MOLECULAR CHARACTERIZATION OF ORGANIC MATTER IN DEVONIAN-MISSISSIPPIAN BLACK SHALES OF THE APPALACHIAN BASIN USING PYROLYSIS-GAS CHROMATOGRAPHY/ION TRAP MASS SPECTROMETRY

Deposition of organic-rich marine Devonian-Mississippian black shales of the Appalachian Basin has been linked to a variety of scenarios by previous researchers including paleoenvironmental redox status (anoxic to intermittently anoxic to dysoxic), sediment starvation, and increased land-derived nutrient input associated with evolving terrestrial plants. In this study, we characterize the molecular nature of the organic matter in the black shales using pyrolysis-gas chromatography/ion trap mass spectrometry in order to assess sources and the mechanisms of organic matter accumulation and kerogen formation. A total of 9 samples of the Givetian (Portwood Member/Harg facies), Famennian (Huron Member, Three Lick Bed, and Cleveland Member), and Tournaisian (Sunbury Shale) horizons of the New Albany Shale encompassing about 147 feet were collected from a drill core (D6) located in east-central Kentucky. The black shales have organic carbon contents ranging from 6.3% to 17.6% by weight and vitrinite reflectances around 0.5% (thus maturation levels are just within the oil window). Organic petrography results indicate that the organic matter is predominantly marine (alginite + bituminite) with variable terrestrial (vitrinite+inertinite) content. Kerogen flash-pyrolysis was performed within a helium flow using a platinum coil at 615^oC for 20 seconds. Our preliminary results indicate that the pyrolysis products are dominated by aromatic hydrocarbons composed primarily of C₁ to C₄ alkylbenzenes followed by aliphatic hydrocarbons composed of C₇ to C₂₀ n-alkene/n-alkane pairs. Other components include minor amounts of C₁ to C₄ alkylthiophenes, C₀ to C₁ alkylphenols, and C₀ to C₃ alkylnaphthalenes. Low abundance of alkylthiophenes indicates that organic-matter sulfurization played a minor role in kerogen formation. 1,2,3,4-tetramethylbenzene is abundant in the pyrolyzates and may result from input of diaromatic carotenoids derived from photosynthetic green sulfur bacteria, a strict anaerobe which requires an euxinic photic zone. However, algal sources for 1,2,3,4-tetramethylbenzene are also possible.