QUANTIFICATION OF WEATHERING, SOIL GEOCHEMISTRY AND SOIL FERTILITY

TLDR

The diagram plots two ratios that quantify feldspar breakdown and enrichment of Al and Si oxides, illustrating how chemical weathering modifies continental surfaces. Chemical weathering is the main agent reshaping continental surfaces, its extent increases with surface age, and recent rock debris inputs from volcanism, glaciation or alluviation enhance global agricultural productivity. No other information.

Abstract

Summary Continental chemical weathering is discussed with reference to a diagram, in which the ratio (CaO + Na 2 O + K 2 O)/(Al 2 O 3 + CaO + Na 2 O + K 2 O) is plotted against the ratio (SiO 2 + CaO + Na 2 O + K 2 O)/(Al 2 O 3 + SiO 2 + Na 2 O + K 2 O). 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.