An Astronomically Validated U-Pb Reference Material for Dating Quaternary Speleothems

Abstract

Well-characterized reference materials (RMs) are essential for advancing laser ablation (LA) U-Pb carbonate geochronology, yet Quaternary carbonate RMs with stringent accuracy constraints are still lacking. Here, we present a comprehensive inter-laboratory study of speleothem sample SB19 (U: 3.5 ±1.8 μg/g) employing both LA and isotope dilution (ID) methods. LA-MC-ICPMS analyses of the stratigraphically distinct subsamples demonstrate excellent inter- and intra-laboratory reproducibility. High-precision δ234U data were also obtained for SB19, allowing accurate corrections for the initial disequilibrium. The resultant chronology reveals a robust correlation between the SB19 δ¹⁸O record and theoretical solar insolation curves on the precession scale, providing a very valuable rigorous and verification of its age accuracy (±6 kyr, 2σ). Notably, (207Pb/206Pb)0 ratios are quite similar among subsamples (RSD <0.5%), which can be used as a reference for the investigation of initial Pb isotopes and their contributions. Syntheses of ID (n=15) and LA datasets of the SB19 yield recommended values: Age = 1.091 ±0.006 Ma and (207Pb/206Pb)0 = 0.809 ±0.004. SB19 meets the stringent requirements of LA carbonate U-Pb dating RMs (~0.5% relative uncertainty in age and initial Pb isotopic ratios at 2σ), particularly for dating Quaternary carbonate samples. This integrated work establishes a new paradigm for carbonate RM validation through combining radiometric, geochemical, and orbital insolation data.