U-SERIES ISOCHRON DATING - A GENERALIZED-METHOD EMPLOYING TOTAL-SAMPLE DISSOLUTION

The age of a sedimentary deposit can be determined by measuring U-238, U-234, Th-232, and Th-230 in two or more samples of the deposit, with the requirement that these samples have different U/Th ratios but an identical Th-230/Th-232 ratio when deposited. This paper presents the theoretical and experimental aspects of the dating method. The latter involves techniques for securing samples of varied U/Th ratios from the same deposit, plotting isochrons of the radiochemical data (obtained on totally dissolved samples) for age analysis, and estimating the errors involved. Although applications to impure carbonates and lacustrine evaporite sediments are given as examples in this paper, the method potentially can be generalized for dating a variety of authigenic deposits such as rock varnish, peat, opal, sulfate minerals, and marine phosphorites.