The retention of precursor biotic signatures in the organonitrogen and organooxygen compounds of immature fine-grained sedimentary rocks

Abstract

To reveal the impact of biomass input (marine algae, terrestrial plants and lacustrine Botryococcus braunii) on the composition of high molecular weight organooxygen and organonitrogen compounds (Ox, Ny and NyOx), solvent extracts of immature–early mature rock and coal samples were systematically characterized by Fourier transform ion cyclotron resonance mass spectrometry using different ionization modes. In total, 16 samples from the marine Schöneck, Dynow and Posidonia formations, the lacustrine Wealden Formation and the terrestrial New Zealand coals were investigated.Coals as the in-situ deposits of terrestrial plants consist to a great degree of aromatic polyoxygenated Ox and N1Ox compounds, representing the degradation products of lignin like phenolic ketones and carboxylic acids as well as their condensation products with the degradation intermediates of labile organonitrogen compounds. Aliphatic Ox moieties derived from plant protective constituents principally waxes and cutan show a pronounced even or odd carbon number predominance of the C23–C33 species with C26, 28, 30 or C27, 29, 31 as the major homologs. In contrast, marine and lacustrine microbial communities contribute plentiful middle-chain C22, C24 or C23, C25 Ox compounds. Marine rock extracts are characterized by abundant organonitrogen compounds, especially N2 and N2Ox classes, interpreted as signatures of protein-rich marine algae that were successfully preserved via a degradation-recondensation pathway, whereas the low protein content of lacustrine Botryococcus braunii is reflected by a low amount of N1Ox and N1 classes. Highly aliphatic algaenan of Botryococcus braunii sterically protected its oxygen-bearing groups from degradation, leading to a great abundance of Ox compounds, furthermore, it characterizes the Botryococcus braunii source by substantial heteroatomic species containing more than 40 carbon atoms.