【作者】 阎春波；

【导师】 赖旭龙；

【作者基本信息】 中国地质大学 ， 古生物学与地层学， 2013， 博士

【摘要】 二叠纪-三叠纪之交的生物大灭绝事件以及之后生态环境的复苏是地球演化史上的一个重要时期,在此期间海洋生态系统发生了重大变革,并完成了古中生代生态类群的转变。二叠纪末生物大灭绝及之后的生态环境恢复一直以来都是国际上研究的热点问题之一,而南盘江区域多条剖面的系统研究为其提供了良好的研究背景,并取得了一系列成果。同样微体化石牙形石的研究可以为其提供很好的年代地层学方面的依据。本研究以早三叠世-中三叠世早期的牙形石生物地层为基础,结合事件地层学和碳、氧稳定同位素的分析来探讨生物与环境协同演化,为此我们选定了南盘江区域的5条早、中三叠世剖面,依次为台地相贵州贵阳改貌和花溪剖面、盆地边缘相贵州罗甸边阳剖面、盆地相广西田东作登剖面和广西凤山金牙湾头剖面。盆地边缘相边阳剖面位于南盘江盆地大贵州滩的西北缘,此次我们主要研究了该剖面从二叠纪末到中三叠世早期的这一段地层,其中对二叠-三叠纪之交至早-中三叠世之交的地层进行了牙形石样品的高精度采集和分析。通过分析,在边阳剖面晚二叠世晚期到早三叠世晚期识别出10个牙形石带,由老到新依次为：Clarkina yini带;Hindeodus changxingensis带；Hindeodus parvus带;Sweetospathodus kummeli带;Neospathodus dieneri带;Neospathodus cristagalli带；Discretella discreta带；Pachycladina-Parach irognathus组合带；Icriospathodus collinsoni带；Triassospathodus homeri带。在边阳Ⅱ剖面早、中三叠世之交识别出5个牙形石带,自下而上依次为：Triassospathodus homeri带,Triassospathodus brochus带,Chiosella timorensis带, Nicoraella germanicus带,Nicoraella kockeli带。依据精细牙形石序列的建立,在边阳剖面将二叠系-三叠系界线以Hindeodus parvus分子的首次出现确定于边阳剖面第6层的底部,同时认为在该剖面牙形石带H. changxingensis带的存在可能从一定程度上反映了大贵州滩甚至南盘江地区当时海平面的下降程度；将Induan-Olenekian界线通过Discretella discreta分子的首次出现确定于第1层之上94.4m的位置,并探讨了Discretella discreta和Novispathodus waageni分子两者之间在地层中的出现的先后关系;在边阳Ⅱ剖面将Olenekian-Anisian阶的界线以Chiosella timorensis分子的首现定于最底部之上15.9m的位置。在盆地相剖面作登剖面中,作登Ⅰ剖面前人的报道较为详细,因此我们对该剖面只进行了控制点牙形石样品的采集,在早三叠世地层中识别出6个牙形石带,从老到新依次为：Hindeodus parvus带,Hindeodus sosioensis带,Neospathodus dieneri带,Discretella discreta带,Icriospathodus collinsoni带,Triassospathodus homeri带；对作登Ⅱ剖面我们进行了大样品高精度牙形石序列的分析,在不到30m的地层中识别出从Dienerian到Spathian期的7个牙形石带,自下而上依次为：Neospathodus dieneri带,Novispathodus waageni带,Pachycladina-Parachirognathus组合带,Novispathodus pingdingshanensis带,Icriospathodus collinsoni带,Triassospathodus homeri带和Triassospathodus brochus带;在作登Ⅲ剖面中主要识别出了早、中三叠世之交的牙形石类型,比如Chiosella timorensis分子。依据高精度牙形石序列的研究,证实作登Ⅰ剖面和作登Ⅱ剖面存在着地层上的重复,并非之前报道的连续地层;在作登Ⅱ剖面将Dienerian-Smithian和Smithian-Spathian的界线分别以Novispathodus waageni和Novispathodus pingdingshanensis的首现定于最底部往上4.50m和11.08m的位置：在作登Ⅲ剖面将Olenekian-Anisian界线以Chiosella timorensis分子的首现确定于最底部地层往上2m的位置。在盆地相凤山金牙湾头剖面不到13m的地层中我们重点进行了早-中三叠世之交的高精度大样品牙形石生物地层的分析,总计在该剖面识别出3个牙形石带,从老到新依次为：Triassospathodus homeri带,Triassospathodus brochus带,Chiosella timorensis带,将Olenekian-Anisian的界线依据Chiosella timorensis分子的首次出现确定于该剖面底部之上8.22m的位置。此外,在盆地相凤山金牙拉仁剖面进行了Smithian-Spathian界线处牙形石序列的分析,并依据Novispathodus pingdingshanensis的首次出现将Smithian-Spathian界线确定于剖面底部往上10m的位置。在台地相剖面贵州贵阳花溪剖面和改貌剖面,牙形石材料主要来自于安顺组顶部和花溪组底部地层,岩性以白云岩为主,牙形石丰度较低。但从牙形石序列来看,在改貌剖面花溪组底部识别出的牙形石主要为：Icriospathodus? crassatus, Icriospathodus collinsoni, Novispathodus abruptus, Triassospathodus symmetricus和Triassospathodus homeri,其地层时代应当为Spathian中晚期；花溪剖面花溪组产出的牙形石主要为：Novispathodus abruptus, Triassospathodus symmetricus和Triassospathodus homeri,所采集样品的地层时代应当为Spathian晚期。这改变了传统认为的花溪组地层全部归属于中三叠世的观点。通过南盘江盆地沉积相不完全相同的五条剖面牙形石序列的研究,有利于我们对于不同沉积环境下的早三叠世牙形石序列进行对比和完善。此次研究在盆地边缘相贵州边阳剖面、盆地相广西作登Ⅱ剖面Smithian晚期以及斜坡相甲戎剖面的牙形石材料中均识别出Pachycladina和Parachirognathus这两个属,说明南盘江盆地在该时期均处于水深较浅的阶段;结合剖面材料及前人研究成果,本文在Spathian晚期新建立了牙形石带Triassospathodus brochus带,其首现点晚于Triassospathodus homeri,特征明显,在边阳Ⅱ剖面、作登Ⅱ和Ⅲ剖面以及凤山湾头剖面均可识别。不同的牙形石类型可以反映不同的生态环境,此次研究我们侧重于早三叠世生态环境波动时牙形石属种的变化。经分析,我们认为Eurygnathodus和Icriospathodus这两个属的出现往往出现在其后相对较冷的时期,同时对应着δ13Ccarb的相对正偏,因此我们认为这两个属的分子有可能是凉水型分子的代表,其出现往往伴随着生物多样性的增加；Novispathodus pingdingshanensis被提议作为划分Smithian-Spathian界线的标准分子,具有重要的地质意义,其分子延限范围处于Spathian期新属种还未全面出现的过渡期,首现点往往对应于δ13Ccarb负偏的高值、贫氧的极高值和古海洋温度的最大值,因此推断该分子是极端环境下的产物。针对近年来关于在南盘江区域早中三叠世之交广泛发育的绿豆岩的分布时间和Chiosella timorensis首现点之间的争论。通过我们牙形石材料的研究,证实绿豆岩和Chiosellatimorensis并不存在明显的地层上出现的先后关系,且在各个剖面绿豆岩的层数多少也有很大差异,而关于绿豆岩年龄值的时间跨度很大,因此我们认为在南盘江区域绿豆岩不适合作为事件层来划分下中三叠统的界限。此外,虽然被证实Chiosella timorensis分子可以出现在Spathian晚期的菊石Haugi带中,但综合考虑,仍然建议以Chiosella timorensis分子的首现作为划分早-中三叠世之交的标准化石,而且Chiosella timorensis分子的出现应当具有等时性。更多还原

【Abstract】 The end-Permian mass extinction event and subsequent ecological environment recovery were one key period in the Earth history; meanwhile marine ecosystems had evolved from Paleozoic type to Mesozoic one. As a hot topic in scientific researching, the end-Permian mass extinction and its recovery in ecological environment had been under investigated for many years. The sections in the Nanpanjiang Basin could provide some important breakthroughs for a comprehensive recognition of the nature of the end-Permian mass extinction and the extraordinary nature of the Early Triassic world that followed. Marine microfossil, conodont, as a good index in biochronology, was used to subdivide the Early-Middle Triassic biostratigraphy, especially Olenekian Stage in this study. Meanwhile, event stratigraphy and Carbon stable isotope was combined to explain interrelationship between organism and environment. Five sections in the Early-middle Triassic were chosen in Nanpanjiang region, including platform facies Gaomao and Huaxi section (Guiyang, Guizhou province), basin margin facies Bianyang section (Luodian county, Guizhou province), basin facies Zuodeng section (Tiandong county, Guangxi province) and Wantou section (Fengshan county, Guangxi province).Bianyang section is located on the northwest flank of the Great Bank of Guizhou (GBG) in Nanpanjiang area. Strata from end-Permian and earlier Middle-Triassic were analysed through the high-resolution conodont biostratigraphy.10conodont zones was established in Bianyang section, in ascending order, they are:Clarkina yini Zone; Hindeodus changxingensis Zone; Hindeodus parvus Zone; Sweetospathodus kummeli Zone; Neospathodus dieneri Zone; Neospathodus cristagalli Zone; Discretella discreta Zone; Pachycladina-Parachirognathus assemblage zone; Icriospathodus collinsoni Zone and Triassospathodus homeri Zone, respectively. In Bianyang section II,5conodont zones were set up, in ascending order: Triassospathodus homeri Zone, Triassospathodus brochus Zone, Chiosella timorensis Zone, Nicoraella germanicus Zone and Nicoraella kockeli Zone. Based on the high-resolution conodont sequences, two conclusions were concluded:1) the Permian-Triassic boundary should be placed in the basal part of Bed6as the first appearance datum (FAD) of Hindeodus parvus. Whilst, we suggest the existence of H. changxingensis zone at this section represents the extent of sea level fall in the GBG and even the Nanpangjiang area.2) the Induan-Olenekian boundary was defined by the first occurrance of Discretella discreta and located at the94.4m higher than the basement of Bed1. Furthermore, the correlation of Discretella discrete and Novispathodus waageni was discussed. At the Bianyang section Ⅱ, Olenekian-Anisian boundary was defined at15.9m above the basal part of this section by the FAD of Chiosella timorensis.The previous study had demonstrated detailed conodont sequences at Zuodeng section Ⅰ. In this study, we just simply clarify conodont bioastratigrphy of the key strata through the controlled conodont samples collected. Six conodont zones are recognized, in ascending order:Hindeodus parvus Zone, Hindeodus sosioensis Zone, Neospathodus dieneri Zone, Discretella discreta Zone, Icriospathodus collinsoni Zone and Triassospathodus homeri Zone. Large samples were collected in the Zuodeng section Ⅱ,7conodont zones were recognized in the less than30m thickness strata, in ascending order, they are:Neospathodus dieneri Zone, Novispathodus waageni Zone, Pachycladina-Parachirognathus assemblage Zone, Novispathodus pingdingshanensis Zone, Icriospathodus collinsoni Zone, Triassospathodus homeri Zone and Triassospathodus brochus Zone. Some conodont elements were also identified in the Early-Middle Triassic boundary interval at Zuodeng section Ⅲ, such as Chiosella timorensis. According to the high resolution conodont sequences at Zuodeng section Ⅱ, Dienerian-Smithian boundary and Smithian-Spathian boundary can be defined at4.50m and11.08m above the base of Bed1by the FO of Novispathodus waageni and Novispathodus pingdingshanensis, respectively. The same situaiton is Olenekian-Anisian boundary can be placed at2m above the basal part by the FO of Chiosella timorensis at Zuodeng section Ⅲ. Comparing with previous study, the Permian-Triassic boundary is still defined at basal part of microbiolites. Additionally, conodont research reveals the existence of stratigraphic repetition between Zuodeng section Ⅰ and Zuodeng section Ⅱ, which is different from the earlier research.Large conodont samples were collected in the less than thickness13m strata in Wantou section. Three conodont zones were established as follows:Triassospathodus homeri Zone, Triassospathodus brochus Zone and Chiosella timorensis Zone. Moreover, the Olenekian-Anisian boundary was placed at8.22m higher than the base of Bed1according to the FAD of Chiosella timorensis. Meanwhile, conodont sequence was investigated in the Smithian-Spanthian boundary interval in the Laren section, Fengshan County. Then the Smithian-Spathian boundary was defined at the10m higher than the basal level by the FAD of Novispathodus pingdingshanensis.In platform facies Huaxi and Gaomao sections, Guiyang city, Guizhou province, Anshun Formation and Huaxi Formation mainly consist of dolomite, traditionally assigned to Middle Triassic strata. Whereas, conodont materials from the Gaomao section (comprising of Icriospathodus? crassatus, Icriospathodus collinsoni, Novispathodus abruptus, Triassospathodus symmetricus and Triassospathodus homeri) turned out that the lower part of Huaxi Formation in Gaomao section deposited in the mid-late Spathian period; conodont sequences from the Huaxi section (comprising of Novispathodus abruptus, Triassospathodus symmetricus and Triassospathodus homeri) revealed that the basal part of Huaxi Formation should correspond to the late-Spathian substage. Through the study of5sections from different sedimentary facies in the Nanpanjiang basin, it is in favor of better understanding of the Early Triassic conodont sequences in different facies. Two genera of Pachycladina and Parachirognathus can be found in the late-Spathian strata at Bianyang section (basin margin facies), Zuodeng section (basin facies) and Jiarong section (ramp facies). Therefore, we conclude that the sea level would be shallower in Nanpanjiang basin in this period. Based on the new and abundant conodont materials in the study, Triassospathodus brochus Zone was proposed to as one new conodont Zone to be established in the late-Spathian strata, the FAD of which is later than Triassospathodus homeri. This Zone can also be distinguished in Bianyang section II, Zuodeng section Ⅱ, Wantou section and other regions of the world.Different ecological condition could be reflected by different conodont genera. In this study the research focuses on the change of conodont genera and species in the episode of environment fluctuation in Early Triassic. Through analysis, Eurygnathodus and Icriospathodus appear usually in cooler climate period, corresponding to the positive fluctuation of δ13Ccarb. Therefore the two genera were suggested as the representative of cooler water elements and the biodiversity increasing was accompanied in this period. In this study, although Novispathodus pingdingshanensis had been confirmed to exist in ammoniod Xenocelites Zone in the latest-Smithian strata, it was still proposed as an index fossil to define Smithian-Spathian Boundary, because the species Novispathodus pingdingshanensis have the typical geological significance. The FAD of Novispathodus pingdingshanensis generally matched ralativly negative δ13Ccarb values, the highest values in the anoxic period and the hottest palaeo-ocean temperature value. Moreover, the range of Novispathodus pingdingshanensis was in the transitional phase. Afterwards, some new Spathian species had appeared."Green Bean Rock" beds were widely recongnized in Nanpangjian basin in Early-Middle Triassic boundary interval. For better understanding of this dispute on the correlation of "Green Bean Rock" and the FAD of Chiosella timorensis, conodont research was made in this interval. It convinces us that there is no exact temporal relationship between those two. Moreover, the numbers of "Green Bean Rock" beds were different in. the different regions and the range of the age was very longer than the former study. In the study, we tend to think the first appearance datum of Chiosella timorensis is contemporaneous in the different areas. Overall consideration, the FAD of Chiosella timorensis is more suitbale to define the early-middle Triassic Boundary, although it was identified that Chiosella timorensis could appear in the Haugi Zone in the latest-Spathian strata.更多还原