Organic matter (OM) is produced via primary production and then oxidized such that a minor percentage of the primary production is actually preserved. What is particularly confounding about the preserved OM is that the majority of it is uncharacterized. Indeed, during the conversion of fresh biomass to degraded geopolymers, the percentage of molecularly recognizable carbon decreases dramatically and the carbon becomes refractory. Over geologic time, the relationship between OM destruction and preservation regulates climate and fossil fuel formation. Thus, it is important to understand the chemistry of refractory OM, including its formation.

Traditional methods of OM characterization invariably come up against an analytical wall in that only a portion is actually identifiable. To address this deficiency, we have developed a novel tool to decipher the chemistry of refractory OM. The technique, hydrogen-pyrolysis (Hy-Py) involves a catalytic high temperature (520 ^oC) reaction in the presence of H₂ at high flow rates and high pressures (15 MPa). With this method, we can isolate desorbed molecules as well as identify molecules that are covalently bound in the geopolymer matrix. All volatilized compounds are captured downstream in a silica trap, which is then solvent-extracted and analyzed for molecular signatures. The method is presently qualitative but offers a wealth of information about refractory OM formation mechanisms. We will discuss the application of Hy-Py to “fingerprint” carbonaceous reference materials from the headwaters in watersheds (e.g. rock carbon, soil carbon) and compare those to the Hy-Py signatures of refractory OM in sediments throughout various watersheds.