Absence of extraterrestrial 3He in Permian-Triassic age sedimentary rocks

While no extraterrestrial 3He was detected at Opal Creek, there is a sharp increase in nucleogenic 3He very close to or at the Permian-Triassic boundary. This presumably arises from the major lithologic change at this time, from cherts in the Permian to shales and siltstones in the Triassic. Increased nucleogenic 3He is associated with increases in both lithium and organic carbon content into the Triassic. Either the production rate or the retention of this 3He is higher in the shales and siltstones than in the cherts. Care must be taken to eliminate such artifacts before interpreting changes in 3He concentration in terms of fluctuations in the delivery of 3He from space.