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71.
The Zhejue Section is an excellent terrestrial permian-Triassic boundary (TPTB) section not only for its convenient accessibility and good outcrop, but also for its abundant fossils. In addition, there are two claystone beds that were formed by events across the Permian-Triassic boundary (PTB) at this section. The claystones provide a bridge for high-resolution correlation between marine and terrestrial PTBs. Another advantage is that the PTB at the Zhejue Section can be correlated with that of littoral and neritic facies by tracing estwards. Synthesized stratigraphic studies, including biostratigraphy, eventostratigraphy )susceptibilities and carbon isotopes across the TPTB, and microspherules found in the boundary claystones) and sequence stratigraphy, are carried out at this section. 相似文献
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东昆仑东段巴隆花岗质片麻岩年代学、地球化学特征及地质意义 总被引:9,自引:5,他引:4
东昆仑东段巴隆南侧古元古界白沙河岩组中可识别出一套花岗质片麻岩。采用LA-MC-ICP-MS方法进行锆石UPb年代学分析,获得加权平均年龄为870.6±7.7Ma(MSWD=2.6)和875.3±6.3Ma(MSWD=0.92),显示该岩体形成于新元古代早期,并经历了早古生代变质作用。地球化学特征显示,岩石具有高Si O2、Al2O3、K2O,低Ti O2、Na2O的特征,A/CNK平均为1.14,A/NK平均为1.47,矿物组合中出现石榴子石和白云母等富铝矿物,显示S型过铝质花岗岩特征;球粒陨石标准化配分曲线显示轻稀土元素富集((La/Yb)N=6.22~25.37),有明显的铕负异常(δEu=0.16~0.44)。原始地幔标准化蛛网图显示,岩石富集Rb、Th,明显亏损Ba、Ta、Nb、Sr、P和Ti元素。综合分析,岩浆来源于陆壳部分熔融,可能为古元古界白沙河岩组长英质岩石发生脱水熔融的产物,形成于同碰撞环境,是东昆仑地区响应Rodinia超大陆汇聚事件的物质记录。 相似文献
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针对避雷针对天气雷达回波影响的问题,通过对天气雷达的盲区及雷达散射截面(RCS)的理论分析,利用HFSS仿真软件及实验的方法,研究水平极化下,不同材料不同尺寸的避雷针的雷达散射截面,结论是:在相同材料避雷针及相同雷达波长情况下,避雷针高度、半径与其雷达散射截面呈正相关;在相同雷达波长情况下,避雷针为理想金属的雷达散射截面比塑钢与理想金属组合材料的雷达散射截面大;实验结果表明避雷针架设在X波段多普勒天气雷达天线附近时,对雷达回波造成的影响可忽略不计.研究结果为在天气雷达附近架设避雷针提供了理论和实验依据,具有应用价值. 相似文献
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二叠系-三叠系界线全球层型剖面——回顾和进展 总被引:3,自引:0,他引:3
综合评述了5年来对二叠系—三叠系界线(PTB)全球层型剖面——煤山D剖面的研究进展。简要介绍剖面的研究历史、地理和地质背景,叙述了世界上最完整的二叠纪长兴期至三叠纪格里斯巴赫期的牙形石和菊石带,并简短讨论了Otoceras的年代。叙述了煤山与其他剖面长兴期至格里斯巴赫期磁性地层学的对比。介绍了δ13C和δ34S的化学地层学最新研究进展,特别是在PTB附近多个δ13C负漂移的发现。两项重要的分子地层学研究显示了基础生态系统的深刻变化——微生物生态系的灾变和在二叠纪—三叠纪生态系之交严重缺氧事件期间透光带的静海相环境。文章报道了自2001年以来PTB年代测定的进展。PTB之下14cm处火山成因的粘土层25层的年代,现在定为(252·4±0·3)Ma(Mundil等,2004)。文章还讨论了事件地层学,认为尽管在25-26层有一个主事件,煤山PTB附近的事件是多幕式的,并且开始于事件层25-26层之前。因此,PTB大绝灭主因是外星撞击导致的可能性是不大的。 相似文献
78.
End-Permian conodont fauna from Dongpan section: Correlation between the deep-and shallow-water facies 总被引:1,自引:1,他引:0
GenMing Luo XuLong Lai QingLai Feng HaiShui Jiang Paul Wignall KeXin Zhang YaDong Sun Jun Wu 《中国科学D辑(英文版)》2008,51(11):1611-1622
This paper systematically investigated the conodonts from the uppermost Permian to the Lower Triassic at the Dongpan Section, Southern Guangxi, South China, and obtained abundant Late Permian conodonts from the syndepositional limestone lenses of beds 3 and 5-2 at this section. One genus and eight species of conodont P1 element including one new species, Neogondolella dongpanensis sp. nov., have been identified. The feature of conodont fauna indicates that conodonts collected from beds 3 and 5 at the Dongpan Section belong to the Neogondolella yini conodont zone, and correspond to bed 24 at the Meishan Section. Based on these conodont data, we suggest that the Neoalbaillella optima radiolarian zone at the Dongpan Section at least extended to the upper part of the N. yini conodont zone. 相似文献
79.
Dynamics and fluxes of organic carbon and nitrogen in two Guiana Shield river basins impacted by deforestation and mining activities
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Marjorie Gallay Abrahan Mora Jean‐Michel Martinez Antoine Gardel Alain Laraque Max Sarrazin Eric Beaucher Jean‐Claude Doudou Christelle Lagane 《水文研究》2018,32(1):17-29
Deforestation and mining activities have proven to be very damaging to rivers because these activities disturb the environmental characteristics of rivers. Thus, the concentrations of dissolved organic carbon (DOC), particulate organic carbon (POC), particulate nitrogen (PN), and Chlorophyll‐a (Chl‐a) were measured monthly during 2 hydrological years in the Maroni and Oyapock Rivers to assess the dynamics and fluxes of organic carbon and nitrogen in these 2 Guiana Shield basins, which have been strongly (Maroni) and weakly (Oyapock) impacted by deforestation and mining activities. The 2‐year time series show that DOC, POC, PN, and Chl‐a concentrations vary seasonally with discharge in both rivers, indicating a hydrologically dominated control. Temporal patterns of DOC, POC, and PN indicate that these variables show maximum concentrations in rising waters due to the yield of organic matter and nitrogen accumulated in soils, which are incorporated into the rivers during rainfall. However, the Chl‐a concentrations were at a maximum during low‐water stages. The C/N and C/Chl‐a ratios also showed a seasonal trend, with lower values during the low water periods due to an increase in algal biomass. During high water, the POC in both rivers is the result of terrestrial organic matter, whereas during low‐water autochthonous organic matter can reach up to 34% of the POC. The mean annual fluxes of TOC and PN were higher (4.56 × 105 tonC year?1 and 1.77 × 104 tonN year?1, respectively) in the Maroni River than those (1.84 × 105 tonC year?1 and 0.54 × 104 tonN year?1, respectively) in the Oyapock River. However, the specific fluxes of DOC, POC, and PN from both basins were nearly the same. Although gold mining activities are performed in both basins, there is no conclusive evidence regarding the impact of these activities on the dynamics of organic matter and particulate nitrogen in the Maroni and Oyapock Rivers. 相似文献
80.
石炭纪维宪阶全球界线层型剖面和点位补遗 总被引:2,自引:0,他引:2
经国际地质科学联合会批准,我国广西柳州北岸乡碰冲剖面为石炭纪维宪阶全球界线层型剖面和点位.层型剖面位于柳州市东北15 km之碰冲村南小溪(24°26'N,109°27'E).层型点位在剖面83层之底,与底栖有孔虫"E.ovalis种群"至Eoparastaffella simplex谱系中Eoparastaffella simplex的首次出现吻合.辅助标志是点位之上近5m处,牙形石Gnathodus homopunctatus首现,其下约30 m为Scaliognathus anchoralis europensis的最高出现.本文补充介绍了层型点位的岩石特征和区域上的对比. 相似文献