Origin of Molar-Tooth Structure Based on Sequence- Stratigraphic Position and Macroscopic Features： Example from Mesoproterozoic Gaoyuzhuang Formation at Jixian Section, Tianjin, North China   总被引：2，自引：1，他引：2  

梅冥相 《中国地质大学学报(英文版)》2006,17(3):201-208,271

INTRODUCTION Located at the famous Jixian Section in Tianjinin the North China , the MesoproterozoicGaoyuzhuang Formationis a set of 1 600 mthick car-bonates that formed over about 200 Ma in the Clym-Figure 1 .Section location of the Mesoprotero-zoic Gaoyuzhuang Formation at the Jixian Sec-tion in Tianjin.mian (1 600 Ma to 1 400 Ma ;Zhu et al .,1994 ; Du,1992 ;Fig.1) . The Gaoyuzhuang Formation at theJixian Section can be divided into four members thatare characterized by differ…  相似文献   

天津蓟县中元古界高于庄组“球形臼齿状构造”新解——1400 Ma以前球形或似球形实体宏观藻类化石的细胞显微结构   总被引：1，自引：0，他引：1  

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   

河北省赤城县温泉环斑花岗岩的地质特征及形成时代   总被引：2，自引：0，他引：2       下载免费PDF全文

刘振锋  王继明吕金波郑桂森 《中国地质》2006,33(5):1052-1058

温泉环斑花岗岩分布于河北省赤城县温泉一带,面积约50km2。在1:25万延庆县幅区域地质调查工作的基础上,笔者研究了该岩体的产出状况、侵入关系等地质特征。结合岩石学、地球化学及同位素年龄等证据,探讨了温泉环斑花岗岩的形成时代。研究表明,该岩体为富钾、过铝、高铁、低钙、低镁A型花岗岩,形成于中元古代,相当于长城纪大红峪期,与北京市密云县沙厂环斑花岗岩可以对比。同时也为华北板块基底的克拉通化时间及其在中元古代发生的裂解事件提供了岩石学及同位素年龄依据。  相似文献   

华北中部古元古代末期构造－热事件性质及其构造成因模式   总被引：2，自引：1，他引：2       下载免费PDF全文

李江海刘守偈  侯贵廷 《中国地质》2006,33(6):1256-1266

古元古代末期为华北克拉通演化的重大转折时期。但这一时期重大构造热事件序列及其构造格局的研究较薄弱。笔者在区域构造分析基础上。结合最新的同位素年龄制约。探讨古元古代末期区域构造演化过程及其成因模式。太行山-恒山基性岩墙群对应于燕辽坳拉谷与太行坳拉谷的夭折支，它们共同构成非对称的三叉坳拉谷系。非造山的岩浆活动序次依次为：花岗岩、伟晶岩（1．85～1．80Ga）、基性岩墙群侵位（1．80-1．77Ga）、斜长岩、碱性花岗岩、环斑花岗岩（1．71-1．70Ga）、火山岩喷发（1．68Ga）等。下伏基底性质对比及其同位素年龄表明，18亿年前后燕辽-太行山地区发生大规模隆升。隆升范围达上千千米，核心区处于燕辽-太行山坳拉谷系中心位置。基底隆升事件与浅表层伸展构造-非造山岩浆活动在时空上相吻合，表明地幔柱模式可以合理解释上述区域隆升及其伸展裂解事件。  相似文献   

Intrusion age, geochemistry and metamorphic conditions of a quartz-monzosyenite intrusion at the craton–Eastern Ghats Belt contact near Jojuru, India     

D. Upadhyay  M.M. Raith 《Gondwana Research》2006,10(3-4):267-276

The boundary between the Archean cratons and the Eastern Ghats Belt in peninsular India represents a rifted Mesoproterozoic continental margin which was overprinted by a Pan-African collisional event associated with the westward thrusting of the Eastern Ghats granulites over the cratonic foreland. The contact zone contains a number of deformed and metamorphosed nepheline syenite complexes of rift-related geochemical affinities. In addition to the nepheline-bearing rocks, metamorphosed quartz-bearing monzosyenitic bodies can also be identified along the suture in the region between the Godavari-Pranhita graben and the Prakasam Igneous Province. One such occurrence at Jojuru near Kondapalle is geochemically comparable to the nepheline syenites and furnishes a weighted mean concordant U–Th–Pb SHRIMP zircon age of 1263 ± 23 Ma (2σ), which provides a lower age bracket for the rift-related magmatic activity. The original igneous mineral assemblage in the monzosyenite was partially replaced by the formation of coronitic garnet during the Pan-African metamorphism of the rocks. P–T estimates of garnet corona formation at the interface between clinopyroxene–orthopyroxene–ilmenite clusters and plagioclase indicate mid to upper amphibolite facies condition (5.5–7.0 kbar and 600–700 °C) during the thrust induced deformation and metamorphism associated with the Pan-African collisional tectonics.  相似文献   

Hydrothermal Mineralization on the Mesoproterozoic Passive Continental Margins of China: A Case Study of the Langshan-Zha''ertaishan Belt,Inner Mongolia, China     

PENG Runmin  ZHAI YushengKey Laboratory of Lithospheric Tectonics  Lithoprobing Technology  China University of Geosciences  Ministry of Education  Beijing 《《地质学报》英文版》2004,78(2)

Most ore-forming characteristics of the Langshan-Zha'ertaishan hydrothermal exhalation belt, which consists of the Dongshengmiao, Huogeqi, Tanyaokou and Jiashengpan large-superlarge Zn-Pb-Cu-Fe sulfide deposits, are most similar to those of Mesoproterozoic SEDEX-type provinces of the world. The characteristics include: (1) All deposits of this type in the belt occur in third-order fault-basins in the Langshan-Zha'ertaishan aulacogen along the northern margin of the North China Platform; (2) these deposits with all their orebodies hosted in the Mesoproterozoic impure dolomite-marble and carbonaceous phyllite (or schists) have an apparent stratabound nature; ores display laminated and banded structures, showing clear depositional features; (3) there is some evidence of syn-sedimentary faulting, which to a certain extent accounts for the temporal and spatial distribution and the size of the orebodies in all deposits and the formation of intrabed conglomerates and breccias; (4) they show lateral and vertical  相似文献   

Hydrothermal Mineralization on the Mesoproterozoic Passive Continental Margins of China: A Case Study of the Langshan-Zha'ertaishan Belt,Inner Mongolia, China     

PENG Runmin  ZHAI YushengKey Laboratory of Lithospheric Tectonics  Lithoprobing Technology  China University of Geosciences  Ministry of Education  Beijing 《《地质学报》英文版》2004,78(2)

Most ore-forming characteristics of the Langshan-Zha'ertaishan hydrothermal exhalation belt, which consists of the Dongshengmiao, Huogeqi, Tanyaokou and Jiashengpan large-superlarge Zn-Pb-Cu-Fe sulfide deposits, are most similar to those of Mesoproterozoic SEDEX-type provinces of the world. The characteristics include: (1) All deposits of this type in the belt occur in third-order fault-basins in the Langshan-Zha'ertaishan aulacogen along the northern margin of the North China Platform; (2) these deposits with all their orebodies hosted in the Mesoproterozoic impure dolomite-marble and carbonaceous phyllite (or schists) have an apparent stratabound nature; ores display laminated and banded structures, showing clear depositional features; (3) there is some evidence of syn-sedimentary faulting, which to a certain extent accounts for the temporal and spatial distribution and the size of the orebodies in all deposits and the formation of intrabed conglomerates and breccias; (4) they show lateral and vertical  相似文献   

Fine‐grained agglutinated elongate columnar stromatolites: Tieling Formation,ca 1420 Ma,North China          下载免费PDF全文

Fabio Tosti  Robert Riding 《Sedimentology》2017,64(4):871-902

The Mesoproterozoic Tieling Formation, near Jixian, northern China, contains thick beds of vertically branched, laterally elongate, columnar stromatolites. Carbonate mud is the primary component of both the stromatolites and their intervening matrix. Mud abundance is attributed to water column ‘whiting’ precipitation stimulated by cyanobacterial photosynthesis. Neomorphic microspar gives the stromatolites a ‘streaky’ microfabric and small mud flakes are common in the matrix. The columns consist of low‐relief, mainly non‐enveloping, laminae that show erosive truncation and well‐defined repetitive lamination. In plan view, the columns form disjunct elongate ridges <10 cm wide separated by narrow matrix‐filled runnels. The stromatolite surfaces were initially cohesive, rather than rigid, and prone to scour, and are interpreted as current aligned microbial mats that trapped carbonate mud. The pervasive ridge–runnel system suggests scale‐dependent biophysical feedback between: (i) carbonate mud supply; (ii) current duration, strength and direction; and (iii) growth and trapping by prolific mat growth. Together, these factors determined the size, morphology and arrangement of the stromatolite columns and their laminae, as well as their branching patterns, alignment and ridge–runnel spacing. Ridge–runnel surfaces resemble ripple mark patterns, but whether currents were parallel and/or normal to stromatolite alignment remains unclear. The formation and preservation of Tieling columns required plentiful supply of carbonate mud, mat‐building microbes well‐adapted to cope with this abundant sediment, and absence of both significant early lithification and bioturbation. These factors were time limited, and Tieling stromatolites closely resemble coeval examples in the Belt‐Purcell Supergroup of Laurentia. The dynamic interactions between mat growth, currents and sediment supply that determined the shape of Tieling columns contributed to the morphotypical diversity that characterizes mid–late Proterozoic branched stromatolites.  相似文献   

华北中元古代鱼骨状方解石: 成因机制和古环境意义^*          下载免费PDF全文

汤冬杰  史晓颖  张文浩  刘云  吴金键 《古地理学报》2017,19(2):227-240

鱼骨状方解石是一种特殊的碳酸盐沉积,由锯齿状亮暗交互的亚毫米级条带组成,主要见于太古宙。以往认为,鱼骨状方解石属无机化学沉淀成因,形成于水体缺氧、碳酸盐过饱和、富Fe²⁺、Mn²⁺等碳酸盐沉淀抑制剂的环境条件;在地质记录中其丰度随时间的减少反映了海洋的长期氧化趋势。文中首次在华北地台中元古界高于庄组四段微生物礁内发现了大量鱼骨状方解石。宏观观察表明,这些鱼骨状方解石主要以微生物礁孔洞充填物形式产出,明显区别于太古宙以海底沉淀形式直接产出在海底的鱼骨状方解石。显微研究发现,鱼骨状方解石晶体纤维具有沿晶体生长方向旋转消光特征,证明其内部亚晶的光学C轴从纤维底部的随机排列逐步旋转至上部垂直纤维生长方向。这符合球状晶体生长模式,需要方解石沉淀抑制剂的参与。鱼骨状方解石产出具有丰度随时间减少以及产出形式由海底沉淀向孔洞胶结物转变的特征。这些特征与海洋氧化逐渐增强以及具氧化还原敏感属性的碳酸盐沉淀抑制剂逐渐从水体中移除相吻合。笔者认为鱼骨状方解石的沉淀抑制剂为Fe²⁺和Mn²⁺,这与微生物岩无明显Ce异常和Fe²⁺极强的抑制能力相一致。因此,鱼骨状方解石可用于指示缺氧环境条件。此外,显微和超微研究也表明鱼骨状方解石晶体内存在有大量与其生长方向一致的菌丝体残余和与之密切伴生的有机矿物,表明微生物为鱼骨状方解石成核和初始沉淀提供了重要垫板。  相似文献   

天津蓟县中元古界雾迷山组复合海平面变化旋回层序的初步研究   总被引：2，自引：0，他引：2  

梅冥相  杜本明  周洪瑞  罗志清 《沉积与特提斯地质》1999,19(5):12-22

天津蓟县中元古界雾迷山组为一套厚３０００ 余米的碳酸盐岩地层,叠层石生物层和凝块石生物丘特别发育。它们与潮坪相泥晶白云岩和泥质白云岩构成具对称相序组构的环潮坪型碳酸盐米级旋回层序。米级旋回层序之顶覆以厚度不等的澲湖相白云质泥页岩。常常３ ～５ 个米级旋回层序呈有序叠加构成五级准层序组,少数米级旋回层序还可识别出５ 个七级韵律层而呈现出１∶５ 的叠加关系。因此,七级韵律层、米级旋回层和五级准层序组分别与岁差旋回、短偏心率旋回、长偏心率旋回间存在有成因联系。根据米级旋回层序在长周期层序中的有序垂直叠加形式,在雾迷山组中可识别出２６ 个三级层序,进一步归为６ 个二级层序。  相似文献