Chemostratigraphy of deep-sea sediments in the western North Pacific Ocean: Implications for genesis of mud highly enriched in rare-earth elements and yttrium
Chemostratigraphy of deep-sea sediments in the western North Pacific Ocean: Implications for genesis of mud highly enriched in rare-earth elements and yttrium
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DOI：
10.1016/j.oregeorev.2020.103392
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发表时间：
2020-04
影响因子：
3.3
通讯作者：
E. Tanaka;Kentaro Nakamura;K. Yasukawa;K. Mimura;K. Fujinaga;K. Iijima;T. Nozaki;Y. Kato
中科院分区：
文献类型：
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作者：
E. Tanaka;Kentaro Nakamura;K. Yasukawa;K. Mimura;K. Fujinaga;K. Iijima;T. Nozaki;Y. Kato
深海沉积物中含有高浓度的稀土元素和Y(REY)，被称为富REY泥浆，广泛分布于太平洋和印度洋。在北太平洋西部南岛周围的日本专属经济区内发现了总稀土(ΣRey)浓度非常高的泥层(>；5000ppmΣRey和~1000ppm重稀土元素)。然而，在几十公里的尺度上，沉积物柱中高REY富集层的数量、出现这些层的深度以及这些层的最大ΣRey值是相当不同的。控制稀土富集层的形成和分布的因素仍然知之甚少。在这里，我们对南岛专属经济区内采集的49个活塞岩心的1240个沉积物样品进行了化学地层学研究。对块状沉积物地球化学的详细研究表明，除Rey峰(>；2000ppm)外，样品还可分为五个单元(单元I至单元V)，其中多元素亚空间显示出独特的组成数据结构。这些单位在所研究的岩心中以一致的地层序列出现。这一化学地层学显示，高REY富集层至少形成了三次，并且几乎所有这些层在沉积过程中都伴随着侵蚀。我们的结果表明，深海沉积物的侵蚀事件在高稀土泥层的形成中起着重要作用。
Deep-sea sediments containing high concentrations of rare-earth elements and yttrium (REY), termed REY-rich mud, are widely distributed in the Pacific and Indian oceans. Mud layers with very high total REY (ΣREY) concentrations (>5000 ppm of ΣREY with ~1000 ppm of heavy rare-earth elements) have been discovered within the Japanese exclusive economic zone surrounding Minamitorishima Island, western North Pacific. The number of highly REY-enriched layers in the sediment column, the depths at which the layers occur, and the maximum ΣREY values of the layers are, however, quite variable on a scale of several tens of kilometers. The factors controlling the formation and distribution of the REY-enriched layers are still poorly understood. Here, we produce a chemostratigraphic scheme for 1240 sediment samples from 49 piston cores collected within the Minamitorishima exclusive economic zone. Detailed investigation of the bulk sediment geochemistry, which exhibits distinctive compositional data structures in multi-elemental subspaces, revealed that the samples can be categorized into five units (Units I to V) in addition to REY peaks (>2000 ppm). These units appear in a consistent stratigraphic sequence in the studied cores. This chemostratigraphy reveals that highly REY-enriched layers formed at least three times, and that almost all of these layers were accompanied by erosion during deposition. Our results suggest that erosion events of deep-sea sediment play an important role in the formation of highly REY-rich mud layers.