Unusual open-system behaviour revealed by LA-MC-ICP-MS U–Th dating of coral and coralline algae bio-carbonates
This paper presents new U–Th ages obtained by LA-MC-CP-MS (laser ablation - multi-collector - inductively coupled plasma - mass spectrometry) on coral samples from a sedimentary core of the Tunis lagoon. The ages and calculated ($\mbox {}^{234}$U/$\mbox {}^{238}$U)$_{0}$ initial ratios, similar to t...
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Académie des sciences
2023-06-01
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| Series: | Comptes Rendus. Géoscience |
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| Online Access: | https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.5802/crgeos.221/ |
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| author | Condomines, Michel Bruguier, Olivier Hajji, Inès Zaara-Ben Mosbah, Chedia |
| author_facet | Condomines, Michel Bruguier, Olivier Hajji, Inès Zaara-Ben Mosbah, Chedia |
| author_sort | Condomines, Michel |
| collection | DOAJ |
| description | This paper presents new U–Th ages obtained by LA-MC-CP-MS (laser ablation - multi-collector - inductively coupled plasma - mass spectrometry) on coral samples from a sedimentary core of the Tunis lagoon. The ages and calculated ($\mbox {}^{234}$U/$\mbox {}^{238}$U)$_{0}$ initial ratios, similar to the seawater value for most corals demonstrate that they behaved as closed systems, or with only a very limited loss of $\mbox {}^{234}$U and $\mbox {}^{230}$Th. The ages (from 196 to 182 ka) show that the coral-rich sediments were deposited near the end of isotope stage 7. The precision on the dates is comparable to those of alpha-spectrometry (around 7.6% on average), but the possibility of multiple in-situ analyses offers other advantages. An example is provided by the very unusual open-system behaviour found in the outer Mg-calcite border of a coral branch, formed by a coralline red alga. The very high ($\mbox {}^{234}$U/$\mbox {}^{238}$U) and ($\mbox {}^{230}$Th/$\mbox {}^{238}$U) activity ratios (1.41 and 2.04, respectively) are tentatively explained using the model proposed by [Thompson et al., 2003], that involves continuous enrichment of $\mbox {}^{234}$Th ($\mbox {}^{234}$U) and $\mbox {}^{230}$Th recoil nuclei provided by an U-enriched source. We suggest that this source might come from the bio-mineral itself, in the form of organic matter originally involved in the encrusting algal activity, and eventually degraded with an almost complete U-loss. |
| format | Article |
| id | doaj-art-e44a2b870fc54f58b74a83249bc6a1b5 |
| institution | Kabale University |
| issn | 1778-7025 |
| language | English |
| publishDate | 2023-06-01 |
| publisher | Académie des sciences |
| record_format | Article |
| series | Comptes Rendus. Géoscience |
| spelling | doaj-art-e44a2b870fc54f58b74a83249bc6a1b52025-02-07T10:40:42ZengAcadémie des sciencesComptes Rendus. Géoscience1778-70252023-06-01355G220321410.5802/crgeos.22110.5802/crgeos.221Unusual open-system behaviour revealed by LA-MC-ICP-MS U–Th dating of coral and coralline algae bio-carbonatesCondomines, Michel0Bruguier, Olivier1https://orcid.org/0000-0002-4399-1903Hajji, Inès2Zaara-Ben Mosbah, Chedia3Géosciences Montpellier, Université de Montpellier, CNRS UMR 5243, FranceGéosciences Montpellier, Université de Montpellier, CNRS UMR 5243, FranceLaboratoire des Ressources Minérales et Environnement-Département de Géologie, Faculté des Sciences de Tunis, Université Tunis El Manar, TunisieLaboratoire des Ressources Minérales et Environnement-Département de Géologie, Faculté des Sciences de Tunis, Université Tunis El Manar, TunisieThis paper presents new U–Th ages obtained by LA-MC-CP-MS (laser ablation - multi-collector - inductively coupled plasma - mass spectrometry) on coral samples from a sedimentary core of the Tunis lagoon. The ages and calculated ($\mbox {}^{234}$U/$\mbox {}^{238}$U)$_{0}$ initial ratios, similar to the seawater value for most corals demonstrate that they behaved as closed systems, or with only a very limited loss of $\mbox {}^{234}$U and $\mbox {}^{230}$Th. The ages (from 196 to 182 ka) show that the coral-rich sediments were deposited near the end of isotope stage 7. The precision on the dates is comparable to those of alpha-spectrometry (around 7.6% on average), but the possibility of multiple in-situ analyses offers other advantages. An example is provided by the very unusual open-system behaviour found in the outer Mg-calcite border of a coral branch, formed by a coralline red alga. The very high ($\mbox {}^{234}$U/$\mbox {}^{238}$U) and ($\mbox {}^{230}$Th/$\mbox {}^{238}$U) activity ratios (1.41 and 2.04, respectively) are tentatively explained using the model proposed by [Thompson et al., 2003], that involves continuous enrichment of $\mbox {}^{234}$Th ($\mbox {}^{234}$U) and $\mbox {}^{230}$Th recoil nuclei provided by an U-enriched source. We suggest that this source might come from the bio-mineral itself, in the form of organic matter originally involved in the encrusting algal activity, and eventually degraded with an almost complete U-loss.https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.5802/crgeos.221/<i>In situ</i> U–Th dating of coralsLA-MC-ICP-MSOpen-system modelRecoil nucleiCoralline red algae |
| spellingShingle | Condomines, Michel Bruguier, Olivier Hajji, Inès Zaara-Ben Mosbah, Chedia Unusual open-system behaviour revealed by LA-MC-ICP-MS U–Th dating of coral and coralline algae bio-carbonates Comptes Rendus. Géoscience <i>In situ</i> U–Th dating of corals LA-MC-ICP-MS Open-system model Recoil nuclei Coralline red algae |
| title | Unusual open-system behaviour revealed by LA-MC-ICP-MS U–Th dating of coral and coralline algae bio-carbonates |
| title_full | Unusual open-system behaviour revealed by LA-MC-ICP-MS U–Th dating of coral and coralline algae bio-carbonates |
| title_fullStr | Unusual open-system behaviour revealed by LA-MC-ICP-MS U–Th dating of coral and coralline algae bio-carbonates |
| title_full_unstemmed | Unusual open-system behaviour revealed by LA-MC-ICP-MS U–Th dating of coral and coralline algae bio-carbonates |
| title_short | Unusual open-system behaviour revealed by LA-MC-ICP-MS U–Th dating of coral and coralline algae bio-carbonates |
| title_sort | unusual open system behaviour revealed by la mc icp ms u th dating of coral and coralline algae bio carbonates |
| topic | <i>In situ</i> U–Th dating of corals LA-MC-ICP-MS Open-system model Recoil nuclei Coralline red algae |
| url | https://comptes-rendus.academie-sciences.fr/geoscience/articles/10.5802/crgeos.221/ |
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