11:30 〜 11:50
[BCG08-03] ペルム紀／三畳紀境界における地球外3Heフラックスの増加イベント
★招待講演
キーワード：ペルム紀、三畳紀、層状チャート、ヘリウム、惑星間塵、白金族元素
The Solar System contains abundant submillimetre interplanetary dust particles (IDPs) that are enriched in 3He. 3He concentrations in ancient deep-sea sediments have been used to constrain the flux of IDPs onto the Earth for at least the last 100 Myr. However, the use of 3He in detecting IDP flux is often compromised by the diffusional loss of 3He in sedimentary rocks, with the exception of some Ordovician samples that record a period of unusually high extraterrestrial3He (3HeET) flux. In this study, we report for the first time the preservation of extra-terrestrial 3Hein deep-sea bedded chertfrom a continuous Permian-Triassic boundary (PTB) section at Waidani in Japan, which was deposited in the Panthalassa superocean.
High 3He/4He ratios (up to 150 Ra; 1Ra = the atmospheric ratio) were detected from acid-insoluble residues fromthe uppermost Permian deposits, which suggeststhe existence of extraterrestrial He hosted mainly in IDPs. The estimated extraterrestrial fraction of 3He across the PTB revealsthat3HeETconcentrations are higher in the topmost ~1.5 m ofthe studied Permian deposits, which is 4–5 times greater than that measured in the overlying Triassic unit. Based on the 3HeET concentration and sedimentary mass accumulation rate of the PTB section at Waidani, we calculated 3HeET fluxacross the PTB.The data document the presence of an up to 4-fold increase in IDP flux for the last 500 kyr interval of the Permian.This unusual signal suggests a significant increase in the influx of interplanetary dust particles, likely related to an asteroid showerin the inner Solar System. High-resolution stratigraphy indicates that peak IDP flux occurred during the final 500 kyr of the Permian, concurrent with a pre-extinction decline in radiolarian diversity.
High 3He/4He ratios (up to 150 Ra; 1Ra = the atmospheric ratio) were detected from acid-insoluble residues fromthe uppermost Permian deposits, which suggeststhe existence of extraterrestrial He hosted mainly in IDPs. The estimated extraterrestrial fraction of 3He across the PTB revealsthat3HeETconcentrations are higher in the topmost ~1.5 m ofthe studied Permian deposits, which is 4–5 times greater than that measured in the overlying Triassic unit. Based on the 3HeET concentration and sedimentary mass accumulation rate of the PTB section at Waidani, we calculated 3HeET fluxacross the PTB.The data document the presence of an up to 4-fold increase in IDP flux for the last 500 kyr interval of the Permian.This unusual signal suggests a significant increase in the influx of interplanetary dust particles, likely related to an asteroid showerin the inner Solar System. High-resolution stratigraphy indicates that peak IDP flux occurred during the final 500 kyr of the Permian, concurrent with a pre-extinction decline in radiolarian diversity.