Sedimentary record ratios

Bjerrum and Canfield (2004) have used the relationship in Fig. 5.13 to calculate the ratio of organic carbon burial to the total amount of carbon buried in the sedimentary record over time. They show (Fig. 5.13b) that organic carbon burial was less in the Archaean than at the present day. These authors also calculated the effects of a third carbon isotope reservoir - that of carbonate in the oceanic crust - and showed that in this case the degree of organic carbon burial was much less in the Archaean than at present. This result would imply that oxygen levels were low in the Archaean, not because... 

The concept for a marine paleoredox proxy based on variations in the U isotope ratio in sediments is very similar to the Mo isotope paleoredox proxy described earlier in this chapter. Since incorporation of U in oxidizing sediments such as ferromanganese crusts results in preferential removal of isotopically light U, and incorporation of U in reducing sediments results in preferential removal of isotopically heavy U, changes in the relative proportions of these two sinks over time should drive systematic shifts in the isotopic composition of U in seawater. In turn, these temporal shifts in the isotopic composition of seawater should be manifested as vertical fluctuations in in the sedimentary record. Excursions in the sedimentary record towards lighter values of (in any of these... 

Altabet, M.A., and R. Francois. 1994. Sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization. Global Biogeochemical Cycles 8(1) 103-116. 

Altabet, M. A., and Francois, R. (1994). Sedimentary nitrogen isotopic ratio records surface ocean nitrate utilization. Global Biogeochem. Cycles 8, 103—116. 

Potassium, which occurs in many volcanic rocks, has an isotope, potassium O, which decays to argon-39. This parent-daughter ratio proved widely useful in studies of a number of volcanic rocks and became perhaps the most widely used radiochronometric method. It has been used to date many parts of the sedimentary-rock record through analyses of the relationships of volcanic rocks with sedimentary rocks. In an effort to achieve greater precision in radiochronometry, specialists in the study of decay of potassium-40... 

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