13C and 15N NMR spectroscopic investigation on the formation of fossil algal residues

13C and 15N NMR spectroscopy was applied to modern (a mixed algal culture, its algaenan and its compost), ancient (algal derived sediments from Mangrove Lake, Bermuda) and fossilized algal residues (Torbanite, Green River Shale) for the purpose of establishing the forms of nitrogen algal remains and evaluating their long-term stabilities. The results indicate that proteinaceous material can resist microbial degradation in sediments as old as 4000 yr, possibly in refractory biopolymers, by encapsulation into their macromolecular network. The 15N NMR spectra of the Torbanite and the Green River Shale show a relative enrichment of heterocyclic-N, which may derive from selective preservation of biogenic heterocyclic compounds or by rearrangement of peptide chains during diagenesis.