Kerogen Proterozoic

Hold I.M., Brussee N.J., Schouten S., and Sinninghe Damste J. S. (1997) Occurrence of bound monoterpenoids in Palaeozoic and Proterozoic marine kerogens. Abstr. I8th Int Meet. Org. Geochem. Maastricht, 493-494. 

Sulfur isotope studies have also provided insights into the transition from Archean low Po to higher values in the Proterozoic. In the same studies that revealed extremely low Archean ocean sulfate concentrations, it was found that by —2.2 Ga, isotopic compositions of sedimentary sulfates and sulfides indicate bacterial sulfate reduction under more elevated seawater sulfate concentrations compared with the sulfate-poor Archean (Habicht et al., 2002 Canfield et al., 2000). As described above, nitrogen isotope ratios in sedimentary kerogens show a large and permanent shift at —2.0 Ga, consistent with denitrification, significant seawater nitrate concentrations, and thus available atmospheric O2. 

Figure 4. Plot of 8org versus H/C values for Proterozoic kerogens in the age range 2.1 to...

Figure 5. Plot of age versus 5carb (crosses) and 5org for Archean and Proterozoic kerogens. Kerogen data (filled circles) are corrected for the effects of thermal alteration (Des Marais 1997a). Uncorrected data are shown as open circles. Between 2.2 to 2.0 bilhon years ago, note the high 8carb values and the virtual disappearance thereafter of 5org values more negative than -36. Other evidence indicates that atmospheric O2 increased substantially at this time (see text).

Strauss H. and Moore T. B. (1992) Abundances and isotopic compositions of carbon and sulfur species in whole rock and kerogen samples. In The Proterozoic Biosphere, a Multidisciplinary Study (eds. J. W. SCHOPF and C. Klein), pp. 709-798. Cambridge University Press, Cambridge. 

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