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1.
The author argues for a pragmatic approach to the problem of defining the Precambrian-Cambrian boundary. A boundary at first occurrence of shelly fauna as recommended by the Precambrian-Cambrian working group will create severe difficulties in worldwide correlation. By placing the boundary stratigraphically somewhat higher (i.e. the Fallotaspis zone) with a more abundant fauna, there is a much better basis for biostratigraphic correlation.Eustatic sea-level changes may be another important tool for late Precambrian-early Palaeozoic correlation, and more detailed facies interpretation of such sequences should be carried out in order to recognise these eustatic sea-level changes.  相似文献   

2.
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3.
陈孟莪 《地质科学》1982,(3):253-263
研究剖面位于峨眉山东坡,距峨眉县城约14公里。峨眉山区在大地构造上处于川滇南北向构造带的东侧——峨眉山块断带。震旦系-寒武系出露在蛾眉山背斜两翼,构造简单,地层连续,化石丰富。此剖面先后经过多人研究。  相似文献   

4.
This paper gives a brief report on the latest results in litho-, bio-, and chrono-stratigraphy obtained fromthe authors' further research on the Meishucun section during 1987-1988. More attention was paid to the studyof the microtexture of Lapworthella and some new materials of trace fossils. Phycodes pendum Seilacher, animportant index for correlation, was also discovered in the Zhongyicun Member. In the Yu' anshan Membermany worms, medusas and arthropods of the Chengjiang fauna have been found by other workers. Asupplemental study was made on the fossil zones of the Meishucunian stage. Based on new isotopic data, theage of the Precambrian-Cambrian boundary should now be 597 Ma. It is further suggested that point "B" re-mains as an optimum selection for defining the Precambrian-Cambrian boundary.  相似文献   

5.
A carbon isotope stratigraphy from the lowest Cambrian strata in the Adelaide fold belt of South Australia is interpreted in terms of the geological context of the sequence: major transgression, developing circulation patterns and upwelling resulting from an adjacent opening ocean, and biomass increases stemming from the Cambrian radiation event. There is also evidence from the textures of ooids and cements in late Precambrian-Cambrian strata for subtle variations in seawater chemistry across the boundary and these may well have been instrumental in the development of calcareous skeletons in the early metazoans.  相似文献   

6.
The thick, richly fossiliferous succession of the upper Windermere Supergroup, Mackenzie Mountains, northwestern Canada, provides a test of integrated biostratigraphic and chemostratigraphic frameworks in terminal Proterozoic correlation. The C- and Sr-isotopic abundances of lower Keele Formation carbonates approximate those for other pre-Varanger samples, confirming that the simple disc-like fossils of the underlying Twitya Formation predate all known diverse Ediacaran faunas. "Tepee" and Sheepbed carbonates record strong post-glacial isotopic excursions; in contrast, delta13C values for Gametrail through Risky carbonates vary only within the narrow range of about +l% to +2%. A second negative excursion occurs in Ingta Formation carbonates that immediately underlie the paleontologically determined Precambrian-Cambrian boundary. The upper Windermere profile as a whole compares closely with curves determined for other terminal Proterozoic successions. The lowermost diverse Ediacaran assemblages in the Sheepbed Formation correlate chemostratigraphically with the oldest fauna in Namibia, but the two assemblages differ in taxonomic composition. Blueflower assemblages correlate both chemostratigraphically and taxonomically with faunas from Australia, China, Siberia, and elsewhere. Increasing data support the hypothesis that paleontological and geochemical data together provide a reliable means of correlating terminal Proterozoic sedimentary rocks throughout the world.  相似文献   

7.
The Carboniferous System of South China is famous for its well-developed rock sequence, variety of depositional types, and abundant fossils. Three established Global Boundary Stratotype Section and Point (GSSP) markers have been identified in several sections in South China. Of these sections, the Pengchong section is the GSSP for the base of the Visean Stage, whereas the Dapoushang and Naqing (Nashui) sections are excellent reference sections for the bases of the Tournaisian and Bashkirian stages, respectively. Other sections have good potential for the four unestablished GSSPs and the Devonian–Carboniferous boundary in South China. The Naqing (Nashui) section is a candidate for the GSSPs of four stages: the Serpukhovian, Moscovian, Kasimovian, and Gzhelian stages. The regional stages of China include the Tangbagouan, Jiusian, Shangsian, Dewuan, Luosuan, Huashibanian, Dalaun, and Xiaodushanian. The history, definitions, reference sections, sedimentary characteristics, biostratigraphy, and correlations of these Chinese regional stages are summarized. A Carboniferous stratigraphic chart of South China is provided, showing the correlation of global chronostratigraphic and biostratigraphic units with those in South China and the lithostratigraphic units of various areas in South China. The chart is presented as a new practical framework for the stratigraphic subdivision and correlation of the Carboniferous System in South China.  相似文献   

8.
贵州台江五河剖面灯影组顶部微体动物化石   总被引：2，自引：0，他引：2  
杨瑞东  钱逸 《地质科学》2005,40(1):40-46
贵州台江灯影组白云岩中发现了30～70μm的锥形微体动物化石,它们具有典型的锥管状、似几丁质壳壁和平行纤维结构等生物结构,可能分属软体动物Carinachitids、Arthrochites、Punctatus、Spondylotubus和似几丁虫类化石等5种类型。其中建立了一新属、种Spondylotubus taijiangensis Yang(gen.etsp.nov.)。在灯影组白云岩中这一类群的发现对研究前寒武纪寒武纪界线附近生物的多样性和生物地层,以及寒武纪生物大爆发都具有一定的科学意义。  相似文献   

9.
Secular variations of carbon isotopic composition of organic carbon can be used in the study of global environmental variation, the carbon cycle, stratigraphic delimitation, and biological evolution, etc. Organic carbon isotopic analysis of the Nangao and Zhalagou sections in eastern Guizhou reveals a negative excursion near the Precambrian-Cambrian boundary that correlates with a distinct carbonate carbon isotopic negative excursion at this boundary globally. Our results also demonstrate that several alternating positive and negative shifts occur in the Meishucunian, and an obvious negative anomaly appears at the boundary between the Meishucunian and Qiongzhusian. The isotope values are stable in the middle and lower parts but became more positive in the upper part of the Qiongzhusian. Evolution of organic carbon isotopes from the two sections in the deepwater facies can be well correlated with that of the carbonate carbon isotopes from the section in the shallow water facies. Integrated with other stratigraphic tools, we can precisely establish a lower Cambrian stratigraphic framework from shallow shelf to deep basin of the Yangtze Platform.  相似文献   

10.
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.  相似文献   

11.
我国南方的古老动物群及有关问题的初步探讨   总被引：10，自引：0，他引：10       下载免费PDF全文
忠华 《地质科学》1977,12(2):118-128
须腕动物门(Pogonophora)皱节虫科(Sabelliditidae)的化石(图版Ⅲ,图2)在前寒武纪和寒武纪沉积内均大量发现,最近此种化石还发现于苏联的中里菲界(约11亿年),被认为是一种可靠的最古老的后生动物化石。  相似文献   

12.
广西中-上泥盆统界线附近的化学地层学特征   总被引：5，自引：1，他引：5  
中国广西是世界上泥盆系发育最好的地区之一 ,沉积相齐全、出露良好 ,是进行地层学及沉积相研究的理想地区。大乐剖面与马鞍山剖面直线距离约为 7km,根据生物地层学的研究 ,两剖面中 -上泥盆统 (D2 - D3 )界线附近发生了明显的穿时现象。化学地层学的研究表明在这两条剖面上的界线附近 disparilis带内碳同位素组成发生了明显的两次负向波动 ,波动幅度分别可达 1.1‰和 0 .8‰ (马鞍山军田剖面 )和 1.5‰和 1.3‰ (大乐剖面 ) ;两条剖面上该牙形石化石带内及上下地层中元素锶 (Sr)的含量波动趋势同样可以很好地对比 ,本研究结果显示了岩石地层学界线的穿时现象并纠正了以往用岩石地层学特征划定 D2 - D3 界线的错误  相似文献   

13.
准噶尔盆地南缘侏罗纪沉积相演化与盆地格局   总被引：28，自引：4，他引：24  
通过对准噶尔盆地南缘侏罗系5条剖面的沉积特征对比,结合钻井资料和地震资料,确定了准噶尔盆地南缘侏罗纪盆地边界、沉积相演化及盆地格局。头屯河剖面和后峡剖面的沉积相对比及古流向测量表明二者在早、中侏罗世形成于同一沉积体系。在早、中侏罗世,沉积相逐渐从以辫状河-三角洲-湖泊相为主过渡到以河流相-湖泊相为主,沉积水体逐渐变浅;其中三工河组沉积时期盆地沉积范围达到最大,西山窑组沼泽相发育,车排子-莫索湾凸起自西山窑组沉积时期开始形成;早、中侏罗世的盆地边界至少位于后峡以南附近,此时不存在地理分割明显的天山山脉。晚侏罗世－早白垩世早期,沉积相从辫状河-滨浅湖相为主迅速演变为以辫状河-冲积扇相为主。在此期间盆地边界明显向北迁移,天山山脉明显隆升并造就天山南北沉积环境的巨大差异,博格达山构成盆地南缘的又一重要物源体系。  相似文献   

14.
本文系统描述了中国南部二叠、三叠纪“混生生物群”。根据笔者的统计,目前巳经发现有“二叠纪型”分子36属53种与三叠纪菊石、双壳类、牙形剌共生。 笔者认为中国南部可以以牙形剌Anchignathodus parvus 的出现作为三叠系的底界,双壳类Pteria ussurica variabilis,菊石 Hypophiceras的出现可以作为三叠系开始的辅助标志。文中还将这一界线与世界上其它地区的二叠、三叠系界线进行了对比。  相似文献   

15.
胡列群  李帅  梁凤超 《冰川冻土》2013,35(4):793-800
利用新疆91个气象台站1960-2011年的观测资料, 对南北疆及天山山区冬春年(10月-翌年5月)的积雪日数、最大积雪深度、积雪初始、终止日期等因子进行了统计分析, 并通过Kringing插值计算了新疆区域平均最大积雪深度的空间分布.结果表明: 新疆冬春季积雪主要分布在天山以北, 厚度可达30 cm以上, 天山以南积雪比较浅薄, 大部分在10 cm以下;50 a来, 南北疆及天山山区的积雪深度均呈小幅增长(天山山区增幅最大), 积雪日数呈略微降低趋势, 积雪初始、终止日期无明显变化. 天山山区的积雪变化与北疆有较高的相关性, 它们积雪深度和积雪日数的相关系数分别达0.708和0.614, 南疆积雪变化与它们几乎没有相关性;积雪深度与冬春年降水量的变化均有很好的一致性, 尤其在北疆,二者相关系数高达0.702, 但与平均温度呈低的负相关;积雪日数与冬春年降水量变化没有明显相关关系, 但均与气温呈较好的负相关, 在北疆二者的相关系数达-0.742.  相似文献   

16.
The Longtan Formation was originally thought to belong to the Late Permian, but this study reveals that the lower part of this formation belongs to the Middle Permian. The study proposes the corresponding chro-nostratigraphic boundary and new schemes for the correlation of geological sections. Based on these schemes a new understanding on the accumulation regularity of Permian coal measures in South China is reached.  相似文献   

17.
The world-class Imiter silver deposit, in the Anti-Atlas Mountains of Morocco, is a Neoproterozoic epithermal vein deposit genetically associated with a felsic volcanic event, and formed within a regional extensional tectonic regime. Rhyolitic volcanism related to ore formation has been dated at 550Dž Ma by ion-probe U/Pb on zircons. The economic silver mineralization is superimposed on an older, discrete base-metal assemblage associated with calc-alkaline granodioritic magmatism. The magmatism is dated at 572LJ Ma by ion-probe U/Pb dating on zircons, and by 40Ar/39Ar dating on hydrothermal muscovites. In the Anti-Atlas Mountains, the Precambrian-Cambrian transition appears as an important period for the formation of major, productive precious-metal deposits associated with volcanic events and extensional tectonics. The Imiter silver deposit constitutes a Precambrian analogue to modern epithermal deposits.  相似文献   

18.
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  相似文献   

19.
INTRODUCTION TheDabieMountainsareacollisionalorogenbe tweentheSouthandNorthChinablocks.Theageof theultrahighpressuremetamorphism(Hackeretal., 1998;Rowleyetal.,1997;Amesetal.,1993;Liet al.,1993)andthelateststratainvolvedintheforeland fold thrustbelt(Xueta…  相似文献   

20.
One major difficulty in geology is high-resolution correlation among widely separated sections, especially in the Paleozoic where magnetostratigraphy polarity is not well established because rocks are often remagnetized, where critical biostratigraphic zonation may be poor or lacking, or where structural complexities make correlations very difficult. To address this problem, we have been using magnetostratigraphy susceptibility measurements. Here, we report our work from the Middle Devonian in Europe and North Africa. The Middle Devonian (Emsian–Eifelian) global boundary stratotype section and point (GSSP), located in the Eifel Hills, western Germany, was ratified by the International Subcommission on Stratigraphy in 1985, after careful evaluation of the biostratigraphy for this and many other sections. The boundary interval has been characterized using biostratigraphy, and the beginning of the Eifelian stage has been specifically defined by the first occurrence of the conodont Polygnathus costatus partitus. We have collected the Eifel Hills section for magnetic susceptibility (MS) measurement and here we establish it as the magnetostratotype for the Emsian–Eifelian stage boundary, by formally defining the magnetostratigraphy susceptibility for the section. We then collected, measured and compared the magnetostratotype to four other sections for which conodont biostratigraphy has been studied and where P. costatus partitus is present; two Emsian–Eifelian sections in Morocco and two sections in the Czech Republic (including the Emsian–Eifelian parastratotype). Finally, we have measured the MS for the El Puerto Creek section in the Cantabrian Mountains of Spain and identified the location of the Emsian–Eifelian boundary within the section based on MS comparison to the GSSP in conjunction with excellent biostratigraphic indicators, primarily brachiopods. While the conodont zonation in the El Puerto Creek section is poorly defined, we believe that the correspondence between the MS and biostratigraphy in the section allows the identification of the Emsian–Eifelian boundary. These results indicate that this method can be successfully applied to marine sequences where ambiguities in correlation exist.  相似文献   

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