleted in 13C, leaving a residue that is enriched in 13C, but this is not typically observed in the intruded coals.
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Intruded coals:
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Examples of coals and carbonaceous shales that have been intruded by dikes or sills have been reported from many locales around the world. The impact of the intrusion is extreme alteration of the organic matter within the contact metamorphic aureole. But does this alteration follow the same maturation pathway as coals and other organic matter that has experienced normal heating in the Earth's crust following burial? Data from our recent studies suggests that there are differences, probably resulting from the very rapid heating rates associated with intrusion.
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Geochemistry of black shales: redox conditions
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Trace-element paleoredox indicators show that Devonian–Mississippian black shales of central Kentucky (Appalachian Basin) accumulated under variable bottom-water conditions. At least anoxic conditions prevailed during accumulation of much of the Sunbury Shale and the upper part of the Cleveland Member, and possibly euxinic conditions for the Sunbury. Bottom-water conditions may have been intermittently anoxic and dysoxic during deposition of the lower Cleveland. During accumulation of the Huron Member, it is likely that conditions ranged from anoxic to dysoxic to marginally oxic, possibly being close to normal marine conditions at times during accumulation of the lowermost Huron sediments.
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Density-gradient centrifugation: kerogen macerals in Devonian source rocks
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Density-gradient centrifugation (DGC) is a process that separates out the individual kerogen macerals based on differences in their density. Kerogen macerals in the Devonian Ohio Shale include marine components (alginite and bituminite) and terrestrial components (vitrinite and inertinite). These macerals have different densities, C, N, and H contents, and different isotopic compositions. DGC is an effective means for separation of kerogen macerals in source rocks for subsequent analyses (e.g., Rock-Eval pyrolysis, GC-MS, isotopic analyses). We operate the only such facility that is dedicated to the separation of macerals in geological materials.
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