The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
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Volume 127, Issue 6
Displaying 1-4 of 4 articles from this issue
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Excursion Guidebook: 128th Annual Meeting of the Geological Society of Japan, 2021 Nagoya
Articles
  • Latest Pleistocene to Holocene calcareous microfossil assemblages from the Shinjima (Moeshima) Island and reconstruction of the paleoenvironments in the inner part of Kagoshima Bay, SW Japan
    Yuta Maehama, Kazuhiko Kano, Kimihiko Oki, Toshiaki Irizuki, Hiroki Ha ...
    2021 Volume 127 Issue 6 Pages 363-376
    Published: June 15, 2021
    Released on J-STAGE: September 30, 2021
    DOIhttps://doi.org/10.5575/geosoc.2021.0009
    JOURNAL FREE ACCESS
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    Latest Pleistocene and Holocene marine sediments that accumulated on the floor of the Aira Caldera are exposed on Shinjima Island, which was uplifted above the sea in 1780 by intrusion of dacite magma. In this study, fossil assemblages of benthic and planktonic foraminifers and ostracods from the marine sediments were analyzed to establish the palaeoenvironmental history of Kagoshima Bay. Initially fresh water lake, Aira Caldera became part of Kagoshima Bay shortly before 13,000 years ago, with a depth of > 100 m as sea level rose with global warming and a warm ocean current flowed into there. The caldera has remained open to the sea ever since, despite the growth and intermittent eruptions of Sakurajima volcano on the southern caldera rim. The population and number of species of calcareous microfossils were kept significantly lower during the period 13,000 to 8,000 years ago, possibly in response to the spreading of acidic water from progressive dissolution of the volcanic gas emitted from the Wakamiko Caldera in the northeastern part of the Aira Caldera. About 8,000 years ago, the warm ocean current strengthened, resulting in penetration of warm seawater to the caldera floor, which has a present water depth of 140 m.

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