In addition, it has an exceptional ability to remain closed to element mobility during later thermal events, and commonly yields concordant and precise dates.
The problem is most pronounced for Precambrian rocks, where the low diversity and abundance of organisms have prevented the establishment of any meaningful biostratigraphic framework for correlating strata.Also, most Precambrian successions have been metamorphosed, rendering original minerals and textures difficult to interpret, and resetting diagenetic minerals.Xenotime (YPO) is an isotopically robust chronometer, which is increasingly being recognized as a trace constituent in siliciclastic sedimentary rocks.It may start to grow during early diagenesis, typically forming syntaxial outgrowths on detrital zircon grains.Diagenetic xenotime occurs in a wide variety of rock types, including conglomerate, sandstone, siltstone, shale, phosphorite and volcaniclastic rocks, varying from early Archaean to Mesozoic in age.
The formation of diagenetic xenotime is principally related to redox cycling of Fe-oxyhydroxides and microbial decomposition of organic matter, leading to elevated concentrations of dissolved phosphate and rare earth elements (REE) in sediment pore-waters.
Xenotime has the properties of an ideal U–Pb chronometer, containing elevated levels of U (generally 1000 ppm) and very low concentrations of initial common Pb.
Absolute dating is necessary for knowing specific time e.g.
by isotope K/Ar in mica, especially in the crystalline rock: igneous and metamorphic rock.
On the other hand, the sedimentary rock (as I know) usually provide the time of formation by age range of fossil e.g. Is there any method to make it more specific like the crystalline one?
Recent advances in the field of geochronology have led to a greater understanding of the scale and duration of geological processes.