Yoshihiro Ganzawa

TL color images from quartzes of loess and tephra in China and Japan

Abstract The influence of loess originating in inland China to paleosoils in Japan is currently investigated from the aspect of late Pleistocene environmental change in East Asia. Since there are many weathered brownish tephras of similar color to the loess deposits, a useful method is needed for distinction between loess and tephra deposits. TL and TLCI (TL color image) are attempted for distinguishing between two deposits using the red and blue colorations of quartz particles separated from these deposits. The natural TL measurement of red (RTL) and blue (BTL) wavelengths shows the quite different mean values of RTL/BTL = 1.72 for loess deposits and 26.58 for tephra deposits. The quartz coloration of TLCI is also divided into two groups of blue and red particles, originating desert deposits in inland China and tephras in Japan. These results show that TL and TLCI methods are useful for distinguishing the source of deposits in the late Pleistocene in Japan.

Possible Age Models for Lake Onuma Lacustrine Sediments Based on Tuffs Recovered in Three Cores

Lake Onuma, Hokkaido, Japan, is located south of Hokkaido-Komagatake volcano. The present Lake Onuma was formed by an intensive eruption and partial collapse of the volcanic cone in 1640 AD, which caused a debris flow that dammed the drainage. Three cores (ON12A, C, and D) were recovered from Lake Onuma to examine the environmental change in the region. These three cores are correlated based on lithological descriptions and water content fluctuation. Volcanic deposits Ko-a (1929 AD), Ko-c1 (1856 AD), Ko-d (1640 AD), and possibly Ko-c2 (1694 AD) were successfully identified with the help of radiocarbon age dating, 137Cs radioactivity measurement, and chemical analyses, to construct an age model of these cores.

Absolute measurements of thermal neutron fluence and fission track dating

Abstract Absolute measurements of thermal neutron fluence for fission track dating have been carried out in order to determine the calibration factor ( B th ) for dosimeter glasses and a zeta- a value (ζ a ) calculated from B th , the fission cross-section of 235 U (ovbar|σ f ), 235 U/ 238 U isotopic abundance ratio ( I ), and and 238 U spontaneous fission decay constant (λ f ). The zeta- a value is in close agreement with the zeta- b value calculated from Fish Canyon Tuff zircon. Fission track ages determined for Tertiary Formations in eastern Hokkaido using zeta- a agree well with the ages indicated by fossil fauna and K-Ar dating.

TL/IRSL dating of wide spread aeolian deposits.

東北地方に分布する風成塵堆積物からなるいわゆるロームについて, 4-11μmポリミネラル粒子を用いて, 7試料の熱ルミネセンス, 光ルミネセンス年代測定を日本ではじめて試みた.石英や長石類の細粒粒子は, 中国内陸から日本への輸送過程で太陽に曝されてブリーチされているので, ルミネセンス年代測定に最適な物質である.additive dose法とregeneration法の2種類の測定法によって検出されたTLとIRSLのDe(等価線量)はサンプル地点の地質層準に従って, 40 Gyから209 Gyまでの値を示した.原子吸光法と放射分析で研究したDose rate(年間線量)はDBD(乾燥容積重)から計算された含水率を考慮に入れて1.2 mGy/年から2.5 mGy/年までを示す.50 ka以下のIRSLとTL年代は挟在テフラから導かれる推定年代とよく一致した.さらに, TL法のAD年代は50 kaから120 kaまで推定年代とよく一致した.しかし, IRSLとTL regeneration法では50 kaを越えると推定される年代と比較して, 年代の減少(age short-fall)を示す.