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1.
华北中元古界串岭沟组暗色页岩中普遍发育的砂脉构造被解释为气体逃逸形成的沉积构造。在砂脉和相邻围岩中发现有自生碳酸盐沉淀和自生黄铁矿。自生碳酸盐主要由白云石组成,表现为微晶质条带或隐晶质斑块状胶结物。微晶白云石条带多出现在有机质纹层密集发育的部位,沿微生物膜两侧发育;而隐晶质斑块多以胶结物形式充填粒间孔隙或沿砂脉外缘密集产出。围岩中共生草莓状黄铁矿,砂脉中有具环带黄铁矿。这种特殊的矿物组构以及富有机质沉积和丰富的微生物成因构造(MISS)均表明串岭沟组形成于缺氧环境。层面发育的气泡构造为砂脉的气体逃逸成因提供了支持,而自生碳酸盐和黄铁矿则是沉积浅层硫酸盐-甲烷转换带(SMTZ)甲烷厌氧氧化(AOM)和细菌硫酸盐还原(BSR)的产物;气体源于有机质的厌氧分解和甲烷菌活动。砂脉中发现有疑似微生物化石,围岩含古菌和硫细菌生物标志物,表明有发生AOM和BSR作用的条件。串岭沟组砂脉中识别的自生碳酸盐沉淀及其AOM成因对进一步认识中元古代古海洋与古气候条件具有重要意义。由于海洋的低硫酸盐浓度,SMTZ带很浅,海底沉积层的甲烷仅少量被AOM消耗;而大量甲烷进入大气必然导致中元古代强烈的温室气候效应。 相似文献
2.
在山西黎城县西井镇彭庄至大井盘公路旁剖面以及黄崖洞景区发育大量的微生物成因构造(MISS),多发育在砂岩表面。由于构造形态奇特,被误以为各种遗迹化石或是不规则的泥裂构造。依据其形态特征、成因构造和前人分类方案,将研究区此类构造分为3种类型,即微生物席生长构造、微生物席破坏构造和微生物席腐烂构造,以及9个不同形态构造,即小瘤状突起、圆顶大瘤状突起、不规则侧向生长脊、大脊状生长构造、纺锤状脱水裂痕、多边形网状脱水裂痕、曲形脱水裂痕、微生物席砂片、砂火山构造,对9种不同形态的MISS进行了详细的论述。对研究区微生物成因构造(MISS)的成因进行了探讨,与豫西鲁山地区、贺兰山苏峪口地区、北京南口地区、河北兴隆地区发育的MISS及地层特征进行类比,认为MISS对华北地台中元古代地层对比以及古环境研究有重要的指导意义。 相似文献
3.
河北兴隆一带的中元古界长城系大红峪组(1 650～1 600 Ma)以潮下坪灰白色厚层块状细粒石英砂岩为主,在砂岩层面上产出丰富的微生物成因构造(MISS).详细描述了MISS的沉积特征,并对其成因进行了初步分析.这些微生物成因构造可能反映了华北中元古代浅海潮坪环境被大面积分布的微生物席所覆盖,微生物席对砂质沉积物表面起到有效的保护作用,在一定程度上降低了沉积物的侵蚀和改造作用,从而影响基本沉积作用过程.大红峪组砂岩层面上发育的MISS为探索元古宙浅海环境微生物-沉积作用关系提供了研究材料,对这些MISS的深入研究可以加深对元古宙碎屑沉积体系的理解,从而促进微生物席沉积学的发展. 相似文献
4.
华北地台中元古代串岭沟组页岩中的砂脉构造:17亿年前甲烷气逃逸的沉积标识? 总被引：2，自引：0，他引：2
华北地台中元古界串岭沟组暗色页岩中发育一种特殊的砂质脉状构造;层面上表现为不规则密集分布的细砂脊,垂向上由不连续薄砂层和近于直立的"肠状"砂脉体相交互组成.浅色砂脉由较纯的石英粉砂-细砂组成,含微量自生白云石、菱铁矿及微晶碳酸盐岩斑块,与黑色泥质围岩边界截然.研究表明,砂脉构造可能是在早期成岩阶段前由来自薄砂层的细-粉砂灌入甲烷缓慢逃逸通道而成,并由于压实缩短而褶皱成"肠状".薄砂层与黑色页岩形成的能量条件完全不同,可能系由风暴将海岸带或砂坝细砂带入低能环境而形成;甲烷源自沉积中埋藏的微生物席腐烂分解.围岩层面有微生物席成因微皱痕和气体逃逸形成的气泡构造,围岩中发现有细菌化石和草霉状黄铁矿.串岭沟组中密集发育的砂脉构造是目前地层中识别的最古老的甲烷排放证据,并有可能作为指示地质时期陆源碎屑沉积环境甲烷逃逸的沉积标识.大量高效温室气体进入大气圈可能是导致元古宙地球表层高温室气候和无冰川发育的重要原因. 相似文献
5.
贺兰山地区中元古代微生物席成因构造 总被引：23，自引：2，他引：21
贺兰山中段中元古界黄旗口组石英砂岩中发现丰富的微生物席成因构造(MISS),包括由微生物席生长、破坏和腐烂过程形成的3种类型、9种不同形态的构造;与华北大红峪组发现的同类构造在成因类型与多样性方面具有很强的可对比性.砂岩中发育双向交错层理、冲洗层理、高角度单斜层理系和波痕,泥质粉砂岩夹层中发育波痕与泥裂,表明微生物席主要发育于潮间带上部至潮上带下部环境.MISS构造在华北地台长城系下部砂岩中的广泛存在表明在1.6 Ga前以蓝细菌为主的微生物群在环潮坪碎屑环境也很活跃.可能代表了微生物由海洋向陆地环境发展的过渡阶段.具光合作用功能的制氧蓝细菌的蓬勃发展可能是引发中元古代海洋化学条件发生转变、含氧量增高的重要原因,并为真核生物及宏观藻类的兴起创造了条件.研究表明,黄旗口组与华北大红峪组大致同时,反映了Columbia超大陆裂解期华北地台开始拉伸-张裂、缓慢沉降的构造古地理背景. 相似文献
6.
7.
贺兰山地区中元古代微生物席成因构造 总被引：3，自引：1，他引：2
贺兰山中段中元古界黄旗口组石英砂岩中发现丰富的微生物席成因构造（MISS）,包括由微生物席生长、破坏和腐烂过程形成的3种类型、9种不同形态的构造;与华北大红峪组发现的同类构造在成因类型与多样性方面具有很强的可对比性。砂岩中发育双向交错层理、冲洗层理、高角度单斜层理系和波痕,泥质粉砂岩夹层中发育波痕与泥裂,表明微生物席主要发育于潮间带上部至潮上带下部环境。MISS构造在华北地台长城系下部砂岩中的广泛存在表明在16 Ga前以蓝细菌为主的微生物群在环潮坪碎屑环境也很活跃,可能代表了微生物由海洋向陆地环境发展的过渡阶段。具光合作用功能的制氧蓝细菌的蓬勃发展可能是引发中元古代海洋化学条件发生转变、含氧量增高的重要原因,并为真核生物及宏观藻类的兴起创造了条件。研究表明,黄旗口组与华北大红峪组大致同时,反映了Columbia超大陆裂解期华北地台开始拉伸—张裂、缓慢沉降的构造古地理背景。 相似文献
8.
前寒武纪的生物界是以微生物为主导的,微生物所引起的生物沉积构造的研究一直受到地质学家重视。以往的研究多集中在碳酸盐岩地层,近年来以发育在碎屑岩地层为主的微生物成因沉积构造(MISS)也成为地学界的研究热点之一。豫西鲁山地区云梦山组隶属于中元古界汝阳群,在构造古地理上属于华北地台南缘,主要为一套陆源碎屑岩沉积,其层面发育了大量的MISS,且类型多样。MISS类型的分布特征对精细环境有良好的指示作用;MISS的大量发育表明了当时微生物群落的繁盛,揭示了当时的微生物群落对古环境具有的强大改造功能。 相似文献
9.
微生物席成因构造(microbial induced sedimentary structures, MISS)是由微生物与沉积物相互作用形成的生物沉积构造,表现形式有变余波痕、皱饰构造、微生物席碎片、纺锤状或次圆状收缩裂缝等。首次在华北地台东北部辽宁兴城中元古代初期常州沟组底部粗碎屑岩交错层理面上发现了大量的微生物砂质颗粒,在中元古代底部粗碎屑岩中发现大量微生物砂质碎片。这一发现对于了解华北地台MISS的活跃时代以及恢复中元古代早期粗碎屑岩的形成古环境有重要的科学意义,特别是为华北地台古元古代、中元古代的地层划分与对比提供一定的生物地层学参考。发现的微生物砂质颗粒大小在0.1~0.2 mm,形态以球形为主。这些微生物砂质颗粒形成于静水环境的潮上带或泥坪之中的微生物席底,在剧烈的构造运动以及海侵初期高频的海平面运动中被风暴、海啸等灾难性事件破坏,并随着退潮水流被搬运至发育交错层理的潮道区域,与粗碎屑物质一起沉积。这些被风暴破坏的微生物砂质颗粒在搬运过程中被磨圆并产生一定的分选。 相似文献
10.
通过1∶5万区域地质调查及剖面研究,在扬子西缘云南东川地区黑山组发现大套流纹质凝灰质板岩夹层,获得LA ICP MS锆石U Pb 年龄加权平均值为1522±15 Ma,同时在中元古界黑山组泥质板岩中发现微生物成因沉积构造（MISS）,通过对MISS及围岩进行电子探针、XRF分析及能谱分析,研究发现MISS主要成分为P、 S、 Fe、Cr,明显是微生物沉积过程中形成的化合物特征;而围岩主要为Al、 Si、 K、 Mg、 Ti,为正常黏土质矿物组成元素,两者存在较大差别。本次发现的MISS是目前扬子西缘已知发现的最古老的MISS;MISS在黑山组的出现表明了中元古代时期微生物群落的繁盛,反映了当时沉积环境为滨岸浅水潮上带,在凹陷的位置微生物参与形成了这样不规则的条带皱饰构造,为中元古代地层微生物区域对比、古环境研究提供重要的参考资料,对于恢复康滇裂谷盆地的生物—沉积作用和环境演化具有重要意义。 相似文献
11.
Microbial Mats in the Mesoproterozoic Carbonates of the North China Platform and Their Potential for Hydrocarbon Generation 总被引：2，自引：0，他引：2
The well-preserved Mesoproterozoic succession in the North China platform consists mainly of three llthological associations including peritidal quartz sandstone, shallow marine and lagoonai dark to black shales, and shallow epeiric carbonates, with a total thickness of up to 8 000 m. In addition to well-documented microplants, macroalgae, and microbial buildups, abundant microbially induced sedimentary structures (MISS) and mat-related sediments have been recognized in these rocks. Intensive microbial mat layers and MISS are especially well preserved in the carbonates of the upper Gaoyuzhuang (高于庄) (ca. 1.5 Ga) and lower Wumishan (雾迷山) (ca. 1.45 Ga) formations, Indicating diversified microbial activities and a high organic production. In these petrified blomats, putative microbial fossils (both coccoidal and filamentous) and framboidal pyrites have been identified. The abundance of authigenic carbonate minerals in the host rocks, such as, acicular aragnnites, rosette barites, radial siderites, ankerites, and botryoidai carbonate cements, suggests authigenlc carbonate precipitation from anaerobic oxidation of methane (AOM) under anoxic/euxinic conditions. Warm climate and anoxic/euxinic conditions in the Mesoproterozoic oceans may have facilitated high microbial productivity and organic burial in sediments. Although authigenic carbonate cements may record carbonate precipitation from anaerobic methane oxidation, gas blister (or dome) structures may indicate gas release from active methanogenesls during shallow burial Bituminous fragments in mat-related carbonates also provide evidence for hydrocarbon generation. Under proper conditions, the Mesoproterozoic mat-rich carbonates will have the potential for hydrocarbon generation and serve as source rocks. On the basis of petrified biomats, a rough estimation suggests that the Mesoproterozoic carbonates of the North China platform might have a hydrocarbon production potential in theorder of 10×108t. 相似文献
12.
Late Devonian (Famennian) marine successions globally are typified by organic-rich black shales deposited in anoxic and euxinic waters and the cessation of shelf carbonate sedimentation. This global ‘carbonate crisis’, known as the Hangenberg Event, coincides with a major extinction of reef-building metazoans and perturbations to the global carbon cycle, evidenced by positive carbon-isotope excursions of up to 4‰. It has been suggested that authigenic carbonate, formed as cements in sedimentary pore spaces during early burial diagenesis, is a significant mass fraction of the total global carbon burial flux, particularly during periods of low oxygen concentration. Because some authigenic carbonate could have originated from remineralization of organic carbon in sediments, it is possible for this reservoir to be isotopically depleted and thereby drive changes in the carbon isotopic composition of seawater. This study presents bulk isotopic and elemental analyses from fine-grained siliciclastics of the Late Devonian–Early Mississippian Bakken Formation (Williston Basin, USA) to assess the volume and isotopic composition of carbonates in these sediments. Carbonate in the Bakken black shales occurs primarily as microscopic disseminated dolomite rhombs and calcite cements that, together, comprise a significant mass-fraction (ca 9%). The elemental composition of the shales is indicative of a dynamic anoxic to sulphidic palaeoenvironment, likely supported by a fluctuating chemocline. Despite forming in an environment favourable to remineralization of organic matter and the precipitation of isotopically depleted authigenic carbonates, the majority of carbon isotope measurements of disseminated carbonate fall between −3‰ and +3‰, with systematically more depleted carbonates in the deeper-water portions of the basin. Thus, although there is evidence for a significant total mass-fraction of carbonate with contribution from remineralized organic matter, Bakken authigenic carbonates suggest that Famennian black shales are unlikely to be sufficiently 13C-depleted relative to water column dissolved inorganic carbon to serve as a major lever on seawater isotopic composition. 相似文献
13.
Authigenic Carbonate Formation in the Ocean 总被引：1，自引：0，他引：1
Oceanic authigenic carbonates are classified according to the origin of carbonate carbon source using a complex methodology that includes methods of sedimentary petrography, mineralogy, isotope geochemistry, and microbiology. Mg-calcite (proto-dolomite) and aragonite predominate among the authigenic carbonates. All authigenic carbonates are depleted in heavy carbon isotope 13 and enriched in heavy oxygen isotope 18O (in PDB system), indicating biological fractionation of isotopes during the carbonate formation. Results obtained show that authigenic carbonate formation is a biogeochemical (microbial) process, which involves carbon from ancient sedimentary rocks, abiogenic methane, and bicarbonate-ion of hydrothermal fluids into the modern carbon cycle. 相似文献
14.
Calcite cementation during bacterial manganese, iron and sulphate reduction in Jurassic shallow marine carbonates 总被引：4，自引：0，他引：4
JAMES P. HENDRY 《Sedimentology》1993,40(1):87-106
Faunally restricted argillaceous wackestones from the Middle Jurassic of eastern England contain evidence of early diagenetic skeletal aragonite dissolution and stabilization of the carbonate matrix, closely followed by precipitation of zoned calcite cements, and precipitation of pyrite. Distinctive cathodoluminescence and trace element trends through the authigenic calcites, their negative δ13C compositions and the location of pyrite in the paragenetic sequence indicate that calcite precipitation took place during sequential bacterial Mn, Fe and sulphate reduction. Calcite δ18O values are compatible with cementation from essentially marine pore fluids, although compositions vary owing to minor contamination with 18O-depleted ‘late’cements. Mg and Sr concentrations in the calcites are lower than those in recent marine calcite cements. This may be a result of kinetic factors associated with the shallow burial cementation microenvironments. Bicarbonate for sustained precipitation of the authigenic calcites was derived largely from aragonite remobilization, augmented by that produced through anaerobic organic matter oxidation in the metal and sulphate reduction environments. Aragonite dissolution is thought to have been induced by acidity generated during aerobic bacterial oxidation of organic matter. Distinction of post-oxic metal reduction and anoxic sulphate reduction diagenetic environments in modern carbonate sediments is uncommon outside pelagic settings, and early bacterially mediated diagenesis in modern platform carbonates is associated with extensive carbonate dissolution. High detrital Fe contents of the Jurassic sediments, and their restricted depositional environment, were probably the critical factors promoting early cementation. These precipitates constitute a unique example of calcite authigenesis in shallow water limestones during bacterial Mn and Fe reduction. 相似文献
15.
海相碳酸盐的沉淀方式被认为与水体氧化还原条件密切相关,即太古宙至古元古代缺氧的铁化海水中碳酸盐沉淀抑制剂Fe2+和Mn2+强力抑制灰泥在水柱中成核,但允许文石直接在海底生长,从而导致大量文石以海底沉淀方式产出,而新元古代适度的氧化海水则有利于灰泥以水柱沉淀方式形成。然而,碳酸盐沉淀方式的长期变化还可能受控于其他因素,其与海水氧化还原条件之间的关系还需要通过大量具体实例来验证。针对上述科学问题,笔者选择碳酸盐沉淀方式尚处于过渡时期的华北中元古界碳酸盐岩为研究对象,开展碳酸盐沉淀方式及与之对应的氧化还原条件研究。结果表明,华北高于庄组三段(约1.56 Ga)、雾迷山组四段下部(约1.48 Ga)和铁岭组二段(约1.44 Ga)发育大量灰泥水柱沉淀,其Ⅰ/(Ca+Mg)值较高(普遍大于0.5 μmol/mol)、Ce负异常(低至0.8),指示适度氧化的条件;而高于庄组四段下部(约1.55 Ga)和雾迷山组二段中部(约1.50 Ga)则发育大量纤维状文石海底沉淀,其Ⅰ/(Ca+Mg)值约为0,指示次氧化至缺氧的环境。因此,本研究首次用大量实例证实了前寒武纪海水氧化还原条件对碳酸盐沉淀方式的重要调控作用,并且后者可作为海水氧化还原条件分析的重要指标,适用于高效开展长序列、多剖面的低氧背景下前寒武纪碳酸盐岩地层的氧化还原条件分析。 相似文献
16.
Biogeochemical controls on authigenic carbonate formation at the Chapopote “asphalt volcano”, Bay of Campeche 总被引：1，自引：0，他引：1
Thomas H. Naehr Daniel Birgel Gerhard Bohrmann Ian R. MacDonald Sabine Kasten 《Chemical Geology》2009,266(3-4):399-411
The Campeche Knolls in the Bay of Campeche, southern Gulf of Mexico, were investigated through detailed seafloor mapping, ROV surveys, and sediment and pore water sampling. The knolls are elongated, submarine hills created by salt tectonics with a positive relief of up to 800 m above the surrounding seafloor. Several of the knolls are associated with sea-surface oil slicks identified from satellite data, indicating the presence of hydrocarbon seeps on the seafloor. One of the knolls, named “Chapopote”, was studied in detail during two international research expeditions (SO174/2 and M67/2) and is characterized by extensive hydrocarbon seepage including large asphalt flows, oil and gas seeps, and seafloor gas hydrate deposits. Chemosymbiotic biological communities and authigenic carbonate deposits are associated with the seeps and are the result of both biogeochemical turnover and the interaction between downward-diffusing seawater and hydrocarbon-rich pore fluids at shallow sediment depth. Authigenic carbonates are characterized by aragonite, exhibit a porous texture, and are cemented by a matrix of microsparitic to sparitic aragonite. Macropores of the carbonates were completely filled with liquid oil. Carbonate microfabrics include peloidal or clotted fabrics that may indicate the existence of microenvironments resulting from microbial metabolism. Banded/botryoidal aragonite cements line the intra- and bioclasts and incompletely fill the pore spaces. The stable carbon isotopic composition of authigenic aragonite varies between − 28.6‰ and − 17.9‰ (PDB), identifying oil oxidation as the primary source of carbon to the DIC pool, while lipid biomarker data demonstrate the concurrent existence of microbial communities responsible for anaerobic oxidation of methane (AOM). These observations indicate the presence of additional, AOM-independent reactions responsible for carbon sequestration at hydrocarbon seeps and demonstrate the complexity of biogeochemical processes at seep sites in the Gulf of Mexico basin. Oxygen isotope data of authigenic aragonite vary from + 2.5‰ to + 3.8‰ (PDB), indicating carbonate precipitation in slight disequilibrium with the surrounding pore fluids. 相似文献