华南寒武纪早期海洋化学时空演化及其对早期动物演化的影响

发布时间：2019-06-05 21:21

【摘要】：越来越多的研究表明：早期生命的起源和演化,特别是真核生物,与地球大气-海洋的氧化还原状态存在密切的联系。继新元古代埃迪卡拉纪真核生物辐射之后,寒武纪早期出现两侧对称和骨骼化动物的快速演化,建立了现今动物门类和海洋生态系统的总体格架,被称为“寒武纪生命大爆发”。过去几十年内,国内外学者主要集中于动物群的形态特征和组成、地层划分与对比、磷矿和Ni-Mo多金属矿机制等方面的研究,取得很大的进展,如澄江动物群。然而,对寒武纪早期海洋化学及其与这次重大生命演化间关系的理解还不够深入。传统观点认为：环境的改变,尤其是深部海洋的完全氧化是“寒武纪生命大爆发”的触发原因。然而,一些学者则认为环境的改变(如海洋的完全氧化,硫酸盐浓度的变化等)却是这次重大生物事件的结果。虽然上述关于海洋化学与“寒武纪生命大爆发”间关系的认知存在本质性的差别,但都认为“寒武纪生命大爆发”与海洋的完全氧化密切相关。此外,寒武纪早期海洋化学及其化石记录间存在诸多矛盾：如深部水体的氧化记录与缺氧记录,海洋硫酸盐库容量的高低记录,目前推测的海洋化学状态与古生物记录间的矛盾等。近来,埃迪卡拉纪高度动态分层的海洋化学结构较好解决了这一时期海洋化学自身及其与古生物化石记录间的矛盾,为寒武纪早期上述矛盾的解决提供了新的思路。我国华南出露了相对完整的不同沉积相(近岸-远洋)寒武纪早期地层,此外,这些地层已进行了大量的岩石地层、古生物地层、年代地层、化学地层等工作,不仅为这一时期的地层划分和对比提供基础,而且为海洋化学的时空波动性及其与生命演化间关系的调查提供可能。我们研究和分析了华南寒武纪早期贵州内陆架金沙岩孔和外陆架瓮安朵丁地区铁-硫-碳(Fe-S-C)地球化学数据。基于已有的独立岩性和古生物地层划分和对比依据,我们将获得的新数据与来自内陆架云南肖滩外、陆架贵州遵义、斜坡相贵州松桃和盆地相湖南龙鼻嘴等剖面的已发表数据进行对比,重建当时的古海洋化学的时空波动性(包括氧化还原条件和硫酸盐含量),并进一步分析了硫酸盐含量波动引起的气候效应,最后,初步探讨了海洋化学的波动与生命演化间的关系。近岸-远洋铁组分化学与Mo含量的数据表明,虽然华南寒武纪早期表层海洋已被氧化,但深部海洋依旧为缺氧铁化的环境,且楔状的硫化水体动态发展于陆架至斜坡地区。这一海洋化学结构已被证实存在于晚太古代、中元古代和新元古代,表明前寒武纪的海洋化学结构特征已延续至寒武纪早期。我们还发现近岸-远洋黄铁矿硫同位素(834Spy)存在较大的梯度,表明这一时期海洋中硫酸盐库容量较小,这与前人认为寒武纪早期硫酸盐含量已接近现今水平的观点不符。此外,较低的硫酸盐含量会促使产甲烷古菌和甲烷好氧氧化细菌的繁盛,可能导致大量甲烷释放至表层海洋和大气中,从而对寒武纪的温室气候具有重要的贡献。另一方面,寒武纪梅树村阶向南皋阶转变时,斜坡相松桃和盆地相龙鼻嘴等地区δ34Spy出现逐渐变重,而内陆架金沙地区逐渐变轻,外陆架瓮安呈现没有上述特征,我们认为上述δ34Spy波动的不同是上述地区陆源输入硫酸盐和海洋中硫酸盐贡献比例的不同引起的。此外,依据平衡条件下硫的循环,即黄铁矿硫同位素(δ34Spy)的波动与陆源输入,黄铁矿埋藏和细菌硫酸盐还原过程中的硫同位素分馏有关,我们认为深部水体硫酸盐的降低是斜坡相松桃和盆地相龙鼻嘴地区δ34Spy升高的原因。通过对比华南寒武纪早期海洋化学状态和化石记录,我们发现以节肢动物为主的化石群存在于氧化水体下的沉积物中,而此时深部水体为缺氧甚至硫化的水体；以海绵为主的动物化石群或小壳动物化石群化石发现于缺氧非硫化水体沉积物中,硫化水体沉积物中未见到化石。此外,随着寒武纪早期复杂动物的不断出现,生物扰动逐渐增强,而深水地区如松桃和龙鼻嘴的硫酸盐含量却出现降低,表明生物扰动作用对硫酸盐含量的影响较小。因此,我们认为寒武纪生命大爆发仅与当地的海洋化学条件相关,而与开阔海洋(特别是深部海洋)的海洋化学状态无明显直接的关系,这与前人关于寒武纪生命大爆发需要深部海洋的氧化或其导致深部海洋氧化和极高的硫酸盐浓度的传统观点不一致。
[Abstract]:An increasing number of studies have shown that the origin and evolution of early life, in particular eukaryotes, have a close relationship with the redox state of the Earth's atmosphere. The rapid evolution of both sides of the Cambrian in the early part of the Cambrian and the rapid evolution of the bone-based animals in the early part of the Cambrian in the early part of the new proterozoic Ediacaran, and the establishment of the total physical frame of the present animal and marine ecosystem, is called the "Cambrian explosion". In the past few decades, domestic and foreign scholars mainly focus on the morphological characteristics and composition of the animal group, the formation division and the comparison, the phosphate rock and the Ni-Mo multi-metal ore mechanism and so on, and has made great progress, such as the Chengjiang fauna. However, understanding of the early Cambrian marine chemistry and its relationship with this major life evolution is not in depth. The traditional view is that the change of the environment, especially the complete oxidation of deep ocean, is the trigger of the "Cambrian explosion" However, some scholars believe that the change of the environment (such as the complete oxidation of the ocean, the change of the sulfate concentration, etc.) is the junction of this major biological event. Although the above-mentioned cognition of the relationship between the marine chemistry and the "Cambrian explosion" is different, it is considered that the "Cambrian explosion" is closely related to the complete oxidation of the sea In addition, there are many contradictions between the early-Cambrian marine chemistry and its fossil records, such as the oxidation record of deep water body and the oxygen-deficient record, the high and low record of the capacity of the marine sulfate reservoir, and the contradiction between the predicted marine chemical state and the ancient biological record. Recently, the highly dynamic layered marine chemical structure of the Ediacaran has better solved the contradiction between the marine chemistry itself and the records of the fossil-biological fossils during the period, and provided a new thought for solving the above-mentioned contradictions in the early part of the Cambrian. The early formation of the relatively complete sedimentary facies (inshore-ocean) is exposed in South China of China. In addition, the formation has carried out a lot of work such as rock formation, paleontology, age formation, chemical formation and so on, which not only provides basis for stratigraphic division and contrast in this period. In addition, the time-and-space fluctuation of marine chemistry and its relationship with the evolution of life are provided. The study and analysis of the geodesizing of iron-sulfur-carbon (Fe-S-C) in the southern part of the Cambrian in the early part of the Cambrian in the southern China The data is based on the existing independent lithology and the ancient biostratigraphic division and the comparative basis, and we will obtain the new data and the published data from the Yunnan Shoal, the land frame, the Zunyi, the slope, the Songtao of Guizhou, and the dragon nose of Hunan, etc. By contrast, the time-space fluctuation of the ancient marine chemistry at the time (including the oxidation reduction condition and the sulfate content) was reconstructed, and the climatic effect caused by the fluctuation of the sulfate content was further analyzed. The data of the chemical and Mo content of the near-shore-ocean-water component show that, although the early surface of the Cambrian in South China has been oxidized, the deep ocean is still an environment with an oxygen-deficient iron, and the wedge-shaped sulfide water is developed dynamically on the shelf The chemical structure of the ocean has been proved to be present in the late Archaean, Middle Proterozoic and Neoproterozoic, indicating that the marine chemical structure of the Precambrian has been extended to In the early part of the Cambrian, we have also found that the near-shore-pelagic pyrite-sulfur isotope (834 Spy) has a large gradient, indicating that the content of sulfate in the ocean during this period is small, which is similar to that of the previous time that the early-Cambrian sulfate content has been close to the present level In addition, the lower sulfate content can lead to the growth of the methane-producing archaea and the aerobic oxidation bacteria of methane, which can lead to the release of a large amount of methane to the surface of the sea and the atmosphere, so that the greenhouse climate of the Cambrian is On the other hand, on the other hand, when the order of the Precambrian Meishu Village was changed to the south, there appeared to be a gradual change in the Q34 Spy in the slope of the Songtao and the Xianglong nose of the basin, while the Jinsha area of the inland shelf was gradually lighter, and the outer continental shelf was not present. With the above-mentioned characteristics, we believe that the above-mentioned R34 Spy fluctuation is the proportion of the land-source input sulfate in the above-mentioned area and the sulfate contribution in the sea. In addition, the circulation of sulfur under equilibrium conditions, i.e., the fluctuation of the pyrite-sulfur isotope ({34 Spy), is the same as that of the sulphur isotope in the process of land-source input, pyrite burial and bacterial sulfate reduction The reduction of the sulfate in the deep water body is about 34 Spy in the slope of the Songtao and the Xianglong nose area of the basin. The reason of the increase is that by comparing the early marine chemical status and the fossil record of the Cambrian in South China, we find that an arthropod-based chemical stone group is present in the sediment of the oxidized water body, and at this time, the deep water body is oxygen-deficient. even a water body which is vulcanized; a sponge-based animal chemical stone group or small-shell animal chemical stone group fossil is found in the oxygen-deficient non-vulcanized water body deposit, and the sulfide water body is deposited; In addition, as the early and complex animals of the Cambrian appear, the biological disturbance is gradually enhanced, while the sulfate content of the deep water area such as the pine and the dragon nose is reduced, indicating the effect of the biological disturbance on the sulfate. The effect of the content is small. Therefore, we believe that the explosion of the Cambrian life is only related to the local marine chemical conditions, while the marine chemical state of the open ocean, especially the deep ocean, is not There is a clear direct relationship, which is closely related to the previous oxidation of the deep ocean or the deep ocean oxidation and extremely high sulfate concentration in the deep ocean due to the great explosion of the Precambrian life.
【学位授予单位】：中国地质大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：Q915;P534.41;P734

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