Earth Science Frontiers ›› 2022, Vol. 29 ›› Issue (4): 73-83.DOI: 10.13745/j.esf.sf.2022.1.8

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Provenance and paleoclimatic significance of clay minerals from Izu-Ogasawara Ridge since Pliocene

YANG Jiayi1,3(), JIANG Fuqing1,2,3,4,*(), YAN Yu1,3, ZHENG Hao1,3, CHANG Fengming1,2,3,4   

  1. 1. Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
    2. Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China
    3. University of Chinese Academy of Sciences, Beijing 100049, China
    4. Pilot National laboratory for Marine Science and Technology(Qingdao), Qingdao 266061, China
  • Received:2021-09-20 Revised:2021-11-21 Online:2022-07-25 Published:2022-07-28
  • Contact: JIANG Fuqing

Abstract:

The composition and mineralogical characteristics of clay minerals in sediments from ODP Hole 782A, Izu-Ogasawara Ridge since the Pliocene were analyzed. According to the results, the clay minerals were mainly composed of illite (average 42%) and smectite (average 42%), with moderate chlorite (average 14%) and minor kaolinite (average 2%). The low crystallinity (average 0.25°Δ2θ) and chemical index (average 0.31) of illite indicated the mineral was mainly from a cold, dry environment. By comparing clay mineralogy and clay mineral assemblages and contents between ODP Hole 782A and potential source areas, we argue that smectite is mainly derived from island arc volcanic materials around Izu-Ogasawara Ridge, and that illite, chlorite and kaolinite are mainly from aeolian dust of the Asian continent. The (illite + chlorite)/smectite ratio increased overall since the Pliocene and varied in three stages: 5.3-3.6 Ma, 3.6-1.6 Ma and 1.6-0 Ma. The variations are roughly synchronized with the global cooling recorded by deep sea δ18O, the enhanced aridity in Asia recorded by dust flux in ODP Hole 885/886 in North Pacific, the sedimentary rate of Lingtai loess, and the illite/smectite ratio in IODP Site U1430 in Japan Sea. These evidences suggested that the (illite + chlorite)/smectite ratio in ODP Hole 782A is sensitive to global cooling and aridity in Asia. Since the Pliocene, the (illite + chlorite)/kaolinite ratio oscillates between high and low in accordance with the high/low changes of magnetic susceptibility of Lingtai loess. As the loess magnetic susceptibility records the dry/wet changes in Asia, we argue that the (illite + chlorite)/kaolinite ratio in ODP Hole 782A is sensitive to the paleoclimate changes in Asian inland, and, therefore, can be used as a reliable proxy of the dry/wet changes in Asia.

Key words: Izu-Ogasawara Ridge, clay minerals, provenance, Pliocene

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