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1.
贵州台江中、下寒武统界线附近碳同位素负异常的生物和地层意义 总被引：2，自引：0，他引：2
中、下寒武统界线研究是至今尚未圆满解决的全球性难题. 这是早寒武世到中寒武世全球范围存在两个不同的生物地理分区的结果. 尽管目前研究从古生物方面进行了大量的工作, 也取得了大量的成果, 但是它们同样由于存在大西洋生物区和印度-太平洋生物区生物组合不同的影响, 目前还没有一个能进行全球性对比的生物组合. 因此, 寻找其他的中、下寒武统界线全球划分和对比方法是解决中、下寒武统界线难题的途径. 对贵州台江中、下寒武统界线剖面的凯里组疑源类进行系统研究, 利用疑源类划分了中、下寒武统界线, 所划分的界线与三叶虫带划分的界线基本一致, 并可与西伯利亚、欧洲在地台上利用疑源类划分的中、下寒武统界线可进行对比. 在此基础上, 利用全球性早寒武世到中寒武世过渡期间有一个明显的碳同位素负异常来划分中、下寒武统界线, 并与西伯利亚、北美中、下寒武统界线上的碳同位素负异常进行对比. 这一新的碳同位素划分对比中、下寒武统界线的方法, 有助于解决中、下寒武统界线这一全球性难题, 也说明了早寒武世末三叶虫动物大绝灭与这次碳同位素负异常有密切的关系. 相似文献
2.
本文利用Geant4模拟了FD3013数字γ辐射仪探测器探测晶体,对137Cs(0.661MeV)的γ射线的探测效率,和TH-PPLCT教学仪防护铅罐对137Cs源的防护效果,并建立了简易人体模型,仿真计算了人体吸收剂量,结果显示防护铅罐屏蔽后的辐射剂量在可接受的水平内。 相似文献
3.
贵州遵义下寒武统黑色页岩镍、钼多金属矿床的形态硫特征及成矿模式 总被引：2，自引：0，他引：2
黄家湾矿是贵州遵义地区寒武系底部新发现的黑色页岩镍钼多金属元素矿床。根据形态硫测试结果,文章分析了黄家湾下寒武统牛蹄塘组黑色页岩剖面和矿石中不同形态硫（硫酸盐硫、黄铁矿硫、有机硫）的特征,推测镍、钼金属富集层处还原性硫的来源。 相似文献
4.
目的:探讨结合迭代重建算法的低剂量CT在颈部应用价值。方法:172例疑头颈部病变患者行CT检查,随机分为常规剂量组（86例,管电流125 mAs）和低剂量组（86例,40~110 mAs）,分别采用滤波反投影和三维自适应迭代剂量降低（AIDR3D）重建。在下颌角及上纵隔水平分别测量不同组织的CT均值及标准差,由两位CT影像医师采用4分法标准对图像盲法评分;比较图像质量差异和不同扫描方式下患者的辐射剂量。结果:下颌角水平,低剂量组颈内静脉噪声高于常规剂量组（P<0.05）,两组间胸锁乳突肌噪声、信噪比、对比噪声比及背景噪声无明显差异（P>0.05）;上纵隔水平,低剂量组上腔静脉、胸大肌及胸壁皮下脂肪噪声低于常规剂量组（P<0.05）,信噪比更高（P<0.05）,对比噪声比相仿（P>0.05）。常规剂量和低剂量组图像质量的评分一致性均良好,下颌角水平低剂量组图像质量评分与常规剂量组图像无明显差异（P>0.05）;上纵隔水平低剂量组图像评分优于常规剂量组（P<0.05）;与常规剂量组相比,低剂量组有效辐射剂量显著降低（P<0.05）,剂量指数减低63.34%,有效辐射剂量减低63.16%。结论:结合三维自适应迭代剂量降低重建的低剂量CT技术可以用于颈部CT扫描,可以减少辐射剂量并提供优质的图像。 相似文献
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6.
目的:探讨儿童气管性支气管微剂量MSCT应用价值。方法:搜集近3年儿童气管性支气管528例,对5个年龄段的低剂量组、微剂量组和微剂量联合迭代重建技术组的有效辐射剂量进行对比分析,并通过后处理技术获得支气管树的重建图像观察诊断效能。结果:不同年龄段的三组图像质量评价两两比较,差异无统计学意义(P>0.05),而对三组患儿所受有效辐射剂量进行两两比较,除10~14岁年龄段低剂量组与微剂量组差异无统计学意义(P>0.05)外,其余年龄段差异均有统计学意义(P<0.05);在儿童气管性支气管新分3型中:Ⅰ型356例(占67.4%),其中ⅠA型198例(37.5%),ⅠB型158例(29.9%);Ⅱ型172例(32.6%)。结论:微剂量MSCT联合迭代重建技术在儿童气管性支气管诊断中明显降低了患儿的有效辐射剂量,具有较高的应用价值;有效分型对儿科临床治疗有一定的特异性指导作用。 相似文献
7.
奥陶纪笔石动物的多样性演变与环境背景 总被引：2，自引：0，他引：2
基于全球性统计数据的分析表明, 在奥陶纪生物大辐射期间, 营漂浮生活的笔石呈现出一种与底栖生物完全不同的多样性演变轨迹, 即在奥陶纪初就开始辐射并于中奥陶世早期达到高峰, 然后逐步递减, 这期间伴随着多个重要类群的起源、繁盛和演替. 另一方面, 在世界不同地区和不同环境下, 笔石动物可能有不同的辐射过程和演化模式, 需要加以检验. 对华南上扬子区(台地)和江南区(斜坡)的早、中奥陶世笔石多样性的详细分析表明, 在两种环境下, 笔石分异度(属级、种级)都有较显著的增长, 但在规模、幅度、过程和型式上存在较大差异. 上扬子区的辐射规模和幅度相对较小, 整个过程可识别为4个阶段, 其中有两次高峰. 江南区笔石的辐射规模和幅度均较大, 可识别为3个阶段, 多样性的主要增长期在第二阶段. 根据这两种典型环境下笔石动物群的组成及多样性演变的显著差异, 提出奥陶纪笔石动物的“深水起源与浅水扩散模式”: 大陆斜坡的深水区域是笔石演化新质的源泉, 奥陶纪的主要笔石类群均从这里起源, 然后扩散到浅水区域. 此外, 对华南与世界其他主要地区的奥陶纪笔石多样性的比较研究表明, 笔石动物在奥陶纪早、中期发生了全球性辐射. 在奥陶纪初笔石动物发生了一次重大的生态变革: 从原先的海底固着类型衍生出浮游或漂浮类型; 在早奥陶世晚期(弗洛期), 全球几乎同时发生了笔石多样性激增事件(均分笔石动物群); 从弗洛期到中奥陶世末, 笔石多样性的增长大体呈现3个峰值, 但在不同地区峰值的大小和位置均有差异, 其中达瑞威尔期的多样性峰值在华南和波罗的板块均较显著, 但在澳洲板块上没有明显的响应. 总体而言, 奥陶纪笔石动物的辐射与古纬度没有密切关联, 但辐射的时间与当时的全球性海平面变化事件基本一致, 表明两者可能存在密切关系. 相似文献
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在分析了浙江北部地区地下水类型、特征、地下水开采现状和水位变化基础上,通过对不同类型地下水深井样品测试数据的研究,查明了区域地下水高氟和高砷的分布特点。高氟区主要出现于妙西花岗岩裂隙水和白雀岩溶水分布区,高砷区主要位于南浔第Ⅱ承压含水层局部区域。研究认为高氟和高砷地下水分布区与区域土壤和浅层地下水中总氟和总砷含量没有直接联系,深井地下水中的高氟和高砷主要与深部断裂构造有关。研究地区的这种高氟和高砷地下水目前仍然为很多居民所饮用,作者认为长期饮用这种高氟和高砷地下水容易导致地方病的产生,建议在高氟和高砷地下水分布区停止生活用水开采,有条件的企事业单位应实行改水方案。 相似文献
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目的:探讨基于下颈部横径的低辐射剂量颈部增强MDCT的可行性。方法:对126例临床拟诊为颈部病变的患者行颈部CT检查,其中42例为常规剂量组,84例为低剂量组。低剂量组再根据患者下颈部横径的大小分为3个亚组:A组大横径组,横径≥40cm(21例);B组中等横径组,35cm≤横径<40cm(35例);C组小横径组,横径<35cm(28例)。常规剂量组管电压/管电流采用120kV/350mA,低剂量A、B、C3组分别采用120kV/300mA、100kV/300mA和80kV/300mA。对常规剂量组与低价量组扫描图像进行主观及客观评价,记录A、B、C3组不同扫描方案的剂量长度乘积(DLP)和CT容积剂量指数(CTDIvol),并计算有效辐射剂量(ED)。比较各组辐射剂量及图像质量的差异。结果:常规剂量组与低剂量A、B、C三组有效吸收剂量ED分别为(1.34±0.13)mSv、(1.17±0.10)mSv、(0.74±0.08)mSv和(0.34±0.04)mSv,差异有统计学意义(F=606.13,P<0.01),各低剂量组的有效辐射剂量均低于常规组。组间两两比较ED差异均有统计学差异(P值均<0.01)。Kappa一致性检验显示两名医师对颈部图像质量的评分一致性较高(3组Kappa值均>0.70),常规剂量组与低剂量A、B、C3组比较图像质量评分均无统计学差异(Z=-0.258,P>0.05),各组的图像对比噪声比无统计学差异(F=0.750,P>0.05)。结论:根据患者下颈部横径的大小采用不同管电压行颈部增强CT扫描可以明显降低患者的辐射剂量,而不影响图像的诊断质量,该扫描方案显示颈部结构可行。 相似文献
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目的：探讨使用320排螺旋CT前瞻性心电门控窄窗采集技术,在降低辐射剂量方面的应用。方法：研究组50例采用前瞻性心电门控技术,对照组50例患者采用回顾性心电门控技术,分别测量两组间图像质量以及辐射剂量。结果：两组数据比较,患者的基本情况如年龄、心率、体重和体重指数以及图像质量差异无统计学意义（P〉0．05）,有效放射剂量两组间的差异有统计学意义（P=0．0001）,前瞻性心电门控组辐射剂量（8．80±2．78）mSv显著低于回顾心电门控组（25．82±8．84）mSv。结论：前瞻性心电门控窄窗采集技术在确保图像质量的同时可以降低辐射剂量。 相似文献
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SPECT是对植入患者体内的放射性粒子发射的γ射线进行成像,其图像中灰度信息反映了γ射线的计数值,变换后相应于射线剂量值。临床中通常为了观察剂量在病灶附近的分布情况,需要将SPECT图像进行伪彩色处理,再与CT图像进行融合。但是,SPECT/CT常用的处理软件中伪彩色处理很难提供足够的剂量细节分辨,难以满足临床诊疗的需求。针对脑部肿瘤治疗中对γ射线剂量分布细节的需求,本文基于SPECT的DICOM数据,提出一种含有可调双向量参数的伪彩色映射显示模型,创建多层次的映射关系。该方法不仅可以控制伪彩色显示区域还可以调整剂量显示的多分段细节。Python的数值实验结果表明,本文所提伪彩色映射模型和算法能够更加清晰、准确地显示SPECT图像中感兴趣的剂量区域和数据范围,与CT图像融合后可明显增强SPECT/CT的病灶区域和剂量分布层次感,精准显示病灶部位的粒子空间和放射剂量分布信息,为临床疗效的判定提供可靠依据。 相似文献
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The Lower Cambrian on the Yangtze Platform in South China (internationally equivalent to the Nerreneuvian and 2nd series of the Cambrian) is valuable for understanding the early evolution of life, the global biogeochemical circles, and the major changes of the ocean. In particular, a precise radiometric calibration of the Lower Cambrian of this region is a critical realm in its multidisciplinary studies. A SHRIMP U-Pb geochronology study of the K-bentonite in the topmost Laobao Formation at the Pingyin section, Guizhou, South China yielded an age of 536±5 Ma (MSWD = 0.75), suggesting that the K-bentonite here can be correlated with the intensely studied K-bentonite within the middle Zhongyicun Member (Bed 5) of the Zhujiaqing Formation at the Meishucun section in Yunnan. Such a regional correlation result reveals that the Bed 5 K-bentonite also extends into deeper-water environments rather than being deposited merely in the shallow platform interior of the Yangtze Platform. The age of the K-bentonite at the Pingyin section also implies that its overlying polymetallic Ni-Mo layer should be younger than 536±5 Ma. Hence the previous placement of the Precambrian/Cambrian boundary at this layer is inappropriate. Combined with the results of stratigraphic correlations, it is suggested that the K-bentonites in the middle Zhongyicun Member of the Zhujiaqing Formation (or the equivalents) and the base of the Shiyantou Formation (or its equivalents), together with the polymetallic Ni-Mo layer, serve as three important marker beds. Their self-consistent radiometric ages have established an improved geochronologic framework for the Lower Cambrian in South China. 相似文献
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The stratigraphic division and correlation of the Lower/Middle Cambrian boundary is a global problem that has not yet been solved even up to now. That is because there existed two distinctly different biogeographic regions during the Early and Middle Cambrian[1]—— the Indian-Pacific biogeographic region and the Atlantic biogeographic region. In the Atlantic biogeographic region the traditional Lower/Middle Cambrian boundary was marked by the extinction of Olenellids trilobite and the in… 相似文献
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Anachronistic facies in the Lower Triassic of South China and their implications to the ecosystems during the recovery time 总被引：3，自引：1，他引：2
The end-Permian mass extinction not only severely distressed the Paleozoic ecosystems but also dramatically changed the sedimentary systems, resulting in a peculiar Early Triassic ecosystem and submarine environment during the recovery time following the mass extinction. The Lower Triassic is characteristic of the wide occurrence of various distinctive sediments and related sedimentary structures, such as flatpebble conglomerates, vermicular limestone, subtidal wrinkle structures, microbialite, carbonate seafloor fans, thin-bedded limestone and zebra limestone-mudstone. These sediments were common in the Precambrian to Early Ordovician marine settings, and then they occurred only in some extreme and unusual environments with the expansion of metazoan faunas. However, the Early Triassic witnessed an "anachronistic" reappearance of some distinctive sedimentary records in normal shallow marine settings. The study of these anachronistic facies should be of great importance for the understanding of the unique ecosystem and marine environment through the great Paleozoic-Mesozoic transition. The anachronistic facies characterized by vermicular limestone have been documented in many localities in South China and occur at various horizons of the Lower Triassic. Most types of re- ported distinctive sediments over the world have been observed in the Lower Triassic of South China. This provides an excellent opportunity for understanding the Early Triassic environment and its co- evolution with the biotic recovery. Among the anachronistic facies the vermicular limestone is the most characteristic and common distinctive sediments in the Lower Triassic of South China but has received relatively few investigations. Taking it as a case study, we will detail the variation of vermicular limestone and its stratigraphic distribution in the Three Gorges area, Hubei Province. The investigation on the vermicular limestone and other distinctive sediments from the Lower Triassic of South China further indicates that the appearance of anachronistic facies immediately following the mass extinction and the elimination from normal shallow marine facies with the radiation of Mesozoic marine faunas imply the natural response of the sedimentary systems and ecosystems to the great Paleozoic-Mesozoic transitional events and their induced harsh environments. Therefore, the ups and downs of the anachronistic facies may act as a proxy for the evolution of ecosystems independent of fossil analyses. 相似文献
15.
Oil and gas breakthroughs have been achieved in the Zhongshen 1(ZS1) and 1 C(ZS1 C) wells in Cambrian pre-salt from the Tarim Basin in northwest China. However, Middle and Lower Cambrian reservoirs reveal substantial differences in the geochemistry and secondary alteration characteristics between the oils collected from the two wells. High concentrations of thiadiamondoids and diamondoidthiols, including thiatetramantanes, tetramantanethiols, thiapentamantanes, and pentamantanethiols, are detected in the organic sulfur compound fraction of concentrated oil collected from the ZS1 C well, which samples the Lower Cambrian Xiaoerbulake Formation. Higher diamondoids, such as tetramantanes, pentamantanes, hexamantanes, and cyclohexamantane, also occur in the saturate fractions of the concentrated ZS1 C oil. The presence of these compounds is verified by mass spectra analysis and comparison with previous studies. During thermochemical sulfate reduction(TSR), the cage of higher diamondoids is interpreted to open because of sulfur radicals forming open-cage higher diamondoid-like thiols, followed by cyclization that leads to the formation of high thiadiamondoids. Using D_(16)-adamantane as an internal standard, the concentrations of lower diamondoids and thiadiamondoids of non-concentrated Cambrian oil from well ZS1 C are 83874 and8578 μg/g, respectively, which are far higher than Cambrian oil from well ZS1 and most Ordovician oils in the Tarim Basin. The high concentrations of lower thiadiamondoids and occurrence of higher thiadiamondoids and diamondoidthiols support that the oil from well ZS1 C is a product of severe TSR alteration. 相似文献
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Thick terminal Proterozoic–lowest Cambrian successions allow reference of the Saint John, New Brunswick, and MacCodrum Brook, southern Cape Breton Island, areas to the marginal platform of the Avalon microcontinent. Marginal-platform siliciclastic-dominated sequences form a cover on Late Precambrian arc successions from southern New Brunswick to North Wales. Their deposition in fault-bounded basins began with the origin of the Avalon microcontinent and development of a persistent transtensional regime in the latest Precambrian. The terminal Proterozoic–lowest Cambrian on the Avalonian marginal platform consists of three successive lithofacies associations: lower subaerial rift to marginal-marine facies; overlying cool-water, wave-influenced, marine platform sandstones and shales; and higher macrotidal quartz arenites (=Avalonian depositional sequences 1–2). Only the Lower Cambrian macrotidal quartz arenites onlap southeast, where they form the oldest Cambrian unit on the inner platform. These major lithofacies are the Rencontre, Chapel Island, and Random formations, respectively, in Avalonian North America. Southwest thinning of the Rencontre–Chapel Island–Random interval in southern New Brunswick reflects slower subsidence of a fault-bounded area in the city of Saint John. The depositional sequence 1–2 unconformity, which falls in the sub-trilobitic Lower Cambrian Watsonella crosbyi Zone of the Chapel Island Formation, persists for 650 km along the marginal platform from southeastern Newfoundland to southern New Brunswick and, potentially, appears in Cape Breton Island. Latest Precambrian-earliest Cambrian epeirogenic and depositional history was very uniform along the marginal platform, and a unified lithostratigraphic nomenclature is appropriate. 相似文献
17.
烃源岩热演化是含油气盆地烃源岩评价的基本内容之一,也是油气动态成藏研究的基础.通过系统分析地层沉积样式,结合盆地热史恢复结果,应用Easy%Ro化学动力学模型,模拟了四川盆地86口代表性钻井和200余口人工井点震旦系-下古生界烃源岩热演化史.结果表明,在盆地不同构造单元,下寒武统和下志留统烃源岩热演化特征存在明显差异,并据此建立了四种热演化模式:①加里东期成熟,早晚二叠世期间快速演化定型,以川南地区下寒武统烃源岩为代表;②加里东期未熟,早晚二叠世期间一次快速演化定型,以川西南下寒武统和川南下志留统烃源岩为代表;③加里东期成熟,晚海西-燕山期再次增熟,以川东、川北地区下寒武统烃源岩为代表;④加里东期未熟,晚海西-燕山期持续增熟,以川中地区下寒武统和川东、川北下志留统烃源岩为代表.通过对比研究沉积速率、热流和增温速率之间的耦合关系,剖析了四川盆地震旦系-下古生界烃源岩热演化的控制因素,即川西南和川南局部地区主要受控于早晚二叠世期间峨眉山地幔柱和玄武岩的异常热效应,而盆地其它地区则受沉积地层埋深增热和盆地热流演化的共同作用,其中沉积地层埋深增热对烃源岩增温效应更加显著. 相似文献
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《Journal of Applied Geophysics》2007,61(2):111-131
This paper describes a method to calibrate a neutron capture sonde equipped with a high resolution γ-ray detector, and analyze log data. The method utilizes the 1460.8-keV passive γ-ray of 40K, the 770.3-keV capture γ-ray of 39K, and a capture γ-ray from a target element. An equation containing the spectral line intensities for the two capture γ-rays, nuclear capture data, and the detector efficiency function expresses the concentration of the target element as a multiple of the 39K concentration. The concentration of 39K is easily deduced from the 40K concentration, which is calculated directly from the line intensity for the 1460.8-keV γ-ray in a passive γ-ray spectrum.The calibration automatically adjusts to changes in the neutron transport properties of the logged medium that may result, for example, from variations in the H density and the concentrations of neutron poisons. Fluctuations in the neutron source output are similarly accommodated. The calibration utilizes U.S. Department of Energy (DOE) passive γ-ray calibration standards that contain well established concentrations of K, U, and Th. The passive γ-rays from K, U, and Th (and the U and Th decay progenies) provide data for the detector efficiency function determination.Data for proof-of-principle demonstrations of the method were acquired by logging boreholes penetrating the shallow subsurface at a DOE waste site with a simple, reliable neutron capture logging system. The system had a 252Cf source and a high purity germanium (HPGe) detector. Time gating could not be used to sort signals originating from capture and activation, but the excellent energy resolution permitted capture γ-ray identifications based solely on the γ-ray energies. Cl, H, and other elements were detected and assessed.A conventional calibration and data analysis method was also employed. The method was specific to Cl and was based on measurements in two Cl-impregnated concrete blocks. Cl concentrations inferred with this method were often consistent with the concentrations determined with the new method. When the two methods produced different Cl concentrations, the discrepancies could be explained by variations in formation parameters. 相似文献
20.
In 2013, a great breakthrough of deep petroleum exploration was achieved in the Cambrian pre-salt intervals of Wells Zhongshen1 (ZS1) and Zhongshen1C (ZS1C), Tazhong Uplift. However, the hydrocarbon discovery in the Cambrian pre-salt intervals has triggered extensive controversy regarding the source of marine oils in the Tarim Basin. The geochemistry and origin of the Cambrian pre-salt hydrocarbons in Wells ZS1 and ZS1C were investigated using GC, GC-MS and stable carbon isotope technique. These hydrocarbons can be easily distinguished into two genetic families based on their geochemical and carbon isotopic compositions. The oil and natural gases from the Awatage Formation of Well ZS1 are derived from Middle- Upper Ordovician source rocks. In contrast, the condensate and gases from the Xiaoerbulake Formation of Wells ZS1 and ZS1C probably originate from Cambrian source rocks. The recent discovery of these hydrocarbons with two different sources in Wells ZS1 and ZS1C suggests that both Middle-Upper Ordovician-sourced hydrocarbons and Cambrian-sourced petroleums are accumulated in the Tazhong Uplift, presenting a great exploration potential. 相似文献