巻号一覧
39 巻 (2005)
- 4 号 p. 173-
- 3 号 p. 91-
- 2 号 p. 65-
- 1 号 p. 1-
39 巻, 2 号
選択された号の論文の3件中1～3を表示しています
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総説
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田中 万也2005 年 39 巻 2 号 p. 65-72
発行日: 2005/05/30
公開日: 2017/01/21
ジャーナル フリーThe seamount-type limestone formed on the top of seamount away from continents, preserves chemical features of ancient seawater. Chondrite-normalized rare earth element (REE) abundance patterns for Japanese Permian seamount-type limestones show seawater-like characteristics of convex tetrad effects and Y fractionation from Ho as well as negative Ce and Eu anomalies. Apparent REE partition coefficients between marine limestone and present-day seawater suggest that REE fractionation and enrichment occurred when seawater REEs were incorporated into limestone. Laboratory REE partition experiments between calcite and aqueous solution have been carried out in order to elucidate the incorporation process. Experimentally determined REE partitioning patterns show concave tetrad effect variations and Y fractionation from Ho. Combining REE analyses of ancient limestone samples and the experimental partition coefficients, it is possible in principle to estimate REE abundances in ancient seawater. REE abundances in Permian seawater estimated by this new method quite resemble those in the present-day seawater samples in chondrite-normalized patterns.抄録全体を表示PDF形式でダウンロード (913K)
2004年度日本地球化学会奨励賞受賞記念論文
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丸岡 照幸2005 年 39 巻 2 号 p. 73-88
発行日: 2005/05/30
公開日: 2017/01/21
ジャーナル フリーEnvironmental perturbations at mass extinction events are reviewed based on isotopic compositions of sulfur and carbon. Large negative excursions in marine carbonate δ13C are commonly associated with mass extinctions. The δ13C excursion after the Cretaceous-Teriary (K-T) boundary event has been linked to a collapse of the vertical carbon isotope gradient. As a vertical carbon isotope gradient is a function of photosynthetic productivity, the collapse of the isotope gradient implies cessation of photosynthesis. Some mechanisms for the decrease in sunlight after the K-T impact event were proposed so far, such as dust cloud, sulfate aerosol, and soot from global wildfires; however there is no consensus for the cause of the cessation of photosynthesis. Both two major events that can initiate mass extinctions, i.e., bolide impact and intense volcanic activity, should release sulfur-bearing gases into the atmosphere. Such gases should be converted to sulfate aerosol and, eventually, sulfuric acid rain, which raises sulfate concentration in freshwaters. Increase of sulfate concentration in freshwaters enhances accumulation of sulfide produced by sulfate-reducing bacteria. Actually, sulfide enrichments were observed in the sedimentary rocks from the terrestrial K-T and Permian-Triassic (P-T) boundary sections. The duration of the sulfide enrichments can be used for the discussion of the causes of the mass extinction events.抄録全体を表示PDF形式でダウンロード (2062K)
博士論文抄録
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本郷 やよい2005 年 39 巻 2 号 p. 89-
発行日: 2005/05/30
公開日: 2017/01/21
ジャーナル フリーPDF形式でダウンロード (152K)
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