QUANTIFICATION OF WEATHERING, SOIL GEOCHEMISTRY AND SOIL FERTILITY |
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| Authors: | B I KRONBERG H W NESBITT |
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| Institution: | Geology Department University of Western Ontario London —Canada N6A 5B7 |
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| Abstract: | Continental chemical weathering is discussed with reference to a diagram, in which the ratio (CaO + Na2O + K2O)/(Al2O3+ CaO + Na2O + K2O) is plotted against the ratio (SiO2+ CaO + Na2O + K2O)/(Al2O3+ SiO2+ Na2O + K2O). The former ratio is a measure of the degree of feldspar breakdown, which is accompanied by the formation of secondary minerals (illite, smectite, etc.). The second ratio is a measure of the enrichment during weathering of Al, Si oxide phases such as kaolinite, quartz and gibbsite. The application of the diagram to a series of global examples leads to the statement: 1) Chemical weathering is the principal process by which continental surfaces are modified. 2) The extent of chemical weathering is correlated with the age of continental surfaces. 3) Global agricultural productivity is correlated with geologically recent additions of fresh rock debris by processes of volcanism, glaciation or alluviation. |
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