The effect of Aeolian accessions on soil development on granitic-rocks in south eastern Australia. II. Oxygen-isotope, mineralogical and geochemical evidence for Aeolian deposition

Abstract

Oxygen-isotope abundance in quartz grains, total chemical analyses and clay mineral data are used to identify aeolian deposits in four soil profiles developed on granitic rocks. Results indicate that quartz fractions derived from I-type granitic rocks have ä18O values less than 10.7%, whereas fine sand-sized (50-31 µm) quartz separates from the same soils have ä18O values of > 11.6¿. Similar, but less marked, differences were observed in a soil on an S-type granitic rock, suggesting that addition of aeolian material to all the soils investigated has been an important process of soil formation. X-ray diffraction data indicate the presence of decreasing proportions of clay mica h the soils with increasing distance from probable sources of aeolianites in the Riverine Plain, raising the possibility that clay mica, along with other clay minerals and clay-size quartz, may have been also deposited by wind in the soils. Titanium/zirconium elemental ratios are less useful indicators of aeolian accession because of complications arising from the weathering of biotite in the underlying granitic rocks. Probable losses of yttrium from the soils also appear to result from weathering of materials derived from the granitic rocks, although some data indicate that zirconium/yttrium ratios for the 50-2 µm fractions may also be indicative of aeolian accession.