UC Riverside

The preservation of organic matter in the sedimentary rock record is strongly controlled by thermal maturity. This poses a problem when investigating Precambrian or extraterrestrial samples as they are typically heavily altered. In order to preform detailed biomarker analysis on very ancient samples, one must either scour for unusually well preserved specimens or develop new organic matter parameters suitable at high thermal maturities. Presented here are two such studies, the first is a detailed investigation of exceptionally preserved Ediacaran rocks while the second is a broad study of preservation of polycyclic aromatic compounds (PAH) bound in kerogen.

In the first study I perform a lipid biomarker, stable isotope (δ15Ntotal and δ13CTOC) and compound specific δ13C investigation of exceptionally immature late Ediacaran strata from across Baltica. The biomarker assemblages encompass an exceptionally wide range of high hopane/sterane ratios (1.6–119), which is a broad measure of bacterial/eukaryotic source organism inputs. A high contribution of bacteria to the overall low productivity was most likely the result of persistent oligotrophic conditions. Total organic carbon (CTOC) isotope values range from –23.0‰ to –33.9‰, with the largest differences observed between the different drill-core locations. Pico-CSIA suggests the cause of these site-varying δ13CTOC was regional environmental heterogeneity and a microbial populations shift between the Redkino and Kotlin horizons.

In the second study I report the distribution of bound PAHs in biogenic kerogens and in a selection of insoluble organic matter (IOM) from carbonaceous residues. The degree of thermal maturity of the sedimentary organic matter exerts the primary control on the preservation and distributions of the major 5-ring and 6-ring PAH compounds generated by catalytic hydropyrolysis (HyPy) from kerogens. All ancient biogenic kerogens analyzed contain detectable amounts of perylene, even for the most thermally transformed samples. A suite of PAH abundance ratios were identified which succeeded in separating biogenic kerogens (including highly overmature samples) versus abiogenic IOM formed from high temperature thermal cracking reactions. While not a definitive biosignature, the ability to recognize aromatics formed from low-temperature processing of organic material will aid in the search for past and extant life on extraterrestrial bodies such as Mars.