日本地球惑星科学連合2018年大会

講演情報

[EE] ポスター発表

セッション記号 B (地球生命科学) » B-PT 古生物学・古生態学

[B-PT04] バイオミネラリゼーションと環境指標

2018年5月20日(日) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:豊福 高志(国立研究開発法人海洋研究開発機構)、北里 洋(国立大学法人東京海洋大学)、Bijma Jelle(アルフレッドウェゲナー極域海洋研究所、共同)、廣瀬 孝太郎(早稲田大学  大学院創造理工学研究科 地球・環境資源理工学専攻)

[BPT04-P02] Estimation of the practical partition coefficients of rare earth elements between limestone and seawater: discussion and application

*外山 浩太郎1,2寺門 靖高2 (1.金沢大学、2.神戸大学)

キーワード:石灰岩、希土類元素、古海水、分配係数

The rare earth element (REE) abundances in seawater are controlled by factors concerning different input sources (e.g., terrestrial input due to weathering, hydrothermal fluid) and scavenging process related to depth, salinity and oxygen levels (e.g., Piepgras and Jacobsen, 1992). In order to examine paleo-oceanic environments, the REE abundances in paleoseawater can be utilized as a clue, and estimated combining the REE data of limestone with the REE partition coefficients between limestone and seawater (Webb and Kamber, 2000).

In the present study, the practical REE partition coefficients between limestone and seawater were examined by comparing the data of some young limestones, the present-day biogenic carbonates and the experimentally obtained ones. The plausible REE partition coefficients for limestone were obtained from the REE data of Quaternary limestones and modern seawaters. The inferred partition coefficients range from 214 for La to 327 for Ce, and show almost flat REE pattern. To estimate the REE pattern in paleoseawater, these partition coefficients were applied to the REE data in some Quaternary to Silurian limestones from Japan. The obtained REE patterns in the paleoseawater show variable sizes of negative Ce anomalies and LREE depletions as seen in those of the modern seawaters. Such obtained REE patterns in the paleoseawaters suggest adequacy of the practical partition coefficients. Moreover, this study includes the examinations on the dissolution methods for limestones using acetic acid and HCl as well as on their residual materials. Furthermore, the effects of terrigenous materials to the REE abundances are discussed.

References: Piepgras and Jacobsen (1992) Geochim. Cosmochim. Acta 56, 1851–1862; Webb and Kamber (2000) Geochim. Cosmochim. Acta 64, 1557–1565.