The nature and possible origins of soluble salts in deeply weathered landscapes of eastern Australia

Abstract

Extensive areas of salt-affected soils in eastern Australia occur on the exposed lower zones of lateritic profiles or in derived materials. Analyses of 96 samples of mottled and pallid zones collected in this study show that they generally contain appreciable soluble salts, predominantly sodium chloride, particularly where they developed in argillaceous sedimentary rocks which underlie about two-thirds of the area, and in some granitic rocks. Analyses of 96 samples of unweathered rocks indicate that some contain moderate to appreciable quantities of sodium and chloride, and it is suggested that these and other soluble ions accumulated in the lower zones as a result of deep weathering in the Mid-Tertiary. Atmospheric accessions of sea salts in rain or dry fallout at present rates account partly for the occurrence of salt-affected soil landscapes in some coastal areas but are unlikely sources of salts far inland. Soils formed in situ on weathered basalt, argillaceous sedimentary and granitic rocks which have been exposed at the surface since the Late Tertiary are not salt-affected, because climatic, topographic and hydrologic conditions are different from those of the Mid-Tertiary and only small volumes of rock are involved.