晚奥陶—早志留世海洋的碳、硫、锶和汞循环

发布时间：2018-05-28 09:17

  本文选题：晚奥陶世生物大灭绝 + 碳循环扰动　； 参考：《中国科学技术大学》2017年博士论文

【摘要】：地质历史时期典型生物灭绝事件期间环境气候条件以及海洋碳硫循环的重建,对人类正确认识现代环境和生物危机以及促进人与自然和谐发展具有重要意义。本课题以晚奥陶世海相沉积岩为载体,探究当时生物大灭绝期间海洋和大气的化学条件及其变化机制以及对生物灭绝的影响。本文主要集中于以下三个方面:1.晚奥陶世海洋碳循环扰动机制的探究在具有详细生物地层控制的基础上,对采自美国内华达州Copenhagen Canyon剖面碳酸盐的无机碳同位素、87Sr/86Sr比值以及微量元素进行分析,并结合模型计算重建了当时海洋碳循环及其扰动的主要控制因素。结果表明,该剖面未受显著的后期成岩蚀变,记录了海水的原始同位素信息:晚奥陶期间存在两次显著的碳同位素正偏移(峰值分别为～+7‰和～+5‰),且与冈瓦纳冰川的开始和消融具有很好的一致性。对应地,87Sr/86Sr比值存在两次快速降低且与碳同位素和冰川协同变化。结合数据以及海洋箱式模型的综合分析,本文认为碳酸盐风化输入的增加是导致全球晚奥陶世碳同位素正偏的主导因素,不一定需要有机碳埋藏增加:冰川开始,海平面下降,碳酸盐台地风化加强,导致河流输入的碳同位素组成变重,从而导致海相碳酸盐的碳同位素组成正偏;冰川融化,海平面上升,碳酸盐台地被海水淹没,风化输入减少,海相碳酸盐的碳同位素组成恢复到初始值。2.贵州红花园剖面的多硫同位素(A33S,δ34S,和△36S)记录及其环境指示意义对采自贵州桐梓红花园剖面的沉积岩样品进行高精确度的多硫同位素组成以及碳、硫含量分析。首次在24.5亿年以来的地质记录中发现了硫同位素的非质量相关分馏(△33S最大可达～0.9‰)。通过对数据和硫同位素分馏原理的综合分析,认为与大规模火山喷发相伴随的平流层光化学反应是产生红花园硫同位素非质量相关分馏的原因。这一发现识别出晚奥陶期间华南曾存在多次平流层火山喷发,并将大规模火山活动和晚奥陶世生物灭绝联系起来;表明硫同位素的非质量相关分馏也能发生并保存在显生宙的地质记录中,为晚奥陶世生物灭绝的机制提供了新的视角,也为重建地史时期火山活动的生态和环境效应提供了新的有效研究手段。这一结论也得到其他地质记录的支持:在华南及全球中晚奥陶世地层中广泛发现大量蚀变火山灰夹层,表明当时全球火山活动频繁,与火山活动相伴随的环境恶化以及臭氧层空洞可能是造成晚奥陶世生物灭绝的原因之一。3.秀山和Vinini Creek剖面的汞(Hg)记录及其环境指示意义对采自重庆秀山和美国内华达州Vinini Creek剖面的沉积岩样品进行Hg浓度、Hg/TOC比值以及Hg同位素组成的分析测试。发现两个剖面在晚奥陶期间均呈现Hg富集特征(Vinini Creek剖面的Hg浓度高达736.6ppb),远高于正常海洋沉积物的Hg含量,表明当时外界Hg输入显著增加。结合Hg同位素数据,本文认为秀山和Vinini Creek异常的Hg富集特征是火山活动导致Hg释放增加的结果。晚奥陶世生物灭绝之前及附近层位的Hg富集信号指示火山活动可能是造成这次生物灭绝的原因之一,与本文多硫同位素研究的结论一致。另外,本文Hg浓度及Hg/TOC数据显示局部的沉积环境条件可能对沉积物Hg异常的记录产生显著影响。火山活动或其他过程导致的Hg输入增加在沉积物中的保存与有机质的埋藏量密切相关:当有机质的埋藏量大大超过Hg沉降的需求时,即使火山活动导致Hg输入增加,Hg/TOC比值仍然因为TOC含量高而偏低,不能真实反映Hg输入的异常;而如果有机质埋藏太少,Hg输入的异常也不能保存在沉积物中。因此,运用沉积物Hg/TOC比值作为古火山活动的指标时,应综合评估Hg浓度、Hg/TOCL比值、TOC含量以及样品的沉积环境和古地理条件,以获得准确的古火山活动及环境效应信息。
[Abstract]:The environmental climate conditions and the reconstruction of marine carbon and sulfur cycle during the period of the typical biological extinction events in the geological history period are of great significance for human beings to correctly understand the modern environment and the biological crisis and to promote the harmonious development of human and nature. The chemical condition and its change mechanism of gas and its influence on the extinction of the organisms. This paper mainly focuses on the following three aspects: 1. late Ordovician Marine carbon cycle disturbance mechanism, on the basis of detailed biostratigraphic control, the inorganic carbon isotopes and 87Sr/86Sr ratios of the Copenhagen Canyon caesarean section of Nevada, USA The main control factors of marine carbon cycle and its disturbance were reconstructed with the analysis of trace elements and combined with the model calculation. The results showed that the section was not subjected to significant late diagenesis and recorded the original isotopic information of the sea water: there were two significant carbon isotopic shifts between the late Ordovician period (peak value of ~ +7 per thousand and ~ ~ (- 1), respectively). +5 per 1000) has a good consistency with the beginning and ablation of the Gondwana glacier. Corresponding, the ratio of 87Sr/86Sr has two rapid decreases and cooperates with carbon isotopes and glaciers. Combined data and the comprehensive analysis of the ocean box model, the increase of the carbonate weathering input is the result of the global late Austrian Tao Shitan isotopes. The leading factors do not necessarily require an increase in organic carbon burial: the glacier begins, the sea level falls, and the weathering of the carbonate platform is strengthened, resulting in a heavy carbon isotope composition of the river, which leads to a positive carbon isotope composition of the marine carbonate; the glaciers melt, the sea level rises, the carbonate platform is inundated by sea water, the weathering input is reduced, marine carbon is reduced. The carbon isotope composition of acid salts is restored to the initial value.2. Guizhou red garden section of polysulfide isotopes (A33S, Delta 34S, and delta 36S) records and their environmental indicator significance for the high accuracy of the polysulfide isotopes and the analysis of carbon and sulfur content in the sedimentary rocks samples collected from the Tongzi red garden section of Guizhou. For the first time, the geological records of 2 billion 450 million years have been recorded. The non mass correlation fractionation of sulfur isotopes (up to 0.9 per 1000) was found in the record. Through a comprehensive analysis of the principle of data and sulfur isotope fractionation, it is believed that the photochemical reaction with the stratospheric photochemical reaction associated with large-scale volcanic eruption is the cause of the non mass fractional distillation of the sulfur isotope in the safflower garden. This discovery recognizes the late Ordovician period. There was a number of stratospheric volcanic eruptions in Southern China, which linked the large-scale volcanic activity to the late Ordovician extinctions, indicating that the non mass correlation of sulfur isotopes could also occur and remain in the Phanerozoic geological record, providing a new perspective for the mechanism of the late Ordovician biological extinction and the reconstruction of the volcanic activity in the period of the geological history. Dynamic ecological and environmental effects provide new and effective means of research. This conclusion has also been supported by other geological records. A large number of altered volcanic interbeds are widely found in Southern China and the middle Late Ordovician strata in the world, indicating the frequent global volcanic activity, environmental deterioration associated with volcanic activity, and the possibility of ozone hole holes. One of the causes of the late Ordovician extinction is one of the mercury (Hg) records of Xiushan and Vinini Creek sections of.3. and its environmental significance. The analysis of Hg concentration, Hg/TOC ratio and Hg isotopes from the sedimentary rocks samples collected from Chongqing Xiushan and the Vinini Creek section of Nevada, USA, found that two sections were in the late Ordovician period. The concentration of Hg (the Hg concentration of the Vinini Creek section is as high as 736.6ppb), which is far higher than the Hg content in the normal marine sediments, indicating that the input of Hg is significantly increased at that time. Combining with the isotopic data of Hg, this paper holds that the Hg enrichment of the anomalies of the Xiushan and Vinini Creek is the result of the increase of the release of the volcanic activity induced Hg. The Hg enrichment signals at the front and near sites indicate that volcanic activity may be one of the causes of this biological extinction. It is in agreement with the conclusion of the study of polysulfide isotopes in this paper. In addition, the concentration and Hg/TOC data in this paper show that the local sedimentary environment conditions may have a significant impact on the record of Hg anomalies in the sediments. Volcanic activity or other processes. The increased storage of Hg input in the sediment is closely related to the amount of organic matter buried in the sediments: when the amount of organic matter is much more than the demand for Hg settlement, even if the volcanic activity leads to the increase of Hg input, the Hg/TOC ratio is still low because of the high TOC content, which can not reflect the abnormal Hg input, but if the organic matter is buried too little, Hg loses. When the sediment Hg/TOC ratio is used as an indicator of paleo volcanic activity, the concentration of Hg, the ratio of Hg/TOCL, the content of TOC, the sedimentary environment and the palaeogeographic conditions of the samples should be comprehensively evaluated in order to obtain accurate paleo volcanic activity and the information of the environment effect.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P736.22
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本文编号：1946146