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.     

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.     

Conodont Biostratigraphy and Age Determination of the Lower–Middle Triassic Boundary in South Guizhou Province, China

The demarcation of the Lower–Middle Triassic boundary is a disputed problem in global stratigraphic research. Lower–Middle Triassic strata of different types, from platform to basin facies, are well developed in Southwest China. This is favorable for the study of the Olenekian–Anisian boundary and establishing a stratotype for the Qingyan Stage. Based on research at the Ganheqiao section in Wangmo county and the Qingyan section in Guiyang city, Guizhou province, six conodont zones have been recognized, which can be correlated with those in other regions, in ascending order as follows: 1, Neospathodus cristagalli Interval-Zone; 2, Neospathodus pakistanensis Interval-Zone; 3, Neospathodus waageni Interval-Zone; 4, Neospathodus homeri-N. triangularis Assemblage-Zone; 5, Chiosella timorensis Interval-Zone; and 6, Neogongdolella regalis Range-Zone. An evolutionary series of the Early–Middle Triassic conodont genera Neospathodus-Chiosella-Neogongdolella discovered in the Ganheqiao and Qingyan sections has an intermediate type named Neospathodus qingyanensis that appears between Neospathodus homeri and Chiosella timorensis in the upper part of the Neospathodus homeri-N. triangularis Zone, showing an excellent evolutionary relationship of conodonts near the Lower–Middle Triassic boundary. The Lower–Middle Triassic boundary is located at 1.5 m below the top of the Ziyun Formation, where Chiosella timorensis Zone first appears in the Qingyan section, whereas this boundary is located 0.5 m below the top of the Ziyun Formation, where Chiosella timorensis Zone first appears in the Ganheqiao section. There exists one nearly 6-m thick vitric tuff bed at the bottom of the Xinyuan Formation in the Ganheqiao section, which is usually regarded as a lithologic symbol of the Lower–Middle Triassic boundary in South China. Based on the analysis of high-precision and high-sensitivity Secondary Ion Mass Spectrum data, the zircon age of this tuff has a weighted mean 206Pb/238U age of 239.0±2.9Ma (2s), which is a directly measured zircon U-Pb age of the Lower–Middle Triassic boundary. The Ganheqiao section in Wangmo county can therefore provide an excellent section through the Lower–Middle Triassic because it is continuous, the evolution of the conodonts is distinctive and the regionally stable distributed vitric tuff near the Lower–Middle Triassic boundary can be regarded as a regional key isochronal layer. This section can be regarded not only as a standard section for the establishment of the Qingyan Stage in China, but also as a reference section for the GSSP of the Lower–Middle Triassic boundary.     

The Huohua Section: a new Devonian-Carboniferous boundary section The Huohua section: a new Devonian-Carboniferous boundary section of deep-water facies in Ziyun County, Guizhou Province, China

This paper introduces a new section of the Devonian-Carboniferous boundary in Huohua area, Ziyun County, Guizhou Province, South China. The Huohua section of Upper Devonian and Lower Carboniferous is well-outcropped along a new countryside road. In this section, the D-C boundary beds can be grouped into three litho-units: the Daihua Formation, the Changshun Shale and the "Wangyou Formation", from which more than 30 conodont samples were collected and processed. According to our current study, some important conodonts in the Daihua Formation and the Changshun Shale have been recognized, such as Palmatolepis tenuipunctata, Pa. glabra, Pa. marginifera, Pa. gracilis, Polygnathus vogesi and Polygnathus purus purus. A few conodonts have been found from the Wangyou Formation, such as Polygnathus communis and Hindeodella subtilis. Based on the comparison with the Muhua section in Changshun county and the Hasselbachtal section in Germany in lithology, sedimentology and conodont biostratigraphy, the D-C boundary could be temporarily placed between Bed 25 and Bed 26, namely between the Changshun Shale and the Wangyou Formation.     

Discussion on Induan—Olenekian Boundary in Chohu,Anhui Province, China

This paper proposes a scheme for the definition of the Lower Triassic Induan-Olenekian boundary(IOB) based on investigation of sections in Chaohu, Anhui Province, China as well as data accunulated from other studies elsewhere. The conodont Neospathodus waageni is suggested as the index fossil of the boundary. According to the FAD of N.waageni, the IOB is at the base of bed 25-2 of the West Pingdingshan Section in Chaohu,42.19 m above the Permian-Triassic boundary, and it is slightly higher than the base of the Flemingites-Euflemingites Ammonoid Zone at the section.     

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.     

The Best Natural Boundary:a New Concept Developed by Combining the Sequence Boundary with the GSSP

Through a detailed study of sequence boundaries, it is concluded that sequence stratigraphy is an independent regional and transitional stratigraphic system between local lithostratigraphy and global chronostratigraphy. Therefore, a new tripartite stratigraphic classification scheme has been proposed. By combining organically the concept of sequence boundaries with the GSSP, it is suggested that the GSSP should be chosen in a conformale portion of a related sequence boundary, and the boundary established in light of this concept is defined as the Best Natural Boundary (BNB). The definition of the BNB points out the working area and stratigraphic level for the GSSP. By referring to a case study of the Permian Guadalupian/Lopingian boundary, the concept of the BNB has been elaborated in detail, and it is proposed that the BNB of the Guadalupian and the Lopingian lies between the Mesogondolella granti Zone and the Ctarkina postbitteri Zone, which is also the sequence chronostratigraphic boundary between th     

The Devonian-Carboniferous Boundary in Shallow-Water Facies Areas of China as Based on Conodonts

Traditionally, the lower boundary of the Aikuanian(Yanguanian) Stage has always been considered as the lower boundary of the Carboniferous in China. marked by the occurrence of the coral Cystophrentis.In recent years, some biostratigraphical research results have shown that the Cystophrentis zone is only distributed in the lower part of the Menggong'ao Formation(or the Gelaohe Formation) and that there is an interval zone namely the Cystophrentis-Pseudouralinia interval zone, wedged in just between the Cystophrertis zone and the Pseudouralinia zone in the upper part of the Menggong'ao Formation(or the GelaoheFormation). According to the current study of the conodont biostratigraphy, the coral Cystophrentis zone appears to be of latest Devonian age. So the lower boundary of the Aikuanian Stage is much lower than the lower Devonian-Carboniferous boundary and should no longer be regarded as the lower boundary of the Carboniferous in China. In this paper, two proposals for the Devonian-Carboniferous boundary in the shallow-water facies areas of China are put forward: 1) that the boundary is marked by the first appearance of the conodont Siphonodella(Eosiphonodella) simplex, and 2) that the boundary is recognized by the extinction of the coral Cystophrentis or the brachiopod Tenticospirifer.In addition, 4 species are newly estabished here: Icriodus obovatus sp. nov., Polygnathus lepidus sp. nov., Polygnathus paucidentatus sp. nov. and Polylophodonta jianghuaensis sp. nov.     

Study on a Terrestrial Permian—Triassic Boundary Section—Zhejue Section, Weining County,Guizhou Province, China

The Zhejue Section is an excellent terrestrial permian-Triassic boundary (TPTB) section not only for its convenient accessibility and good outcrop, but also for its abundant fossils. In addition, there are two claystone beds that were formed by events across the Permian-Triassic boundary (PTB) at this section. The claystones provide a bridge for high-resolution correlation between marine and terrestrial PTBs. Another advantage is that the PTB at the Zhejue Section can be correlated with that of littoral and neritic facies by tracing estwards. Synthesized stratigraphic studies, including biostratigraphy, eventostratigraphy )susceptibilities and carbon isotopes across the TPTB, and microspherules found in the boundary claystones) and sequence stratigraphy, are carried out at this section.     

Devonian–Carboniferous Hangenberg Crisis in South China: Variations in Trace Elements, Strontium and Carbon Isotope Chemostratigraphy in the Nanbiancun Carbonate Section

The global Hangenberg Crisis or Hangenberg Extinction is a mass extinction near the Devonian–Carboniferous boundary. Comprehensive research of petrology and geochemistry on the Devonian–Carboniferous boundary, as exposed in the Nanbiancun auxiliary stratotype section, South China, elucidates paleoenvironmental changes and controls on marine strontium (87Sr/86Sr) and carbonate carbon (δ13Ccarb) isotopes during the Hangenberg Crisis. The new 87Sr/86Sr data reveal a regression in the Middle Siphonodella praesulcata Zone, while the Hangenberg Extinction was occurring in South China. Moreover, the δ13Ccarb data records a negative excursion near the base of the Middle Siphonodella praesulcata Zone that may have been connected with the Hangenberg Extinction. A positive δ13Ccarb excursion, corresponding with the Upper Siphonodella praesulcata Zone, may reflect the effects of a vigorous biological pump. The magnitude of the Hangenberg Carbon Isotopic Excursion in peak δ13carb values and δ13Ccarb gradient in carbonate Devonian–Carboniferous boundary sections of the South China Craton during the Hangenberg Crisis, are a function of depositional water depth and distance from the shore. The carbon cycling during the Hangenberg Carbon Isotopic Excursion had a much stronger impact on oceanic surface waters than on the deep ocean and the δ13Ccarb gradient of local seawater was likely caused by enhanced marine productivity, associated with biological recovery in platform sediments during the Hangenberg Crisis.     

A Comprehensive Evaluation on the Devonian-Carboniferous Boundary Stratotype Candidate Section in Nanbiancun,Guilin, Guangxi1

Abstract This paper presents a comprehensive evaluation on the Devonian-Carboniferous Boundary (DCB) section in Nanbiancun, Guilin, Guangxi on the basis of Palaeontological, biostratigraphical and sedimentary petrological 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 criteria and conditions for selection of the boundary stratotype. Up to 14 fossil groups are contained in the section. The section presents a general biostratigraphical framework with multispecies fossils zones, assemblage zones and multiple groups of fossils and has latent preponderant conditions for magnetostratigraphic and chronostratigraphic studies. The boundary and point occur in a persistent and continuous monofacial carbonate succession, and the section is located in a tourist city with convenient communication, where various facies of DCB sections are developed, allowing the correlation within a small area. So it is an ideal candidate boundary stratotype.     

Ni-Ir Anomaly,Microtektites, and the Biotic Crisis across the Devonian–Carboniferous Boundary,Southern China

Integrative methods of chemostratigraphy and biostratigraphy were used in the study of microtektites and moderate nickel-iridium anomaly beds in the Devonian-Carboniferous boundary beds at Huangmao (Guangxi Autonomous Region) and Muhua (Guizhou Province) in southern China. Microtektites provide evidence for meteoritic impact event(s), whereas the minerals and the chemical composition of the Ni-Ir anomaly beds likely display a submarine hydrothermal origin. It is postulated that the intensification of the rifting-hydrothermal process, and the ensuing pollution, might have been responsible for the Devonian-Carboniferous biotic crisis. This process began in the late Famennian expansa zone, lasted to the Tournaisian duplicata zone, and produced the largest manganese ore deposits of China.     

浙江长兴煤山二叠—三叠系界线系列剖面侧向追索研究

在浙江长兴煤山二叠—三叠系界线地层研究中，人们通常将该区侧向出露宽约１ｋｍ的界线地层分解成７个相互平行、独立的小剖面进行各种地质研究。这不仅导致了研究资料的分散，而且引起了关于候选层型剖面位置的不必要的争议。沿露头剖面的野外追索观察和分析表明，露头区界线地层完全可以精确地追索，各种沉积记录的侧向变化是十分轻微的。已有的地层学研究也表明，各区段（小剖面）的沉积记录具有相同或相似的结果。当某些化石在一处采获后，在另一些小剖面上也肯定能找到，只要工作足够细致和深入。因此我们认为，应该将这些侧向上连续分布的采石场露头作为一个剖面来对待。这样亦符合国际地层委员会方针和章程中关于界线层型剖面露头完整性的要求。     

Magnetostratigraphy of the late Cenozoic of the Boso Peninsula, central Japan

Marine Pliocene and Pleistocene beds of the Boso Peninsula are more than 3 km thick and contain abundant fauna and flora. Almost continuous deposition occurred at a high sedimentation rate from the early part of the last reversed geomagnetic polarity epoch to the middle part of the last normal polarity epoch. Several microbiostratigraphic marker horizons enable correlation with deep-sea sediments fully independent of magnetostratigraphic zonation. Globorotalia truncatulinoides first occurs below the normal polarity event BO-B-2, which is correlated with the Olduvai Event in deep-sea sediments, whereas the disappearance of discoasters and the first occurrence of Gephyrocapsa caribbeanica are recognized at the top of BO-B-2, and the first occurrence of Gephyrocapsa oceanica is recognized at the top of BO-B-1. Based on the correlation of the Boso section with Mediterranean stage stratotype sections, the transition from the Pliocene to Pleistocene is estimated to be in the lower part of the Kazusa Group.     

Biotic characteristics of the Sinian-Cambrian boundary beds in China and the boundary problems

There is general agreement that the first appearance of various small shelly fossils should be used to help delineate the beginning of the Cambrian Period. The history of research on this stratigraphic topic in China is briefly outlined and leads on to a discussion of the boundary problem in the light of information available both inside and outside China.The sections across the Precambrian—Cambrian (Sinian—Cambrian) boundary are described with notes on fossils in: (1) Tianzhushan section, Yichang, Hubei; (2) Maidiping section, Emli, Sichuan; (3) Wangjiawan section, Jinning County, Yunnan; and (4) Kunyang section, Yunnan.This is followed by a consideration of the biotic characteristics of Sinian—Cambrian Period. The history of research on this stratigraphic topic in China is briefly outlined and leads on to a discussion of the boundary problem in the light of information available both inside and outside China. This is followed by a consideration of the biotic characteristics of Sinian—Cambrian boundary beds, with respect to stratigraphy as well as organic evolution. The Precambrian—Cambrian boundary in China is estimated to have an age of 615 ± 20 Ma.It is commented that the above sections are qualified to be important candidates for the selection of the Sinian—Cambrian boundary stratotype and are also important working reference sections for the international Precambrian—Cambrian boundary stratotype.     

全球奥陶系底界的“金钉子”问题及我国特马豆克阶(Tremadocian)的划分与对比

对全球寒武系与奥陶系界线层型剖面和点位(GSSP)——西纽芬兰绿岬(Green Point)剖面和我国吉林白山(原浑江)大阳岔小洋桥原全球寒武系与奥陶系界线候选剖面的对比研究表明,绿岬"金钉子"剖面所指定的界线生物标志——波动古大西洋牙形石(Iapetognathus fluctivagus)并不存在于所指定的界线生物层和点位上,而且在分布和分类上是均存在争议的物种,更遗憾的是,所展示的大部分牙形石和笔石标本图片以及碳氧同位素异常数据也并非来自该"金钉子"剖面,因而完全违背了选择金钉子剖面的原则和要求,有必要进行重新的评估。小洋桥寒武系与奥陶系界线剖面交通方便、环境优美,寒武系与奥陶系界线地层系由一套深水且未变质的黑色、黄绿色页岩与灰色薄层瘤状灰岩所构成的韵律沉积组成,并保存了完整的具有广泛代表性牙形石和笔石序列,在详细研究的34 m界线间隔中,自下而上保存了完整的Cambrostodus、Codylodus proavus、C.intermedius、C.lindstromi和C.angulatus等5牙形石生物带,在C.intermedius带上部至C.angulatus带之间,还依次出现3层笔石,归属于重新厘定的Rhabdinopora parabola和Anisograptus matanensis等2个笔石带,此外还有大量三叶虫和介形类化石共生,结合高精度同位素地球化学的研究,笔者等建议,以全球广泛分布的牙形石C.intermedius的首现,取代Iapetognathus fluctivagus,作为寒武系与奥陶系界线划分对比的标志,其层位与原来所指定的界线层几乎一致或接近,界线之上所记录的最大碳同位素异常和首次出现的最早的浮游正笔石——R.parabola(含R.praeparabola),可作为该界线划分的辅助标志。     

Lower Boundary of the Marine Pleistocene in Northern Shelf of the South China Sea

A marine stratigraphic sequence across the Pliocene / Pleistocene boundary has been found in the north-ern continental shelf of the South China Sea. The marine Quaternary deposits in the Yinggehai Basin may ex-ceed 2,000 m in thickness, probably providing the best section for studying the lower boundary of the marinePleistocene in South China. The vertical succession with planktonic foraminifers and nannofossils revealed inboreholes in the basin has been well correlated with that in the international stratotype section of thePliocene / Pleistocene boundary at Vrica, Italy, resulting in the acquirement of a biostratigraphic boundary at1.64 Ma. This boundary, however, does not coincide with any prominent lithological palaeoenvironmentalchanges in the study area and can hardly be used in geological practice. There are, in contrast, significantchanges at the level of LAD of Globorotalia multicamerata sensu lato located below the above-mentionedboundary. The percentage of planktonic foraminifers in the total population and preservation of foraminiferaltests display great changes at this level corresponding to a clear onlap on the seismic profiles and indicating adepositional hiatus at ca. 2.0-2.5 Ma. Since the level can be widely traced in the Pearl River Mouth Basin andthe Beibu Gulf Basin and well corresponds with the marked depositional environmental changes recorded inthe west Pacific and other regions, it is recommended that the Plio / Pleistocene boundary be drawn at the levelof Gr. multicamerata sensu lato LAD, roughly concurrent with the Gauss / Matuyama turn.     

Palaeomagnetic Study on the Precambrian-Cambrian Boundary Candidate Stratotype Section at Meishucun, Yunnan

The Meishucun secton has been recommended as an international candidate stratotype secton of thePrecambrian-Cambrian boundary. The paper deals with the palaeomagnetic study on the section. A total of159 palaeomagnetic samples were successively collected from the platform-facies sequence of carbonates andphosphates at the section. Thermal demagnetization results indicate a great majority of the rocks at the sectionhave been strongly overprinted by recent magnetic field, but 57 samples have preserved remanentmagnetization with antipodal directions (mean D/I=4.2°/ 7.1°, K=9, α_(95) = 6.6°). Baaed on calculation,the location of the palaeomagnetic pole was at 68.8°N and 270.7°E, which is different from any palaeopolesobtained from younger Phanerozoic rocks in South China. The results reveal a polarity zonation which in-cludes at least 9 reversal events. A comparison of China's magnetostratigraphic records with those fromSiberia, Australia and the western U.S.A. shows that all the sections are characterized by frequent polarity re-versals.