MECHANISMS OF ARGON RETENTION IN CLAYS REVEALED BY LASER AR-40-AR-39 DATING

A method for dating clays is important for studies of weathering, diag enesis, hydrocarbon migration, and the formation of major metalliferou s deposits. However, many attempts have produced imprecise or inaccura te results. Data from shales show that, contrary to expectations, the Ar-40-Ar-39 dating technique can be successfully used to determine the diagenetic age of ancient sediments because Ar-39 losses during irrad iation are controlled by release from low retentivity sites in illite equivalent to those that have lost radiogenic Ar-40 in nature, rather than by direct recoil as is generally assumed.