扬子区震旦纪地层序列和南、北方震旦系对比

198 2年“晚前寒武纪地层分类命名会议”决议“震旦系是青白口系之上的晚元古代最上部的一个年代地层单位 ,以三峡地区的剖面为代表 ,暂以莲沱组底界为底界”。但从区域性对比和同位素年代地层学分析 ,莲沱组底至黄陵花岗岩的侵蚀面之间有约 10 0 Ma的沉积缺失 ,莲沱组和南沱组也不能代表 75 0～ 6 6 0 Ma间的沉积历史。峡东地区震旦系下部地层不完整是显而易见的。本文赞同修订震旦系的含义 ,以下冰碛层 (古城组或铁丝坳组 )之底为震旦系的底界 ,年龄为 70 0 Ma。朝鲜飞浪洞组可与古城组、大塘坡组和南沱组对比 ,祥原系及辽南、徐淮地区的相当地层属“南华冰期”前的沉积地层。建议震旦系之下至青白口系顶 (85 0 Ma)之间建立辽南系 ,从而完善我国晚元古代年代地层框架     

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.     

Early Paleozoic orogeny in southern South America

In northwest Argentina, weakly metamorphic clastic and calcareous sedimentary rocks of latest Precambrian to Lower Cambrian age (Puncoviscana Formation and related units) contain an abundant ichnofauna of both chronostratigraphic and paleoenvironmental value. In the western and central Sierras Pampeanas, metasedimentary and metavolcanic rocks are considered to form part of the same geotectonic unit. This “Pampean orogenic cycle” includes geosynclinal sedimentation of latest Precambrian to Lower Cambrian age, as well as magmatism, metamorphism and deformation of Middle to Upper Cambrian age, documented by an angular unconformity below the Upper Cambrian to Devonian rocks of the “Famatinian orogenic cycle”. In some of the metamorphic rocks of the Pampean Cycle a pre-Ordovician folding is also distinguished from a later tectonic overprinting. Hence, the concept of a Pampean cycle differs from other concepts of late Precambrian orogenic cycles of South America which are only defined by radiometric ages. The Pampean orogenesis may be compared with the Ross orogenesis of the Transantarctic Mts., the Tyennan orogenesis of Australia and some of the deformation phases of the Damara orogen in Namibia.     

淮北地区寒武系/新元古界界线讨论

淮北地区寒武系与新元古界的界线 ,长期以来存在争议 ,主要有 5种划分意见 :猴家山组 /沟后组 ,沟后组 /金山寨组 ,沟后组上段 /沟后组下段 ,金山寨组 /望山组及猴家山组 /金山寨组之间。通过近年来的实地考察和室内研究 ,从叠层石、宏体碳质压膜化石及小壳动物化石组合综合考虑 ,认为该区新元古界最上面的岩组应是沟后组 ,而超覆于区内新元古界不同层位上的长期被描述为猴家山组“豹斑状”灰岩、白云岩 ,实为昌平组 ,属下寒武统     

The Precambrian—Cambrian boundary: A symposium

Contributions to a symposium of the IUGS Subcommission on Cambrian Stratigraphy at the International Geological Congress in Montreal in 1972 are the basis of this paper which is intended to give guidance to further work of what is now a Working Group on the Precambrian—Cambrian boundary of the International Geological Correlation Programme (UNESCO/IUGS). The proposed principles for the definition of the boundary are based on those accepted by the Commission on Stratigraphy, particularly on stratigraphic classification and on defining the Silurian—Devonian boundary. These matters are discussed by the authors in general terms and by W.B. Harland in terms of procedure. They are illustrated by examples of stratigraphic sequences across the boundary in Siberia given by A.Yu. Rozanov and discussed critically by V.E. Savitsky. New relevant discoveries of Early Cambrian faunas and their stratigraphic setting are reviewed by A. Boudda et al. P.E. Cloud's contribution, published elsewhere, and work in Australia are reviewed by the authors.The conclusions, based not only on the symposium material but also on current opinion, are that no single sequence which could serve as a reference standard for the Precambrian—Cambrian boundary has yet been identified but that many significant ones have been described which will be further examined. While the general limits for the choice of a boundary definition should lie between the horizons with fossils of Ediacaran type and those with diversified trilobite assemblages, a number of “Working Reference Points” exist in that interval which are correlatable horizons of faunal change. These cannot be defined simply as horizons of first appearance.     

华北晚前寒武纪（中、新元古代）岩石地层单位及多重划分对比

晚前寒武纪地层是华北早前寒武纪褶皱变质基底之上的第一套沉积盖层。主要发育和分布于华北晚前寒武纪的一些裂谷系－裂陷槽中，但各地沉积开始时间不一，后期遭受剥蚀程度不一。长期以来在地层划分、岩石地层命名、使用及年代属性上认识不统一，在一些地区认识分岐很大。笔者在岩石地层单位、地质特征认识的基础上，进行了全区（群、组）统一对比，明确了可作为华北晚前寒武纪沉积序列的代表性岩石地层单位及岩石组合特征；并介绍晚前寒武纪叠层石组合、微古植物特征性分子和已发现的宏观藻类和后生动物，论述了层型所在地区年代地层划分及层型以外各地层分区岩石地层单位年代属性的确定依据。     

Protoconodont fossils for refining the Cambrian bottom and the contribution to shale gas formation along the southwest margin of Yangtze Block

It has been an intense debate on the exact boundary between Ediacaran and Cambrian in the southwest Yangtze Block. The calibration of this critical boundary has a remarkable influence on the further investigation of the break-up of the Rodinia Supercontinent, the early life evolution, and the mechanism of the phosphorite deposit. Ediacaran and Cambrian strata and fossils are widely distributed in Anning, Yunnan Province in China. In recent years, the Xiaowaitoushan Member from the Lower Yuhucun Formation has been studied. Through this interval with continuous collections, the first appearance datums (FADs) of the protoconodont (Fomitchella cf. inchoate Yang et He, Protohertzina cf. anabarica Missarzhevsky) and globular embryos fossil (Olivooides sp.) earlier than these in the Lower Cambrian strata of the Meishucun Formation were discovered. This discovery indicates that the Xiaowaitoushan Member has included more FADs than the previously discovered single FAD of Anabarites primitivus Qian et Jiang, and the Ediacaran–Cambrian boundary in southwest China should be replaced below the Point “A” of the Meishucun Formation in Yunnan Province. The Point “B” of the Meishucun Formation is younger than the suggested age 541 Ma of the Ediacaran–Cambrian boundary and can no longer reference the Global Boundary Stratotype Section and Point (GSSP) correlation in southwest China. It can be suggested based on the previous stratigraphy and palaeontology studies from northern Sichuan and southern Shaanxi and the FAD of the globular embryos fossils that the Ediacaran−Cambrian boundary in the southwest Yangtze Block should be placed at the base of the Xiaowaitoushan Member; other phosphorite strata refer to Xiaowaitoushan Member. The discovery of the FADs of the shelly fossils in the Xiaowaitoushan Member provides new evidence for the global correlation of the Ediacaran –Cambrian boundary in the southwest Yangtze Block. The conodont discoloration index (CAI) of the specimens in Anning is between 2 and 3, which indicates that the organic matter in Xiaowaitoushan Member is matured and has high potential to form a shale gas reservoir.     

山东青州尧王山地区寒武系-奥陶系界线及地层划分

鲁西地区的晚寒武世——早奥陶世地层，由于发生了较强烈的白云岩化作用，地层中的沉积构造和生物化石几乎消失殆尽，地层划分对比很困难，甚至寒武系与奥陶系的界线也难以确定。调查发现，青州尧王山地区该时期的地层发育齐全，白云岩化程度较弱，牙形石化石丰富，可与国际层型剖面对比，是鲁西地区完善地层划分和确定寒武系与奥陶系界线的理想地区。     

峡东地区震旦系层型剖面的界定与层序划分

通过震旦系研究历史的回顾,在前人研究的基础上,结合近年来综合地层研究的成果,试图建立可供全球对比的中国末元古系层型剖面。我国震旦系研究历史悠久,典型剖面经历南北之争,数十年来存在多种界定意见。通过近十年的研究,笔者依然认为峡东地区震旦系剖面沉积最为连续,出露完整,具有生物演化特征明显和形态多样的特点,可与世界各地的末元古纪地层进行广泛对比。目前,其上界定位于峡东地区灯影组天柱山段小壳化石带之下(即相当云南晋宁梅树村剖面震旦—寒武系界线小壳化石带B点,年龄为539±34Ma),而底界的厘定在国内一直存在多种意见。本文通过对峡东地区震旦系剖面的综合地层研究,结合生物地层学、年代地层学、层序地层学、C/O同位素研究以及沉积相等方面的综合分析,认为震旦系底界应划定在南沱冰期之后的陡山沱期沉积的下界,重申应选定峡东地区剖面为震旦系的层型剖面。     

辽南、苏皖北部、鲁西鲁东晚前寒武纪地层的划分与对比

辽南、苏皖北部地区的晚前寒武纪地层层序,以及鲁东蓬莱群与鲁西土门群的上下层位,存在着"叠接"与"叠置"的错误.本文通过对辽南及苏皖北部地区的晚前寒武纪地层层序和鲁东蓬莱群与鲁西土门群层位问题进行深入剖析,在厘清地层层序的基础上提出新的划分与对比方案.新方案中这些地层在我国晚前寒武纪地层柱中的位置,反应出了震旦系与青白口系的地史演化及生物演化间的重要关系.     

敦煌地区晚震旦世-早寒武世沉积地层的发现及其大地构造意义

近年来,随着敦煌地区越来越多古生代岩浆作用和变质作用等地质信息相继被揭示,许多学者据此提出了"敦煌造山带"的认识,并受到地质学界的广泛关注。本次工作在敦煌地区东北缘发现了大规模露头连续的沉积地层,岩石组合主要为变砂岩和变泥质砂岩,夹少量变砂质泥岩,偶夹变砂砾岩和变硅质岩。通过U-Pb同位素法对该套沉积岩碎屑锆石和侵入其中的花岗岩进行年龄测定,限定其沉积时代为517.3～574.4Ma,属于晚震旦世-早寒武世,由此证明敦煌地区新元古代-古生代沉积地层的存在。综合岩石组合、重矿物特征、岩石地球化学、碎屑锆石结构及年龄频谱等分析,推测该套沉积岩形成于大陆边缘滨海环境,其物源来自敦煌地块甚至塔里木板块前寒武变质基底,揭示了敦煌地区当时应存在着大规模前寒武基底,同时说明敦煌地块的北部古边界应位于疏勒河断裂附近,为确定敦煌地区构造属性、划分区域构造单元提供了关键信息。     

试论华北板块寒武纪地层的穿时性

华北板块寒武系馒头组和毛庄组，徐庄组和张夏组，崮山组、长山组和凤山组分别以紫红色泥质白云岩及页岩、鲕粒灰岩和竹叶状灰岩为特征，依次形成于Xi湖－－塞卜哈、鲕滩和滩外斜坡环境。若按传统的时代划分，必然得出互相矛盾的古地理解释。按Walther相律，应有大量的柴红色泥质白云岩和页岩，鲕粒灰岩与竹叶状灰岩是同时形成的，无论泥质白云岩和页岩，鲕粒灰岩还是竹叶状灰岩都是随着海侵、相迁移而一个地区，一个地区依次形成，并且它们都是穿时的。     

扬子区早寒武世早期磷质小壳化石的再沉积和地层对比问题

扬子区早寒武世早期的磷酸盐化小壳化石的发现,为早期动物演化及震旦系-寒武系界线地层的划分与对比研究做出了重要贡献。但碳酸盐岩地层中的这类小壳化石易于被风化剥离出来并成为磷质颗粒再沉积,这种现象在地层中常能遇到,它会给对某些生物分布时限的确定和地层对比造成混乱。考虑早寒武世一些主要小壳化石的再沉积和地层对比时要注意以下问题:1)带和带的磷质小壳化石产于Paokannia或Hunanocephalus的层位,它们无疑是再沉积的;2)组合带标志性化石与组合带标准化石共生,应判定其沉积时期为组合带时;3)扬子台地区的梅树村阶地层大都不全或缺失,保存的梅树村阶地层普遍与震旦系灯影组不同层位假整合接触,其岩性及生物特征均与下伏地层不同,另建组级地层单位是合理的;4)“杨家沟段”、“西蒿坪段”、“宝石坡组”不能作为灯影组顶部地层,它们是水井沱组沉积旋回的一部分,更不能因它们是筇竹寺期的沉积而把“灯影组”顶界上升到筇竹寺阶;5)滇东北地区大海段中产有丰富的Heraultipegmayunnanensis,它与Siphogonuchitestriangularis和Paragloborilussubglobosus共生,分布局限,其他地区仅在组合带中零星分布,所以在S.triangularis-P.subglo-bosus组合带()的上部建立一个H.yunnanensis组合亚带似乎更合适些。     

地层学的几个基本问题及中国地层学可能的发展趋势

对地层学的几个基本问题,包括地层分类、国际地层表的建立、全球地层标准剖面及剖面点进行了讨论。在各种地层分类体系中,年代地层学和岩石地层学是分类中的主体,其他系统都居于补充或从属的地位。国际地层表是地质学的基本文件和地学研究的主要参照,其建立的基础应是地史上关键性地质事件的记录,其方法应是多学科的综合研究。前寒武纪与显生宙划分的建立标准应是一致的。国际地层委员会制订的GSSP做出了重大贡献,但所定点位不够稳定,点位以外无法对比,在实践上和认知上都有不足。可考虑用多学科综合研究,寻觅接近等时的物理界面取代剖面点作为地层界面。在中国地层研究方面,以三次全国地层会议为准,分阶段概括论述了半世纪以来做出的主要成果。对今后中国地层研究的可能趋势提出了一些看法。主要是:应从系统论、整体观和复杂性观点的高度开展多学科的融合,共同解决地层的时空关系和划分对比等复杂问题;应当扩大服务面和扩展研究面,着重开展以古环境和古气候为中心的地层研究,协助解决与经济建设中的资源与环境两大主题有关的地质课题;制订2008年后的中、长期规划,改进GSSP程序,持续完善《国际地层表》这一永恒任务;开展高分辨率、高精度地层学研究,建立融合及协调多种分支学科的综合地层学;扩大地层学对整个地球科学的服务,使中国地层学研究进入一个新的阶段。     

锶、碳同位素演化在新元古代地层定年中的应用——以胶辽徐淮地层分区为例

根据Sr、C同位素地层学原理，利用胶辽徐淮地区晚前寒武纪地层Sr、C同位素数据，与国际上已有的Sr、C同位素演化曲线对比，结果表明，胶辽徐淮地区晚前寒武纪地层是同一时期的沉积物，沉积主体之间Sr、C同位素比值的对比性很好，沉积时限约在750-860Ma之间，并延续到震旦纪，为北方青白口纪及其后的沉积。同时也表明，Sr、C同位素演化相结合是解决缺乏大化石的晚前寒武纪地层对比的有效方法。     

四川峨眉高桥震旦系—寒武系界线

<正> 一、前言 四川峨眉高桥震旦系—寒武系界线剖面位于峨眉山东麓。其大地构造位置居川滇南北向构造带东侧,扬子台背斜西部边缘地带。这里震旦纪和寒武纪地层广泛发育,构造简单,沉积连续,化石丰富,交通方便,是研究震且系与寒武系界线比较理想的地区之一。     

Solutions in chronostratigraphy: the Paleocene/Eocene boundary debate,and Aubry vs. Hedberg on chronostratigraphic principles

In several recent papers, M.-P. Aubry et al. have argued that “Hedbergian” principles of chronostratigraphy are being violated by the International Commission on Stratigraphy (ICS) when selecting Global Stratotype Sections and Points (GSSPs) for the formal divisions of the geological time scale. The current debate over the definition of the Paleocene/Eocene (P/E) boundary has been a major focus of their arguments. Unfortunately, Aubry et al. have obscured matters by misusing the term “unit stratotype,” and by equivocally using the term “stage” for the very different concepts of “synthem” and “global chronostratigraphic stage.” The P/E boundary option most repugnant to Aubry et al. (Carbon Isotope Excursion (CIE)=P/E=Thanetian/Ypresian boundary) is perfectly compatible with H.D. Hedberg's views. In contrast, another option preferred by Aubry et al. (recognition of new ∼1 m.y. duration age/stage between Thanetian and Ypresian) is inconsistent with Hedberg's views. Additional problems with the P/E boundary arguments of Aubry et al. include the fact that a “Ypresian unit stratotype” does not exist, the fact that the base of the Ypresian synthem is not immutable, and the fact that the nannofossil Tribrachiatus digitalis is of dubious relevance to the boundary debate.As for chronostratigraphy in general, Aubry et al. have misrepresented Hedberg's views by: (1) falsely claiming that the content of a stage is what determines its boundaries; (2) misunderstanding the general concept of the boundary stratotype; (3) distorting the “base defines boundary” principle; (4) falsely claiming that traditional (pre-GSSP) chronostratigraphic boundaries cannot be changed; (5) falsely implying that traditional stage unit stratotype boundaries can be adjusted by no more than 300,000 years when defining formal age/stage boundaries with GSSPs; (6) falsely claiming that the definition of a geochronologic/chronostratigraphic boundary should precede its correlation; (7) claiming that traditional unconformable “stage” boundaries may be suitable horizons for GSSPs; (8) distorting the meaning of “arbitrariness” in regard to the definition of geochronologic/chronostratigraphic boundaries; and (9) claiming that GSSPs are inherently unstable in that they are subject to redefinition whenever a more powerful element of correlation is discovered. If taken seriously, the unit stratotype-sanctifying chronostratigraphic philosophy of Aubry et al. would require the creation of perhaps dozens of new Phanerozoic ages/stages of relatively very short duration wherever there was a significant gap between two successive historical stage unit stratotypes. For all of these reasons, the arguments of Aubry et al. have no merit.     

层序的成因及层序地层格架

层序的成因是沉积基准面变化所引起的 ,沉积基准面是全球性海平面变化、构造升降、沉积物供应和气候四个因素耦合作用导致的。通过对同位素测年、生物地层对比、层序成因、层序地层对比及层序界面性质五个方面的讨论 ,指出层序地层格架不是一个等时地层格架 ,不能作为全球对比的标准 ,它所体现的主要是沉积作用和沉积地层在三维空间的展布规律。     

我国南方的古老动物群及有关问题的初步探讨

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。     

Reclassification of the Meso- and Neoproterozoic Chronostratigraphy of North China by SHRIMP Zircon Ages

Abstract: High-quality zircon U-Pb ages acquired from Meso- and Neoproterozoic strata in North China in recent years has provided a high-resolution chronostratigraphic framework for dating. A basis of this high-level chronostratigraphic system provides the foundation for a global Precambrian study and stratigraphic correlation and so recent geological studies have focused attention on systemic SHRIMP zircon dating. A chronology of Meso- and Neoproterozoic strata and the time of origin of the overlying Changcheng System is given on the basis of new SHRIMP zircon dating from the Qianxi Complex and diabase of the Chuanlinggou Formation. A new tectonostratigraphy for a Neoproterozoic chronostratigraphic framework in the southeastern margin of the North China continent is underpinned by the new SHRIMP zircon dating of a Neoproterozoic mafic magma diabase in the Jiao-Liao-Xu-Huai Sub-Province.