|Alternative Title||Grain-Size Distribution of detrital sediment in the Amami Sankaku Basin since Miocene and Its Provenance and Paleoclimate Implications|
|Place of Conferral||北京|
|Keyword||奄美三角盆地 中新世 晚更新世 粒度特征 古气候|
奄美三角盆地U1438A和U1438B孔碎屑组分粒度分析结果表明，其粒度频率分布曲线总体上呈现四峰态分布特征。U1438A孔约350ka以来沉积物中碎屑组分的平均粒径为13.1μm，粒径变化范围为0.04~160μm。砂、粉砂和黏土的平均含量分别为1.5%、74.7%和23.8%。利用Weibull分布函数对实测数据进行拟合分离出四个独立组分：（1）众数为0.25 μm的超细粒组分，粒径变化范围0.04-0.9μm，平均含量为0.96%，代表海洋自生粘土物质；（2）众数约3.5μm的细粒组分，粒径变化范围0.2-32μm，平均含量为29.2%，代表亚洲大陆来源的风尘物质；（3）众数约10 μm的粗粒组分，粒径变化范围0.3-90 μm，平均含量为54.4%；（4）众数约40 μm的超粗粒组分，粒径变化范围3-160 μm，平均含量为15.5%。粗粒和超粗粒组分主要来自奄美三角盆地周围的海脊和火山岛弧物质。U1438B孔约25Ma以来沉积物碎屑组分的平均粒径为14.8μm，粒径变化范围在0.04-160μm之间。砂含量平均3.3%，粉砂含量平均72%，粘土含量平均24.7%。用Weibull分布函数对粒度数据进行拟合，结果与U1438A孔类似。（1）众数为0.25 μm的超细粒组分，粒径变化范围0.04-0.9 μm，平均含量为1.1%，推测来源于海洋自生粘土；（2）粒度众数约3.5 μm的细粒组分，粒径变化范围0.2-32 μm平均含量为29.5%，主要来自于亚洲大陆风尘；（3）粒度众数约10.3 μm的粗粒组分，粒径变化范围0.3-90 μm,平均含量为60.3%；（4）粒度众数约32.5 μm的超粗粒组分，粒径变化范围3-160 μm，平均含量为9.1%。粗粒组分和超粗粒组分主要来自于奄美三角盆地周围海脊和岛弧的火山物质。
根据U1438B孔粒度参数1.8-6μm/14-22μm、0.9-3μm/>10μm以及细粒组分含量在垂向上的变化，将亚洲大陆风尘向奄美三角盆地的输入变化分为六个阶段：（1）25.8~23Ma，细粒风尘组分含量较高，粗粒组分相对较低。（2）23-17.3Ma，细粒风尘组风呈逐渐增加的趋势，而粗粒火山组分成逐渐减小的趋势。（3）17.3~13.8Ma，细粒风尘组分含量明显增加，而粗粒的火山组分明显降低。（4）13.8~9Ma，细粒风尘组分降低，粗粒火山组分增加。（5）9-2.5Ma，细粒风尘组分明显增加，而粗粒火山组分明显降低。（6）2.5Ma至今，风尘组分与火山组分均出现明显的波动。中新世以来，风尘组分的变化在构造尺度上响应了喜马拉雅-青藏高原的抬升和全球冰量增加所驱动的亚洲大陆干旱化加剧，以及东亚大气环流系统的增强。在轨道时间尺度上，U1438A孔碎屑组分粒度参数1.3~2.2μm/28~40 µm、0.9~3 µm/>10 µm表现为冰期高、间冰期低，与北太平洋风尘通量、亚洲大陆黄土堆积速率，以及黄土粒径所指示的冰期干旱和东亚季风/西风环流增强的气候变化一致，表明冰期由于亚洲大陆的干旱和季风/西风的增强，使得奄美三角盆地中细粒亚洲风尘组分的输入相对增加。因此细粒风尘和粗粒火山物质的比值可以作为亚洲大陆干旱化和大气环流增强的示踪指标。这些研究结果表明,奄美三角盆地沉积物的粒度组成可用于重建中新世以来东亚大陆干旱和大气环流演化历史。
|Other Abstract||The eolian dust from Asia continent is not only a major component of the deep sea sediments in the northwestern Pacific, but also an important proxyof palaeoclimate of Asian continent. Eolian dust in the deep-sea sediment of northwestern Pacific record the aridity history of dust source area (Asian continent) and the atmospheric circulation of East Asia, and plays a significant role in the evolution of the global climate and environment. Amami Sankaku Basin (ASB) is located in the northwestern Philippines Sea，with a relatively flat topography and lack of large-scale ocean currents. The sedimentary section is continuous since Miocene. Furthermore, ASB is influenced by the westerlies and the east Asian monsoon, therefore, ASB is an ideal place to research the eolian dust record and its palaeoclimate implications. The grain size composition in deep-sea sediments is an important indicator to tracing source and palaeoclimate. According to the characteristics of grain size frequency distribution, the component and provenance of eolian dust can be identified, and the grain size of eolian dust can be used to indicate the strength of wind.|
In this paper，the grain size composition of detritalsediments in hole U1438A and hole U1438B was analyzed. Both holes were collected from the ASBin the northwestern Philippine Sea during the International Ocean Discovery Program（IODP）Expedition 351. Differentindependent grain size components were separated by using Weibull function fitting, and the content of each grain-size copmonent is calculated, and the source of each grain-size component was analyzed. In addition， the environmentally sensitive size population in the detrital sedimentwas extracted by using the principle componenet analysis（PCA）and the grain size-standard deviation methods,and compared with the paleoclimate proxies. Based on above study, the input history of Asian dust to the ASB and the response of the different environmentally sensitive size populations to the Asian inland dry/wet condition and the atmospheric circulation model in tectonic and orbital time scale.
The grain size analysis of detrital sediment in hole U1438A and hole U1438B showed that the grain size distribution display a four-peak pattern. In hole U1438A，the mean grain size of the detrital sedimentover the past 350ka is approximately13.1μm, ranging from 0.04 to 160 μm. The average contents of sand, silt and clayareapproximately1.5%, 74.7% and 23.8% respectively. Four independent grain-size components were separated by using Weibull distribution function：(1) the ultra-fine component varies from 0.04 to 0.9 μm, with a size mode at approximately 0.25 μm and occupy about 0.96%, which may be genetically related to marine authigenetic clay; (2) the fine-grained fraction ranges from 0.2 to 32 μm, with a size mode at approximately 3.5 μm，and with an average content of 29.2%. This fraction is mainly derived from Asian dust; (3) the coarse-grained fractions varies from 0.3 to 90 μm, with a size mode at about 10μm, and with an average content of 54.4%; and (4) the ultra-coarse-grained fractions varies from 3 to 160 μm, with a size mode at about 40μm, and witn an average content of 15.5%. Both the coarse and ultra-coarse components represent volcanic materials which are mainly derived from the ridges and islands around ASB. In hole U1438B，the mean grain size of the detrital sedimentover the past 25Ma is approximately14.8 μm, ranging from 0.04 to 160 μm. The contents of sand, silt and clayare approximately3.3%，72% and 24.7% respectively. Four independent grain size components in hole U1438B were separated by using Weibull distribution function and the result is similar to hole U1438A. (1) The ultra-fine component varis from 0.04 to 0.9 μm, with a size mode at about 0.25 μm, and with an average content of 1.1%, which was derived from the authigenic clay;(2) the fine-grained fraction ranges from 0.2 to 32 μm, with a size mode at about 3.5 μm，and with an average content of 29.5%, which was mainly derived from Asian dust;(3) the coarse-grained fractions varies from 0.3 to 90 μm, with a size mode at about 10.3 μm, and an average content of 60.3%; and (4)the ultra-coarse-grained fractions varies from 3 to 160 μm, with a size mode at about 32.5 μm, and with an average of 9.1%. Both the coarse and ultra-coarse components represent volcanic materials which weremainly derived from the ridges and islands around ASB.
Based on the variation of 1.8-6μm/14-22μm ratio and 0.9-3μm/>10μmratio, and the content of fine-grained fractionin hole U1438B, the input history of Asian dust to ASB can be divided into six stages: (1) 25.8~23Ma，the fine-grained dust was high, and the coarse-grained volcanic material was low. (2) 23-17.3Ma，fine-grained dust increased gradually, and coarse-grained volcanic materials decreased. (3)17.3-13.8Ma, fine-grained dust increased significantly, and volcanic material decreased. (4)13.8~9Ma，fine-grained dust decrease and volcanic material increase. (5) 9-2.5Ma，fine-grained dust increased significantlyand volcanic materials decreased. (6) 2.5Ma to present, dust and volcanic material fluctuated significantly.On tectonic time scale,the variation of Asian dust respond to the enhanced aridity in the Asian continent and the strengthened atmospheric circulation forced by the uplift of Tibetan Plateau and the increase of global ice volume.On orbital time scale，the variation of the ratio of 1.3-2.2μm/28-40 μm and 0.9-3 µm/>10 µmin hole U1438Ashow higher value during glacial period than that during interglacial, which is also identical with the variation of the mass accumulation of eolian dust in the North Pacific and Chinese Loess Plateau, and grain size in Chinese Loess Plateau. We argue that the increase of eolian fraction was driven by the enhanced aridity of Asian continent and strengthened East Asia Winter Monsoon (EAWM)/westerly during glacial period.Therefore, the ratio of 0.9-3μm/>10 µm can be used as a proxy of the increased aridity and enhanced atmospheric circulation of Asian continent.
These results suggest that the grain size composition of the detrial sediment in the ASB canbe used to reconstruct the history of Asian aridity and atmospheric circulation since Miocene.
|周烨. 中新世以来奄美三角盆地碎屑沉积物粒度特征及其物源和古气候意义[D]. 北京. 中国科学院大学,2016.|
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