The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 120 , Issue 6
Showing 1-3 articles out of 3 articles from the selected issue
  • Junichiro Kuroda, Toshihiro Yoshimura, Hodaka Kawahata, Francisco J. J ...
    2014 Volume 120 Issue 6 Pages 181-200
    Published: June 15, 2014
    Released: November 12, 2014
    The Mediterranean Sea experienced an extraordinary event at the end of the Miocene, when massive evaporites formed rapidly between 5.97 and 5.33 Ma. This event is referred to as the Messinian Salinity Crisis (MSC), which formed the youngest huge salt mass (106 km3), corresponding to ~ 6% of the total sea salt in the world ocean. Although various scenarios have been proposed to explain the MSC, no general consensus has been achieved. The controversy can be summarized as the crisis being either wet or dry; i.e., either the major portion of the evaporites formed under subaqueous conditions or deep basins dried up to form a Mediterranean desert. Here we review 1) the present-day formation of evaporites in an active salt pond in Sicily, and 2) the basic context of evaporite geology/sedimentology in Sicily, where a deep-sea sedimentary succession that spans the MSC is now preserved on land. Evaporites forming in the presentday saltern in Sicily provide crucial information on how sedimentary structures in gypsum, halite, and potash salts develop through evaporation, which is useful for understanding evaporite depositional environments in the geological past. The Messinian evaporite succession in Sicily is divided into i) the Primary Lower Gypsum unit in peripheral settings, and ii) the Resedimented Lower Gypsum unit, iii) a thick halite unit, and iv) the Upper Gypsum unit that formed in deep basin settings (the Caltanissetta basin). The thick halite appears to have formed simultaneously with or slightly after the Resedimented Lower Gypsum (the second stage of the MSC). The Upper Gypsum unit overlies the Resedimented Lower Gypsum and halite units, which formed during the late stages of the MSC. The Messinian evaporite units are covered by Pliocene hemipelagic sediments; the base of these sediments marks the Zanclean flooding. The lithology of the MSC deposits in Sicily clearly shows that most of the evaporites formed under subaqueous conditions, and only one interval in the halite unit indicates subaerial exposure.
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  • Masaki Matsukawa, Makiko Fukui, Yutaka Ogawa, Takeshi Tago, Kazuto Koa ...
    2014 Volume 120 Issue 6 Pages 201-217
    Published: June 15, 2014
    Released: November 12, 2014
    The Jinzu Group, distributed in the border area between Toyama and Gifu prefectures, can be divided into nine lithofacies that in turn can be grouped into five lithofacies assemblages reflecting deposition in alluvial fan, distal fan, and flood-plain depositional environments. These assemblages are assigned to three formations in the Jinzu Group, interpreted as follows: (1) the Ioridanitoge Formation was deposited in an alluvial fan environment along the basin margin; (2) the Inotani Formation was deposited in fluvial and flood-plain environments; and (3) the Shiroiwagawa Formation was also deposited in flood-plain environments. Fining-upward and fining-basinward trends are evident throughout the Jinzu Group, reflecting ongoing subsidence in the inland part of the basin. A northwestward shift in the location of the Jinzu basin is easily interpreted through thickness and paleoenvironment analyses of the Jinzu Group. The shift is interpreted to have been related to the juxtaposition of Jurassic to earliest Cretaceous accretionary complexes along the eastern margin of the Asian continent during the Hauterivian (Early Cretaceous).
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