With the recent increasing interest in the deep biosphere, the question arises about the origin of the potential carbon sources that support deep microbial communities and their possible interactions within the deep subsurface.
Organic-rich layers like coals and source rocks may provide carbon sources for the deep biosphere by leaching water soluble compounds like low molecular weight organic acids (LMWOA) into the surrounding formation water. We investigated the potential of a series of Eocene-Pleistocene coals, mudstones and sandstones from New Zealand with different maturities (R0 between 0.29 and 0.39) and total organic carbon content (TOC) regarding their potential to release such compounds. The water extraction of these New Zealand coals using Soxhlet apparatus resulted in yields of LMWOA that may feed the local deep terrestrial biosphere over geological periods of time. The presence of living microbial cells within the mudstones and sandstones adjacent to the coal layers has been proven by phospholipids analysis, verifying the hypothesis of organic carbon rich layers feeding the deep biosphere.
The yields of LMWOA dissolved in water appear to be dependent on maturity, organofacies and TOC. To investigate the effect of thermal maturity of the organic matter on the extraction yields, we examined additional coal samples (R0 between 0.29 and 0.80) from New Zealand. Besides this maturity sequence of coal samples also source rock samples from low to medium maturity (R0 between 0.3 to 1.1) from the Bakken Shale (North Dakota, USA) have been investigated concerning their potential to release organic compounds in contact with water.
Within our presentation we would like to show the diversity and variability of organic compounds that are released into the surrounding formation waters from organic carbon rich lithologies and their effects on the deep terrestrial subsurface.