地球化学
Online ISSN : 2188-5923
Print ISSN : 0386-4073
ISSN-L : 0386-4073
51 巻 , 1 号
選択された号の論文の4件中1~4を表示しています
2015年度日本地球化学会奨励賞受賞記念論文
2011年度日本地球化学会奨励賞受賞記念論文
  • 黒田 潤一郎
    2017 年 51 巻 1 号 p. 15-28
    発行日: 2017/03/25
    公開日: 2017/04/03
    ジャーナル フリー
    In this paper I review some key studies on environmental changes during the Mesozoic and Cenozoic Eras, based upon radiogenic isotopic records of heavy elements such as osmium (Os) and lead (Pb). The Earth’s surface has experienced extreme environment events like oceanic anoxic event and/or salinity crisis. Radiogenic isotopic records of marine sediments give us key clues for understanding changes in 1) fluxes of (un)radiogenic isotope species from the mantle or extraterrestrial sources, and 2) water exchange ratios between basins. In the first part, I show a line of evidence of Os and Pb isotopic records of Cretaceous marine sediments that suggest rapid and massive eruptions associated with emplacement of large igneous provinces (LIPs) occurred simultaneously with oceanic anoxic events (OAEs). This implies that a deep‒rooted mantle process drives oceanic environmental extremes. In the second part I show Os isotopic records of Mediterranean sediments of Miocene‒Pliocene time interval that show history of water exchange between Mediterranean basins and the Atlantic Ocean. Mediterranean sediments show a clear drop of Os isotopic ratios during the Messinian Salinity Crisis (MSC) at the end of Miocene, when a huge amount of evaporites was precipitated in the Mediterranean marginal and deep basins. The change in Os isotopic ratios supports the idea that water exchange rate between Atlantic and Mediterranean was decreased substantially, about one thirtieth during the MSC.
企画総説「地球化学の最前線」
  • 鈴木 勝彦, 賞雅 朝子, 渡慶次 聡
    2017 年 51 巻 1 号 p. 29-44
    発行日: 2017/03/25
    公開日: 2017/04/03
    ジャーナル フリー

    The core and mantle are the main constituents of the Earth, which constrain the physical properties, geochemical and isotopic compositions of the bulk Earth. However, the geochemical composition of the core has not been well constrained, regardless of its importance for better understanding of the geochemical evolution of the Earth. Here we review the current hypotheses of interaction between the mantle and core, and the evolution of the early Earth, and discuss the unsolved problems.

    Several radiogenic isotopes such as 186Os–187Os, 182W and 142Nd have been used to elucidate the early evolution of the Earth. In particular, excess of 182W found in the Archean mantle-derived rocks has been ascribed to the core formation and the subsequent “late veneer.”

    Heavy element stable isotopes such as cupper and platinum and abundances of highly siderophile elements such as platinum group elements could provide critical information on core segregation and the core-mantle interaction. These chemical data are recently linked closely with the high-pressure and high-temperature experiments, numerical calculations and present seismic observations. However, interpretation of the data is still on debate, which will be also discussed in this review.

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