Secular Trends in Sedimentary Rock Properties

Because sedimentary carbonates represent primarily chemical and biochemical precipitates from seawater, and because they make up 20% of the common sedimentary rock record, these rock types have been particularly good sources of chemical and mineralogical data for interpretation of the secular and cyclic evolution of the Earth s surface environment. This carbonate rock record as a function of geological age is now explored as are age trends in other rock types and sediment properties. With this information as background material, we can then discuss what these relationships tell us about the history of carbonates and the exogenic system throughout geologic dme. 

SEDIMENTARY CARBONATES IN THE EVOLUTION OF EARTH S SURFACE ENVIRONMENT 

Period Duration (106 years) Total Carbonate (1016 tons) Total Dolomite (1016 tons) Total Calcite (10 6 tons) Calcite/ Dolomite Ratio Total Dolomite (108tons y LogS Dolomite l) Total Calcite (108tons y1 LogS Calcite ) Total Carbonate (108tons y LogS Carbonate ) 

1) A marked increase in the abundance of submarine volcanogenic rocks and immature sandstones (graywackes) with increasing age. 

2) A significant percentage of arkoses in the early and middle Proterozoic, and an increase in the importance of mature sandstones (quartz-rich) with decreasing age. Red beds are significant rock types of Proterozoic and younger age deposits. 

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