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羽地 俊樹, 工藤 崇, 菅森 義晃, 金山 恭子2025 年 131 巻 1 号 p. 39-44
発行日: 2025/03/27
公開日: 2025/03/27
ジャーナル フリーWe propose the name ‘Obaneo Lava’ for Pliocene mafic volcanic rocks at Cape Haneobana, northeastern Tottori Prefecture. We undertook a geological survey of these rocks, measured their whole-rock major element compositions, and subjected them to plagioclase K‒Ar dating. The mafic volcanic rocks comprise at least three lava flows of clinopyroxene–olivine basalt and olivine basalt. Their chemical composition indicates they are alkali basalt. Their uniform compositions and the lack of evidence for dormancy indicate that they were derived from continuous volcanic activity. The plagioclase K‒Ar age of 4.28±0.11 Ma for the upper lava is older than the ages of surrounding Pliocene volcanic units (i.e., the Inabayama Basalt and rocks of Hamasaka Volcano). The Obaneo Lava is distinguished from these surrounding rocks on the basis of chemical composition and radiometric age.
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箱岩 寛晶, 山田 来樹, 長田 充弘, 小北 康弘, 丹羽 正和2025 年 131 巻 1 号 p. 31-38
発行日: 2025/03/27
公開日: 2025/03/27
ジャーナル フリー
J-STAGE DataTo increase the number of radiometric dates of Jurassic accretionary complexes in Japan, we conducted zircon U–Pb dating of a sandstone sample from the Sawando Complex in the eastern Mino Terrane using a multi-collector inductively coupled plasma mass spectrometer coupled with a multi-spot femtosecond laser ablation system (msfsLA-MC-ICP-MS). Thirty two concordant dates from 72 analyzed grains are divided into seven groups: 1920–1850 Ma (Paleoproterozoic), 1110 Ma (Mesoproterozoic), 492 Ma (Cambrian), 442 Ma (Silurian), 262–260 Ma (Permian), 250–218 Ma (Triassic), and 186–168 Ma (Jurassic). The youngest single grain date (YSG) is 168.0±6.9 Ma (±2σ). The YSG is within uncertainty of radiolarian ages reported in previous studies (late Callovian to middle Oxfordian).
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羽田 裕貴, 本郷 美佐緒, 水野 清秀, 納谷 友規, 中谷 是崇, 中島 礼, 西山 賢一2025 年 131 巻 1 号 p. 11-30
発行日: 2025/03/27
公開日: 2025/03/27
ジャーナル フリー
J-STAGE Data徳島平野地下に分布する更新統は，堆積盆の発達史を解明する上で重要な鍵層となるが，その年代や堆積環境については明らかになっていない．本稿では，テフラ，泥質堆積物の懸濁液の電気伝導度（EC）およびpH分析，珪藻化石，花粉化石を用いることで，徳島平野南東部沿岸地域における地下更新統の汽水～海成層を認定し，年代層序を構築した．既存ボーリングコア試料から見出した4枚のテフラをG9L，鳴尾浜IV（Nh-IV），加久藤（Kkt），阿多鳥浜（Ata-Th）テフラに対比した．また，EC，珪藻化石，花粉化石層序に基づき，海洋酸素同位体ステージ（MIS）11～5eの高海水準期に相当する5枚の汽水～海成層を認定した．MIS 11，9，5eに相当する海成層は平野北部からも報告されており，徳島平野で広く追跡できると考えられる．
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高下 裕章, 村上 文敏, 大塚 宏徳, 中西 諒, 三澤 文慶2025 年 131 巻 1 号 p. 1-9
発行日: 2025/03/27
公開日: 2025/03/27
ジャーナル フリー
J-STAGE DataSub-bottom profilers (SBPs) are essential tools for investigating geological structures beneath sea or lake floors. SBPs are widely deployed because they do not interfere with other onboard survey methods such as sediment sampling and seismic profiling. However, SBP data are underutilized because they are stored in multiple different proprietary formats and commercial software is expensive. To improve this situation, we initially targeted a SyQwest Bathy-2010 installed on the R/V Hakuho Maru (JAMSTEC) and developed a procedure for SBP data visualization. This note aims to be a practical manual, with step-by-step guidance and screenshots, allowing interested users to easily process SBP data. The procedure involves three key steps: onboard data conversion, running a Python script, and creation of an index map. To ensure accessibility, the workflow has been tailored for free platforms, including Google Colab, enabling users with limited technical resources or programming experience to process SBP data effectively. We hope this effort democratizes the use of SBP data and facilitates its broader application in marine geological research.
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