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1.
叠层石和臼齿构造是前寒武纪较为引人注目的两种沉积现象.叠层石作为微生物碳酸盐岩的典型代表,在前寒武纪由于对叠层石的形成缺乏直接的微生物证据而成为一个"前寒武纪谜";臼齿构造复杂的宏观形态和奇特的微亮晶方解石填充物以及对其成因机制的持续争论而成为又一个"前寒武纪谜".最新研究表明,叠层石形态种数量在元古宙达到繁盛的顶峰之后开始衰减,而仅产出于前寒武纪地层记录中的臼齿构造似乎总是以较高的丰度呈幕式发育于叠层石的衰减事件之后,在空间上臼齿构造多产出于比叠层石更深的水体环境.叠层石的衰减和臼齿构造的幕式发育历史可能主要与环境因素发生重大变化有关,而后生动物的竞争不是直接原因.  相似文献   

2.
臼齿构造碳酸盐岩是一种具有类似于大象臼齿特征的特殊碳酸盐岩，其微亮晶脉由纯净的、基本等粒的方解石（或白云岩）构成，而基质物质则由细粒的、富泥质的灰岩组成。通过对中朝板块东部吉辽徐淮地区前寒武纪臼齿构造碳酸盐岩研究，结合国外研究资料，臼齿构造碳酸盐岩具有特定的生存时限，目前只在前寒武纪（主要发育在中、新元古代）地层中发现。研究表明，臼齿构造碳酸盐岩发育在缓坡型台地，宿主岩性以富含泥质的粉屑灰岩、泥晶灰岩为主，位于潮汐流、风暴流影响范围内，为浅潮下和环潮坪环境，潮上带与深缓坡均不发育，具有鲜明的环境和相指示意义。由于缺乏现代相似沉积物，臼齿构造碳酸盐岩的成因还是一个谜，需要进一步研究和探索。   相似文献   

3.
梅冥相 《现代地质》2007,21(1):45-56
在燕山地区中元古代高于庄组一套厚度千余米的碳酸盐沉积序列中,第三段组成一个特别的非叠层石碳酸盐岩序列。两个剖面(天津蓟县剖面和北京延庆千沟剖面）的详尽观察与研究结果表明：高于庄组第三段的非叠层石碳酸盐岩沉积序列以灰岩序列为特征,厚度为300 m至600 m不等,在蓟县剖面发育有存在成因争论的臼齿状构造,在延庆千沟剖面发育奇形怪状的席底构造。该非叠层石碳酸盐岩沉积序列表明,在前寒武纪除了3次叠层石衰减事件(分别发生在2 000 Ma、1 000 Ma和675 Ma）外,在1 450 Ma左右还可能发生过一次叠层石衰减事件。再者,高于庄组第三段构成的非叠层石碳酸盐岩沉积序列,可以大致与北美地区的Belt超群中的Helena组非叠层石碳酸盐岩沉积序列相对比,从而表明了1 450 Ma左右的叠层石衰减事件因具有全球性而有重要意义。在漫长的前寒武纪,臼齿状构造常常集中发育在叠层石衰减事件之后,因此,尽管这两种沉积构造的成因还不完全清楚却成为了解前寒武纪世界的重要线索。1 450 Ma左右的叠层石衰减事件,正好处于叠层石发育的黄金时段(2 800 Ma至1 000 Ma）,对该次事件的识别,有助于正确认识漫长而复杂多变的前寒武纪碳酸盐世界。  相似文献   

4.
郭峰  孟祥化  葛铭 《安徽地质》2009,19(3):176-180
微亮晶碳酸盐岩是一种发育在前寒武纪尤其是元古代的特殊类型碳酸盐岩,它在结构上与基质有明显区别,是由均一、等轴、多边形的微亮晶方解石组成,个体为5～15μm。安徽灵璧地区微亮晶碳酸盐岩按其成因可分为原地和异地两类。原地微亮晶主要分布于泥晶灰岩、粉屑泥晶灰岩、泥灰岩或泥岩中;异地微亮晶主要发育在粉屑灰岩或砾屑灰岩中。微亮晶碳酸盐岩的岩石学特征指示其形成并发育于稳定克拉通浅海潮下及环潮坪环境,特别是中浅缓坡向上变浅旋回的底部,风暴浪基面是其发育的最大深度。微亮晶碳酸盐岩作为一种具有全球性意义的沉积碳酸盐岩类,具有特定的时限分布范围,这对于提高前寒武纪地层对比精度具有重要意义。  相似文献   

5.
梅冥相 《古地理学报》2005,7(4):437-447
天津蓟县剖面的中元古界高于庄组为一套厚度约为1 600m的碳酸盐岩地层，包括四个段：第一段以潮坪相叠层石白云岩为主；第二段主要为含锰白云岩；第三段发育较多的纹理化石灰岩和泥晶灰岩；第四段则以叠层石岩礁（叠层石生物丘和生物层）的发育为特点。根据岩相到岩相序列可在该套碳酸盐岩地层中识别出L-M型、潮下型、环潮坪型米级旋回层序。根据米级旋回层序的有序垂直叠加形式所反映出的沉积相序列可以把高于庄组划分为13个三级层序（SQ1至SQ13），并进一步归为4个二级层序。在以灰岩为主的高于庄组第三段中，其中的第三个三级层序（SQ11）中部的灰岩层中发育臼齿状构造。这种臼齿状构造以特别的形态、富含有机质、易硅化等特点可能表明了前寒武纪碳酸盐岩沉积作用的一些基本特征：第一、在浅水环境中发育叠层石而在较深水环境（中缓坡）中发育臼齿状构造，臼齿状构造就象叠层石一样是一种极为特别的与生物沉积作用相关的沉积构造；第二、在发育叠层石的潮坪环境中有利于发生白云石化作用，发育臼齿状构造的地层则以灰岩为主，这从一个侧面反映了前寒武纪白云岩似乎又不是原生白云岩。实际上，这些特征本身即代表了一些前寒武纪沉积学问题，随着研究的深入对这些问题将会得出更加接近自然事实的答案。  相似文献   

6.
梅冥相 《现代地质》2007,21(4):738-748
天津蓟县剖面高于庄组,组成一个复杂而特别的叠层石—非叠层石碳酸盐岩沉积序列,其中,第三段构成一个特征迥异的非叠层石碳酸盐岩沉积序列。在该非叠层石序列上部的均一石灰岩(隐晶质泥晶灰岩)中普遍发育大小不等的带状臼齿状构造,与臼齿状构造共同产出的是一些数毫米乃至厘米级的球形体或似球形体。这些球形体或似球形体,曾经被解释为球形臼齿状构造,也被解释为灰岩结核、燧石结核或凝灰岩结核。岩石薄片的显微镜观察表明,这些球形体或似球形体的内部,显示出较为明显但又较为原始的多细胞组织,如分生组织和类似于薄壁组织的成熟组织,其中一些成熟细胞还保留着较为明显的细胞显微结构,表明这些球形体或似球形体的内部结构明显不同于臼齿状构造的特殊填充物——等粒状微亮晶方解石。因此,这些球形体或似球形体应该归为丘尔藻或拟丘尔藻之类的宏观藻类化石,而不是球形臼齿状构造。尽管前人在前寒武纪地层之中描述了若干宏观藻类化石,但多以碳质压型的形式保存在泥岩之类的细粒沉积之中。发现于天津蓟县剖面高于庄组灰岩中的实体球形或似球形宏观藻类化石,以其较老的地质年代(大于1400Ma)、较为明显而又原始的多细胞组织和一些成熟细胞的可能细胞显微结构,表明该球形实体化石具明显的多细胞真核生物属性。这些初步研究和发现为探讨真核生物的起源演变、揭示宏观藻类化石的生物学属性提供了罕见的实际材料,因而具有重要的意义。  相似文献   

7.
前寒武纪碳酸盐岩多以叠层石碳酸盐岩序列为特征。燕山地区中元古界高于庄组,其中的第三段(张家裕亚组)则为一个以灰岩为主、贫乏叠层石的碳酸盐岩沉积序列,该序列被定义为前寒武纪非叠层石碳酸盐岩序列。该非叠层石碳酸盐岩沉积序列,尤其以燕山西部的延庆千沟剖面最为典型。根据沉积相序列及其所反映的旋回性,可以将该剖面的高于庄组第三段划分为3个三级层序。在这些三级层序的海侵体系域和早期高水位体系域中,中薄层隐晶质泥晶灰岩(均一石灰岩)和灰黑色薄层泥灰岩组成若干潮下型米级旋回;而在隐晶质泥晶灰岩层面上,普遍发育各种奇形怪状的沉积构造。这些沉积构造包括穹窿状构造、规则网状和杂乱的帐篷脊、变余波痕等,构成一个潮下相灰岩层面上的特别的微生物形成的沉积构造(Microbial Induced Sedimentary Structure,MISS)组合。因此,延庆千沟剖面的高于庄组第三段,特别的岩石类型和沉积构造成为前寒武纪碳酸盐岩沉积中非叠层石碳酸盐岩沉积序列的典型代表,尤其是那些奇形怪状的MISS所代表的沉积学特点表明:在前寒武纪,即使在叠层石生长的黄金时段,也发育非叠层石碳酸盐岩沉积序列。因此,这些现象将特别有助于对前寒武纪非叠层石生态系所造成的另一类席底生境的深入理解,也有助于复杂多变的碳酸盐岩世界。  相似文献   

8.
大连金石滩兴民村组臼齿碳酸盐岩及其沉积环境研究   总被引：2，自引：0，他引：2  
Molar-tooth构造(简称臼齿构造或MT)是前寒武纪碳酸盐岩中产出特殊的沉积构造,发育于特定的沉积环境。臼齿碳酸盐岩及其沉积环境的研究有助于其成因解释。大连金石滩新元古代兴民村组臼齿碳酸盐岩的研究表明,兴民村组的MT形成于开阔陆表海浅潮下带—潮间带动荡环境,海平面升降频繁;沉积序列主要为泥晶灰岩与含泥灰岩、砂屑灰岩与泥晶灰岩、纹层状泥晶灰岩与泥晶灰岩和砂屑灰岩与纹层状泥晶灰岩的韵律。MT形成于过饱和CaCO3的微高盐度和高古温度环境,少有陆源物质影响。  相似文献   

9.
在综述臼齿碳酸盐岩成因研究历程和国内外最新研究成果的基础上,总结评述了6种主要的臼齿构造成因模式,其核心问题是在元古代正常潮下浅海环境中构建成岩作用早期臼齿构造裂缝形成及等粒微亮晶方解石快速沉淀充填的物理、化学及微生物条件。其中,气泡扩张裂缝模式、微生物-地球化学模式和同沉积地震脱水模式等具有一定的代表性。臼齿构造多产出于正常浅海潮下环境,并且呈幕式特点产出于前寒武纪地层记录中,其时空发育特点似乎表明与叠层石发育的不相容性。臼齿碳酸盐岩在中新元古代集中发育的事实可能反映了有利的物理、化学和生物条件在地质历史上的唯一结合。理清臼齿构造成因问题是认识前寒武纪复杂的碳酸盐岩世界的重要线索。  相似文献   

10.
吉林南部通化二道江剖面新元古界万隆组广泛发育缓坡碳酸盐岩沉积,其中发育的一种特殊的碳酸盐岩——臼齿碳酸盐岩,近年来引起了中国乃至世界各国地质学家的重视。通过对野外露头的详细观察和描述、室内薄片观察、扫描电镜、能谱分析等测试手段,揭示了二道江剖面万隆组的地层、岩石、臼齿构造(MT)及沉积岩相和沉积环境特征。臼齿构造是特指那些发育在前寒武纪细粒碳酸盐岩中有清晰边界、粒度在0·01mm左右的由等轴或多边形的微亮晶方解石组成的集合体,其形态可分为条带状构造、瘤状构造及棱角碎块状构造。臼齿构造的形成严格受沉积岩相和沉积环境的控制。万隆组由下而上可分为3段第1段下部为发育臼齿构造的纹层状泥晶灰岩、砂屑灰岩及风暴砾屑灰岩,为中—深缓坡沉积环境的产物;上部由浅缓坡相的泥灰岩、钙质页岩、砂屑灰岩与叠层石灰岩组成;第2段为厚层泥晶灰岩和粉屑泥晶灰岩、瘤状灰岩组成的深缓坡相沉积;第3段本剖面未出露。万隆组形成于缓坡沉积环境,其中浅缓坡相可分为4种岩相组合,中缓坡相可分为11种岩相组合,深缓坡相有6种岩相组合。  相似文献   

11.
Molar-tooth (MT) structure is an enigmatic sedimentary structure consisting of variously-shaped cracks and voids filled with a characteristically uniform, equant calcite microspar. It is globally distributed but temporally restricted to rocks from Neoarchean to Neoproterozoic age. The origin of MT structures has been debated for more than a century and the topic continues to be highly contentious. Some features of MT structure occurring in micritic limestones of the Mesoproterozoic Gaoyuzhuang Formation (ca. 1500 Ma to ca. 1400 Ma), Jixian section, Tianjin City, North China show that: 1) there is a definite interface or lining, rich in organic material and pyrite, between the MT crack-filling calcite microspar and the micritic host rock, which is also rich in organic matter; 2) the micritic host rocks are notable for the absence of stromatolites and microbial laminites; 3) distinctive conglomeratic lag deposits made up of intraclasts of MT microspar result from storm reworking of the MT structures; 4) the MT structure is associated with possible algal megafossils such as Chuaria; 5) the MT microspar is made up of the larger calcite crystal and the MT crack is marked by the diversity of configurations; 6) both the TOC content and the carbon-isotopic value (δ13CPDB) among the host rock, the MT microspar and the possible algae fossil are obviously different. For the forming mechanism of the Gaoyuzhuang MT structure, these features can still indicate that: A) the MT microspar was formed by rapid precipitation and lithification; B) the MT microspar precipitated directly within the cracks; C) the decomposition of organic matter within the host micrite might be the chief mechanism producing gas bubbles; D) microscale gas-sediment interaction led to the generation of the MT cracks and the precipitation of microspar therein; E) the MT cracks might represent the track of migration and expansion of gas bubbles, and that the recrystallization of host micrites cannot be eliminated during forming process of the MT microspar; F) the MT structure is occurred in early diagenetic period; and G) the formation of MT microspars is a complex diagenetic process. Therefore, model of the microbially-induced gas-bubble expansion and migration is the best interpretation for the formation of the MT structure. Effectively, MT structures are a type of sedimentary structure that is formed in the early diagenetic period and is related to microbial activities and organic matter degradation.  相似文献   

12.
Molar tooth (MT) structures are enigmatic, contorted millimetre‐ to decimetre‐long veins and spheroids of microcrystalline calcite that formed during very early diagenesis in Precambrian sediments. MT structures in the ca 2·6 Ga Monteville Formation are 600–800 Myr older than previously reported occurrences and establish that conditions necessary for MT genesis were met locally throughout much of the Precambrian. In the Monteville Formation, MT structures were formed shallow subtidally, extending to depths near storm wave base, in shale host sediments intercalated with storm‐generated carbonate sand lenses. They are filled with microcrystalline calcite and rare pyrite. Microcrystalline calcite identical to that in MT structures fills other pore space, including porosity between grains in carbonate sand lenses, moldic porosity in sand grains, sheet cracks in columnar stromatolites, and shallow cracks on sandy bedding planes. Relationships in the Monteville Formation demonstrate that microcrystalline CaCO3 precipitated in fluid‐filled cracks and pores; microcrystalline calcite characteristics, as well as the paucity of carbonate mud in host rocks, are inconsistent with injection of lime mud as the origin of MT structures. Locally, MT cracks were filled by detrital sediment before or during precipitation. Precipitation occurred in stages, and MT CaCO3 evolved from granular cores to a rigid mass of cores with overgrowths – allowing both plastic and brittle deformation of MT structures, as well as reworking of eroded MT structures as rigid clasts and lime mud. Crystal size distributions and morphology suggest that cores precipitated through nucleation, Ostwald ripening and size‐dependent crystal growth, whereas overgrowths formed during size‐independent crystal growth.  相似文献   

13.
Special interest is attached to the Bhander Limestone because it is the only calcareous formation in the very thick elastic sequence of Precambrian age, designated informally as the “Upper” Vindhyan. The sedimentology of the Bhander Limestone was studied in the Mandalgarh-Singoli area of southeastern Rajasthan and adjoining Madhya Pradesh with a view to interpreting the depositional environments of the formation. This study has an important bearing on the exploration for oil in India and presents one of the few examples of Precambrian limestones of which thorough modern sedimentological analysis has been made.The Bhander Limestone comprises micritic limestones, crystalline dolostones, siltstones and shales that show desiccation structures (horizontal fenestrae, bird's-eye structures, mud cracks), very shallow small channels filled with flat-pebble breccia, algal lamination, palisade structure, and occasional ripple marks, ripple lamination and micro-cross-lamination. The major petrographic constituents are micrite, intraclasts, sparry-calcite cement, pseudospar and replacement dolomite. Seven environmentally significant microfacies have been recognized: micrite, silty micrite, graded micrite, dolomitized micrite, neomorphosed micrite, intrasparrudite and intramicrudite.The Bhander Limestone Formation has been divided vertically into four lithofacies: red argillaceous micritic limestones (lithofacies A), interlaminated blue micritic limestones and red dolomite (lithofacies B), olive calcareous shales (lithofacies C), and black micritic limestones (lithofacies D). Each lithofacies is characterized by certain megascopic sedimentary features and microfacies. The various lithofacies have been interpreted as representing deposition in the different subenvironments of a generally low-energy, marginal marine environment comprising tidal flats and lagoons. The vertical changes from one lithofacies to another are interpreted as reflecting the change from one subenvironment to another brought about by the landward shifting of the boundaries of these subenvironments in response to a transgression.  相似文献   

14.
Sedimentological, morphological, and geochemical characteristics of molar tooth (MT) structures in the ca 2·6 Ga Monteville Formation suggest a new fluid flow model for MT formation: (i) intercalated shales and carbonate sands were deposited near to above storm wave base; (ii) sediments cracked, forming an interconnected network of MT cracks that were also open to pores in sand lenses; (iii) storm waves pumped sea water into open MT crack networks, causing rapid microcrystalline carbonate nucleation, Ostwald ripening of nuclei, and growth of granular carbonate cores; some of these cores were transported by water flowing through the cracks; (iv) unfilled MT cracks collapsed, and filled MT ribbons deformed plastically as host sediments compacted and dewatered; (v) carbonate cores were overgrown by polygonal rims; and (vi) MT structures deformed brittlely with additional compaction and produced pebbly lags if reworked. MT cracks may have formed by multiple mechanisms; however, expansion of gas from organic decay and sediment heaving due to wave loading best explain MT crack morphology and are most consistent with the fluid flow model for MT CaCO3 presented here.  相似文献   

15.
Along with the progress in research on the Precambrian, Molar-tooth carbonates (simplified as MT, or microsparite carbonates or MT structure) which were formed in the Middle-Late Proterozoic have become a hot subject recently. The Proterozoic Molar-tooth (MT) carbonate rocks refer to those Meso- to Neoproterozoic (1600-650 Ma) carbonates with MT structure, i.e., a series of peculiar, ptygmatically folded and spar-filled cracks in fine-grained carbonates of Precambrian age, located in the environment of mid- to inner ramp and shallow platform. MTS, like a bridge connecting the inorganic world with the organic one, are closely related to the evolution of paleo-oceans, atmosphere and biosphere. Their development and/or recession are/is related to the origin of life and the abruption of sedimentary geochemistry events of marine carbonates. By using modern instruments and testing methods adequately, the contents of oxides in sandstones were measured and the REE distribution pattern curves were established; an accurate value of isotopic ratio of 87Sr/86Sr was obtained, that is, the age of MT formation is about 750-900 Ma; C and O isotopes of some fresh micrite limestone samples were analyzed; the energy spectrum analysis revealed that the MT consists mainly of microspar calcite, while as for its chemical composition, the matrix shows outstanding peaks of Ca, Mg, Al, Si, and K. The geochemical indicators proved that Neoproterozoic MT carbonates in the Jilin-Liaoning region were developed at the margin of a stable continent, in the torrid zone where the paleo-temperature was about 50℃, the seawater had normal salinity when MT was formed during the Wanlong period in southern Jilin and during the Yingchengzi and Xingmincun periods in eastern Liaoning. The sedimentary environment was located in the inner ramp. In summary, it is of great importance to understand the origin of MT, ascertain the paleo-climate and paleo-environment characteristics, constrain the age and the stratigraphic division and comparison of the Proterozoic so as to study the geochemical characteristics of MT carbonates and their formation environment.  相似文献   

16.
柴达木盆地西部地区古近系及新近系碳酸盐岩沉积相   总被引：10，自引：3，他引：7       下载免费PDF全文
柴达木盆地西部地区古近系和新近系湖相碳酸盐岩主要分布于下干柴沟组上段到油砂山组,其中,下干柴沟组上段和上干柴沟组的碳酸盐岩更发育。碳酸盐岩主要岩石类型有泥晶灰岩、藻灰岩和颗粒灰岩等三大类,此外,还普遍发育由石灰质、白云质和陆源碎屑等3种组分构成的混积岩。碳酸盐岩沉积相可划分为滨湖灰泥坪、滨湖藻坪、浅湖颗粒滩、浅湖藻丘以及半深湖泥灰岩相。滨湖灰泥坪的主要岩石类型有泥晶灰岩、含陆屑泥晶灰岩、陆屑泥晶灰岩以及陆屑泥灰岩等;滨湖藻坪为藻泥晶灰岩、藻纹层灰岩、含陆屑藻泥晶灰岩;浅湖颗粒滩有亮晶或泥微晶的鲕粒灰岩、生屑灰岩和内碎屑灰岩,其次为含陆屑颗粒灰岩;浅湖藻丘为藻叠层灰岩、藻团块灰岩、藻泥晶灰岩和含陆屑藻泥晶灰岩;而半深湖泥灰岩相的主要岩石类型为泥晶灰岩、泥灰岩以及含少量陆屑泥和粉砂的泥晶灰岩或泥灰岩。碳酸盐岩沉积相表现出很强的由西南向东北的迁移性。  相似文献   

17.
臼齿构造碳酸盐岩是全球各大陆中、新元古代时期普遍发育的、具有特殊成因意义的碳酸盐岩类型,到目前为止,已在全球20多个地区近50多个中、新元古代地层剖面中被发现。百余年来,有关MT的研究越来越深入,进展显著。从前期和前人较少关注的有关MT与宿主岩石的关系,尤其是从MT与宿主岩石地球化学特征的关系及其所揭示的地质意义出发,通过薄片、电子探针、背散射、阴极发光等测试手段及C、O、Sr同位素的系统测试,对辽东地区新元古代南关岭组、营城子组及兴民村组MT及其宿主岩石的成分、结构、微观组构等特征进行了深入研究。研究证明,MT是原生或早期成岩的产物,由原生海水埋藏成岩和海水直接成岩形成;MT与宿主岩石具有相似的地球化学特征,具有同生或准同生的特点,形成于温暖的正常海水环境,并于Sturtian冰期前终止发育。锶、碳同位素同全球中、新元古代碳锶同位素理论曲线类比表明,大连新元古代南关岭组和营城子组的形成时限为760~950 Ma,兴民村组形成时限为720~800 Ma,与胶辽徐淮地区新古代地层具有良好可对比性。  相似文献   

18.
梅冥相 《沉积学报》2008,26(4):565-574
在前寒武纪碳酸盐岩中,最为普遍的是叠层石碳酸盐岩沉积序列,而以潮下相沉积为主的非叠层石碳酸盐岩沉积序列与前者形成了较大的差异;因此,与叠层石碳酸盐岩沉积序列一样,非叠层石序列成为了解前寒武纪复杂多变的碳酸盐世界的重要线索。燕山地区中元古代高于庄组为一套厚度千余米的碳酸盐沉积序列,包括四大部分:第一段（或称为官地亚组）为发育在海侵砂岩上的叠层石白云岩地层;第二段（或称为桑树鞍亚组）为发育少量叠层石的含锰白云岩地层;第三段又称为张家峪亚组,为一套以发育灰岩为主的非叠层石碳酸盐岩沉积序列;第四段以叠层石岩礁和叠层石礁白云岩为特征。延庆千沟剖面的高于庄组第三段的非叠层石碳酸盐岩沉积序列,贫乏叠层石是其基本特点,包含3个三级层序,在三级层序的海侵体系域和早期高水位体系域中,层面上发育席底构造的中层均一石灰岩（隐藻泥晶灰岩）和灰黑色薄层泥灰岩组成若干潮下型米级旋回,晚期高水位体系域则以厚层块状纹理石灰质白云岩和白云质灰岩为特征;三级层序的凝缩段单元则以薄层泥灰岩和泥页岩构成的L-M型米级旋回为特征。因此,每一个三级层序均以一个有序的沉积相序列为特征。高于庄组的分布时限大致为200 Ma（1 600～1 400 Ma）,考虑到下伏的大红峪组和高于庄组之间的地层间断时限大致为50 Ma至100 Ma,所以推断高于庄组的堆积作用时限为100 Ma（1 500～1 400 Ma）左右,其中高于庄组第一段与第二段的分界线正好处于该组的中部而可以推断该界线的大致为1 450 Ma左右;因此,高于庄组第三段非叠层石碳酸盐岩沉积序列的发育表明,在1 450 Ma左右可能发生过一次可以与前寒武纪其他已经被识别出的三次叠层石衰减事件（2 000 Ma、1 000 Ma和675 Ma）相比拟的又一次叠层石衰减事件。延庆千沟剖面高于庄组第三段的非叠层石碳酸盐岩沉积序列,可以大致与北美地区的起始时限为1 450 Ma左右、Belt超群中的Helena组非叠层石碳酸盐岩沉积序列相对比,表明了1 450 Ma左右的叠层石衰减事件具有全球性,从而赋予高于庄组第三段非叠层石碳酸盐岩沉积序列重要的沉积学意义。延庆千沟剖面高于庄组第三段非叠层石碳酸盐岩沉积序列,特别的岩石类型和沉积构造,成为前寒武纪碳酸盐岩沉积中非叠层石碳酸盐岩沉积序列的典型代表,由其所代表的沉积学特点将有助于深入理解漫长的前寒武纪碳酸盐沉积作用的变化规律而具有重要意义。  相似文献   

19.
In the long Precambrian period, stromatolitic carbonate successions were very common. However, the non-stromatolitic carbonate succession that is marked by subtidal deposits shows a sharp contrast to the stromatolitic carbonate succession. Both the non-stromatolitic and the stromatolitic carbonate successions are important clues for the further understanding of the evolving carbonate world of the Precambrian. The Mesoproterozoic Gaoyuzhuang Formation at the Qiangou section in northwestern suburb of Beijing is a set of more than 1000 m-thick carbonate strata that can be divided into four members （or subformations）, in which a non-stromatolitic carbonate succession marked by the scarcity of stromatolites makes up the third member of the formation. This non-stromatolitic carbonate succession can further be subdivided into three third-order sequences that are marked by the regular succession of sedimentary facies. In third-order sequences, a lot of subtidal carbonate meter-scale cycles made up of medium-bedded leiolite limestones and thin-bedded marls constitute their transgressive system tracts （TSTs） and the early high-stand system tracts （EHSTs）, a lot of meter- scale cycles made up by thin-bedded limestones and marls constitute their condensed sections （CSs）, and thick-bedded to massive dolomitic limestones or lime dolomites make up the late high-stand system tracts （LHSTs）. The particularly non-stromatolitic carbonate succession making up the third member of the Mesoproterozoic Gaoyuzhuang Formation at the Qiangou section might be the representative of the non-stromatolitic carbonate succession of the Precambrian because of its special lithological features and particular sedimentary structures, and its general sedimentary features are helpful and meaningful for the further understanding of the evolution rules of the sophisticate and evolving carbonate world of the Precambrian. The time scale of the Gaoyuzhuang Formation is deduced as that from 1600 Ma to 1400 Ma; thus, the non-stromatolitic  相似文献   

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