A THEORETICAL APPROACH TO P_(co_2) EVOLUTION IN THE ATMOSPHERE BASED ON ASSOCIATIONS OF SEDIMENTARY MINERALS

摘要

Based on the theory of pH evolution of sea water and the balance between the seawater and the atmosphere the authors discussed the problems about （i） the method ofcalculating PCO2 in the ancient atmosphere with the associations of sedimentary miner-als; （ii） the evolution of PCO2 values in the geologic history; （iii） the relations of thepH evolution of sea water with carbonate precipitations; and （iv） calculation of the pHlimit for some associations of sedimentary minerals and its corresponding PCO2 valuesin the atmosphere. The authors pointed out that though carbonates had deposited little in the Archaean,the content of CO2 gas in the Archaean atmosphere was very high and was gradually go-ing up to form a thick CO2 atmosphere. Up to 2600 Ma ago, the PCO2 had reached a gradeof 10- 50 atm. There was a general trend of evolution that from the early Proterozoicera to the present the depositional horizon of carbonate layers was gradually risingand finally surpassed the horizons of clay