Problem of excess argon-40 in volcanic rocks, in Radioactive dating and methods of low-level counting

Geochronology, Geochemistry, Volcanic, Sandy Point basalt - Pliocene, [Fortification Basalt Mbr][Fortification Hill basalt][basalt of Fortification Hill] - Muddy Creek Fm - Miocene/Pliocene, [Black Point basalt][basalt flow of Black Point][Black Point flow], [Anderson Mesa basalt][Anderson Mesa flow], Vulcan's Throne basalt - Pleistocene,