南盘江盆地早—中三叠世层序地层格架及相对海平面变化研究

南盘江盆地的早—中三叠世地层中 ,沉积相形成复杂而有序的空间变化和时间变化。二叠纪与三叠纪之交的大规模台地淹没事件之后 ,三叠纪碳酸盐台地从缓坡型演化为镶嵌陆架型 ;空间上 ,从连陆台地到浊积盆地相分异特别明显 ,而且在盆地中发育若干的孤立台地 ,特别是南宁和靖西一带 ,孤立台地上早三叠世的鲕粒滩以及连陆台地边缘的礁滩相灰岩更是引人注目。尽管不同相带的三级沉积层序相序组构千差万变 ,并且它们的形成时限也不尽相同 ,但是由其所表征的相对海平面变化则具有大致的同步性 ,因此在早—中三叠世地层中可以识别出 6个三级沉积层序。以地层记录中的两种相变面和两种穿时性为基本要素 ,可以建立南盘江盆地早—中三叠世的层序地层格架。     

南盘江盆地中部西林断隆南翼中-下三叠统沉积学特征及其大地构造意义

印支造山带对华南地质演化具有重要影响,南盘江盆地作为华南与印支造山带相关的最大的盆地,其构造演化过程备受关注,然而对于盆地由伸展到挤压的构造转换时限还存在争议。西林县位于南盘江盆地的中部,古生界和中-下三叠统出露良好,是进行沉积大地构造学研究的理想地区。为进一步明确南盘江盆地的构造演化过程,本文选取南盘江盆地中部西林县一带中-下三叠统进行了详细的沉积相分布和演化、古水流以及碎屑组成分析。结果表明,空间上,下三叠统自下而上自北向南依次出露:(1)泥岩、泥灰岩、砂屑灰岩和凝灰岩构成的潮坪-泻湖相沉积;(2)砾岩、含砾砂岩、细砂岩和粉砂岩构成的块体搬运沉积(MTD,Mass-transport deposit)与浊积扇相沉积互层;(3)中粗砂岩、粉砂岩、泥岩组成的浊积扇相沉积,构成向上水体急剧加深的沉积序列。中三叠统为一套浊积扇相沉积,由粗砂岩、细砂岩、粉砂岩和泥岩组成。古水流和碎屑组成分析结果显示,西林县一带下三叠统碎屑物主要来自北侧西林-隆林一带的碳酸盐岩台地,而中三叠统碎屑除来自北侧相邻碳酸盐岩台地外,还可能来自江南造山带、康滇古陆、云开地块和峨眉山玄武岩。沉积相的垂向变化记录了西林一带由古生代孤立碳酸盐岩台地向三叠纪半深海浊积岩盆地的演化过程,而早三叠世MTD是盆地张开过程中的直接沉积记录,以上地质事实暗示了南盘江盆地在早三叠世受控于区域伸展体制,西林一带的古生代孤立碳酸盐岩台地则是伸展过程中形成的断隆。盆地内的基性岩墙侵位(258~248Ma)以及西林一带早三叠世晶屑沉凝灰岩的锆石U-Pb年代学分析结果(249.4±1.2Ma)表明南盘江盆地在晚二叠世至早三叠世处于伸展构造背景之下,中三叠统为半深海浊积岩沉积则表明这一伸展过程至少持续至中三叠世。由于在时间上和空间上,南盘江盆地的张开都与古特提斯分支洋盆的俯冲消减有关,因而我们认为南盘江盆地也是晚二叠世到中三叠世古特提斯洋岩石圈俯冲体系的一部分。由于南盘江盆地及其邻近区缺失上三叠统沉积,这可能说明古特提斯洋俯冲结束于中三叠世。     

南盘江坳陷晚古生代隆林孤立台地沉积特征与演化阶段

南盘江坳陷隆林孤立碳酸盐台地在中泥盆世至晚二叠世的大部分时间内属于四周被深水海槽围绕的、受南盘江海演化拉张断裂而形成的一个孤立碳酸盐台地环境(其中早石炭世晚期-晚石炭世为连陆台地阶段)。通过对隆林地区晚古生代野外地层踏勘成果表明,孤台-台间海槽相区共识别出碳酸盐潮坪、台地边缘浅滩、台地边缘礁、台缘斜坡、台棚及台盆相等6种沉积相类型,并建立了其独具特色的孤立台地沉积模式。研究表明,它的演化经历了边缘碳酸盐台地(D1-D2)、孤立碳酸盐台地(D3-C11)、连陆台地(C12-C2)、孤立-淹没碳酸盐台地(P)4个发展阶段,反映了南盘江盆地在晚古生代强烈扩张、沉降,扬子地台边缘拉伸、破裂,微地块向盆地滑移的构造背景。     

贵阳花溪地区下中三叠统露头层序地层研究

贵阳花溪地区下、中三叠统可划分为碳酸盐台地相、台缘相和盆地相三个沉积相区。在对不同相区内典型剖面详细观测、层序界面识别基础上,将下、中三叠统划分为5个Ⅰ型沉积层序和1个Ⅱ型层序。通过研究实测剖面纵向的沉积相变和横向低位岩楔的位置迁移,讨论了区内相对海平面变化。研究区在早-中三叠世经历了一次完整的二级海平面升降旋回:早三叠世与全球海平面变化基本一致,呈上升趋势;中三叠世由于构造作用,海平面总体呈下降趋势,表现出区域特殊性。     

滇黔桂盆地及邻区二叠纪层序地层格架及古地理演化

滇黔桂盆地及邻区的二叠系包括船山统、阳新统和乐平统。船山统与阳新统之交的黔桂运动主幕不整合面、阳新统和乐平统之交的东吴运动主幕不整合面的不整合特征明显,同时因其代表了研究区沉积盆地性质发生较大变化的界面而成为较为典型的I型层序界面。滇黔桂盆地及邻区的二叠系以其明显的沉积相分异而引人注目：在连陆台地上发育含煤地层,而在连陆台地边缘及孤立台地上发育海绵生物礁,形成一个典型的“台-盆-丘-槽”的古地理格局。伴随着强烈的东吴运动第一幕,研究区西北部发生强烈的火山活动,形成分布范围较广的峨嵋山玄武岩;东南部的“钦防残留海槽”关闭,使研究区的古地理格局发生了较大变化。二叠系与三叠系之交发生的较为典型的台地淹没事件形成了一个较为典型的淹没不整合面。根据沉积物的时间演化序列和沉积相的空间展布形式所指示的规律,研究区的二叠系可以划分为以下三级层序：船山统与下伏石炭系顶部的地层构成一个三级层序(SQ¹⁹),阳新统包含四个三级层序(SQ²⁰到SQ²³),乐平统包括两个三级层序(SQ²⁴和SQ²⁵)。在层序地层框架内,系列古地理图和系列层序地层格架栅状图较为系统地反映了研究区二叠纪复杂而有序的时间和空间相变特征。主要的时间相变面即形成层序界面,具有明显的“跳相”和地层间断现象,由于在不同地点间断的时限不一致而造成“间断面穿时”;沉积环境的空间变化,以及伴随着时间变化中的相带迁移所造成的空间相变,其相应的相变面总是斜交时间面而造成“相变面穿时”;不同沉积阶段的层序具有不同的相序组构,并在空间上形成有序的变化,从而代表了不同的古地理背景。因此,层序地层研究的核心内容是“沉积物的时间演变序列和沉积相的空间展布形式所代表的规律性”,结合生物地层特征,这种规律性本身也可以作为地层划分和对比的标志。     

Sequence stratigraphy of a Mesozoic carbonate platform-to-basin system in western Sicily

Sequence stratigraphic studies of the Triassic through Paleogene carbonate successions of platform, slope and basin in western Sicily (Palermo and Termini Imerese Mountains) have identified a sedimentary cyclicity mostly caused by relative oscillations of sea level. The stratigraphic successions of the Imerese and Panormide palaeogeographic domains of the southern Tethyan continental margin were studied with physical-stratigraphy and facies analysis to reconstruct the sedimentary evolution of this platform-to-basin system. The Imerese Basin is characterized by a carbonate and siliceous-calcareous succession, 1200–1400m thick, Late Triassic to Eocene in age. The strata display a typical example of a carbonate platform margin, characterized by resedimented facies with progradational stacking patterns. The Panormide Carbonate Platform is characterized by a carbonate succession, 1000–1200 m thick, Late Triassic to Late Eocene, mostly consisting of shallow-water facies with periodic subaerial exposure. The cyclic arrangement has been obtained by the study of the stratigraphic signatures (unconformities, facies sequences, erosional surfaces and stratal geometries) found in the slope successions. The recognized pattern has been compared with coeval facies of the shelf. This correlation provided evidence of sedimentary evolution, influenced by progradation and backstepping of the shelf deposits. The stratigraphic architecture of the platform-to-basin system is characterized by four major transgressive/regressive cycles during the late Triassic to late Eocene. These cycles, framed in a chronostratigraphic chart, allows the correlation of the investigated shelf-to-basin system with the geological evolution of the African continental margin during the Mesozoic, showing tectono-eustatic cycles. The first cycle, encompassing the late Triassic to early Jurassic, appears to be related to the late syn-rift stage of the continental margin evolution. The following three cycles, spanning from the Jurassic to Eocene, can be related to the post-rift evolution and to thermal subsidence changes.     

黔中、黔南下、中三叠统沉积相和层序地层

本文记述了对黔中、黔南地区早、中三叠世的碳酸盐岩和陆源的屑岩沉积的分析研究结果,着重讨论了该区沉积层序及其形成机制。早二叠世该区为缓坡,中三叠世演变为陡坡,沉积层序发生了变化。沉积盆地边缘沉积与海平面波动有密切关系,对斜坡上的层序地层及海平面波动作了初步研究。     

Late Paleozoic Sequence-Stratigraphic Frameworks and Sea Level Changes in Dianqiangui Basin and Its Adjacent Areas with Systematic Revision of Regional Unconformities

The formation process of the Dianqiangui basin, a special basin, occurred after the Caledonian orogeny, in the south of Guizhou, the west of Giamgxo and the southeast of Yunnan, experienced three periods:it began in the Devonian, persisted in the Carboniferous, and became fiercer in the Permian. Controlled by syndepositional fault-zones, varieties of isolated carbonate platforms, large and small, were developed in the of a deep-water basin, namely, an inter-platform ditch. And a special paleogeographical Late Paleozoic pattern marked by “platform-basin-hill-trough” was produced in both the Dianqiangui basin and its adjacent arms. Affected by regional tectonic activities and the global changes in the sea level, the platform carbonates and coal measures superimposed each other cyclically on the attached platform. The reef-building on the isolated platform and the margin of the attached platform corresponds to the development of the shale succession in the deep-water basin. All of these elementary characteristics reflect a regular and sophisticated filling sucoession of the Dianqiangui basin, a result of the dual controls of the regionally tectonic activities and the eustacy.Based on the two elementary features of the third-order sequences, i.e. the regularity of sedimentary-facies succession in space and the simultaneity of environmental changes in time, 25 third-order sequences could be discerned in the Upper Paleozoic strata in the Dianqiangui basin and its adjacent areas. On the basis of the two kinds of facies-changing surfaces and the two kinds of diachronisms in stratigraphic records, the regional Late Paleozoic sequence-sequence-stratigraphic framework in the Dianqiangui basin and its adjacent areas can be established.There are two types of facies-changing surfaces and two types of diachronisms in stratigraphic records: the static type, a result of the change in sedimentary facies in space, and the dynamic type, a remit of the change in time. These two types of facies-changing surfaces led to the generation of the two types of diachronisms: the diachronism of facies-changing surfaces that was formed by the static facies-changing surfaces, and the diachronism of punactuated surfaces that was formed by the dynamic facies-changing surfaces. The two types of facieschanging surfaces and the two types of diachronisms in stratigraphic records are the key to the establishment of the sequence-stratigraphic framework, The sequence boundaries could be divided geologically into four types:tectonic unconformity, sedimentary unconformity,drowned unconformity and their correlative surfaces,All of these four types can be further grouped into exposed punctuated surfaces and deepened punctuated surfaces,The tectonic unconformity in similar to Type Ⅰ sequence boundary,and the sedimentary unconformity is similar to Type Ⅱ sequence boundary defined by Vail et al.In terms of sequence stratigraphy,the tectonic unconformities of the Ziyun movement,the Qiangui epeirogeny and the Dongwu revolution as well as the drowned unconformity in the transitional period from the Permian to the Triassic can be systematically defined and their geological characteristics are briefly presented.     

桂西北晚古生代乐业孤立碳酸盐岩台地沉积特征与演化阶段

桂西北乐业台地是右江盆地北部典型的晚古生代孤立碳酸盐岩台地。从中泥盆统唐家湾组至上二叠统合山组均由碳酸盐岩构成,与北侧陆棚区多样的沉积类型及台地周边泥质-硅质岩深水沉积形成鲜明对比。台地内上古生界主要由台缘生物礁组合和礁后澙湖组合两种浅水碳酸盐沉积类型构成。地层发育与沉积特征主要受基底沉降、海平面波动、气候变化和盆地内生碳酸盐沉积速率控制。研究表明,乐业台地是在右江盆地强烈扩张、沉降过程中由扬子地台南缘破裂的微地块向盆地滑移而形成的孤立台地。它的演化经历了边缘台地（D1-D2）、孤立台地（D3-P2）和淹没台地（P3-T1）3个发展阶段。孤立台地是其最重要的主体特征,反映了右江盆地在晚古生代强烈扩张、沉降,扬子地台边缘拉伸、破裂,微地块向盆地滑移的构造背景。乐业孤立台地的形成及演化模式可能具有普遍性,也适用于右江盆地西北部其他晚古生代孤立碳酸盐岩台地。     

Stratigraphic Correlation of Middle Triassic Sequences among Different Paleogeographic Sedimentary Facies in South China

INTRODUCTIONIn South China,the marine Middle Triassic is distributedmainly over the Yangtze region along the present YangtzeRiver,where the Hercynian orogeny did not happen but thesubsequent Indosinian m ovement greatly changed thepaleogeographic pattern and depositional history.The TriassicIndosinian movement troansfered most parts of the Yangtzeplatform from marine to terrestrial in early or late MiddleTriassic (Table 1) and finally ended the marine history of theseareas.The first …     

贵州南部二叠系层序地层格架

通过对贵州南部典型的二叠系剖面(包括石炭系上部的地层)的层序地层研究,共识别出7个三级沉积层序,在对不同相带剖面三级层序对比的基础上建立了贵州南部二叠系的层序地层格架。该二叠系层序地层具有以下明显的特征:在连陆台地上发育煤系地层,连陆台地边缘则发育海绵生物礁和颗粒滩,相分异最明显的时期正好与生物礁发育的时期相对应;此外,在二叠系与三叠系之交发生了大规模的台地淹没事件,因此,二叠系最顶部的三级层序的顶界面为一个典型的淹没不整合面。在二叠系层序地层格架图中较明显地表现出复杂而有序的时间和空间相变。     

四川盆地东北部下三叠统飞一—飞三段孤立碳酸盐岩台地沉积相及相关研究

四川盆地东北部在早三叠世飞仙关期的大部分时间内(飞一—飞三期)属于四周被深水海槽围绕的、受南秦岭海演化拉张断裂而形成的一个碳酸盐孤立台地环境,随四级海平面的升降变化、开江—梁平海槽的逐渐关闭和城口—鄂西海槽的东移,各种孤立台地亚相发生移动和转变,最终在飞三晚期至飞四早期孤立台地转化合并为川东北大型连陆台地。根据区域地质背景和地层沉积特征(岩性、古生物、沉积构造、测井)研究,划分了潟湖(包括蒸发潟湖、局限潟湖、半局限潟湖和点滩)、台地边缘鲕滩、斜坡、海槽4个亚相;建立出孤立台地的沉积立体模式并分析了沉积相从飞一飞三期的展布及演化过程;最后着重剖析了具备后期形成良好储层条件的孤立台地边缘鲕滩相带的迁移性、储层发育不均一性、测井和地震特征,沉积相对鲕滩气藏分布的控制,最后对孤立台地边缘鲕滩相中有望成为新的天然气勘探突破区进行了地震横向分布预测。     

Controls on carbonate platform architecture and reef recovery across the Palaeozoic to Mesozoic transition: A high-resolution analysis of the Great Bank of Guizhou

Carbonate platforms spanning intervals of global change provide an opportunity to identify causal links between the evolution of marine environment and depositional architecture. This study investigates the controls on platform geometry across the Palaeozoic to Mesozoic transition and yields new stratigraphic and palaeoenvironmental constraints on the Great Bank of Guizhou, a latest Permian to earliest Late Triassic isolated carbonate platform in the Nanpanjiang Basin of south China. Reconstruction of platform architecture was achieved by integrating field mapping, petrography, biostratigraphy, satellite imagery analysis and δ¹³C chemostratigraphy. In contrast to previous interpretations, this study indicates that: (i) the Great Bank of Guizhou transitioned during Early Triassic time from a low-relief bank to a platform with high relief above the basin floor (up to 600 m) and steep slope angles (preserved up to 50°); and (ii) the oldest-known platform-margin reef of the Mesozoic Era grew along steep, prograding clinoforms in an outer-margin to lower-slope environment. Increasing platform relief during Early Triassic time was caused by limited sediment delivery to the basin margin and a high rate of accommodation creation driven by Indosinian convergence. The steep upper Olenekian (upper Lower Triassic) slope is dominated by well-cemented grainstone, suggesting that high carbonate saturation states led to syndepositional or rapid post-depositional sediment stabilization. Latest Spathian reef initiation coincided with global cooling following Early Triassic global warmth. The first Triassic framework-building metazoans on the Great Bank of Guizhou were small calcareous sponges restricted to deeper water settings, but early Mesozoic reef builders were volumetrically dominated by Tubiphytes, a fossil genus of uncertain taxonomic affinity. In aggregate, the stratigraphic architecture of the Great Bank of Guizhou records sedimentary response to long-term environmental and biological recovery from the end-Permian mass extinction, highlighting the close connections among marine chemistry, marine ecosystems and carbonate depositional systems.     

中东地区阿普特阶Shuaiba组碳酸盐岩沉积体系特征及模式探究

中东地区主力产油层系Shuaiba组的勘探及研究逐渐以地层岩性圈闭为主,笔者通过总结Bab盆地阿普特阶Shuaiba组沉积相类型,多油田地层格架及空间展布特征的对比,为系统恢复Shuaiba组沉积演化过程及模式提供地质依据。研究表明,阿普特阶Shuaiba组共发育开阔台地、台地边缘、台缘斜坡及盆地相4种沉积相单元和6种亚相类型,各相带单元受控于四个三级层序且沿Bab盆地周缘呈带状展布。开阔台地一侧,主要沉积了第二个三级层序对应的Lower Shuaiba地层;台地边缘往Bab台内盆地区域,则以第三和第四个三级层序对应的Upper Shuaiba地层为主。Shuaiba组生物礁、滩建造集中发育在第二个三级层序的高位域阶段,滩间海、缓坡及盆地相受控于海进和低位体系域。阿普特阶Shuaiba台地边缘生物建隆、台内浅滩在空间上相互叠置并成带展布,符合弱镶边型缓坡台地沉积模式,该类型台地具备深水陆棚性质的非常宽缓的斜坡,且缓坡往盆地一侧发育一个镶边台地边缘。     

扬子地台与华南南盘江盆地大贵州滩三叠系沉积演化史

扬子地台是一个横跨华南地块的以浅海沉积为主的大型碳酸盐岩台地,南盘江盆地是发育在扬子地台碳酸盐岩台地背景之上的一个沉积盆地,从晚元古代到晚三叠世长期海相沉积演化历史中,扬子地台一南盘江盆地体系经历了多次重要的构造演化阶段。扬子地台从晚元古代到早三叠世末期一直保持为一个稳定的碳酸盐岩台地,在中三叠世末期扬子地块整体抬升,海平面下降,形成了遍及扬子主体的拉丁期大海退,从而使扬子地块大部分地区抬升为陆。南盘江盆地位于华南地块南缘,从晚元古代到晚三叠世沉积了一套厚度巨大的海相碳酸盐岩,晚三叠世发育了一套硅质碎屑的浊流沉积,区域沉积也由此转化为河流相沉积。二叠纪和三叠纪碳酸盐岩地层记录了碳酸盐岩台地长期演化历史及其特征多样的沉积建造和沉积环境,而硅质碎屑流和构造沉降速率的变化反映了盆地在三叠纪期间经历的聚合构造和前陆盆地发展过程。在三叠纪时期扬子地台沿西南一北东方向从云南围绕南盘江盆地向贵州延伸,在南盘江盆地中发育了几个孤立的碳酸盐岩台地,包括位于贵州南部和广西境内的大贵州滩和崇左平果台地。南盘江盆地在晚二叠世发生过一次区域性的海侵事件,早三叠世时期扬子地台和几个孤立台地为由鲕粒边滩组成的低角度斜坡,中三叠世（安尼期）变为由Tubiphytes边礁组成的陡倾斜坡。盆地范围内斜坡变陡激发了Tubiphytes礁和其它的生物体发育,而且它们组成了稳定碳酸盐岩台地的边缘。位于扬子地台西部地区的关林和贞丰一带与最北部的孤立台地（大贵州滩）在安尼期发育了陡倾的边礁。在拉丁期,扬子地台在关林一带进积并与盆地碎屑沉积互层穿插沉积,而位于贞丰的台地边缘出现了由断层控制的地貌特征。与此同时,扬子地     

中国南方中三叠世地层及沉积古地理分异

中三叠世是中国南方沉积盆地从海相沉积向陆相沉积转变的重要时期, 因此阐明该期的地层结构和沉积古地理分异对于揭示该区域构造和地质发展历史是相当重要的。本文将中国南方划分为四个沉积区 :东南沉积区、下扬子沉积区、上扬子沉积区及右江沉积区。同时对各沉积区序列、岩相生物群的分布和分异进行了总结。从而认为当时东南沉积区与下扬子沉积区是一个直接关联的沉积古地理整体, 而上扬子沉积区与右江沉积区为另个沉积古地理整体。前者在中三叠世时是一个南东高, 北西低的向北西方向倾斜的陆缘海沉积盆地, 从安尼期至拉丁期, 沉积相带不断向北西方向迁移, 并在安尼期与拉丁期之交完成从海向陆的转变。     

安徽中南部震旦纪-三叠纪二级层序的划分

安徽中南部震旦纪至三叠纪各时期为陆源碎屑沉积环境和碳酸盐沉积环境的交替,据沉积盆地内或滨、浅海交接地带沉积相序的变化、相的叠置变化关系,结合关键部位的层序界面和凝缩层特征,将其分为８个二级层序,每一个二级层序在盆地内或滨、浅诲交接部位,在沉积相序上总的趋势均表现为由浅→深→浅的变化,且与海平面变化曲线相吻合。二级层序的界线和凝结层往往是该二级层序内若干个三级层序中海平面下降或上升最为显著的转折部位,这些界面类型往往与构造运动、海平面变化、冰川事件有关。     

南盘江盆地中三叠统复理石韵律的马尔科夫链特征及其地质意义

本文利用南盘江盆地中三叠统复理石韵律的野外测量数据,从马尔柯夫链原理出发,对其进行了频数转移矩阵、概率转移矩阵、极限概率矩阵和环流矩阵等沉积旋回最优分解综合分析.分析过程中发现并命名了循环链和二级循环链,并对循环链进行了特殊处理.通过分析模拟获得的状态循环模式图,建立了不同地点实测段的代表性韵律结构模式并绘制了韵律结构...     

东秦岭陕西聂家沟剖面二叠纪—三叠纪之交沉积特征及其古环境意义*

东秦岭陕西镇安聂家沟地区二叠纪—三叠纪之交发育一套海相碳酸盐岩沉积序列,较完整地记录了二叠纪末生物大灭绝事件前后浅海碳酸盐岩台地相生物群落演替及环境变化等信息,是研究二叠纪末生物大灭绝事件前后生态环境变化与沉积响应的理想区域。通过碳酸盐岩微相分析方法,对陕西镇安聂家沟剖面二叠系—三叠系界线附近的碳酸盐岩生物组合和微相类型进行了详细分析,共识别出11个微相类型: 斑点状凝块石、叠层石灰岩、鲕粒—纹层状叠层石灰岩、有孔虫颗粒灰岩、藻—海百合泥粒灰岩、含有被包壳和被磨蚀骨屑颗粒的粒泥灰岩、鲕粒颗粒灰岩、集合颗粒灰岩、含鲕粒的粒泥灰岩、泥晶灰岩和泥岩。根据碳酸盐岩微相特征及沉积相标志,在二叠系—三叠系界限附近划分出台地边缘、开阔台地和局限台地3种沉积相,其反映了二叠纪—三叠纪之交频繁的沉积相带变更的特点。该剖面碳酸盐岩微相反映的古生态和生物群落演替特征与中国华南同时期其他剖面具有较好的一致性,即二叠纪末生物大灭绝事件之后,早三叠世正常浅水碳酸盐岩台地生物类型和丰度极低,仅含有少量的双壳类、海百合等,灭绝事件界线附近以微生物碳酸盐岩等特殊微生物沉积构造占主导,之后微生物岩等消失,又出现了以双壳类为首的生物碎屑石灰岩。研究结果为了解二叠纪末生物大灭绝事件中生物和环境的协同演化提供了新的材料和认识。     

From Cycles to Sequences:Sequence Stratigraphy and Relative Sea Level Change for the Late Cambrian of the North China Platform

In the Late Cambrian, the North China Platform was a typical carbonate ramp platform. The Upper Cambrian of the northern part of the North China Platform is famous for the development of bioherm limestones and storm calcirudites and can be divided from bottom to top into the Gushan, Changshan and Fengshan formations. In this set of strata, the deep-ramp mudstone and marls and the shallow-ramp packstones and grainstones constitute many carbonate meter-scale cycles of subtidal type. More tidal-flat dolomites axe developed in the Upper Cambrian of the southern margin of the North China platform, in which limestone and dolomite beds also constitute many carbonate meter-scale cycles of the peritidal type. These cycles are marked by a variety of litho-facies successions. There are regularly vertical stacking patterns of meter-scale cycles in long-term third-order sequences, which is the key to discerning such sequences. Third-order sequence is marked by a particular sedimentary-facies succession that is the result of the environment-changing process of deepening and shoaling, which is genetically related to third-order sea level changes. Furthermore, four third-order sequences can be grouped in the Upper Cambrian of the North China Platform. The main features of these four third-order sequences in the northern part of the platform can be summarized as follows: firstly, sequence-boundaries are characterized by drowning unconformities; secondly, the sedimentary-facies succession is generally constituted by one from deep-ramp facies to shallow-ramp facies; thirdly, a succession of “CS (?) HST” (i.e., “condensed section and highstand system”) forms these four third-order sequences. The chief features for the third-order sequences in the southern part of the North China Platform comprises: more dolomites are developed in the HSTs of third-order sequences and also developed more carbonate meter-scale cycles of peritidal types; the sedimentary-facies succession of the third-order sequences is marked by “shallow ramp-tidal flat”; the sequence boundaries are characterized by exposure punctuated surfaces. According to the changes for the third-order sequences from the north to the south, a regular sequence-stratigraphic framework can be established. From cycles to sequences, the study of sequence stratigraphy from litho-facies successions to sedimentary-facies successions exposes that as follows: meter-scale cycles that are used as the basic working unit actually are litho-facies successions formed by the mechanism of a punctuated aggradational cycle, and third-order sequences that are constituted by regularly vertical stacking patterns of meter-scale cycles are marked by sedimentary-facies successions. On the basis of the changing curve of water depth at each section, the curve of the relative third-order sea level changes in the late Cambrian of the North China Platform can be integrated qualitatively from changing curve of water depth. The correlation of Late Cambrian long-term sea level changes between North China and North America demonstrates that there are not only similarities but also differences, reflecting control of long-term sea level changes both by global eustacy and by regional factors.