Issue 6, 2024

PXCG-1 and PXCG-2: two reference materials for gypsum U–Th dating

Abstract

Gypsum is a widespread mineral in various sedimentary deposits. It precipitates from natural aqueous systems with trace amounts of U but almost no Th, rendering it a potentially valuable U–Th geochronometer. However, no gypsum RM for U–Th dating has been available. In this work, two natural gypsum reference materials (PXCG-1, PXCG-2) from the PiXiao cave, southwest China were prepared and characterized for U–Th dating. U–Th contents and isotope ratios were measured on a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) using the isotope dilution technique. Data from three different laboratories show good agreement in 238U content, δ234U (234U/238U relative to secular equilibrium value), 230Th/238U activity ratio, and 230Th ages (corrected) (corrected by assuming the initial 230Th/232Th ratio of the average crust value). The recommended values with the uncertainties (2σ) of these two gypsum RMs, 238U content = 1844 ± 39 ng g−1, δ234U = 229.3 ± 3.9‰, 230Th/238Uactivity = 0.5741 ± 0.0036, 230Th ages (corrected) = 66.97 ± 0.31 ka BP for PXCG-1, and 238U content = 1636 ± 50 ng g−1, δ234U = 61.0 ± 2.4‰, 230Th/238Uactivity = 0.9797 ± 0.0034, 230Th ages (corrected) = 260.82 ± 3.39 ka BP for PXCG-2, respectively. Information values of 232Th content, 230Th/232Th atomic ratio, 230Th age (uncorrected), and δ234Uinitial are also provided. PXCG-1 and PXCG-2 are the first reported gypsum age RMs for U–Th dating, making them a useful complement to the widely distributed carbonate age reference materials for U–Th disequilibrium dating in Pleistocene–Holocene deposits.

Graphical abstract: PXCG-1 and PXCG-2: two reference materials for gypsum U–Th dating

Supplementary files

Article information

Article type
Paper
Submitted
27 Feb 2024
Accepted
18 Apr 2024
First published
22 Apr 2024

J. Anal. At. Spectrom., 2024,39, 1461-1469

PXCG-1 and PXCG-2: two reference materials for gypsum U–Th dating

X. Wang, Z. Xiao, C. Xu, W. Zhou, X. Jia, Y. Ning, H. Cheng, Y. Liu, Q. Shao, L. Wang, Z. Ma, W. Duan, X. Wang, M. Tan, J. Xiao and X. Li, J. Anal. At. Spectrom., 2024, 39, 1461 DOI: 10.1039/D4JA00067F

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