Southeastern Section - 63rd Annual Meeting (10–11 April 2014)

Paper No. 5
Presentation Time: 8:00 AM-12:00 PM

CARBON ISOTOPES AS INDICATORS OF PALEO-PRODUCTIVITY CHANGES DURING THE MARCELLUS SHALE DEPOSITION


CHEN, Ruiqian, Department of Geology and Geography, West Virginia University, 330 Brooks Hall, 98 Beechurst Ave, Morgantown, WV 26506, SHARMA, Shikha, Geology and Geography, West Virginia University, 330 Brooks Hall, 98 Beechurst Avenue, Morgantown, WV 26506, EASTMAN, Harvey, U.S. Department of Energy, National Energy Technology Laboratory, Morgantown, WV 26507 and SOEDER, Dan, Doe, National Energy Technology Laboratory, 3610 Collins Ferry Road, Morgantown, WV 25607, richen@mix.wvu.edu

Measurement of the carbon isotopic composition of inorganic carbon (δ13Ccarb) and organic carbon (δ13Ccarb) in about 100 samples of the Marcellus Shale in Eastern Gas Shales Project cores WV6 and WV7 suggest that carbon isotopes can be used to understand changes in paleo-productivity during shale deposition. In both cores, we found higher total organic carbon (TOC) content and δ13Ccarb values at the base of the Marcellus Shale. We hypothesize that these relatively higher δ13Ccarb values are the result of rapid burial of large amounts of organic carbon from high algal paleo-productivity. The higher photosynthetic demand was expected to preferentially remove lighter 12C, leaving the dissolved inorganic carbon pool enriched in 13C and resulting in an increase in δ13Ccarb in the precipitating carbonate. We found instead that δ13Corg values decrease (average = 1‰) through the basal organic-rich intervals in both WV6 and WV7. This has been interpreted as higher isotopic fractionation because of the tenfold higher atmospheric CO2 concentration during the Devonian time period. We propose that higher atmospheric CO2 could also have resulted in high paleo-productivity and larger carbon isotopic fractionation between dissolved inorganic carbon and produced organic carbon at the base of Marcellus Shale. Our preliminary results indicate the carbon isotopes can be used to better understand the paleo-productivity changes during the shale deposition.