| Autor: |
Condomines, Michel, Bruguier, Olivier, Hajji, Inès, Zaara-Ben Mosbah, Chedia |
| Jazyk: |
English<br />French |
| Rok vydání: |
2023 |
| Předmět: |
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| Zdroj: |
Comptes Rendus. Géoscience, Vol 355, Iss G2, Pp 203-214 (2023) |
| Druh dokumentu: |
article |
| ISSN: |
1778-7025 |
| DOI: |
10.5802/crgeos.221 |
| Popis: |
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. |
| Databáze: |
Directory of Open Access Journals |
| Externí odkaz: |
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