EXTRATERRESTRIAL HELIUM-3 FLUX ACROSS THE PERMIAN/TRIASSIC BOUNDARY

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 (³He_ET) 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 revealsthat³He_ETconcentrations are higher in the topmost ~1 m ofthe studied Permian deposits, which is 4–5 times greater than that measured in the overlying Triassic unit. Based on the ³He_ET concentration and sedimentary mass accumulation rate of the PTB section at Waidani, we calculated³He_ETfluxacross the PTB.The data document the presence of an up to 6-fold increase in IDP flux for the last 100–200 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 flux of interplanetary dust particles occurred during the final 100–200 kyr of the Permian, concurrent with a carbon isotopic excursion event and the development of highly anoxic–euxinic bottom-water conditions.