Cristiano Lana Ricardo Scholz Ian Buick Sandra K. Kamo Nick M.W. Roberts Axel Gerdes Michael Wiedenbeck Blair Schoene Francisco E. Apen Sean Patrick Gaynor Marco Silva 2025 <p><span>Determining absolute ages of carbonate diagenesis, faulting, fossil formation, speleothem growth, carbonate-hosted hydrocarbon deposits, vein mineralisation and hydrothermal alteration has become increasingly accessible through LA-ICP-MS U-Pb dating of calcite, complementing traditional isotope dilution methods still applicable to certain materials (e.g., speleothems via micro-drilling). However, well-calibrated reference materials for LA-ICP-MS calcite geochronology remain scarce. Here, we characterise the Rio Maior calcite, designated ‘RioM-1’, as a potential reference material for U-Pb dating by LA-ICP-MS. Fragments (0.1 to 1 cm</span>³<span>) from a single scalenohedral crystal were analysed by ID-TIMS (U-Pb), LA-ICP-MS (U-Pb and&nbsp;</span>⁸⁷<span>Sr/</span>⁸⁶<span>Sr), and SIMS (O isotopes). RioM-1 displays high U mass fraction and low, though variable, proportions of common Pb. Combined ID-TIMS analyses from two independent laboratories yielded a Tera-Wasserburg lower intercept date of 63.93 ± 0.11 Ma (2</span><i>s</i><span>, MSWD&nbsp;=&nbsp;1.3,&nbsp;</span><i>n</i><span>&nbsp;= 16). LA-ICP-MS U-Pb data from three independent laboratories are concordant with the TIMS age, producing a pooled date of 64.10 ± 0.12/1.2 Ma (2</span><i>s</i><span>, MSWD&nbsp;=&nbsp;7.7,&nbsp;</span><i>n</i><span>&nbsp;= 708) and an initial&nbsp;</span>²⁰⁷<span>Pb/</span>²⁰⁶<span>Pb ratio of 0.85 ± 0.01. Other calcite reference materials, when normalised to RioM-1, yielded dates within uncertainty of their published values. SIMS measurements returned a mean&nbsp;</span>¹⁸<span>O/</span>¹⁶<span>O of 0.002044450 ± 181 (1</span><i>s</i><span>) and δ</span>¹⁸<span>O</span>_SMOW<span>&nbsp;of 19.57 ± 0.92‰ (1</span><i>s</i><span>), while LA-ICP-MS strontium isotope measurement yielded a mean&nbsp;</span>⁸⁷<span>Sr/</span>⁸⁶<span>Sr of 0.708177 ± 9 (2</span><i>s</i><span>).</span></p> application/pdf 10.1111/ggr.70018 en Wiley RioM-1: A new calcite reference material for U-Pb LA-ICP-MS geochronology article