Past 250 ka Volcanic Activities in Southwest Ontong Java Plateau, West Equatorial Pacific: Evidences from Element Geochemistry
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摘要: 赤道西太平洋作为全球变化关键海区, 其沉积物组成对揭示古海洋、古环境变化具有重要意义.本文利用元素地球化学分析方法, 对赤道西太平洋翁通爪哇海台WP7站位(3°56'S, 156°00'E)柱状沉积物进行了研究.结果显示元素Al、Na、K、Be、Ga、Rb、Zr、Nb、Cs、Ce、Hf、Ta、Th、Fe和Mg经Ti标准化后, 无法用单独的碎屑物质来源解释, 而是分别同偏酸性和偏基性火山灰相关, 指示了249.5 ka以来, 共发生了4次偏酸性火山灰输入(2.5~6.4 ka、57.0~61.2 ka、79.7~88.4 ka和193.7~249.5 ka)和4次偏基性火山灰输入(19.8~24.4 ka、50.0~62.6 ka、143.2~150.5 ka和160.8~171.1 ka).火山灰的输入使沉积物元素地球化学组成发生了相应变化, 也使沉积物中碳酸钙产生了稀释效应, 从而沉积物颜色相应加深, 沉积速率显著提高.Abstract: West equatorial Pacific is the key area of global change, and are important to paleo-ocean and paleo-environment reconstruction. Based on elements geochemistry of sediments of core WP7, recovered from southwest Ontong Java plateau, 4 acidic tephra inputs (2.5-6.4 ka, 57.0-61.2 ka, 79.7-88.4 ka, and 193.7-249.5 ka) and 4 mafic tephra inputs (19.8-24.4 ka, 50.0-62.6 ka, 143.2-150.5 ka, and 160.8-171.1 ka) were deciphered after normalization of Al, Na, K, Be, Ga, Rb, Zr, Nb, Cs, Ce, Hf, Ta, Th, Fe and Mg to Ti. The input of tephra changed the sediment constituents, diluted the biotic CaCO3, darkened the sediment color, and raised the sedimentation rate.
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Key words:
- elements /
- geochemistry /
- tephra /
- sediments /
- west equatorial Pacific /
- Ontong Java plateau
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图 1 赤道西太平洋翁通爪哇海台附近地形及WP7站位(3°56′S,156°00′E)
水深据GEBCO(http://www.gebco.net/);构造特征据Hall(2002);底图通过gridview软件制作(https://www.bodc.ac.uk/products/software_products/gebco_grid_display/)
Fig. 1. Bathymetry of Ontong Java plateau and nearby area in west equatorial Pacific, and location of core WP7 (3°56′S, 156°00′E)
图 3 WP7站位偏酸性火山物质相关元素与Ti比值
竖线表示PAAS(Taylor and McLennan, 1985)中元素与Ti比值
Fig. 3. The content ratio of acidic tephra related elements and some magor elements to element Ti in core WP7
图 4 WP7站位偏基性火山物质相关元素与Ti比值
竖线表示PAAS(Taylor and McLennan, 1985)中元素与Ti比值
Fig. 4. The content ratio of acidic tephra related elements and CaCO3 to element Ti in core WP7
表 1 WP7沉积物元素分析方法精确度
Table 1. Precision of element content analysis in core WP7
元素 测量次数 最大值 最小值 平均值 标准偏差 相对标准偏差 TiO2(%) 19 0.2 0.2 0.2 0.0 5.7 Al2O3(%) 19 7.8 6.2 7.1 0.4 5.7 K2O(%) 19 1.4 1.1 1.3 0.1 6.2 Na2O(%) 19 2.9 2.2 2.6 0.2 6.5 TFe2O3(%) 19 2.2 1.8 2.0 0.1 5.9 MgO(%) 19 1.0 0.8 0.9 0.1 5.6 Be(μg/g) 19 0.6 0.4 0.5 0.1 12.1 Ga(μg/g) 19 8.6 7.2 8.1 0.4 4.7 Rb(μg/g) 19 22.8 18.7 21.2 1.0 4.9 Zr(μg/g) 19 41.9 34.4 39.3 2.2 5.7 Nb(μg/g) 19 3.0 2.4 2.8 0.1 5.2 Cs(μg/g) 19 0.6 0.5 0.6 0.0 4.8 Ce(μg/g) 19 13.0 10.8 12.1 0.5 4.2 Hf(μg/g) 19 1.2 1.0 1.1 0.1 5.0 Ta(μg/g) 19 0.2 0.2 0.2 0.0 5.7 Th(μg/g) 19 1.0 0.9 1.0 0.0 4.1 -
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