風成石英粒子の酸素同位体組成

そのトレーサーとしての意義

抄録

Oxygen isotopic composition (δ¹⁸O notation, expressed as ‰ deviation relative to Standard Mean Ocean Water, SMOW) of quartz provides a direct evidence for provenance of soils and sediments in which quartz is an ubiquitous mineral constituent. The δ¹⁸O values can be used as a tracer in evaluation of eolian contribution. Principle of temperature-dependence of ¹⁸O/¹⁶ O fractionation between silica and water and procedures for isolation of monomineralic quartz from soils and sediments were outlined. Relevant data for the oxygen isotopic composition of eolian quartz from various parts of the world were compiled and discussed in relation to their geographic distribution. The oxygen isotopic composition of eolian quartz is in the intermediate values of high and low-temperature origins, the extent being dependent upon the proportion of each types of rocks in the source regions. Three distinctive provenances of the eolian dusts were established. The first group (δ¹⁸O=+19-+20‰) consists of those from mid-continental U. S. A. and desert regions of Afganistan and India, the second (δ¹⁸O=+16‰) from Sahara-Sahel and interior China, the third (δ¹⁸O=+13-15‰) from South Africa, Australia and New Zealand. The δ¹⁸O values (+18‰) from Hawaiian Islands are in between the first two gropus. Further systematic sampling and determination ofδ¹⁸O of quartz in desert materials from which eolian dust derives were emphasized.