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Abstract:
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Deep subsurface rock samples from Upper Ordovician strata in the Michigan Basin were analyzed for the presence of microbial communities. High concentrations of biogenic methane were observed in the Upper and Middle Ordovician formations. Total porosity values for the shale, shale hard bed and limestone samples were 7.4%, 2.5% and 1.9%, respectively. Hydrocarbon presence ranged from petroliferous shale, to bituminous layering in shale hard beds, to hydrocarbon odour in limestone. Organic carbon content ranged from 0.5 to 2.5%, highest amount being present in the shale. Environmental DNA was extracted from core samples and PCR amplified using 16S rDNA bacterial primers. PCR performed with archaeal 16S rDNA and methanogen-specific (mcrA) primers did not yield DNA amplification. Gene analysis indicated that bacterial sequences similar to Proteobacteria, Cyanobacteria, Firmicutes, and Actinobacteria were present. Most sequences were not related to known cultivated species. Proteobacteria was the most dominant phyla at all depths and included heterotrophic, lithotrophic, acidophilic, radiotolerant, and sulphate-reducing species of bacteria. This study concludes that the observed biogenic methane is a product of ancient methanogenesis. |
