Use of U-Pb ages of detrital zircons to infer maximum depositional ages of strata: A test against a Colorado Plateau Mesozoic database

We test the research strategy of using youngest U-Pb ages of detrital zircons to constrain the maximum depositional ages of strata containing the zircon grains by comparing U-Pb ages of detrital zircons in 58 samples of Mesozoic sandstone from the Colorado Plateau and adjacent areas with depositional ages known independently from biostratigraphy. Our analysis confirms the validity of the research strategy but indicates that results vary somewhat depending upon how youngest grain age is specified. We use four alternate measures of youngest age which vary from least to most statistically robust as follows: (a) youngest single grain age, (b) youngest graphical age peak controlled by more than one grain age; (c) mean age of the youngest two or more grains that overlap in age at 1σ, (d) mean age of the youngest three or more grains that overlap in age at 2σ. We also calculated the "youngest detrital zircon age" generated by Isoplot 2008 but do not recommend that model age as a youngest-age measure. In general, the youngest-age measures based on multiple grain ages are more consistently compatible with depositional ages, but the youngest single grain ages are compatible with depositional age for > 90% of samples, and lie within 5 Ma of depositional age for ~60% of samples. Selected minor discrepancies between youngest grain age and depositional age may reflect stratigraphic miscorrelations rather than errors in U-Pb geochronology.