【作者】 刘焱光；

【导师】 吴世迎； 石学法；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2005， 博士

【摘要】 深入揭示冰期/间冰期气候旋回中冲绳海槽沉积物记录的海洋环境、物质来源和通量变化及其对古气候和海平面变化的响应信息,是该区古海洋学研究的前沿课题。 根据对冲绳海槽4个岩芯的沉积物粒度特征、元素地球化学和Sr-Nd同位素组成的细致分析,结合AMS¹⁴C测年数据,利用地球化学指标的因子分析、粒度组分的端员模拟分析和二端员定量分析等计算方法,围绕冲绳海槽地区近4万年以来的火山喷发事件、物质来源、陆源物质通量的变化规律及其对气候变化的响应等问题进行了探讨。结果表明,冲绳海槽沉积物的硅酸盐碎屑是由陆源物质（主要为长江输运的中国大陆物质）和火山源物质（火山玻璃和浮岩碎屑）组成的混合物,风尘物质所占比例较小。虽然冲绳海槽北部和中部的物源供应和沉积环境有明显差异,但陆源沉积物中对环境变化敏感粒度组分的众数值却几乎一致,都在7.81μm左右,证明了冲绳海槽沉积物中陆源物质主要由中国大陆河流输运,源区气候和海平面变化是制约陆源物质通量的主要因素。 冲绳海槽中部35cal.kaBP以来的陆源物质通量变化与气候变化关系密切,表现出暖期低冷期高的特点。且在末次盛冰期低海平面时,陆源物质通量高而稳定,长江和东亚冬季风输运的粘土粒级碎屑物质增多。在海平面上升速度较快的冰消期,冲绳海槽中部陆源物质的通量比末次盛冰期还高,说明源区气候和海平面变化在控制冲绳海槽地区陆源物质通量的过程中还可能相互牵制。 冲绳海槽周边的火山活动在气候温暖期时最强,火山物质的影响几乎贯穿整个全新世地层。氧同位素3期以来,九州岛和冲绳海槽的三次大规模火山喷发作用在海底沉积物中形成了数层火山碎屑沉积。沉积物中Si、Na、Zr等元素含量的变化可很好地显示火山物质输入的变化。在冲绳海槽北部和中部的岩芯中火山灰层的分布有很好的对应关系,其对应的喷发年代分别为7563、25000和42000 cal.a BP左右,其中最近的两次分别对应了K-Ah和AT火山喷发事件。42000 cal.a BP左右的火山喷发事件（本文称之为Okinawa Ⅰ）目前未见报道,其在DGKS9603岩芯中的粒度组成明显与K-Ah和AT火山灰不同,表明它们火山物质来源的不同。 利用粒度组分的端员模拟方法,从沉积物硅酸盐碎屑<63μm部分的粒度数据中提取出具有物源指示意义的两个端员组分,并计算了DGKS9603岩芯最上部沉积物（O-225cm）中的陆源物质通量,其结果与Sr-Nd同位素二端员定量分离结果非常相近,证明该方法在冲绳海槽地区的物质来源判识方面也是很有效的。 对155岩芯粘土粒级沉积物中火山源和陆源物质的混合比例进行了计算。结果显更多还原

【Abstract】 Deeply study on changes of marine environment, provenance and flux of the sediments during the glaciation-interglaciation climatic cycle is a highlight field of the paleoceanography studies in the Okinawa Trough.Based on detailed analysis for grain-size distributions, AMS¹⁴C dating, element and Sr-Nd isotopes compositions in the sediments of four cores that collected from the Okinawa Trough, the present thesis focus on the volcanic eruption events and terrigenous flux changes and its’ response to the climatic evolution since the late 40 kaBP. There are several mathematical methods have been selected for data processing, such as Q-mode factor analysis for element content, end-member modeling for grain-size data, quantitative partition of mixed sediments using Sr and Nd isotopes composition, etc. The studies indicate that the main sources of siliciclastic detritus in the sediments of the Okinawa Trough are terrigenous materials from the China mainland and volcanic substances （volcanic glass and pumice）. In addition, the proportion of aeolian detritus in the bulk sediments is not as high as expected. According to the grain-size distribution of siliciclastic detritus, the fraction of the terrigenous detritus with sedimentary environment sensitivities in the Okinawa Trough is identified and has the mode at about 7.81 μ m even various sediments sources and environmental characteristics are associated with different part of the Okinawa Trough. Which may provide evidence for ’terrigenous materials of the Okinawa Trough are mainly transported by the rivers of China’. As a result, the terrigenous flux in the sediments of Okinawa Trough is controlled not only by sea-level fluctuations, but also by palaeoclimatic changes in source region.Terrigenous supply in marine sediments is a function of interaction between land and ocean in response to climatic and oceanographic changes. At the middle Okinawa Trough, terrigenous flux since 35 cal. kaBP was calculated using Sr and Nd isotopes compositions in the sediments of Core DGKS9603. The results demonstrate that the terrigenous flux is higher in cool period than in warm period. The clay-size terrigenous detritus supplied by Yangtze River and East Asia winter monsoon also higher in the last glaciation maximum （LGM） while terrigenous flux is high and changes smoothly. But in the last deglaciation period, which has high sea-level rise speed, the terrigenous flux is higher than in the LGM suggests that there is a interactional connection between sea-level fluctuations and palaeoclimatic changes in source region during the process of controlling the terrigenous materials input into the middle Okinawa Trough.The volcanic materials imprint in the sediments of Holocene stratum indicates that volcanoes around the Okinawa Trough are more active in warm climate period. There arethree widespread volcanic eruptions occurred in Kyushu Island and Okinawa Trough and formed several volcanic tephra layers in the sea bottom sediments of the Okinawa Trough since the isotope stage 3. Changes of SiOz, Na20 and Zr contents in the sediments are good indicators for changes of volcanic materials input. The horizons of these three volcanic tephra layers in cores from the north and middle Okinawa Trough have homologous sedimentary ages. The eruptive ages of three volcanoes are 7563 ^ 25000 and 42000 cal. a BP and corresponding to K-Ah. AT and Okinawa I volcanic eruption event respectively. Compared with the K-Ah and AT tephra layers, great variation of grain-size distribution in the sediments of Okinawa I tephra demonstrates that Okinawa I tephra has different source against the former two tephra.Two end members, which are considered as good indicators for sediments sources, are extracted from the <63 U m fraction of the total grain-size distribution of siliciclatic detritus by grain-size end member modeling method. For the uppermost part （0-225em） of Core DGKS9603, the terrigenous flux in sediments is also calculated based on end member modeling software. The same trend is shown by the changes of terrigenous flux in sediments of DGKS9603 when calculated by grain-size end member modeling method and quantitative partition of mixed sediments using Sr and Nd isotopes composition. Which means that the grain-size end member modeling method is effective in sediment sources identification when it be used in the Okinawa Trough.The mixture rates of terrigenous and volcanic materials in the clay-size sediments of Core 155 are obtained by quantitative partition formula using Sr-Nd isotopes data. According to the results, the mixture rates of clay-size terrigenous detritus in sediments are decreasing with the depth decreasing during the isotope stage 1, on the contrary, the mixture rates of clay-size volcanic materials are increasing. In the isotope 3, the mixture situations in the sediments are conversely with the isotope stage 1. During the isotope 2, clay-size sediments are almost composed of terrigenous detritus. Compared with the grain-size characteristics of the bulk siliciclatic detritus in the sediments of Core 155. the changes of the mixture rates of clay-size volcanic detritus imply that the volcanic materials have different influence on clay-size sediments with different distance to the crater.The abruptly cooling events, such as Younger Dryas and Heinrich events, were identified from many cores at the Okinawa Trough. During the LGM. terrigenous flux in sediments are nearly invariable in Core DGKS9603 imply that there was no influence of thermohaline circulation changes in the Okinawa Trough during the episodes of H1 and H2 events. But the terrigenous flux in sediments is decreasing rapidly during the episodes of YD and H3 events may indicates that the occun-ence of these abruptly cooling events can speedup the decreasing trend of terrigenous flux which is controlled by sea-level changes in the Okinawa Trough during warm climatic period.更多还原