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1.
Spectacularly developed lower Eocene chert in the Corones platform carbonates of the Spanish Pyrenees is concentrated within a restricted, brackish-water, laminated ostracod-rich facies, which also contains abundant sponge spicules. The chert occurs as nodular, bedded and mottled varieties, and four petrographic types of quartz are developed: microquartz; length-fast (LF) chalcedony; megaquartz; and microspheres. δ18O values of chert range from 29·6‰ to 30·9‰ (SMOW), which correspond to a broad isotope rank common for biogenic and diagenetic replacement cherts. Calcian dolomite crystals with high Fe and Na are disseminated within the microquartz and LF-chalcedony, but are absent from the megaquartz and host carbonate. The chert is closely associated with desiccation cracks and with interstratal dewatering structures. Load casts are silicified, and laminae rich in sponge spicules are convoluted. Early cracks related to dewatering are filled by microquartz and quartz cements. Ostracod shells within chert are locally fractured; those in the host carbonate are commonly flattened. Late fractures are filled by LF-chalcedony and megaquartz. There is much evidence for the dissolution of sponge spicules and their calcitization in the carbonate host rock. Silica for the Corones cherts was derived from sponges during early diagenesis and shallow burial. Early mechanical compaction and sediment dewatering played a major role in sponge spicule dissolution, migration of silica-rich fluids and the consequent precipitation of chert. Quartz cements continued to be precipitated into the burial environment.  相似文献   

2.
The Abu Ruweis Formation is composed of carbonates, evaporites, and mudstones, with some locally developed pelletic, oolitic and stromatolitic limestones. The lateral persistence of bedding, the purity of the evaporite rocks, the alternating arrangement of marine carbonates and evaporites indicates periodic deposition in subaqueous conditions (salina). Petrographic investigations, X-ray diffraction analysis as well as chemical analysis have shown that the outcropping evaporite beds are mainly composed of secondary gypsum, with rare anhydrite relics. Five microfacies of gypsum were recognized according to their fabrics: porphyroblastic and granoblastic gypsum showing polarization texture, gypsum pseudomorph after anhydrite laths, and satin spar gypsum. The textures they display indicate a hydration origin of precursor anhydrite, which is in turn rehydrated from primary gypsum. Some of these anhydrites were formed as a result of replacement processes of the carbonate sediments associated with the evaporites, as evidenced from the textural relationships of the carbonate and sulfate minerals. The O18 content ranges from 1.45 to 8.38% PDB and the C13 content ranges from −1.52 to 4.73% PDB. Trace elements analysis has shown that the Abu Ruweis dolomites are rich in strontium (up to 600 ppm), and sodium (up to 835 ppm). The isotope composition and trace elements content, as well as the petrographic characteristics point to a penecontemporaneous hypersaline dolomitization origin for the Abu Ruweis dolomites. The evaporites were deposited during a regressive lowstand systems tract, whereas the carbonates were deposited under shallow water marine conditions during a highstand systems tract. The Abu Ruweis succession represents a relatively stable arid climate within a rapidly subsiding basin. Restricted conditions were provided by the development of beach barriers.  相似文献   

3.
The Malmani Subgroup northwest of Johannesburg consists of dolomite and chert with only minor clastic sediments.A precise upper intertidal to marginal supratidal analogy and the associated relationship of varied structures suggest that much of the succession represents a tidal flat to intertidal complex formed within differing semiprotected to protected conditions. The dolomites from these environments are recrystallized, reflecting a meteoric influence, and the cherts which are commonly developed within them are also related to prevailing lower pH's. This dolomitization is considered to have been enhanced by the influx of meteoric waters which however resulted in the dolomites having undersaturated iron-manganese ratios. Rare colour-banded dolomites containing columnar stromatolites are thought to represent more steeply shelving intertidal conditions than are normally encountered in the epeiric sea. These dolomites contain quartz crystals rather than chert, suggestive of a lower concentration of silica in the original alkaline solutions. The exposure is part of a very widespread carbonate unit, dated at ca. 2.250 m.y.Subtidal conditions in which large elongate stromatolitic domes developed can be related to a marine transgression across a basal clastic beach sand; and secondly to a progradational tidal flat seawards of which a talus breccia developed on a steepened slope leading down to the subtidal regime. These dolomites formed by interaction with marine waters saturated with respect to iron and manganese, while the absence of chert reflects persisting alkaline conditions.A dark chert-free dolomitic facies with high iron and manganese contents of saturated ratios is considered to have developed in an alkaline lagoonal environment behind a subaqueous bar that is now represented by an overlying thick oolitic unit.The succession contains numerous chert breccias with which shales are associated. The breccias represent subaerial exposure phenomena related to regressions which were followed by periods of short-lived terrigenous influx.  相似文献   

4.
天津蓟县元古界剖面具有极高的综合研究价值,而高于庄组在该剖面中居于承上启下的位置。高于庄组在整个中、新元古界剖面中厚度较大,岩石类型多样且成因特殊,主要岩石类型包括碳酸盐岩、泥岩、硅质岩和石英砂岩。碳酸盐岩主要为泥晶灰岩、瘤状灰岩、砂屑灰岩、臼齿灰岩及粉细晶白云岩等。硅质岩包括燧石和沉积石英岩,沉积石英岩具鲕状或砾状结构。仅在本组底部见石英砂岩。上述岩石特征表明,蓟县地区在中元古代长城纪晚期的高于庄期以浅海中深缓坡沉积为主,有短期的潮坪碳酸盐沉积环境,沉积作用受大红峪时期火山物质的影响。臼齿灰岩的存在可能提供华北地区中元古代年代地层学和构造沉积演化研究的新证据。  相似文献   

5.
ENNO NICKEL 《Sedimentology》1982,29(6):761-796
Continental carbonates of the basal part of the Guarga Formation, Upper Eocene, have been studied in the field and in the laboratory. Both geographic pattern and vertical sequences served as a basis for sedimentary models. The pattern reveals that carbonate deposition was greater in the western part of the Tremp-Graus Basin than in the eastern part. Studies of slabs and thin sections suggest high energy deposition in the eastern part of the basin and low energy deposition in the western part. Gross lithology, petrography, and faunal/floral associations indicate sedimentary environments which include calcimorphic palaeosoils, caliche nodule zones, solid caliche nodule zones, caliche crusts, fluvial carbonates, paludal carbonates, and pond/lake carbonates. Distribution pattern of the carbonate bodies and lithologies seem to be controlled by alluvial-fan processes. They are typical fining-upward sequences in the sense of Collinson (1978) which furthermore can be assigned to a channel-bound group and a succession independent of fluvial channels. Referring to fan-physiography the sequences can be subdivided into fluvial proximal interchannel, fluvial distal interchannel, lacustrine distal interchannel, nearshore lacustrine-paludine, and lacustrine offshore carbonate facies. The two last categories are distal alluvial plain and/or fan-edge associations. The presence of especially charophyte oogonia adjacent to pseudomorphs of lenticular gypsum in the lacustrine carbonates of the western Tremp-Graus Basin indicates that their depositional environment was that of shallow lakes with alternating salinities. Diagenetic alterations consist of three major phenomena: (a) general cementation of the carbonates by low-Mg calcite, (b) pseudomorphs of lenticular gypsum, and (c) silification. The relationship of gypsum and silica diagenesis to the regional distribution of lacustrine carbonates suggests early diagenetic processes for their formation. Gypsum pseudomorphs are small and are found to be replaced by Fe-calcite throughout the whole area, or are large and replaced preferentially by silica in the west only. There is experimental evidence (Cody, 1979) that distribution of gypsum morphology and crystal sizes can be related to increased salinities and increased organic production in the west. Chert-gypsum fabrics from that area resemble the ‘silex nectique’ of Cayeux (1929). The occurrence of this noteworthy type of chert together with length-slow chalcedony is an indication of relatively early silification of the gypsum. It is suggested that the sediments containing the silicified lenticular gypsum hosted brines of partly marine origin which alternately became brackish or fresh. An attempt was made to check the influence of evaporation during carbonate deposition by determining the stable isotope composition of the carbonates and of the chert. The data show no distinct variations with respect to the presumed palaeoenvironments. The ranges in the carbonates (δ13C ? 5,0 to ?7,9; δ18 O ?4,5 to ?7,7) fit among the data given in the literature. The values derived from chert (δ18O 26,9 to 31 SMOW) support a concept of alternating salinities. Distribution of carbonate lithofacies indicate a systematic change in sedimentation from fluvial/ephemeral to permanent lacustrine from east to west. Diagenetic alterations suggest an increase of salinities of pore waters in the same direction. In addition the lacustrine limestones in the west were due to frequent changes in pore-water salinity. Similar sequences lacking subtidal and/or lagoonal fossil associations but including pseudomorphs of carbonate and chert after lenticular gypsum were described from the Lower Purbeckian of Dorset (West, 1964, 1975, 1979), and from the Tertiary of the Paris Basin (Fontes, 1968). Guarga limestone environments of especially the western Tremp-Graus Basin probably resembled the modern semi-arid ephemeral saline lakes in Australia (Burne, Bauld & De Dekker, 1980). Gypsum precipitation in these environments can be compared to the one in modern sabkhas from the Mediterranean coast of Egypt (West, Ali & Hilmy, 1979; Ali West & Hilmy, 1980).  相似文献   

6.
洛阳龙门地区中寒武统张夏组为一套富含生物扰动的薄层微晶灰岩和厚层鲕粒灰岩沉积,根据沉积学和遗迹学特征,从中识别出6个遗迹组构,从下到上依次是:潮下低能碳酸盐岩台地中的Planolites montanus遗迹组构,潮下浅水较高能碳酸盐岩台地中的Palaeophycus tubularis-Thalassinoides horizontalis遗迹组构,高、低能交替的滨岸浅滩或开阔台地滩间坪或滩前沉积中的Skolithos linearis-Planolites montanus遗迹组构,深水低能开阔台地沉积中的模糊生物扰动遗迹组构,高能鲕粒浅滩中的Macaronichnus segregatis遗迹组构和潮下低能局限台地环境中的Palaeophycus heberti遗迹组构.龙门地区张夏组由无鲕粒滩的碳酸盐岩台地逐渐向发育厚层鲕粒滩的碳酸盐岩台地演化,沉积环境从滨岸浅滩逐渐演变为无鲕粒滩的开阔台地,并随着海退由深水、开阔台地逐渐变浅形成鲕粒滩、局限台地.   相似文献   

7.
梅冥相  郭荣涛  胡媛 《岩石学报》2011,27(8):2473-2486
北京西郊下苇甸剖面的崮山组,属于寒武系第三统顶部,自下而上从陆棚相泥灰岩向上变浅至鲕粒滩相灰岩,组成一个淹没不整合型三级沉积层序。在该组上部的一层块状鲕粒滩相颗粒灰岩中,发育串珠状分布的、可以归为叠层石生物丘的穹窿状构造。这些叠层石生物丘,典型的地势隆起和突变的边界代表了明显的早期石化作用特征。叠层石生物丘中的柱状叠层石,为典型的泥晶相叠层石,其内部除了黏结较多的三叶虫生物碎屑外,还不均匀地分布着放射-纤维状方解石(或文石？)组成的底栖鲕粒。这些底栖鲕粒,以其较小的粒径、多样的类型、平滑但不连续的鲕粒圈层以及外部边缘的泥晶套等特征,明显区别于宿主岩石中的颗粒滩相悬浮鲕粒,而且表现出较为明显的与微生物活动相关的微组构。鉴于叠层石是典型的微生物席建造物,该叠层石生物丘特别的宏观和微观沉积组构还可以进一步将其归为较为典型的"微生物礁",从而成为研究中奥陶生物大辐射事件之前贫乏骨骼的浅海环境的沉积作用样式、以及更加深入理解这一特殊时期的微生物造礁作用特征提供了一个较为典型的实例。  相似文献   

8.
Mesoproterozoic (∼ 1600 Ma old) Salkhan Limestone (Semri Group) of the Vindhyan Supergroup, exposed in Rohtas district of Bihar, India, preserves an abundant and varied ancient microbial assemblage. These microfossils are recorded in three distinctly occurring cherts viz., bedded chert, stromatolitic chert and cherty stromatolites. 27 morphoforms belonging to 14 genera and 21 species have been recognized. Six unnamed forms are also described. The microbial assemblage, almost exclusively composed of the remnants of cyanobacteria, is dominated by entophysalidacean members and short trichomes and can be termed as ‘typical Mesoproterozoic microbiotas’. The assemblage includes characteristic mat-forming scytonematacean and entophysalidacean cyanobacteria.Eoentophysalis is the dominant organism in the assemblage. Ellipsoidal akinetes of nostocalean cyanobacteria(Archaeollipsoides) and spherical unicells also occur; both are distinct from mat forming assemblage, allochthonous and possibly planktic. Co-occurrence of the microbiotas and precipitates is related to the depositional environment of the Mesoproterozoic tidal flats with high carbonate saturation.  相似文献   

9.
Near the Ontario—Minnesota boundary, the middle Precambriansedimentary Gunflint Iron Formation has been contact metamorphosedby the Duluth Complex to the pyroxene hornfels facies. Threemetamorphic zones have been recognized based on mineralogicalchanges observed within the aureole; a fourth zone correspondsto essentially unmetamorphosed iron formation. Each zone maybe recognized by the dominant iron silicate present: zone 1—greenalitezone (unmetamorphosed), zone 2—minnesotaite zone (slightlymetamorphosed), zone 3—grunerite zone (moderately metamorphosed),zone4—ferrohypersthene zone (highly metamorphosed). Granule bearing cherty rocks of zone 2 are characterized bythe reduction of hematite to magnetite and reaction of greenaliteand siderite to minnesotaite ± magnetite. Relict texturesare well preserved in zone 2 and retrograde reactions are minimal.Grunerite first appears in banded slaty rocks of zone 3. ‘Slaty’grunerite formed principally by reaction between carbonate andstilpnomelane, while in cherty rocks grunerite formed by reactionbetween greenalite and silica. Original bulk chemical differencesbetween cherty and slaty iron formation is reflected by amphibolechemistry as shown by the higher Al content and lower Fe/Fe+ Mg ratio of slaty grunerite, and by the greater ahundanceof Na, Al-bearing amphiboles such as ferrotschermakite in slatyrocks. Hedenbergite and fayalite appear in the upper part ofzone 3; both formed by silication of carbonates and both arepartially retrograded to amphibole. Prograde grunerite-cummingtoniteis partially replaced by minnesotaite in cherty rocks of zones3 and 4. In zone 4, greenalite and siderite-bearing assemblagesreacted to ferrohypersthene, fayalite (±quartz), pigeoniteand grunerite-cummingtonite. Retrogradation is widespread andresulted mainly in the formation of grunerite. Primary textureswere destroyed in slaty rocks but are still recognizable incherty rocks. Preservation of sedimentary textures within the contact aureoleis a characteristic feature of cherty rocks. In zone l theserocks typically consist of the following textural-mineralogicalassociation: granules (greenalite, quartz, hematite), cement(quartz, siderite, ankerite, calcite) and mottles (various carbonates).Retention of these textural elements, combined with compositionaldata for assemblages in the low to moderate grade rocks, enablesidentification of numerous metamorphic reactions. In the absenceof relict phases or relict textures sedimentary assemblagescan sometimes be inferred from abundances of minor elementssuch as Al and Mn. In some slaty rocks the presence of carbonaceous or graphiticmaterial has preserved perfectly premetamorphic structures suchas siderite spherules and ankerite rhombs, enabling the recognitionof several amphibole-forming reactions. Chemographic analysis of simplified subsystems for cherty rocksof zone 1, zone 2, and the lower part of zone 3, are consistentwith observed assemblages and reactions.  相似文献   

10.
The Nolichucky Formation (0–300 m thick) formed on the Cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton. Lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp. Peritidal facies of the regional shelf are cyclic, upward-shallowing stromatolitic carbonates. These grade toward the intrashelf basin into shallow ramp, cross-bedded, ooid and oncolitic, intraclast grain-stones that pass downslope into deeper ramp, subwave base, ribbon carbonates and thin limestone conglomerate. Ribbon limestones are layers and lenses of trilobite packstone, parallel and wave-ripple-laminated, quartzose calcisiltite, and lime mudstone arranged in storm-generated, fining upward sequences (1–5 cm thick) that may be burrowed. Shallow basin facies are storm generated, upward coarsening and upward fining sequences of green, calcareous shale with open marine biota; parallel to hummocky laminated calcareous siltstone; and intraformational flat pebble conglomerate. There are also rare debris-flow paraconglomerate (10–60 cm thick) and shaly packstone/wackestone with trace fossils, glauconite horizons and erosional surfaces/hardgrounds. A 15-m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin. Understanding the Nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the Lower Palaeozoic elsewhere. The study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation. Finally, recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks, whose trends may be unrelated to regional shelf-edge trends.  相似文献   

11.
The Campbell Group carbonates were deposited in a basin transgressing from southwest to the east and to northeast. At the southwestern margin of the Kaapvaal craton, in Griqualand West, mainly tidal flat carbonates and shallow marine deposits are found to be followed by subtidal carbonates marking the slow transgression. North of the Griquatown Fault, where the center of the Griqualand West sub-basin developed, continuous subsidence matched by stromatolitic carbonate growth, led to accumulation of the thickest carbonate pile (> 2000 m). There, the largest limestone deposits of South Africa are located. The deposit at Lime Acres and mining operations of the PPC Lime Ltd. are described and discussed in respect to diagenetic processes that permitted limestone preservation.  相似文献   

12.
Jaisalmer Formation consists of 360m thick succession of medium to coarse grained sandstones with interbeds of shale, claystone and occasional lignite that rest over Lathi Formation, is the basal part of the Jaisalmer basin. The rocks are exposed amidst desert, low mounds and shallow stone quarries. Sandstones were deposited in shallow marine to deltaic environments. The studied sandstones consist of abundant quartz followed by feldspar, mica, chert, rock fragments and heavy minerals. The study mainly deals with identification of various diagenetic features such as compaction, cementation and porosity evolution. During mechanical compaction rearrangement of grains took place and point, long and suture contacts were formed. The sandstones are cemented by iron oxide, silica overgrowth, carbonate and clay. Porosity has developed due to dissolution of iron, carbonate cement and feldspar grains. Dissolution and alteration of feldspar, lithic fragments and pressure solution were the main source of quartz cements. The sandstones show good amount of existing optical porosity with an average of 7.19%. Porosity reduction is mainly due to early stage of mechanical compaction and subsequent pervasive calcite and iron oxide cementation. Further, porosity reduced due to deposition of clay cement.  相似文献   

13.
华北地台中元古界主要由环潮坪石英砂岩、浅海碳酸盐岩和浅海—泻湖相暗色页岩3种沉积相组合构成,以陆表海浅水碳酸盐岩占主导。碳酸盐岩中除含有丰富的微古植物、宏观藻类和微生物建隆外,还发育大量的微生物成因构造(MISS)和微生物诱发的碳酸盐沉淀(MMCP)。微生物席和MISS构造在高于庄组上部(约1.6 Ga)和雾迷山组下部(约1.45 Ga)碳酸盐岩中尤为发育,表明活跃的微生物活动和高有机质产量。在石化微生物席中,发现有丝状、球状细菌化石和草莓状黄铁矿;围岩中发现有针状文石、花瓣状重晶石、放射状菱铁矿、铁白云石和葡萄状碳酸盐胶结物等多种自生碳酸盐矿物,指示甲烷厌氧氧化(AOM)导致的自生碳酸盐沉淀。中元古代的温暖气候和海洋分层、缺氧、硫化条件有利于微生物的高生产量和高有机质埋藏率。气隆构造和核形石状碳酸盐结核反映浅埋藏条件下活跃的成烷作用和甲烷排放,围岩和MMCP中富沥青质。华北地台中元古界富微生物席碳酸盐岩有良好的生烃潜力,有可能形成重要的烃源岩。据微生物席、MISS构造及MMCP的研究,初步估算华北地台中元古代碳酸盐岩的概略生烃潜力约为10×108t石油当量。  相似文献   

14.
Cuddapah basin is an important uranium province, wherein unconformity related uranium deposit occur in Srisailam sub-basin in northern part and the dolostone hosted strata bound uranium deposit in Vempalle dolostone in southern part. The latter host the low-grade, large-tonnage uranium deposit. Vempalle Formation in Dhone-Gudipadu-Korivipalle (DGK) sector, along western part of the Papaghni sub-basin consists of three major units viz. (a) lower dolostone, (b) middle purple shale and (c) upper cherty dolostone. The lower dolostone has lot of detritus, represented mainly by quartz, feldspar, mica and clay. The upper cherty dolostone has chert as layers, nodules, rip-up clasts and at places do have conspicuous reddish brown shale bands with <2mm size siliceous oolite layers. They exhibit shallowing-upward carbonate depositional system with tidal flat environment. A number of uranium occurrences in Gudipadu-Korivipalle sector are hosted by the lower dolostone unit, especially at its lower stratigraphic level, i.e. 15-42m above the Gulcheru-Vempalle (GV) contact. Micro-stylolites are indicative of comparatively more burial pressure. Presence of fenestral voids filled with recrystallised fibrous calcite and thin mud drapes in the dolostone is indicative of precipitation in a shallow marine-tidal flat environment with late burial dolomitisation. Depletion of heavier C and O isotopes [13C: (-2.31 to 1.32%) and 18O: (-6.21 to -17.3%)] in the lower dolostone indicate mixing of fresh water with sea water in the depositional environment of tidal flat regime  相似文献   

15.
神农架群(约1400—1000 Ma)发育于扬子克拉通北缘鄂西北地区,自下而上发育有下亚群(大岩坪组、马槽园组、乱石沟组、大窝坑组和矿石山组)、中亚群(台子组、野马河组、温水河组和石槽河组)及上亚群(送子园组和瓦岗溪组)。每亚群均由相对较深水相碎屑岩和浅水碳酸盐岩组成。一系列岩石组合特征、宏微观沉积组构和沉积构造等表明,神农架群发育环潮坪相藻碳酸盐岩、浅海相碎屑岩、台缘浅滩颗粒碳酸盐岩和台缘斜坡砾屑碳酸盐岩等4类沉积组合,形成于远端变陡型缓坡型碳酸盐岩台地背景。环潮坪沉积分布最广,遍布于所有碳酸盐岩地层,不同类型叠层石发育,构成向上变浅沉积序列;进积作用强烈,干裂构造、蒸发岩等常见;沉积相带由浅潮下、潮坪及潮上带组成。浅海碎屑岩沉积组合主要见于台子组及大岩坪组,由砂岩、粉砂岩与泥岩组成,石英砂岩分选和磨圆较好,自生海绿石常见,平行层理、水平—波状层理发育,泥岩中自生黄铁矿发育,总体经历了滨岸浅滩—浅海陆棚—碎屑潮坪—局限台地等的高频变化。台缘浅滩颗粒碳酸盐岩以鲕粒白云岩、砾屑白云岩(及内碎屑白云岩)和斜歪锥、柱状叠层石为特征,主要见于乱石沟组、野马河组;大窝坑组及石槽河组以鲕粒和砂—砾屑白云岩及藻碎屑(团块或凝块石)为特征;大中型板状交错层理、递变—平行层理和冲刷—侵蚀构造普遍,表明浅潮下带强水动力条件环境。台缘斜坡砾屑碳酸盐岩发育在大岩坪组中上部及马槽园组,由滑塌堆积的透镜状、巨厚层状巨—粗—细砾岩和砂岩组成,砾岩成分以白云岩等为主,可见大型交错层理、波痕和侵蚀—冲刷等沉积构造。对神农架群沉积序列、沉积特征及沉积演化过程的研究,为扬子克拉通中元古代晚期的盆地演化与重建、沉积充填过程及地层—沉积对比研究提供了基础资料及依据。  相似文献   

16.
王龙  李伟强  王皓  吴海  辛浩 《沉积学报》2019,37(6):1193-1209
华北地台大约从寒武纪第二世的晚期开始接受沉积,超覆在前寒武-寒武纪“巨型不整合面”之上,形成了一套二级海侵背景下的厚层陆表海硅质碎屑岩-碳酸盐岩混积序列,这套特别的地层序列在苗岭统和芙蓉统中包含了多种多样的微生物岩。研究区苗岭统出露较为完整,包括毛庄组、徐庄组、张夏组和崮山组,分别构成4个三级层序即SQ1至SQ4。在SQ2的高位体系域和强迫型海退体系域中,以及SQ3的高位体系域中发育了较为特别的由微生物岩构成的生物层、生物丘或生物丘复合体。微生物岩的种类和沉积环境包括形成于正常浪基面以下、潮下带低能环境的类型I迷宫状微生物岩,潮下带上部至潮间带中-高能环境的类型II和类型III迷宫状微生物岩,风暴浪基面之上浅水环境中的均一石,潮间带短柱状叠层石和潮上带近水平缓波状叠层石,以及高能鲕粒滩中的小型叠层石生物丘。通常认为寒武系苗岭统的微生物岩（礁）以凝块石和树形石为特征,而本次研究在苗岭统中发现了迷宫状微生物岩和均一石,补充丰富了对寒武系微生物岩（礁）多样化和复杂化构成的认识。无论是在迷宫状微生物岩、均一石中,还是叠层石中,都见到了一种或多种钙化蓝细菌（鞘）化石,如葛万菌（Girvanella）、附枝菌（Epithyton）和基座菌（Hedstroemia）等,以及大量的钙化微生物席残余物,表明这些微生物岩是由蓝细菌所主导的微生物席的复杂的钙化作用产物,而大量呈弥散状分布的黄铁矿晶体或颗粒则表明硫酸盐还原菌等非光合作用细菌和异养细菌可能在促进碳酸盐沉淀过程中扮演了重要角色。  相似文献   

17.
山东东辛油田古近系沙河街组一段碳酸盐岩储集特征   总被引：1，自引：0，他引：1  
山东东辛油田古近系沙河街组一段湖相碳酸盐岩过去仅作为盖层而忽视其油气地质意义。研究表明,其岩性以生物灰岩及鲕粒灰岩为主,并有少量螺灰岩。其中生物灰岩中以溶蚀孔隙、生物体腔孔及骨架孔隙等类型构成主要的油气储集空间,使其具有较高的孔渗性;鲕粒灰岩在形态上以长条鲕、圈层鲕最为常见,其核心以生物碎片（化石）为主,鲕粒灰岩以粒间孔和粒内孔作为主要的油气储集空间,亦具有较高的孔渗性。沙一段碳酸盐岩的主要矿物成分为白云石和方解石,且大部分白云石及部分方解石均含铁,不同岩性的储层具有不同的储集类型,储层性质受岩石类型、沉积环境、表生作用及胶结作用、溶解作用及白云岩化等成岩作用影响,且沙一段储层处于油气运聚非常有利的过渡带,在藻滩及高能浅滩部位可形成较好的油气富集带,所以对湖相碳酸盐岩储层的研究有助于老区滚动勘探开发。  相似文献   

18.
国内外元古代碳酸盐岩中常见席状、透镜状、脉状和块状等形态的微亮晶碳酸盐岩。微亮晶体宏观、微观边界清晰,内部充填均一等粒结构的方解石微亮晶。宿主岩相以含泥质或粉砂质的细砂屑、粉泥屑灰岩为主,经常与风暴岩共生。微亮晶构造碳酸盐岩发育在缓坡型台地,沉积层序中常见潮汐流、风暴流侵蚀-充填和浪成交错层理与递变层理。微亮晶构造碳酸盐岩发育严格受沉积环境和岩相约束,形成于 (内缓坡深部-中缓坡浅部 )潮下带和环潮坪,风暴浪基面是其发育的最大深度。垂向序列由高频潮下带和环潮坪微层序加积而成,单个微层序顶部通常为环潮坪为纹层状含铁质有机质泥屑碳酸盐岩披盖层,是一个向上沉积动力减弱、沉积物变细和水体变浅的沉积旋回。  相似文献   

19.
天津蓟县中元古界雾迷山组是一套厚度超过3 000 m的叠层石碳酸盐岩沉积序列,在该序列中潮下相叠层石生物层、凝块石生物丘与潮坪相泥晶白云岩、泻湖相白云质泥页岩一起构成若干个环潮坪型米级旋回--“雾迷山旋回层”。在雾迷山组下部发育微指状叠层石,并被古生物学家定义为“Pseudogymnosolen mopanyuensis-Scuphus-Yangzhuang columnaris”组合,即假裸枝叠层石科叠层石,沉积学家将其解释为元古代文石（灰华）海底沉淀物所构成的叠层石,代表从太古代海底结壳状文石沉淀物叠层石到新元古代碎屑结构相、富泥碳酸盐叠层石过渡时期的特殊产物。因此,雾迷山组巨厚的叠层石碳酸盐岩沉积序列,记录了元古代文石灰华海底沉淀物所构成的特殊的叠层石大规模消亡的层位,为研究前寒武纪以叠层石为代表的微生物碳酸盐岩所经历的漫长而复杂的地质历史演变提供了宝贵的材料。  相似文献   

20.
梅朝佳 《古地理学报》2018,20(3):453-464
作为微生物碳酸盐岩的主要类型之一,叠层石是微生物席的主要建造物已成为共识。天津蓟县中元古界铁岭组二段叠层石生物礁灰岩发育,其中的细粒叠层石被前人解释为微生物席捕获碳酸盐泥的微生物建造物,使得其既不同于现代叠层石,也不同于显生宙尤其是寒武纪的叠层石。更为特殊的是,这些叠层石中的海绿石和黄铁矿代表着2种特殊的矿化作用,其中研究区普遍产出的黄铁矿,作为硫酸盐还原细菌的产物,是了解古代微生物的窗口;而发育在高能浅海的海绿石,产出环境不同于现代海绿石,不能作为慢速沉积环境的指示矿物,亦不具有沉积间断的地质意义。2种矿化作用表明铁岭组叠层石是由沉淀作用而非捕获碳酸盐泥形成,这为了解中元古代叠层石的形成和特征提供了一些有益的线索。  相似文献   

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