Quarterly Journal of Geography
Online ISSN : 1884-1252
Print ISSN : 0916-7889
ISSN-L : 0916-7889
Research Note
Radiocarbon Ages and Chemical Compositions of Cemented Samples Collected from Conglomeratic Beachrocks Developed at Iheya Island, North of Okinawa Island
Kunio OMOTO
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2024 Volume 76 Issue 2 Pages 79-90

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Abstract

A total of eleven samples of conglomeratic beachrocks that developed on the northwest and the southern coast of Iheya Island were collected and subjected to 14C dating. They were radiocarbon dated with AMS, and the calcium concentrations of the cemented deposits were analyzed with ICP-MS. The 14C ages of cements collected from the northern coast yielded formation ages of 3868±61 yr BP, 3867±61 yr BP, and 3185±59 yr BP, while the southern coast cements yielded formation ages of 3050±60 yr BP, 2216±62 yr BP, and 1824±56 yr BP. The younger 14C ages of cements over those of the fossil coral and shell samples indicate that the fossil coral and shell samples had been washed ashore prior to the beginning of the cementation process. The results of the elemental analyses of the three southern coast samples indicated 31.9% of average Ca wt concentration, while the three northern coast samples indicated 35.8% of Ca concentrations, which is equivalent to 79.8% and 89.5% of CaCO3, respectively. The high concentrations of Ca in the samples of the intertidal deposits led to the sedimentation allowing the formation of conglomeratic beachrock.

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© 2024 The Tohoku Geographical Association
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