Relationship Between Ca/Mg Ratio and Geologic Age

Abstract

The analyses of numerous limestone samples showed that there is a general increase in the average Ca/Mg ratio in going up the geologic column with superimposed periodic fluctuations. A general decline in abundance of dolomites in going up the geologic column was previously shown by R. A. Daly (1910). The writer, however, failed to establish a simple relationship between the Ca/Mg ratio and the age of carbonate rocks. The cyclic occurrence of dolomitic and calcitic limestones, observed by the writer, suggests that the formation of dolomites was occurring in cycles with a gradual accumulation of magnesium in sea water until favorable conditions were established for the formation of dolomites. Inasmuch as high CO2 pressure of the atmosphere during pre-Cambrian and Paleozoic time is advanced by Russian geologists as a possible explanation for the abundance of dolomites, an attempt was made to precipitate dolomite directly out of sea water at high CO2 pressure. This attempt was successful and indicated that some pre-Cambrian and Paleozoic dolomites may have been formed by direct chemical precipitation out of sea water.