Pre-nuclear level of 129I in Chinese loess-paleosol sections: A search for the natural 129I level for dating in terrestrial environments. (15th June 2018)

• Record Type: Journal Article
• Authors: Fan, Yukun; Zhou, Weijian; Hou, Xiaolin
• Is Part Of: Geochimica et cosmochimica acta. Volume 231(2018)
• Page Start: 64
• Page End: 72
• Publication Date: 2018-06-15
• Subjects: 129I -- Dating -- Initial 129I/127I ratio -- Loess -- AMS; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2018.04.014
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: Due to its long half-life (15.7 Myr), radioactive 129 I has great potential for dating geologic materials as old as 100 Myr. Thus, knowing the natural level of 129 I is crucial to dating applications. The initial ratio of 129 I/ 127 I in the ocean has been quantified by a number of researchers who have reached a consensus value. However, the applicability of 129 I dating in the terrestrial environment remains problematic because the lack of an initial 129 I/ 127 I value. In this work, samples of loess-paleosol sections from the Chinese Loess Plateau (CLP) were analyzed for 129 I/ 127 I, aiming to provide an initial 129 I/ 127 I ratio that can be adopted for dating purposes in terrestrial environments. A value of (2.0 ± 1.0) × 10 −11 for the 129 I/ 127 I ratio was found in two investigated loess-paleosol sections from Xifeng and Luochuan, China. This ratio is one order of magnitude higher than the initial value reported for the marine environment. Alteration of the natural initial 129 I in the investigated samples due to the downward migration of anthropogenic 129 I and by excess fissiogenic 129 I from uranium was not supported. Consequently, the 129 I/ 127 I ratio measured is considered to be a pristine value, and the difference from that in the marine systems is attributed to an isotopic dilution effect.