Helium isotope investigation on magnetic reversal boundaries of loess-paleosol sequence at Luochuan,central Chinese Loess Plateau

摘要

Extraterrestrial particles have higher ~3He/~4He ratio than those of terrestrial sediments (> 100 Ra versus < 0.03 Ra, where Ra is the ~3He/~4He ratio normalized to the atmospheric value of 1.4×10~(-6)). The interplanetary dust particles (IDPs), which are very rich in ~3He, continuously bombard the Earth and can accumulate in deposits. IDPs sedimentation rate changes can significantly influence ~3He concentration in the Earth surface sediments. Since IDPs are not easy to detect in terrestrial deposits, measuring helium isotopes is a helpful approach to examine changes in IDPs. Helium concentration and helium isotopic composition magnetic substances and the quartz particles were examined for helium concentration and helium isotopic ratio. Results show that the ~3He/~4He ratio and the ~3He concentrations of the magnetic substances are clearly higher than those of the bulk samples and the quartz particles, and, the ~He/~4He ratio of the extracted magnetic substances is also higher than that of the average level of the Earth's crust. The higher helium content in the magnetic fractions can be explained by an influx of IDPs.