並列タイトル等日本海堆積物の粒度別粉末X線回折プロファイルの統計的端成分分解に基づくアジア起源風成塵供給源別定量とその時代変化の復元
一般注記Japan sea sediments consist of various detrital materials of eolian and riverine origin. Understanding the provenance of eolian dust is vital for reconstructing the variability of wind patterns and monsoons in the past. A total of 180 samples were collected from the Hole 1425D, which had 370 m in length and 9.69 Ma geological age. Grain size separation was conducted to evaluate the mineral composition in silt (>4 μm) and clay (<4 μm) fractions by X-ray diffractometer (XRD). The mineral composition suggests the source variabilities in silt and clay fractions, which could be interpreted as provenance shifts occurring in 8 and 2.7 Ma. Parallel factor analysis (PARAFAC) was applied to decompose X-ray diffractograms into individual subcomponents to identify the sources and quantify their contributions. A six-end-member PARAFAC model was established, and 3 Asian dust sources, Taklimakan (EM1), Gobi (EM2) and Ordos (EM5); a riverine source from the Japanese islands (EM3); and two biogenic sources, diatomaceous (EM4) and Opal-CT (EM6), were identified, and their contributions were quantified. Based on the provenance unmixing by PARAFAC, new and complete eolian accumulation rates from Taklimakan, Gobi and Ordos were reconstructed at Integrated Ocean Drilling Program (IODP) Site U1425 in the Japan Sea. In the late Miocene, the high mass accumulation rate (MAR) of riverine input from the Japan Islands reflected a strong summer monsoon during 9.7-8 Ma. Provenance shift occurred between 8 and 7 Ma from riverine source to eolian for a short period, which implied that Asian aridification was intensified at about 8 Ma, coinciding with the late Miocene cooling. Eolian flux increased dramatically in Pleistocene to the maximum of 3.1 g/cm2/kyr, and the Gobi Desert, Taklimakan Desert and Ordos Plateau were the three main contributors of eolian flux to the Japan Sea. The contribution of Taklimakan source to the Japan Sea ranged from 10 to 50% and the dust flux increased gradually in the Pleistocene to the highest of 1.67 g/cm2/kyr at 0.29 Ma. Lower flux occurred in the Late Miocene to Pliocene of <0.5 g/cm2/kyr. MAR of Taklimakan eolian in silt fraction was generally higher than clay fraction. The contribution of Gobi dust to the Japan Sea has ranged from 20-60% since 10 Ma. The highest MAR of 1.7 g/cm2/kyr occurred in 0.96 Ma and the lowest in Pliocene. MAR of Gobi dust in clay fraction was higher than silt fraction from 9.24 to 0.73 Ma. The results show that Taklimakan dust is dominated by the silt fraction, while Gobi dust is dominated by the clay fraction, and they are controlled by the relative contributions of different pathways of dust transport, such as the westerly winds and East Asian winter monsoon (EAWM). Clay-size dust from the Gobi Desert increased during three periods, late Miocene global cooling (LMGC), intensification of Northern Hemisphere Glaciation (iNHG), and mid-Pleistocene Transition (MPT), which reflected increased EAWM winds associated with global cooling and glaciation. Taklimakan became the major dust contributor to the Japan Sea sediments during the warmer climate periods in the latest Miocene to early Pliocene and the Late Pleistocene, where westerly wind activity dominated eolian transport. Dust from the Ordos Plateau increased greatly from 0.95-0.85 Ma due to enhanced Asian aridification since 2 Ma in Northwest China.
(主査) 准教授 入野 智久, 教授 鈴木 光次, 教授 山本 正伸, 准教授 関 宰, 准教授 山下 洋平, 教授 沢田 健 （大学院理学研究院）
環境科学院（地球圏科学専攻）
コレクション（個別）国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
受理日（W3CDTF）2023-03-02T11:18:11+09:00
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