Source Areas of Eolian Dust Quartz in East Asia

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  • 電子スピン共嗚 (ESR) による東アジアの風成麈石英の産地同定
  • 電子スピン共鳴(ESR)による東アジアの風成塵石英の産地同定--アイソトープステージ2の卓越風復元への試み
  • デンシ スピン キョウメイ ESR ニヨル ヒガシ アジア ノ フウセイジン
  • Source areas of eolian dust quartz in East Asia: a tentative reconstruction of prevailing winds in isotope stage 2 using electron spin resonance
  • アイソトープステージ2の卓越風復元への試み
  • A Tentative Reconstruction of Prevailing Winds in Isotope Stage 2 Using Electron Spin Resonance

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Abstract

Electron spin resonance (ESR) spectra of quartz grains of 43 samples of loesses, soils, paleosols, and bore cores from China, Korea, and Japan were measured in order to identify the source area of eolian dust and to recreate prevailing winds during isotope stage (MIS) 2 in East Asia (Table 1 and Fig. 1). Fine quartz grains less than 20 μm from desert loesses and wadi sediment in the Taklamakan Desert and Quidam Basin, which are known source areas of eolian dust, showed ESR intensities ranging from 6.2 to 8.2 (in arbitrary units). Quartz grains of Upper Malan loess from the Loess Plateau and Beijing showed intensities ranging from 5.8 to 8.3, while Korean soil quartz grains showed similar values from 6.0 to 7.4. This similarity is attributed to their common eolian origin in the desert loess and wadi sediment in Central Asia in MIS 2. In the Japanese islands, ESR intensities of fine quartz are significantly different from those of coarser quartz (more than 20μm) which have been derived from local sources such as old bedrock. The intensities of coarser quartz depend on the age of bedrock (Fig. 4). Fine quartz grains of soils, paleosols, and bore cores in the Japanese islands were identified to be eolian dust based on ESR intensities ranging from 4.2 to 12.7. ESR intensities of fine quartz depend on the age of deposition: 4.5 to 12.7 for MIS 2; 4.2 to 8.6 for MIS 4; and 4.4 for MIS 1. These intensities decrease in the order of MIS 2, MIS 4, and MIS 1. These values are due to the difference in the amount of eolian dust accumulated during the three stages. The amount of eolian dust accumulated increases in the order of MIS 2, MIS 4, and MIS 1.<br> ESR signal intensities of fine quartz (_??_20μm) during MIS 2 in the Japanese islands vary in different localities (Fig. 3). The values in the northern part of Japan (Hokkaido and Aomori) range from 10.0 to 12.7, suggesting that the fine quartz originated in Precambrian rock areas at high latitude in areas such as north China, Mongolia, and Siberia, and was transported by the northwest monsoon winds (Fig. 5). In the central-southwestern part of Japan (Fukui to Okinawa), intensities range from 5.8 to 8.3, coinciding with those of Chinese loess. It is concluded that this fine quartz was carried from mid-latitude dry areas in Asia by the westerly winds. On Yonaguni Island, the ESR signal intensity of fine quartz is 9.7, indicating that this quartz originated in the Precambrian areas of south China or India and was transported by the subtropical jet stream. Some fine quartz grains with lower values on Miyako Island of the southwestern islands, Tottori, Amino, and Sarukawa in Honshu may have originated on the dried sea floor during the last glacial age.

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