Radiometric dating of Middle Pleistocene carbonates: assessing consistency and performance of the U–Th and U–Pb dating methods
<p>The U–Th and U–Pb dating methods are widely employed for radiometric dating of Pleistocene carbonates, such as speleothems and corals. The U–Th dating method has been progressively refined over recent decades, largely through advances in mass spectrometry, and is now capable of providing ac...
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| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-08-01
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| Series: | Geochronology |
| Online Access: | https://gchron.copernicus.org/articles/7/335/2025/gchron-7-335-2025.pdf |
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| Summary: | <p>The U–Th and U–Pb dating methods are widely employed for radiometric dating of Pleistocene carbonates, such as speleothems and corals. The U–Th dating method has been progressively refined over recent decades, largely through advances in mass spectrometry, and is now capable of providing accurate and precise ages for carbonates as old as <span class="inline-formula">∼</span> 650 000 years under optimal circumstances. Similarly, the U–Pb method, traditionally restricted to dating pre-Quaternary materials, has been adapted in recent years for dating young carbonates. As a result, there is now substantial overlap in the applicable age range of these two dating methods but, thus far, only limited assessment of their consistency and relative performance when dating samples over this shared age interval.</p>
<p>In this study, we conduct a systematic comparison of the U–Th and U–Pb dating methods, focusing on a significant part of their overlapping age range (approximately 630–430 ka). We achieve this by dating speleothem (secondary cave mineral deposit) samples from Corchia Cave, central Italy, using both methods and evaluate their consistency and performance in terms of age precision and other factors. We adopt analytical approaches that employ state-of-the-art multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) measurement protocols, including a U–Th measurement protocol that utilises a Faraday cup equipped with a <span class="inline-formula">10<sup>13</sup></span> <span class="inline-formula">Ω</span> resistor to collect the low-abundance <span class="inline-formula"><sup>234</sup>U<sup>+</sup></span> and <span class="inline-formula"><sup>230</sup>Th<sup>+</sup></span> ion beams. This approach is particularly well-suited to dating samples approaching the limits of the U–Th method but also enables accurate determination of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi/><mn mathvariant="normal">238</mn></msup><mi mathvariant="normal">U</mi><msup><mo>/</mo><mn mathvariant="normal">235</mn></msup><mi mathvariant="normal">U</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="52pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="62b133e2ddbd9f6ca36fd78db1302347"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gchron-7-335-2025-ie00001.svg" width="52pt" height="15pt" src="gchron-7-335-2025-ie00001.png"/></svg:svg></span></span> ratios. Thus, as a secondary component of this study, we compare our <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi/><mn mathvariant="normal">238</mn></msup><mi mathvariant="normal">U</mi><msup><mo>/</mo><mn mathvariant="normal">235</mn></msup><mi mathvariant="normal">U</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="52pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="81e267774a2569df45cc421336a6df91"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gchron-7-335-2025-ie00002.svg" width="52pt" height="15pt" src="gchron-7-335-2025-ie00002.png"/></svg:svg></span></span> measurements with previously published speleothem values.</p>
<p>Our results demonstrate excellent agreement between the U–Th and U–Pb dating methods and suggest that both are capable of providing accurate and precise ages over this interval. We find that U–Pb age uncertainties are generally less predictable than U–Th age uncertainties but, on average, do not increase significantly over the interval considered. U–Th age uncertainties, on the other hand, tend to increase in a more predictable and approximately exponential manner. Additionally, U–Pb age uncertainties are highly dependent on the availability of sub-samples with a substantial spread<span id="page336"/> in parent/daughter ratios and/or highly “radiogenic” (i.e. very low inherited Pb) material. In our dataset, U–Pb isochron age precision surpasses that of U–Th precision at <span class="inline-formula">∼</span> 520 ka, although the exact crossover point is expected to vary for different sample types and depositional settings. Overall, these findings support the prospect of obtaining accurate and internally consistent U-series chronologies spanning the Middle Pleistocene. They also suggest that, for some carbonate samples, the U–Pb dating method may provide superior age precision to the U–Th method prior to the latter reaching its upper age limit.</p>
<p>Finally, our results show that most speleothems exhibit <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi/><mn mathvariant="normal">238</mn></msup><mi mathvariant="normal">U</mi><msup><mo>/</mo><mn mathvariant="normal">235</mn></msup><mi mathvariant="normal">U</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="52pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="799dcbfa9bb5158a64ae5406e891656e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gchron-7-335-2025-ie00003.svg" width="52pt" height="15pt" src="gchron-7-335-2025-ie00003.png"/></svg:svg></span></span> ratios consistent with global carbonate values and that these ratios typically deviate from the conventional value of 137.88, widely adopted in geochronology, in agreement with previous studies.</p> |
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| ISSN: | 2628-3697 2628-3719 |