Source indicators of humic substances and proto-kerogen. Stable isotope ratios,elemental compositions and electron spin resonance spectra

Stable isotope ratios of C, N and H, elemental compositions and electron spin resonance (ESR) data of humic acids and proto-kerogens from twelve widely varying sampling locations are presented. Humic acids and proto-kerogens from algal sources are more aliphatic and higher in N than those from higher plant sources. Oxygen content appears to represent a measure of maturation, even in Recent sediments and S content may reflect redox conditions in the environment of deposition. The ESR data indicate that the transformation of humic substances to proto-kerogens in Recent sediments is accompanied by an increase in aromatic character. A combination of δ¹³C and $\text{H}\text{C}$ ratio may be a simple but reliable source indicator which allows differentiation of marine-derived from terrestrially-derived organic matter. The δ¹⁵N values are useful indicators of nitrogen nutrient source. Deuterium/hydrogen isotope ratios appear to reflect variations in meteoric waters and are not reliable source indicators.