华南与冈瓦纳地区二叠—三叠纪之交牙形石对比研究

发布时间：2018-07-07 22:57

本文选题：牙形石 + 二叠纪—三叠纪　；参考：《中国地质大学》2016年博士论文

【摘要】：二叠-三叠纪(P-T)之交全球发生了地质历史上规模最大的生物灭绝事件,而关于这次灭绝事件的模式和原因一直都是地质学家争论的热点,牙形石作为P-T之交分布广泛的海相微体化石,其生物地层经过了详细地研究,特别是华南地区建立了高精度的牙形石生物地层。冈瓦纳地区是否存在连续的P-T地层记录到目前还存在争议,其牙形石研究是全球生物地层、事件地层及灭绝模式对比研究的基础。为完善P-T之交牙形石生物地层的全球对比,本文在华南地区和冈瓦纳地区选取4条剖面(湖南慈利高化剖面、贵州罗甸边阳剖面、贵州关岭下打翁剖面及西藏聂拉木色龙剖面)对P-T之交Hindeodus changxingensis带到Isarcicella isarcica带期间的牙形石展开对比研究。研究内容包括高精度牙形石生物地层对比、不同古地理区域牙形石的属种分布、牙形石的演化、灭绝及小型化事件等。此外,本研究还利用草莓状黄铁矿的粒径分布重建华南地区的氧化还原条件,进而探讨导致牙形石在P-T之交的变化原因。获得的主要进展如下：1.通过对湖南慈利高化剖面,贵州边阳剖面、下打翁剖面及藏南色龙剖面进行高精度大样牙形石生物地层研究,在6000多枚牙形石标本基础上建立了以下牙形石带：特提斯地区浅水碳酸盐台地相早三叠世H. parvus带和I. isarcica带；台地边缘斜坡相H. changxingensis带和H. parvus带；冈瓦纳地区P-T之交Vjalovognathus carinatus sp. nov.带和H. parvus带。本研究中将冈瓦纳地区V.carinatus sp. nov.带作为该地区二叠纪最年轻的牙形石带与华南地区长兴阶晚期H.changxingensis带进行对比,早三叠世一致以H. parvus的首现作为底界。另外在慈利高化剖面微生物岩底部发现了H. parvus,因此将其全部划入早三叠世,纠正了前人认为此层位沉积于晚二叠世的认识。2.对所获得的牙形石进行属级丰度统计,得出了P-T之交牙形石的古地理分布特征：即Hindeodus属,Isarcicella属及Clarkina属在全球广泛分布,晚二叠世期间,冈瓦纳地区牙形石以Mesogondolella属和Vjalovognathus属为主要特征并混有少量的Clarkina;华南地区较深水区以Clarkina的繁盛为特征,而浅水区仅发现少量Hindeodus分子。早三叠世底部Hindeodus突然大量涌入,尤其是在特提斯华南地区的H. parvus带中占绝对主导；但在高纬度的色龙剖面则不同：虽然早三叠世涌现出大量的Hindeodus属牙形石,但占绝对主导的却是Clarkina属(79%),而Mesogondolella和Vjalovognathus伴随P-T生物大灭绝事件在地层记录中彻底消失。3.通过对Hindeodus属牙形石侧面积统计,首次在色龙地区发现了早三叠世牙形石的小型化事件。色龙剖面Hindeodus的平均面积在H. parvus带下部为1.34mm2,而在H. parvus带的上部明显减小为0.88 mm2,这也是古高纬度地区早三叠世牙形石小型化事件的首次报道。4.本文对P-T之交牙形石的演化和灭绝,特别是针对只分布于冈瓦纳地区的冷水型牙形石-Vjalovognathus属的演化进行了研究,本属牙形石以其细齿发育截顶饰(顶端被磨蚀切平)为特征。建立了牙形石Vjalovognathus属最年轻的二叠纪新种V. carinatus sp. nov.,在此基础上完善了Vjalovognathus在二叠纪的演化序列。V.carinatus sp. nov.在色龙地区长兴阶的发现为冈瓦纳地区的对比提供扎实可靠的证据,可以将色龙地区色龙组上部与克什米尔的Zewan组进行直接对比。5.本研究在湖南慈利高化剖面和贵州关岭地区的下打翁剖面在高精度牙形石生物地层的基础上利用草莓状黄铁矿重建P-T之交氧化还原条件,结果显示以微生物岩为代表的浅水区为贫氧环境,而略深水的下打翁大冶组为缺氧环境,但中间夹有贫氧和氧化间断。微生物岩中的草莓状黄铁矿平均粒径在7.7-9.1μm之间,总体显示为贫氧环境,鲕粒灰岩缺少草莓状黄铁矿表明其沉积于氧化环境中。下打翁地区二叠纪长兴组含有非常丰富的生物化石,包括腕足、苔藓虫、海绵、海百合茎、双壳、三叶虫甚至植物化石,但到了以H. parvus记录的下三叠大冶组,几乎所有生物化石都不复存在,只发现有少量的牙形石和以Claraia sp.为代表的双壳类,水平纹层更为发育。草莓状黄铁矿粒径为4.7μm-8.5μm之间,H. parvus带下部缺氧与贫氧环境交替出现,中间夹有氧化间隔,而贫氧和缺氧沉积中部分草莓状黄铁矿被氧化成氧化铁。通过对冈瓦纳地区与华南地区P-T之交牙形石和氧化还原环境对比可知,牙形石在这次事件中经历了重创,但其与所处的海洋氧化还原条件没有一一对应关系,但与全球快速升温事件同时发生。一直生存于古高纬度冈瓦纳北缘冷水区的Mesogondolella和Vjalovognathus灭绝于晚二叠世,结束了其在地球上长达40 Myr的生存记录,随后Hindodus属在早三叠世突然涌入赤道地区,晚二叠世在赤道地区非常繁盛的Clarkina在早三叠世迁徙到高纬地区；另外,牙形石小型化事件在华南地区和冈瓦纳地区都有出现。虽然同时期的华南地区缺氧环境广泛蔓延,氧化或贫氧不断波动,但色龙沉积环境显示为完全氧化条件。因此,本研究表明P-T之交牙形石的分布与变化受古-中生代之交的全球快速升温事件影响,与缺氧与否无关。
[Abstract]:The two superposition of the Triassic (P-T) occurred the world's largest geological history of the world's largest biological extinction event, and the pattern and cause of the extinction event has always been the hot spot of the geologists. As a marine microbody with extensive distribution of P-T, the biostratigraphy has been studied in detail, especially in the Southern China region. A high precision dentate biostratigraphy has been established. There are still disputes over whether there is a continuous P-T record in Gondwana. The study of ODONTOS is the basis for a comparative study of global biostratigraphy, event stratigraphy and extinction patterns. In order to improve the total sphere comparison of the biocertists of P-T, this article is in Southern China and Gondwana region. 4 sections (Hunan Cili Gao Hua section, Guizhou Luodian edge Yang section, Guizhou Guanling Xia yweng section and Tibet Nielamu salad section) were used to compare the odontoid rocks between Hindeodus changxingensis zone and Isarcicella isarcica zone at the turn of the P-T. The distribution of the genus odontostite, the evolution of the odontoid, the extinction and miniaturization, and so on. In addition, the redox conditions of the Southern China region were rebuilt by the size distribution of the strawberry pyrite, and the causes of the changes in the intersection of P-T were discussed. The main progress was as follows: 1. through the Cili high profile in Hunan, The biologic stratigraphic study of high precision large dentin is carried out in the Guizhou Bian Yang section, the lower yoneng section and the Zangnan salad section. On the basis of more than 6000 dentate specimens, the following dentate belt is established: the early three fold H. parvus belt and the I. isarcica belt in the Tethys shallow water carbonate platform; the H. changxingensis belt and H of the platform edge slope facies and H The parvus band, the Vjalovognathus carinatus sp. Nov. belt and the H. parvus band in the Gondwana region, and the V.carinatus sp. Nov. zone in the Gondwana region as the youngest Permian dentate belt in the area and the late Changxin order H.changxingensis belt in the Southern China region. In addition, H. parvus was found at the bottom of the microorganism rock in Cili Gao Hua section. Therefore, all of them were divided into the early three fold world, which corrected the statistics of the genera abundances of the conodonts obtained by the previous understanding that this layer was deposited in the Late Permian, and obtained the palaeogeographic characteristics of the P-T conodonts: Hindeodus, Isarcicel. La and Clarkina genera are widely distributed throughout the world. During the Late Permian, the conodont in the Gondwana region was characterized by Mesogondolella and Vjalovognathus and mixed with a small amount of Clarkina; the deepwater area in Southern China was characterized by the prosperity of Clarkina, while a small number of Hindeodus molecules were found in the shallow water. The lower Hindeodus of the early three fold was suddenly large. The influx, especially in the H. parvus belt in the Southern China area of Tethys, is dominant; but at high latitudes the color dragon section is different: Although a large number of Hindeodus genera are emerging in the early three fold, the dominant one is the Clarkina (79%), and Mesogondolella and Vjalovognathus are associated with the P-T biological extinction event in the stratigraphic record. Through the total disappearance of.3., the miniaturization of the early three fold conodont was found in the salad area for the first time. The average area of Hindeodus in the salad section was 1.34mm2 at the lower part of the H. parvus zone and 0.88 mm2 in the upper part of the H. parvus belt, which was also the early three fold teeth in the ancient high latitudes. The first report on the miniaturized events of the.4. is the evolution and extinction of the conodont of P-T, especially the evolution of the cold water type -Vjalovognathus in the Gondwana region, which is characterized by its fine tooth development (the tip eroded Qie Ping). The conodont Vjalovognathus has been established. The youngest Permian new species, V. carinatus sp. Nov., is based on which the discovery of the Vjalovognathus evolution sequence of the Permian.V.carinatus sp. Nov. in the Changxin order in the chrolong region provides solid and reliable evidence for the contrast of the Gondwana region, which can direct the upper part of the chrolong area and the Zewan group in Kashmir. On the basis of the Hunan Cili Gao Hua section and the Xia Yate section of Guanling area of Guizhou, Hunan, the redox conditions of P-T with strawberry like pyrite were rebuilt on the basis of high precision dentate stratigraphy. The results showed that the shallow water area represented by microorganism was the oxygen poor environment, while the lower dionaweng Daye group was a hypoxic ring in the shallow water. The average particle size of the strawberry like pyrite in the microorganism rock is between 7.7-9.1 and m, and the overall show is a poor oxygen environment. The lack of strawberry like pyrite in the Oolitic Limestone indicates that it is deposited in the oxidizing environment. The Permian Changxin formation in the lower Weng area contains unusually abundant biological fossils, including brachiopod and bryophyte. Sponges, lilies, bivalves, tribos and even fossil plants, but to the next three cascade Daye groups recorded in H. parvus, almost all biological fossils are absent. Only a small number of conodont and Claraia sp. are found in the double shell, the horizontal lamina is more developed. The raspberry pyrite particle size is between 4.7 Mu m-8.5 and m, H. parvus band The lower anoxia and oxygen poor environment alternately appear in the middle, and there is an oxidizing interval in the middle, while some strawberry like pyrite in oxygen poor and anoxic deposits is oxidized to iron oxide. By comparing the conodont and redox environment of P-T in the Gondwana region and Southern China area, it is known that the ODONTOS have been damaged in this event, but they are with the marine oxygen. There is no one-to-one correspondence between the reduction conditions and the global rapid warming events. The Mesogondolella and Vjalovognathus of the cold water region of the northern margin of Gondwana in the ancient high latitudes were extinct in the Late Permian, ending its 40 Myr survival record on the earth, and then the Hindodus was suddenly flooded into the equatorial region in the early three fold world, In the Late Permian, the very prosperous Clarkina in the equatorial region migrated to the high latitude area in the early three fold. In addition, the miniaturization of the conodont occurred in Southern China and Gondwana. Although the anoxic environment in the same period of Southern China spread widely, oxidation or oxygen poor fluctuated, the depositional environment of the color dragon showed complete oxidation condition. Therefore, this study shows that the distribution and variation of conodont at the intersection of P-T is affected by the global rapid warming event at the Paleozoic Mesozoic era, and has nothing to do with hypoxia.
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：Q915

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