相模層群長沼層(中部更新統)産の介形虫化石群に基づく古環境解析 Paleoenvironmental analysis from fossil ostracod assemblages of the Middle Pleistocene Naganuma Formation in the Sagami Group, central Japan

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Abstract

<p>本研究は,神奈川県に分布する相模層群長沼層産の海生介形虫化石群に基づき,海洋酸素同位体ステージ15(MIS 15)の約60万年前の古環境(水深,水温)を現生アナログ法(MAT)を用いて推定した.その結果,長沼層の古環境は,現在の瀬戸内海などの西南日本沿岸の水深25~41 mの海域に,最も類似することが明らかになった.これらの西南日本沿岸域の水温値 (夏:16~28℃,冬:6~11℃)を,現在の相模湾の水温データと比較したところ,夏の水温は水深30 m以浅では少なくとも2℃ほど高いが,40 m付近では現在とほぼ同じか2℃ほど低く,冬の水温は40 m以浅で少なくとも2℃ほど低いことが明らかになった.本研究は約60万年前(MIS 15)の日本列島沿岸浅海域における古水温の変動を,定量的に推定した初の研究例である.</p>

<p>This study estimates paleoenvironmental changes in water depths and temperatures from approximately 0.6 Ma during the marine oxygen isotope stage (MIS) 15 of the Middle Pleistocene along coastal Japan. We used the modern analog technique (MAT), which is based on ostracod assemblages from the Naganuma Formation in the Sagami Group of Kanagawa Prefecture in central Japan. The analysis revealed that the Naganuma Formation was deposited in the shallow-marine environment at paleo-water depths of 25–41 m, similar to current depths of southwestern Japan coastal areas such as the Setonaikai Sea. The estimated summer paleo-water temperature (ca. 28℃) was approximately 2℃ higher than current Sagami Bay water temperatures at depths of shallower than 30 m. The estimated temperatures were also similar to or slightly lower (~2℃) than current summer temperatures in Sagami Bay at depths of 40 m. The estimated winter paleo-water temperatures (6–11℃) were slightly lower (~2℃) than current Sagami Bay temperatures at depths of shallower than 40 m. This study reports for the first time fluctuations in paleo-water temperature estimates quantitatively from 0.6 Ma during the MIS 15 along coastal Japan.</p>

Journal

  • BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN

    BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN 70(1-2), 5-16, 2019

    National Institute of Advanced Industrial Science and Technology, Geological Survey of Japan

Codes

  • NII Article ID (NAID)
    130007631567
  • NII NACSIS-CAT ID (NCID)
    AA11587519
  • Text Lang
    ENG
  • ISSN
    1346-4272
  • NDL Article ID
    029727362
  • NDL Call No.
    Z15-177
  • Data Source
    NDL  J-STAGE 
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