Petrology and geochemistry of chert on the marginal zone of Yangtze Platform,western Hunan,South China,during the Ediacaran–Cambrian transition     

JIANGUO WANG  DAIZHAO CHEN  DAN WANG  DETIAN YAN  XIQIANG ZHOU  QINGCHEN WANG 《Sedimentology》2012,59(3):809-829

The Ediacaran–Cambrian transition was one of the most critical intervals in Earth history. During this interval, widespread chert was precipitated, commonly as a stratal wedge in carbonates, along the southern margin of the Yangtze Platform, South China. The chert wedge passes into a full chert succession further basinward to the south‐east. Four lithotypes of chert are identified across the marginal zone in western Hunan: mounded, vein, brecciated and bedded chert. The mounded chert is characterized by irregular to digitiform internal fabrics, generally with abundant original vesicles and/or channels that mostly are lined by botryoidal chalcedony cements with minor quartz and barite crystals. The host chert (or matrix) of these mounds is dominated by amorphous cryptocrystalline silica, commonly disseminated with pyrite. The vein chert, with minor quartz locally, generally cross‐cuts the overlying dolostone and chert horizons and terminates under the mounded and/or bedded chert bodies. The brecciated chert commonly occurs as splayed ‘intrusions’ or funnel‐shaped wedges and cross‐cuts the topmost dolostones. The bedded chert, the most common type, generally is thin to medium‐bedded and laminated locally; it is composed of amorphous silica with minor amounts of black lumps. Microthermometry of fluid inclusions from vein and void‐lining minerals (mainly quartz and barite) revealed homogenization temperatures from 120 to 180°C for the trapped primary fluids. Compositionally, these chert deposits generally are pure, with SiO₂ > 92 wt%, and only minor Fe₂O₃ and Al₂O₃ contents, most of which show positive Europium anomalies in rare earth element patterns, especially for the mounded chert. All these data suggest that the marginal zone chert deposits resulted from a low‐temperature, silica‐rich hydrothermal system, in which the mounded chert was precipitated around the releasing vents, i.e. as silica chimneys. The vein and splayed brecciated chert, however, was formed along the syndepositional fault/fracture conduits that linked downward, while the bedded chert was precipitated in the quieter water column from the fallout of hydrothermal plumes onto the sea floor. These petrological and geochemical data provide compelling evidence and a new clue to the understanding of the extensive silica precipitation; rapid tectono‐depositional and oceanic changes during the Ediacaran–Cambrian transition in South China.  相似文献   

Hydraulic and Thermal Conductivities of Kaolin–Silica Mixtures under Different Consolidation Stresses     

Keunbo Park  Junhwan Lee  Hyung-Koo Yoon 《Marine Georesources & Geotechnology》2016,34(6):532-541

Stable backfill materials for the heat sensitive structures of buried power cables, hot water pipes, and gas pipelines are suggested to have low permeability and high heat transfer characteristics. The hydraulic and thermal conductivities of backfill materials or clay liners are important parameters in proper design and construction of geotechnical structures involved with heat transfers. In this study, to investigate the optimal natural backfill or liner materials, thermal and hydraulic conductivities of kaolin–silica mixtures examined based on the results from laboratory tests under different consolidation conditions. From the experiment results, the thermal conductivity increases while hydraulic conductivity decreases with increasing density during consolidation process. As a result, back-fill materials with high kaolin content under low consolidation stress were desirable materials for burial of heat sensitive structures.  相似文献   

纳克级铅同位素分析中硅胶-高铼酸发射剂体系的建立     

刘雪梅  汤磊  傅中华  龙开明 《岩矿测试》2014,33(2):178-185

核取证分析中需要实施纳克级（ng）铅的同位素全谱分析,质谱测量中要求铅的电离效率较高（大于10^-3）。传统硅胶-磷酸技术多用于微克级（μg）铅分析,电离效率一般为10^-4~10^-3;尽管后来发展的硅胶-硼酸技术可以得到10^-3以上的发射效率,但是由于铅在电离过程中存在离子流反复升高-衰减的过程,导致离子流发射不稳定,质谱测量条件难以掌握。本文改进了传统的硅胶发射剂,建立了一种新型硅胶加载体系——硅胶-高铼酸体系。与硅胶-硼酸技术相比,采用硅胶-高铼酸体系可显著提高铅的发射效率并获得稳定的离子流。对于1 ng铅的同位素质谱全谱测量,²⁰⁴Pb/²⁰⁶Pb、²⁰⁷Pb/²⁰⁶Pb、²⁰⁸Pb/²⁰⁶Pb的相对标准偏差分别为0.4%、0.2%和0.1%,测试精度优于采用其他硅胶技术。通过实验比较了硅胶-高铼酸体系与多种传统硅胶发射剂体系对铅离子流的发射效果,优化了硅胶试剂用量为0.5~3.0 μL,采用“夹心饼干”的涂样顺序,对1~100 ng铅样品的发射效率达到6.0×10^-3~4.6×10^-2,比传统硅胶-磷酸体系的发射效率（10^-4~10^-3）高了近10倍,与硅胶-硼酸技术的发射效率相当（10^-3~10^-2）,但铅离子发射更为稳定。本文建立的硅胶-高铼酸体系在测量精度上可满足核取证研究中铅作为地域指示剂的需求。  相似文献   

柴东欧南凹陷石炭系烃源岩有机质富集的影响因素     

施辉  李宗星  杨元元  彭博  胡俊杰  方欣欣  张浩  魏小洁 《地质力学学报》2022,28(2):203-216

柴达木盆地东部地区欧南凹陷是石炭系油气运聚成藏的有利构造单元,具有一定勘探潜力,但对有机质富集机理认识不清导致对优质烃源岩分布的预测缺乏有效指导,制约了油气勘探进程.基于地球化学分析、XRD、SEM等分析测试,对石炭系烃源岩矿物组分、 有机质丰度、 干酪根类型、 热演化程度、 形成环境、TOC与主要矿物关系等进行了综合...  相似文献   

生物硅早期成岩作用研究进展   总被引：1，自引：0，他引：1  

秦亚超 《地质论评》2010,56(1):89-98

硅质浮游生物是海洋初级生产力的主要提供者,其死亡后所产生的硅质残骸(生物硅)向海底的传输,是保持海洋硅循环动态平衡的重要环节。由于海洋沉积物中的硅质微体生物化石记录了古海洋初级生产力的变化及其时空分布,因而生物硅也成为古环境重建的重要替代指标。本文对生物硅在水柱沉降和表层沉积物埋藏过程中所发生的早期成岩转变及其主要影响因素进行了综述,为全面了解最近几十年来该领域的研究进展提供参考。  相似文献   

南海南部17962柱状样生物硅沉积记录及其古海洋意义   总被引：21，自引：2，他引：19  

贾国东  翦知湣  彭平安  汪品先  傅家谟 《地球化学》2000,29(3):293-296

生物硅沉积记录可以反映海洋表层水体的古生产力。南海南部１７９６２柱状样３万余年来的生物硅堆积速率曲线表明,南沙海区古生产力的升高与一系列变冷事件,如冰期中的Ｈｅｉｎｒｉｃｈ事件、冰消期新仙女木事件、中晚全新世变冷事件等有良好的对应关系。冬季风的强化及由此导致的海洋古生产力的升高可能是上述良好对应关系的内在原因。  相似文献   

Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance     

G. Parthiban 《Marine Georesources & Geotechnology》2000,18(3):223-235

Particle fluxes were measured 7 m above the sea bottom during the predisturbance, disturbance, and postdisturbance periods by using time series sediment traps attached to seven deep-sea moorings deployed in the INDEX experiment site in the Central Indian Basin. The predisturbance particle fluxes varied between 22.3 to 55.1 mg m -2 day -1 . Increased and variable particle fluxes were recorded by the sediment traps during the disturbance period. The increase observed was 0.5 to 4 times more than the background predisturbance fluxes. The increases in particle fluxes (~4 times) recorded by the sediment trap located in the southwestern direction (DMS-1) were the greatest, which could be the result of preferential movement of resuspended particles generated during the deep-sea benthic disturbance along the general current direction prevailing in this area during the experimental period. Also, the traps located closer to the disturbance area recorded greater fluxes than did the traps far away, across the Deep Sea Sediment Resuspension System path. This variability in recorded particle fluxes by the traps around the disturbance area clearly indicates that physical characteristics such as grain size and density of the resuspended particles produced during the disturbance had an important effect on particle movement. The postdisturbance measurements during ~5 days showed a reduction in particle fluxes of ~50%, indicating rapid particle settlement.  相似文献   

Reconstructing past eutrophication trends from diatoms and biogenic silica in the sediment and the pelagic zone of Lake Constance, Germany     

Martin Wessels  Kirsten Mohaupt  Reiner Kümmerlin  Angela Lenhard 《Journal of Paleolimnology》1999,21(2):171-192

In Lake Constance, phosphorus concentrations and the seasonal development of phytoplankton communities in water samples from the pelagic zone were regularly recorded since the 1950's. Before the 1950's, there were occasional investigations of plankton communities since 1896. We compared these data with the sedimentary record in two sediment cores. Then, the eutrophication history of Lake Constance was inferred from diatoms. The record of biogenic silica in the cores is discussed with respect to diatom biomass increase.Diatom assemblages in the sediment cores precisely reflected the pelagic diatom development for the period 1971--1992. Both sediment cores and the water samples have a high interannual variability of diatom assemblages. Below a sediment depth of 27 cm (AD 1920), more than 50% of the diatoms were partly corroded, and we limited the reconstruction of trophic state changes to the interval of 1920--1993. Oligotrophic conditions of Lake Constance were indicated by the dominance of various Cyclotella taxa from 1920 to 1940. Since 1939/1940, increasing abundance of it Tabellaria fenestrata showed oligotrophic to mesotrophic conditions. Between 1953 and 1956, increasing Stephanodiscus hantzschii and disappearing Cyclotella indicated advanced eutrophication and total phosphorus values ranged between 8--10 mg m-3 during turnover in late winter. Further eutrophication was shown by disappearing T. fenestrata and increasing S. minutulus in 1963. Maximum TP concentrations of 87 mg m-3 occurred in 1979/80 and was accompanied by increasing abundances of Aulacoseira granulata. From 1986 to 1992, reoccurrence of Tabellaria fenestrata and Cyclotella indicate some recovery of Lake Constance.Biogenic silica and diatom abundances were similar among cores but indicate a 3--4 fold increase of diatom biomass only. This was far below the estimate of biomass increase from sedimentary pigment data (25 fold) and the estimate of phytoplankton data from the literature (70 fold).  相似文献   

Influence of particle composition on thorium scavenging in the marginal China seas     

YANG Weifeng  CHEN Min  CAO Jianping  QIU Yusheng  ZHANG Run  MA Qiang  TONG Jinlu  YANG Junhong  YANG Zhi  L&#; E 《海洋学报(英文版)》2009,28(2):45-53

Thorium-234 and particle composition (organic matter, biogenic silica, carbonate and lithogenic component) were examined in the East China Sea (ECS) and the northern South China Sea (NSCS) in order to constrain the particle types scavenging thorium isotopes. Good positive correlations between particulate organic matter (POM) or carbonate and thorium-234 in suspended particulate matter (SPM) indicates that POM and carbonate are efficient to scavenge thorium-234. No relationship between biogenic silica and thorium-234 suggests that geochemical behavior of thorium-234 may be not influenced by biogenic silica. A simple model was used to evaluate the affinity of thorium-234 to different particle components. The results show that POM is the most efficient scavenger for thorium-234 in the ECS and the NSCS, followed by carbonate. The authors'' results lend support to the utility of thorium-234 as a proxy of POC and carbonate in the upper layer. However, the strong dependence of thorium scavenging on particle composition challenges thorium-230 as a constant flux proxy.  相似文献   

夏季珠江口邻近海域表层浮游植物的碳叶绿素比值及其碳含量     

俞小勇  徐杰  龙爱民  李瑞环  施震  李芊 《海洋学报(英文版)》2020,39(2):123-131

Chlorophyll a(Chl a),particulate organic carbon(POC)and biogenic silica(BSi)were determined in coastal waters adjacent to the Zhujiang(Pearl)River Estuary(ZRE)during summer,in order to examine the C:Chl a ratio of phytoplankton and phytoplankton carbon in the plume-impacted coastal waters during summer,as well as to assess the relative contribution of diatoms to the phytoplankton biomass,by the regression between Chl a,POC and BSi.Our results showed that the C:Chl a ratio(g/g)of phytoplankton was high(up to 142),likely due to high light intensity and nutrient limitation.The river plume input stimulated phytoplankton growth,especially diatoms,resulting in higher relative contribution of phytoplankton carbon(55%)and diatoms(34%)to POC in the plume-impacted region than those(33%and 13%)in high salinity area,respectively.Phytoplankton carbon(up to 538μg/L)in the plume-impacted region was much higher than that(<166μg/L)in high salinity area.Our findings were helpful to improve the biogeochemical model in coastal waters adjacent to the ZRE.  相似文献