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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 P_(CO_2) in the ancient atmosphere with the associations of sedimentary miner-als; (ii) the evolution of P_(CO_2) 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 P_(CO_2) valuesin the atmosphere. The authors pointed out that though carbonates had deposited little in the Archaean,the content of CO_2 gas in the Archaean atmosphere was very high and was gradually go-ing up to form a thick CO_2 atmosphere. Up to 2600 Ma ago, the P_(CO_2) 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 min
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 P_ (CO_2) in the ancient atmosphere with the associations of sedimentary miner-als; (ii (iii) the relations of the pH evolution of sea water with the precipitation of calcium; and (iv) calculation of the pHlimit for some associations of sedimentary minerals and its corresponding P_ (CO_2) valuesin the atmosphere. The authors pointed out that though carbonates had deposited little in the Archaean, the content of CO_2 gas in the Archaean atmosphere was very high and was gradually going up to form a thick CO_2 atmosphere. Up to 2600 Ma ago, the P_ (CO_2) had reached a grade of 10- 50 atm. There was a general trend of evolution that from the early Proterozoicera to the present depositional horizon of carbonate layers was gradually risingand finally surpassed the ho rizons of clay min