Changes in carbon reservoirs over geological time

2 Changes in carbon reservoirs over geological time 

From Eqn 6.6 it can be seen that the geological record of 813C for kerogens and carbonates reflects changes in the sizes of C reservoirs, in addition to changes in the relative importance of the various fractionation pro-cesses (such as C3 photosynthesis). Because the kerogen and carbonate in sedimentary rocks dominate the shallow reservoirs ( 99.9%), the isotopic mass balance in Eqn 6.6 can be written simply as  

Clearly, 13Corganic increased during the Proterozoic. Equation 6.7 can be rearranged to  

The 813Ccarbonate record has remained fairly constant, and 513Ccarbomte values do not appear to be affected by post-depositional alteration (Veizer et al. 1992). So if it is assumed that 813C has likewise remained reason- 

the implications of which can be evaluated using the much simplified expression in Eqn 5.36. The interplay between , , , , , , (allowing for het- 

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