Aproposed Area for Study of Accessory Section and Point of Terrestrial Permian—Triassic Boundary

After the establishment of the global stratotype section and point (GSSP) of the Permian-Triassic boundary (PTB), the definition of the accessory section and point (ASP) of the terrestrial Permian-Triassic boundary (TPTB) is now on the agenda. However, all good TPTB sections so far known have the following shortcoming:(1) the exact TPTB horizon is difficult to define paleontologically with high-resolution, and (2) accurate correlation between marine and terrestrial PTBs in hard to attain. In order to enhance the understanding of the nature of the global life crisis in both the marine and terrestrial environments across the Paleozoic-Mesozoic transition, these shortcomings need to be addressed. In western Guizhou and eastern Yunnan, Southwest China, some fossiliferous PTB sections which include marine, paralic and terrestrial are well-developed, allowing bed-to-bed correlation of the PTB sequences. Fortunately, the marine PTB sequence in this area is almost the same as found at the Meishan Section, where the GSSP of the PTB is located, which may provide a reliable auxiliary marker for high-resolution demarcation of the TPTB. These features fund in estern Guizhou and eastern Yunnan make this area a good place to study the ASP of the TPTB, so we propose to study the ASP of the TPTB in this area.     

A Middle–Upper Devonian Boundary Section in the Open Platform,Platform Margin Facies of Guilin, South China

Abstract: The Caiziyan Middle and Upper Devonian boundary section is located approximately 30 km northeast of Guilin. It hosts relatively abundant benthic and common–rare pelagic fossils, including brachiopods, corals, tentaculites, and conodonts, which may serve as a better suitable section for pelagic and neritic stratigraphic correlation. In this section, 10 “standard” conodont zones are recognized across the Givetian–Frasnian boundary, including, in descending order, the Lower hassi Zone, punctata Zone, transitans Zone, the Upper falsiovalis Zone, the Lower falsiovalis Zone, disparilis Zone, the Upper hermanni–cristatus Zone, the Lower hermanni–cristatus Zone, the Upper varcus Zone, and the Middle varcus Zone, all of which are defined by the first occurrence of their defining conodont species. The Middle–Upper Devonian (Givetian–Frasnian) boundary is defined by the first occurrence of Ancyrodella pristina in accordance with the Global Stratotype Section and Point (GSSP), which is assigned at 6.2m above the base of bed 19 in the Caiziyan section.     

Alkane Biomarkers in Permian—Triassic Boundary Strata at Meishan Section, Changxing, Zhejiang Province

Meishan Section D in Changxing County, Zhejiang Province, China has been selected as the global stratotype of the Permian-Triassic boundary and various studies hav been done at the boundary but the gas chromatographic-mass spectrographic analysis of alkane biomarkers has not been investigated. This paper presents of results of a study of the biomarkers analyzed in a series of samples across the permian-Triassic boundary at both Meishan Section A and Section D. The results show that the overall concentration of alkane biomarkers in the Permian-Triassic boundary strata is high in Bed 26 while it is low in Bed 27. A variety of biomarker parameters demonstrate that the main sources of organic matter in the sediment are algae and bacteria and that the depositional enviroment varied from weakly oxidizing to reducing during the studied interval.     

New Advances in the Study of the Devonian-Carboniferous Boundary Stratotype in Muhua,Changshun,Guizhou——An Introduction to the Daposhang Devonian-Carboniferous Boundary Section

The Daposhang section at Muhua, Changshun. Guizhou. is an excellent and attractive DevonianCarboniferous boundary section. The transitional beds between the Devonian and Carboniferous of the sectionare continuous and well exposed. belonging to the deep-water basin facies Abundant fossil groups have beendiscovered from this section: conodonts. ammonoids. trilobites. ostracods. vertebrate microfossils and so on.So far as known. it has the most continuous and complete conodont zonation for the Devonian-Carboniferousboundary beds in the world. It is especially worth pointing out that both typical Siponodella pracsulcata andthe transitional forms between S. praesulcata and S. sulcata have been found from the upper pracsulcata Zoneof the Daposhang section. Evidently. we can not only prove the actual existence of the evolutionary lineagefrom S. praesulcata to S. sulcata, but also exactly define the level of the Devonian-Carboniferous boundary. Inthis paper. the development of the Devonian-Carboniferous boundary beds at the Daposhang section is dealtwith and the section is compared with the Muhua section and the Nanbiancun section which are the candidatesfor the Devonian-Carboniferous boundary stratotype. In the authous opinion the Daposhang section is obvi-ously better than the Muhua and the Nanbiancun sections. hence it can be recommended as one of the candi-dates for the international Devonian-Carboniferous boundary stratotype.     

Stratigraphical Time——Correlation and Mass Extinction Event Near Permian——Triassic Boundary in South China

Shaw’s method used to correlate40 sections across the Permo-Triassic boundaryin South China is applied in the paper.Two steps are adopted to get an Integral Compo-site Section(ICS)by synthesizing these data:First,South China is divided into fiveareas and composite section developed for each area.Then the second step,theChangxing composite section is regarded as a composite standard(CSRS)while the ICSis produced by matching the CSRS with composite sections of the other areas.Threebiozones in the Changxingian and two biozones in the Griesbachian can be discerned onthe basis of computing Z values in the ICS.These biozones are marked by the Z values which quantitatively represent their time ranges;therefore,they may increase accuracy ofstratigraphic time correlation.The mass extinction at the end of the Permian is an ab-rupt event that is supported by the relative rate of extinction near the P/T boundary.About90％of invertebrate species died out by the end of the Permian.The duration ofthe mass extinction     

A Comprehensive Evaluation on the Devonian-Carboniferous Boundary Stratotype Candidate Section in Nanbiancun, Guilin, Guangxi

This paper presents a comprehensive evaluation on the Devonian-Carboniferous Boundary (DCB) sectionin Nanbiancun. Guilin. Guangxi on the basis of Palaeontological, biostratigraphical and sedimentarypetrological studies as well as microfacies analysis. REE and trace element analysis and isotopic dating. The DCB at this section conforms to the definition of this boundary and essentially measure up the criteriaand conditions for selection of the boundary stratotype. Up to 14 fossil groups are contained in the section. Thesection presents a general biostratigraphical framework with multispecies fossils zones, assemblage zones andmultiple groups of fossils and has latent preponderant conditions for magnetostratigraphic andchronostratigraphic studies. The boundary and point occur in a persistent and continuous monofacialcarbonate succession. and the section is located in a tourist city with convenient communication, where variousfacies of DCB sections are developed. allowing the correlation within a small area. So it is an ideal candidateboundary stratotype.     

Geochemical Anomaly at the Devonian/Carboniferous Boundary, Huangmao, Gnangxi, China

The abundances of nearly 40 elements, Ir included, have been measured using radio-chemical and instrumental neutron activation analysis (RNAA and INAA) across a Devonian/Carboniferous (D/C) boundary section at Huangmao, Guangxi, China. The Ir anomaly has been found in the D/C boundary bed. Its peak value is 156 ppt, richer by a factor of 12 than that in the underlying strata. Besides, as with Ir, other siderophile and chalcophile elements such as Au. Ni. Co. As and Sb are also enriched. The cause for the abundance anomalies of Ir and other elemets is discussed. Neither volcanic eruption nor extraterrestrial impact can explain it satisfactorily. The real mechanism for the anomalies awaits further study.     

Geochemistry of the trace elements and rare-earth elements at the boundary between Cambrian Series 2 and Series 3 at Jianshan, South China: Paleoenvironmental and stratigraphic implications

The Jianshan section in Jianhe County,Guizhou Province,is a very important auxiliary section to the candidate stratotype at the boundary between Cambrian Series 2 and Series 3.Twenty four samples collected from the Jianshan section of the Kaili Formation were analyzed for the concentrations of trace element and rare-earth elements(REEs) by inductively coupled plasma mass spectrometry.The trace element and REE geochemical characteristics of the Kaili Formation at the Jianshan section show that trace element composition and REE distribution patterns across the section are covariant.Notably,at 44 m above the base of the Kaili Formation,most trace element contents and REEs concentrations are lower than those values observed below 44 m.Above 44 m,an increasing trend in the concentration of both trace elements and REEs is observed.These geochemical data indicate important,but subtle,changes at the 44 m horizon.If this is,in fact,verified by work in progress,geochemical criteria can provide additional supports for defining the top surface of Cambrian Series 2,especially in sections where Oryctocephalus indicus is absent.Trace element ratios,specifically Ni/Co,V/Cr,V/(Ni+V) and Th/U as well as Ce and Eu anomalies indicate that the sedimentary environment of the Kaili Formation at the Jianshan section was oxidizing,that benthic redox conditions were less oxic,and may have been influenced by freshwater as compared to the Balang area.Moreover,the Eu anomalies observed in the Kaili Formation are similar to the negative Eu anomalies observed in post-Archean sedimentary rocks,and reveal fluctuations in oxygen content from the bottom to the top of the Kaili Formation.     

A Primary Observation on Palynofacies of the Chuangde Section (Late Jurassic-Cretaceous), Gyangzê, Southern Tibet

A primary study on palynofacies, which concerns the paleoenvironments from the sight of association of sedimentary organic matter preserved in sedimentary rocks, is conducted for a Late Jurassic-Cretaceous succession at Gyangzê, southern Tibet. Two palynofacies are recognized, which are formed in different sedimentary environments. The one in the pelagic is infertile in organic productivity and monotonous in component and is dominated by AOMA, while the other, being closely bound up with the slope, is characterized by abundant black phytoclasts that are possibly of algal origin and contains much AOM. The influence of terrestrial input is clear in the latter, for particles generated from terrestrial plants are common. A number of fossil spores and pollen together with some dinocysts are discovered, but they are normally in a bad condition of preservation. Nevertheless, this convinces us that the late Jurassic-Cretaceous succession in the Gyangzê area has a potential for palynological stratigraphy. We have also proved that the volume of PM can achieve similar results in presenting the productivity of organic matter as the weight of TOC does. This technique is much easier in the laboratory than that we do with TOC.     

A Potential Candidate For the Middle-Upper Cambrian Boundary Stratotype——An Introduction to the Paibi Section in Huayuan,Hunan

The Middle-Upper Cambrian boundary is one of the current stratigraphical problems which remain openin the geological world, since there have been no universally acknowledged delimiting standard and stratotype.Acting on the instruction of Profs. Lu Yanhao and An Taixiang the author studied in details the Paibi Section,which is well exposed as a continuous sequence at an easily accessible locality. The Middle-Upper Cambrianboundary strata are composed of biocalcimicrosparite, indicating the sedimentary environment of anunderwater upheaval on the gentle slope along the frontal margin of the Yangtze carbonate platform. For the upper Middle and lower Upper Cambrian agnostid trilobite zones and conodont zones are erected,and a more accurate correlation between the trilobite and conodont sequences is established. Based on these,the Middle-Upper Cambrian boundary is drawn more reasonably and precisely than what was done before. Inshort, the section studied is superior to other known sections of Middle-Upper Cambrian. and it will probablybe an ideal candidate for the Middle-Upper Cambrian boundary stratotype.     

Recent achievements on the research of the Paleozoic-Mesozoic transitional period in South China

This is a review of research achievements on the Permian-Triassic transition in South China. It comprises of five parts: (1) advances on the biostratigraphy and eventostratigraphy of the Meishan Section, the Global Stratotype Section and Point (GSSP) of the Permian-Triassic boundary (PTB); (2) advances on the PTB research of deep water facies, especially the Dongpan Section in Guangxi; (3) advances on the PTB research of terrestrial facies, especially the Chahe Section in Guizhou; (4) correlation of the global change and biotic extinction between the PTB and modern times and its revelation to the status and future of the earth and mankind; and (5) the pattern and causality of the Permian-Triassic extinction. In the last part, it is concluded that the Permian-Triassic transitional interval constitutes a prolonged crisis period ranging from end-Guadalupian extinction to the end of Early Triassic, totaling 14 Ma. The environmental crisis and mass extinction peaked at the PTB, which displayed multiphase extinction rather than just one phase. Commencement of an extinctions prelude prior to the postulated bolide impact implies that the causes of PTB extinction largely lie in the intrinsic developments of the earth, especially those related with the integration of Pangea.     

陆相二叠系-三叠系界线研究进展

着重介绍了几个目前陆相二叠系—三叠系界线（TPTB）研究的重点剖面及其生物地层学研究进展；分析了陆相二叠系—三叠系界线综合地层学研究现状，包括生物地层学、事件地层学、同位素年代学、磁性地层学和层序地层学等；剖析了陆相二叠系-三叠系界线地层学研究中存在的问题及进一步的研究方向。生物地层方面，陆相二叠系-三叠系界线附近存在晚二叠世与早三叠世生物混生的层位，其中不同类别生物的时间界线常不一致，又由于陆相界线地层中含脊椎动物化石的层位一般较少，以脊椎动物化石（Lystrosaurus）为标准的精确界线常不确定，因而需重新寻找并确定陆相三叠系底界的标准化石。事件地层标志可能会成为连结海、陆相二叠系-三叠系界线地层高精度对比的纽带。     

黔西威宁岔河陆相二叠系-三叠系界线粘土岩研究--基于X射线衍射、扫描电镜分析

利用X射线衍射、扫描电镜等分析方法,对黔西威宁岔河陆相剖面二叠系-三叠系界线附近的粘土岩进行了研究.在界线粘土岩中,粘土矿物组合为伊-蒙混层矿物 蒙脱石 绿泥石;碎屑物质中有六方双锥石英和锆石,无球粒;多种化学成分在界线粘土岩中出现了异常.据此得出岔河剖面的二叠系-三叠系事件地层界线确定在第66f层比较合适;第66f和68a这两层粘土岩为此剖面的界线粘土岩;自第66f层底部至第68a层顶部这一段地层为二叠系-三叠系的界线层(组);界线粘土岩的成因可能是由于火山喷发、火山灰降落伴随正常沉积物沉积形成的.     

地层单位与全球界线层型:概念、术语、有关规定与研究实例

全球二叠系-三叠系界线(PTB)层型及点("金钉子")定位我国浙江省长兴县煤山D剖面,极大地推动了PTB及二叠系和三叠系研究进展。在简要介绍地层单位与全球界线层型与点建立的相关概念、术语和有关规定、地层划分的主要种类及其地层单位术语的基础上,以全球二叠系—三叠系界线层型及点(中国浙江省长兴县煤山D剖面)为研究实例,综述了该金钉子剖面牙形石生物地层和年代地层研究现状。煤山D剖面构建了目前全球最完整的PTB地层牙形石带序列,为研究二叠纪末大灭绝后生物残存和复苏过程提供了重要的时间坐标系,也为相关的地质事件研究奠定了坚实的基础。     

Ophiceras(蛇菊石)在滇东卡以头组的发现及其意义

Ophiceras(蛇菊石)在滇东海陆交互相卡以头组下部(25层下部)的首次发现,是近期海陆交互相和陆相二叠系-三叠系界线(PTB)研究的重要进展之一。该化石的发现为滇东卡以头组地层时代的确定提供了更加确凿的依据。在煤山D剖面,29-37层为Ophiceras(蛇菊石)的顶峰带,因此,可将滇东密德B剖面的25层与煤山D剖面29层对比,那么滇东地区卡以头组主体(甚至全部)的时代可划归早三叠世。     

二叠系-三叠系界线全球层型剖面——回顾和进展

综合评述了5年来对二叠系—三叠系界线(PTB)全球层型剖面——煤山D剖面的研究进展。简要介绍剖面的研究历史、地理和地质背景,叙述了世界上最完整的二叠纪长兴期至三叠纪格里斯巴赫期的牙形石和菊石带,并简短讨论了Otoceras的年代。叙述了煤山与其他剖面长兴期至格里斯巴赫期磁性地层学的对比。介绍了δ13C和δ34S的化学地层学最新研究进展,特别是在PTB附近多个δ13C负漂移的发现。两项重要的分子地层学研究显示了基础生态系统的深刻变化——微生物生态系的灾变和在二叠纪—三叠纪生态系之交严重缺氧事件期间透光带的静海相环境。文章报道了自2001年以来PTB年代测定的进展。PTB之下14cm处火山成因的粘土层25层的年代,现在定为(252·4±0·3)Ma(Mundil等,2004)。文章还讨论了事件地层学,认为尽管在25-26层有一个主事件,煤山PTB附近的事件是多幕式的,并且开始于事件层25-26层之前。因此,PTB大绝灭主因是外星撞击导致的可能性是不大的。     

广西东攀剖面粘土岩的火山岩特征及 LA-ICP-MS锆石U-Pb年龄

广西扶绥县柳桥镇东攀地区出露1套上二叠统大隆组和下三叠统罗楼组,大隆组合Ophiceras sp.,罗楼组合Ophicerastingi Tien生物化石,二者为整合的连续沉积地层.生物特征显示,在第12-3层和第13-1A层之间为二叠系—三叠系的界线,界面附近存在较厚的粘土岩层.从结构上看,粘土岩具有较明显的火山岩碎屑结构和沉凝灰构造,岩石地球化学研究也显示其具有钙碱性中酸性火山岩的特征,沉积环境为大陆边缘环境.在粘土岩中选取自形程度较高的火山成因锆石进行激光剥蚀法U-Th-Pb同位素测年研究,岩石中锆石的结晶年龄为254.7Ma±3.7Ma,表明本区二叠纪—三叠纪之交存在着火山活动.     

贵州威宁金钟二叠系-三叠系界线剖面生物地层及其对比

二叠纪—三叠纪之交发生了显生宙最大的生物灭绝事件,同时发生了复杂的环境变化.由于陆相二叠系-三叠系界线附近生物化石记录没有海相记录完整,同时也缺乏其他可靠的年代地层标志,所以如何标定陆相剖面的二叠纪—三叠纪界线一直是研究热点和难点.贵州威宁金钟地区二叠纪—三叠纪之交位于康滇古陆的东侧,毗邻海陆过渡相区,可以与同期的浅海碎屑岩相、海陆过渡相、陆相剖面进行由海到陆“追索式”的生物地层对比,是我国研究海、陆相二叠系-三叠系界线及对比的关键研究区之一.研究区的金钟二叠系-三叠系界线剖面中化石丰富,共发现双壳类化石4属6种,叶肢介2属4种,植物化石9属及腕足类化石1属,为海、陆相地层对比提供了桥梁.依据叶肢介Euestheria gutta-Palaeolimnadia xuanweiensis组合、植物Annalepis-Peltaspermum组合以及双壳类Pteria ussurica variabilis-Neoschizodus orbicularis组合的生物化石时代归属讨论,识别出金钟剖面的二叠系-三叠系界线应该在卡以头组下部.通过与邻区不同相剖面的对比,提出双壳类Pteria ussurica variabilis-Neoschizodus orbicularis组合以及陆相的叶肢介Euestheria gutta-Palaeolimnadia xuanweiensis组合可以作为三叠纪最早期的识别和对比标志.      

湖北黄石二门二叠系/三叠系界线剖面长兴阶牙形刺分带及有机碳同位素的变化

湖北黄石二门二叠系/三叠系界线剖面出露完好,原始沉积连续,由乐平统龙潭组保安段灰黑色硅质岩、大隆组黑色硅质岩—硅质泥岩和下三叠统大冶组黑灰色泥岩以及泥岩夹灰岩组成,为介于典型浅水碳酸盐岩型与深海硅质岩型二叠系/三叠系界线剖面之间的半深海剖面。长兴阶可划分为Clarkinasubcarinata—Clarkinawangi及Clarkinachangxingensis两个牙形刺带。后者又可划分为3个亚带,自下而上依次为Clarkinachangxingensischangxingensis—Clarkinadeflecta亚带、Clarkinameishanensis亚带及Waning—Clarkina亚带,完全可以与二叠系/三叠系界线的全球层型剖面与点进行对比。另外,二叠纪末牙形刺的生态演化呈阶段性绝灭模式;有机碳同位素值在二叠纪/三叠系界线处出现明显的负偏移,指示了二叠纪/三叠纪之交生物绝灭后海水表层水原始产率的降低以及大气和海水中CO2含量的增加。