共查询到19条相似文献，搜索用时 421 毫秒
1.
四川江油马角坝地区船山组核形石十分发育,类型多样。基于对其内部显微结构的研究发现核形石核心和纹层各有5种类型,并伴随有3种圈层"构造"。基于对其核心、纹层和形态的研究将研究区核形石分为大球状核形石、小球状核形石、长棒状核形石、帽状核形石、不规则状核形石和复合核形石等6大类,并将它们划分成3种沉积环境,即台地边缘滩、开阔台地和局限台地,并探讨了碳酸盐岩地层中核形石的分布、形成环境和沉积环境的耦合关系。高含量、大颗粒、纹层厚度大于核心厚度、纹层复杂、核心组分与基质组分存在较大差异,亮晶胶结的核形石的形成环境与沉积环境不一致,即核形石形成于水动力较弱的局限台地或开阔台地环境,强水动力使核形石发生磨圆,基质生物碎屑破碎,进而沉积于水动力较大的台地边缘滩环境。中等含量、中等粒度、纹层简单、与完整生物碎屑共存且粒径类似、亮晶胶结的核形石的形成环境与沉积环境类似,即部分生物碎屑在中等水动力条件下,处于悬浮状态,捕获和粘附碳酸盐质点,当个体增大和水体环境变化时,核形石就地沉积于中等能量的开阔台地环境。含量低、粒径变化大、纹层厚度小于核心厚度、纹层简单、形状易受核心的影响,纹层外壳凹凸不平,基质生物含量低、泥晶基质含量特别高的核形石的形成环境与沉积环境一致,即形成并沉积于水动力偏弱的局限台地环境。 相似文献
2.
豫西渑池地区寒武系第三统馒头组二段主要由紫红色、褐黄色页岩夹叠层石灰岩、核形石灰岩和鲕粒灰岩组成,其 下部灰岩中富含核形石,形态和纹层结构多不规则,可见弯曲、不分枝的葛万菌(Girvanella )管状体呈密集而不规则的网 状缠绕于核心和暗色纹层中,在亮纹层中则少些。含核形石地层呈薄层或透镜状夹于鲕粒灰岩之间或被潮上带泥岩覆盖, 形成于低能的滨岸鲕粒滩滩间或滩后洼地。从核形石的特征可以看出,后生动物的匮乏或衰退是渑池地区馒头组二段核形 石产生的决定性因素,不同的水动力条件造就了核形石形态类型的多样化,持续动荡的高能条件和大量泥质(陆源物质) 供应直接导致了核形石消亡。 相似文献
3.
山东省平邑盆地古近系官庄组湖相碳酸盐岩露头发育有大量的核形石。为分析其沉积环境,采用野外观测、地球化学测试、偏光显微镜和扫描电镜观察等方法,研究其岩性背景、伴生的生物、沉积构造以及元素地球化学特征。研究表明,核形石主要发育于浅水、中等偏低能量的环境。有少量陆源碎屑物的环境有利于核形石生长;但较多的陆源碎屑物则对其不利。将核形石分为3类:规则泥晶纹层核形石(简称A类核形石),具有大颗粒、多层的规则纹层、复合核心等特点,可以指示浅水、中能、低陆源环境;规则微亮晶纹层核形石(B类),以色浅、粒径小、分选好、微亮晶纹层为特点,可指示浅水、较高能环境;不规则泥晶纹层核形石(C类),以色深、外形不规整、凝块状不规则纹层为特征,指示较深水、低能环境。发育A类和C类核形石的岩石,孔隙发育较差;发育B类核形石的岩石,孔隙发育较好,表现出相对较好的储层潜力。 相似文献
4.
埃迪卡拉系灯影组核形石研究对揭示该期古环境特征及演化具有重要意义。在杨坝剖面埃迪卡拉系灯影组2段核形石发育段的宏观及微观描述（564块薄片）的基础上,分析了核形石组构、类型及垂向分布。该剖面核形石发育段共分为上、下两个亚段,厚度分别为109.53 m、126.2 m,核形石累积厚度分别为22.6 m、49.5 m。核形石核心及壳层的成分、组构、形态多样;核形石类型包括不规则状核形石、椭圆状核形石、次圆状—圆状核形石、帽状核形石等4种,每种类型的粒径、形态、层位分布、形成环境不同;粒度在垂向上表现为10个反旋回。整体上核形石发育不够完善,以薄皮核形石、弥散粒为主,代表着核形石发育的最初阶段。不规则状、次圆状、帽状核形石形成于弱搅动的浅水低能环境,包括潮下低能带、潮间带等;椭球状、圆状核形石形成于连续搅动的潮下高能带。核形石粒度差异大、形态多样、垂向多旋回变化的特征反映了埃迪卡拉纪灯影期海水受限、水体相对深浅及能量频繁动荡,同时受一定物源影响的特征。 相似文献
5.
核形石是微生物岩的一种,长期受到地质学家的广泛关注。目前在核形石的展布模式、沉积环境以及微生物特征和形成机制方面的研究仍显不足。北京西郊丁家滩剖面地层出露良好且保存完整,其寒武系昌平组的早期高位体系域主要沉积在潮下-潟湖环境中。受控于三级以下海平面以及水动力条件,早期高位体系域自下而上发育了三套形态各异的核形石层。第一套毫米级核形石零星分布于早期高位体系域下部,不具明显核心,包壳内见大量泥晶物质及砂屑、生屑。第二套厘米级-亚厘米级椭球状核形石集中分布于早期高位体系域中部,具有明显核心,包壳主要由亮纹层、菌纹层、生屑层和包壳层组成。第三套厘米级椭球/叶状核形石集中分布于早期高位体系域上部,具有明显核心,包壳主要由亮纹层组成,菌纹层含量较少。镜下鉴定结果表明由亮/暗纹层交互而成的核形石包壳具有不同的显微/超微结构,代表了微生物席与沉积环境的不同互动方式。分析其形成环境可知,北京西郊丁家滩剖面寒武系昌平组以核形石为主的微生物岩,生物灭绝事件是其直接成因,但也许不是决定性因素。 相似文献
6.
震旦系灯影组核形石白云岩作为典型的前寒武纪微生物碳酸盐岩,是我国古老深层油气勘探的岩石类型之一.核形石成因模式的研究,对研究古水体、恢复古环境及其成储模式有重要指导意义.根据核形石结构特征和成因机制将灯影组核形石分为6类,结合岩石学、沉积学和地球化学等研究手段,开展了四川盆地北缘核形石分布特征和沉积过程的综合研究.结果显示：灯影组二段核形石发育于潮下带-潮间坪环境下,水动力和微生物条件的差异影响着微生物生长、自身钙化作用、微生物膜粘结和捕获作用、化学沉淀作用4种核形石纹层形成机理;进一步体现在水动力条件控制着核形石纹层发育厚度、形态特征和伴生岩石类型,而微生物活动习性控制影响着核形石主微量、稀土元素分异特征：贫藻纹层较富藻纹层有较高的Fe/Mn比、实体藻较非实体藻有较高Cu/Zn比,纹层稀土元素富集度一般低于核心.综上所述,灯二段核形石的形成存在4种机理,且它们被海平面变化下的微生物和水动力条件联合控制. 相似文献
7.
川西北龙门山前甘溪地区吉维特阶发育一套厚2~3m灰-深灰色微生物岩,由直径0.1~4.0cm的核形石组成,其核心皆由早期葛万藻及其他生物碎屑组成,包壳由具同心圈层结构的亮色和暗色含葛万藻的纹层组成,并可分为球状、帽状和变形状3类核形石微生物岩,垂向上可分4个旋回,从底到顶核形石密度和粒径总体变密、变大,平面上呈不均匀发育。核形石样品具不同程度的δ~(13)C、δ~(18)O值负偏移和~(87)Sr/~(86)Sr正偏移特征,表明核形石微生物岩层遭受过古表生期大气淡水的影响,其中亮色纹层与球状核形石微生物岩受大气淡水影响最为强烈,核形石是在葛万藻发育、水流扰动及大气淡水参与的环境下,葛万藻包覆于生屑的外缘而成,藻类越发育、水体能量越高、沉积环境越稳定,形成的核形石粒径越大、丰度越高。核形石微生物岩在纵、横向分布特征,表明在全球中泥盆统艾菲尔期—吉维特期海平面上升背景下,龙门山地区吉维特金宝石组末期表现为至少6期次脉动式且逐渐强烈的构造抬升作用,造成该地区金宝石组末期海平面大幅下降而暴露于地表遭受大气淡水的淋滤作用。 相似文献
8.
9.
寒武纪微生物岩中的Girvanella化石在地层中广泛分布,这为微生物参与微生物岩的形成提供了更直观的证据.豫西渑池地区寒武系第三统馒头组二段碳酸盐岩中发育了数量丰富的微生物岩类型——核形石,其核心、纹层及围岩中保存的Girvanella丝状体化石具有密度大、完整度高的特点.对核形石的微观分析表明,其核心、包壳等各个部位均大量保存有Girvanella丝状体.这些丝状体为任意弯曲、不分节、不分枝的管状集合体,单管直径约为20 μm,最大延伸长度约为400 μm.核形石核心以丝状体包绕的灰泥团块或砾屑为特征,局部可见丝状体包绕生物碎屑成核;包壳内的丝状体多出现在暗色纹层中,其分布表现为缠绕叠覆、穿层、凸起和匍匐(或水平状)这4种方式.在核形石的任意部位,Girvanella丝状体均具有相似的分布形式,表明它们的生长条件是相似的.核形石中Girvanella丝状体的大量出现与其形成于低能的滨岸鲕粒滩滩间或滩后低洼地带有关,这种低能条件对Girvanella的生长及保存十分有利.对研究区核形石中的Girvanella化石在微生物岩中的分布特征、微组构等的进一步研究将为寒武纪其他微生物岩的成因及微生物与环境的相互作用提供重要实证. 相似文献
10.
平邑盆地下第三系官中段核形石成因分析 总被引：23，自引：0，他引：23
平邑盆地下第三系官中段核形石较为发育,类型多样。通过对其内部结构的研究发现核形石单元纹层有六种类型,作为核心的藻类仅在顶端发生碎屑粘结效应,而其底部则发育厚度小,规则的暗色纹层。纹层组合类型多样,主要受藻类发育程度,水动力强度和藻类种属的控制,是不同水动力环境下的产物。根据颗粒大小、纹层组合类型纹层层数、填隙物将核形石分为浅水高能成因核形石和较深水低能成因核形石。核形石成因分析和分类对沉积环境的判 相似文献
11.
Kapila Dahanayake 《Sedimentary Geology》1977,18(4):337-353
Oncoids occur abundantly in Kimmeridgian limestones and dolomitic limestones of the French Jura Mountains. Microscopic study of these oncoids confirms their algal origin. The variable role played by the alga Bacinella irregularis Radioicic in the construction of oncoids leads to the recognition of three main types of laminations: (1) micritic laminations, (2) grumose laminations, (3) organism-bearing laminations. Depending on the relative proportion of each type of lamination in their constructions, three types of oncoids are recognized. A fourth type, devoid of any laminations is formed of an algal mesh.It has been established that the occurrence of Bacinella irregularis Radioicic in the laminations of the three oncoid types I, II and III increases in abundance in that order and ultimately this alga develops a mesh in type IV. The series of oncoids so formed is interpreted as being an expression of increasingly prolonged calm periods in an environment otherwise subjected to intermittent agitation. 相似文献
12.
ANDRÉ STRASSER 《Sedimentology》1986,33(5):711-727
ABSTRACT Ooids occurring in the shallow-water Purbeckian carbonate sediments of the Jura mountains can be grouped into six types. Gradations from one type to another and coexistence of the various types are common. Type 1 ooids are small and well rounded. They display fine concentric micritic laminae. In many cases their cortices are dissolved and replaced by void-filling spar. Microsparitic neomorphic replacement occurs locally. Type 2 ooids are large and have irregular shapes. They show fine micritic laminae and occasional layers of fine-radial crystals. They commonly evolve into oncoids. Ooids of type 3 display many fine-radial cortical laminae and are patchily micritized. They are medium in size and mostly well rounded. This type of ooid may pass into large, irregularly shaped coated grains. Type 4 ooids have 1 to 4 cortical laminae with a fine-radial structure and patchy micritization. They are medium in size and well rounded. Type 5 ooids have only one lamina with a coarse-radial structure. They are small and well rounded. Associated are spherical grains containing bundles of elongate crystals. Ooids of type 6 show superpositions of two or more different, radial and or fine micritic laminae. The cortical structure may also change laterally in the same lamina. The preferential dissolution of type 1 ooid cortices to form oomoulds indicates a primary composition of unstable carbonate. Sedimentological features and comparison with modern ooid occurrences point to formation on high-energy sandbars in normal-marine waters. Type 2 ooids grew in marine-lagoonal environments with quiet water and abundant cyanobacteria. The radially structured ooid cortices of types 3, 4 and 5 show no dissolution features. This implies that they were originally composed of stable carbonates, or that an unstable carbonate phase was transformed into a stable one at an early stage of diagenesis. Type 3 ooids occur together with marine faunas and indicate high water energy. Ooids of type 4 and type 5 originated probably from relatively quiet water of variable salinity. Coexistence of different ooid types and mixed forms of type 6 implies gradual or rapid changes in hydrodynamic, geochemical and microbiological conditions which were a feature of the Purbeckian depositional environments. 相似文献
13.
鄂西宜昌地区寒武系出露齐全、连续，且岩石类型多样、化石丰富，是我国寒武系的标准剖面之一。其沉积环境以潮下高能浅滩为主，其次为间歇能量的潮间带、滨岸的中小型浅滩，少数为开阔海较深处的静水灰泥沉积。石灰岩集中分布于下寒武统天河板组和水井沱组，其次在下寒武统的石牌组、中寒武统的磕膝包组、官山瑙组有少量夹层出现。其岩石类型有颗粒灰岩（鲕粒灰岩、核形石灰岩、砾屑灰岩及砂屑灰岩）、含颗粒泥粉晶灰岩（含生屑泥粉晶灰岩、含生屑灰岩）及泥晶灰岩。白云岩是本地区数量最多的岩石类型。从下寒武统石龙洞组开始都是白云岩沉积，白云岩可据白云石化作用机理和时间的不同分为准同生白云岩和准同生后白云岩两大类。准同生白云岩广泛出现于中上寒武统，岩石呈土黄色、砖红色，具纹层、鸟眼、干裂构。准同生后白云岩根据残余颗粒的有无可分为残余颗粒白云岩和晶粒白云岩两大类。晶粒白云岩有两种成因。一为回流渗透云化；二为深埋藏云化。根据本区寒武系岩石的岩石学特征、生物组合特征和结构构造特征本文重建了各组段的沉积环境. 相似文献
14.
本文根据野外调查和室内初步研究成果并结合有关地质资料,分析、讨论了荆襄陡山沱组含磷岩系的磷块岩类型、成因和沉积环境。通过分析可知,组成磷块岩的磷灰石有不同的形成方式;磷块岩沉积在海退旋回中粘土和硅质沉积向碳酸盐沉积的转变阶段;磷块岩矿床形成在陆缘海内与深水有联系的浅水地带。 矿区含磷岩系特征综合于图1。 相似文献
15.
根据野外地质剖面宏观分析及室内薄片鉴定,对塔里木盆地巴楚地区上奥陶统吐木休克组和良里塔格组进行碳酸盐岩岩石组分、岩石类型及沉积环境分析。研究认为这2个地层单元具有不同的生物组合、颗粒成分、基质类型及其结构。吐木休克组岩石类型较为单一,主要为介形虫和三叶虫富集的泥晶生屑灰岩;良里塔格组岩石类型较多,包括似球粒藻粘结岩、泥晶生屑灰岩、亮晶砂屑灰岩、泥晶似球粒灰岩和纹层状叠层粘结岩等12种岩石类型。根据岩石学特征及野外露头分析认为,吐木休克组沉积于礁前上斜坡环境,而良里塔格组发育开阔台地相、局限台地相和生物礁相等,反映沉积环境水体相对较浅。研究区Ⅰ号和Ⅱ号剖面间发育台地边缘礁相,由南向北发育3个藻礁。 相似文献
16.
Oligocene oncoids from the lacustrine Süβwasserschichten of the Mainz Basin exhibit a pustular surface and a characteristic cavity on their undersides, which gave rise to their designation as ‘swallow nests’. Oncoids grew in situ, under low-energy conditions during a pause in sedimentation. Three features indicate that they were never overturned: (1) oncoids can be placed in a stable position on a smooth surface; (2) laminae, which are mostly concentric around the entire oncoids, display polar thickenings on the upper side during all growth stages of oncoids; (3) the depression is always situated on the stable side of oncoids. Development of this cavity is favoured by unionid shells, in the stable position, serving as oncoid nuclei, but occurs also under flat nuclei. It is interpreted as a product of reduced growth of cyanobacteria due to oligophotic conditions, on a fine-grained substrate, and is considered as diagnostic of the in situ growth of oncoids. Oncoid cortices are mainly formed by a Scytonema-like cyanobacterium, whose carbonaceous organic remnants are occasionally preserved. Growth stages of individual oncoids were image-processed and compared by means of shape parameters. Due to optimum growth conditions, cyanobacteria try to occupy the entire available space; hence, oncoids tend to achieve a spherical form even during in situ growth. Renewed background sedimentation triggered the formation of pustular surfaces and finally caused the cessation of cyanobacterial growth. 相似文献
17.
云南施甸铺门前组灰岩的微相特征及其环境意义 总被引：1，自引：1，他引：0
<正> 保山地块位于怒江和澜沧江断裂带之间,西为西缅地块及怒江—龙陵—瑞丽缝合带,东为昌宁—双江缝合带,海进自泥盆纪开始,早石炭世发生海退,下石炭统香山组及铺门前组碳酸盐沉积仅局限分布于由保山—施甸呈袋形向南延伸的区域内(图1)。沉积间断发生于早石炭世末、晚石炭世初之间。而后,海进扩大,上石炭统丁家寨组覆于铺门前组灰岩之上。 相似文献
18.
In the Tithonian Solnhofen Plattenkalk (Malm + 2) of southern Germany, layers of purely micritic limestone are rhythmically interbedded with ones of marly micritic limestone. It appears that this alternation was formed under control of the Tithonian orbital variations. The Fourier spectral analysis shows that, on a decimetric to metric scale, the long-term cyclicities in the number of laminae per centimetre are in agreement with those found in the bed-thickness series, varying from 0.7 to 1.3 m cycles. The number of laminae of the Solnhofen Formation ranges from about 5,800 to about 12,800 laminae per main cycle. This indicates that, under an assumption that the main cycle of the Solnhofen Formation corresponds to the Tithonian precessional one, a single lamina represents a multi-year time interval. Particularly, in the short-term cyclic domain, the laminated sequence contains clearly millimetric cycles consisting of about two to three cyclic components. It implies that laminae formation may result from the composite effect of two or three distinct climatic processes. 相似文献
19.
四川龙门山区甘溪剖面中泥盆统金宝石组顶部发育一套核形石灰岩。通过野外剖面实测和镜下详细观察,认为该套核形石灰岩垂向上可分为3个沉积旋回,每个旋回均由核形石灰岩和泥晶灰岩组成。葛万藻(Girvanella)丝状体在核形石的核心和包壳中均有发育,对核形石的形成具有重要的作用。结合核形石中的纹层类型、Girvanella丝状体形态以及渗滤砂与核形石纹层的关系,认为核形石是在浅滩和礁后潟湖环境中沉积形成的,核形石及其围岩中赋存的粒内渗滤砂和粒间渗滤砂,形成于核形石沉积之后的大气水淋滤作用。通过对核形石形成环境的分析可知,龙门山区甘溪剖面中泥盆统金宝石组顶部核形石灰岩形成的水动力条件从下到上逐渐减弱,反映了当时相对海平面由低到高的变化特点。 相似文献