SHRIMP uranium-lead dating of diagenetic xenotime in siliciclastic sedimentary rocks

Diagenetic xenotime is common in silicic lactic sedimentary rocks, where it starts to form on detrital zircon shortly after sediment deposition. It is possible to estimate the age of sedimentary rocks by in situ uranium-lead analysis of that xenotime. Two Proterozoic sandstone units from northwester n Australia, previously constrained to the age interval of 1790 to 750 mill ion years ago, have diagenetic xenotime ages of 1704 +/- 7 and 1704 +/- 14 million years ago. This method has potential for dating sedimentary sequenc es of all ages but should be especially valuable for refining the Precambri an time scale.