The complex diagenetic history of discontinuities in shallow‐marine carbonate rocks: New insights from high‐resolution ion microprobe investigation of δ18O and δ13C of early cements     

《Sedimentology》2018,65(2):360-399

Sedimentary gaps are a major obstacle in the reconstruction of a carbonate platform's history. In order to improve the understanding of the early diagenesis and the succession of events occurring during the formation of discontinuity surfaces in limestones, secondary ion mass spectrometry was used for the first time to measure the δ ¹⁸O and δ ¹³C signatures of 11 early cement and fabric stages in several discontinuity surfaces from the Jurassic carbonate platform of the Paris Basin, France. Pendant cements show a high variability in δ ¹⁸O, which was impossible to detect by the less precise microdrilling method. The morphology of a given cement can be produced in various environments, and dogtooth cements especially can precipitate in marine phreatic and meteoric phreatic to vadose environments. Marine dogtooth cements and micritic microbially induced fabrics precipitated directly as low‐magnesium calcite in marine waters, as attested to by the preservation of their initial δ ¹⁸O and δ ¹³C signals. Five discontinuity types are recognized based on high‐resolution geochemical analyses, and their palaeoenvironmental history can be reconstructed. Two exposure surfaces with non‐ferroan pendant or meniscus cements formed in the oxidizing vadose zone. A hardground displays marine fibrous cements and non‐ferroan dogtooth cements that formed in a subtidal environment in oxidizing water. Two composite surfaces have undergone both marine and subaerial lithification. Composite surface 1 displays non‐luminescent ferroan dogtooth cements that precipitated in reduced conditions in seawater, followed by brown‐luminescent dogtooth cements characteristic of a meteoric phreatic environment. Composite surface 2 exhibits microbially induced fabrics that formed in marine water with abundant organic matter. The latter discontinuity, initially formed in a subtidal environment, was subsequently exposed to meteoric conditions, as evidenced by ferroan geopetal cements. A high‐resolution ion microprobe study is essential to precisely document the successive diagenetic environments that have affected carbonate rocks and discontinuities with a polygenic and intricate history.  相似文献   

基于方向模板的保持边缘平滑后地震图像的不连续性检测   总被引：1，自引：0，他引：1       下载免费PDF全文

高静怀  汪玲玲  Fahamuel Paul 《地球物理学进展》2008,23(5):1398-1405

鉴于地震数据不连续性检测的重要性,本文提出了一种保持和检测地震图像不连续性(如:岩层,断层,河道等)的方法.通常在图象不连续的地方,象素值会有较大的差异,文中用4×4的方向模板计算目标点周围六个方向上的差值,当最大差值超过某个门限值时,则可认为该点为不连续点,由此来检测地震图像的不连续性.由于包含重要信息的区域受噪声的影响通常比其他地方严重,而且基于差值的不连续性检测算法对噪声较为敏感,所以在不连续性检测之前降低地震图像的噪声是很重要的.普通的平滑去噪方法会造成边缘模糊,不利于不连续性检测.本文采用旋转模板的非线性平滑方法,用四个六边形和一个八边形模板在目标像素周围旋转,用与目标像素标准差最小(最同类)的模板内那些点的均值代替目标像素的值,从而实现对地震图象的保边缘平滑去噪处理.理论模型和实际数据处理结果表明:与Y、Luo等人提出的保边缘平滑方法相比,本文的保边缘平滑处理方法提高了计算效率和峰值信噪比;将文中提出的保边缘平滑方法和基于方向模板的不连续性检测方法结合使用,得到的不连续性检测结果比直接检测更清晰.地震数据解释人员可根据检测到的不连续性来识别断层、岩层、河道等.  相似文献   

局部结构熵算法在地震数据不连续性检测中的应用   总被引：2，自引：0，他引：2  

周艳辉  高静怀 《煤田地质与勘探》2007,35(1):71-73

自从相干地震数据体概念被提出以来,许多学者提出了不同的基于相干性检测地质结构不连续性的算法。例如,基于特征结构的相干算法,局部结构熵算法以及第二与第一特征值比值算法等。本文基于小波变换具有多尺度多分辨率分析的优点,提出了在特定的小波变换分频瞬时属性上,利用局部结构熵算法来检测地震数据的局部不连续性。实际地震资料检测结果表明,基于分频瞬时相位的局部结构熵算法更能有效地检测到地震数据的细微变化,对于油气藏的精细刻画有重要意义。   相似文献   

岩体不连续面迹长与直径间的概率关系模型分析   总被引：2，自引：0，他引：2  

钱海涛  马平  秦四清 《岩土力学》2007,28(9):1828-1832

由于“随机”概念的模糊性,在假定不连续面为薄圆盘及弦长作为迹长的前提下,基于迹线端点在圆周上均匀分布、迹线中点在直径上均匀分布、迹线中点在圆面域内均匀分布这3种明确而又不同的“随机”含义,可以得到3种合理的迹长 与直径 间的概率关系模型。通过对这3种模型进行分析认为：其在各自的“随机”含义下都是正确的,只是适用条件各异;野外实际可行的条件是介于模型2 和模型3之间的,合理地分析应该同时考虑这两种模型。在实际应用中,应该首先对所有取样面产状之间的关系进行分析,根据其结果来分配给模型2和模型3以某种权重,这样得到的迹长与不连续面直径之间概率关系更具合理性,其结果弥补了目前国内外进行的相关研究仅仅考虑到第2类模型的不足。  相似文献   

地壳破裂型式和幔根构造间断面形成的成矿控制(英文)   总被引：3，自引：0，他引：3  

Kutina  J 《地学前缘》1999,6(1):29-53

尽管地壳最上部的构造、岩性和地球化学条件控制着内生金属矿床的就位,然而最大量金属富集的地点和空间分布却常被幔根构造间断面（ｍａｎｔｌｅ ｒｏｏｔｅｄｓｔｒｕｃｔｕｒａｌｄｉｓｃｏｎｔｉｎｕｉｔｙ）所控制。这些构造间断面延长几百到几千ｋｍ,这表明它们是在比地壳最上部更为均质环境的应力分布下产生的。这些构造间断面与其它的近于垂直的深部构造的交切面界定了主要的岩石圈块体并提供了热、岩浆和成矿流体上升的通道。金属趋向于富集在这些块体的角上,以及构造间断面与板块边缘、裂谷构造或造山带的穿插部位。对上述组合型式的幔根构造间断面和它们在地表地质投影的识别,可确定金属聚集有较大潜力的靶区。文章还提供了来自不同地质环境的实例。  相似文献   

Fast kinematic ray tracing of first- and later-arriving global seismic phases   总被引：1，自引：0，他引：1  

Harmen Bijwaard  & Wim Spakman 《Geophysical Journal International》1999,139(2):359-369

  相似文献   

A study of phase-steepened Alfvén waves in a high-speed stream at 0.29 AU     

P. Alexander 《Annales Geophysicae》2000,18(8):845-851

This work performs a search of phase-steepened Alfvén waves under a priori ideal conditions: a high-speed solar wind stream observed in one of the closest approaches to the Sun by any spacecraft (Helios 2). Five potential candidates were initially found following procedures established in earlier work. The observed cases exhibited arc-like or elliptical polarizations, and the rotational discontinuities that formed the abrupt wave edges were found at either the leading or the trailing part. The consideration of some additional specific parameters (mainly related to the relative orientation between mean magnetic field, wave and discontinuity) has been suggested here for an ultimate and proper identification of this kind of phenomenon. After the inclusion of these calculations in our analysis, even fewer cases than the five originals remain. It is suggested that optimum conditions for the detection rather than just for the existence of these events have to be reconsidered.  相似文献   

Evaluation of rock slope stability for Yujian River dam site by kinematic and block theory analyses     

P.H.S.W. Kulatilake  Liangqing Wang  Huiming Tang  Ye Liang 《Computers and Geotechnics》2011

Lithological information, rock mass fracture data and discontinuity shear strength obtained through field investigations have been used to conduct kinematic and block theory analyses for the rock slopes that exist in the dam site to evaluate the stability of the slopes. The analyses were performed using mean discontinuity set orientations for each rock mass region under gravitational loading to calculate the maximum safe slope angles (MSSA) for different cut slope directions. Results show that final MSSAs obtained from kinematic analysis are less than or equal to that obtained from block theory analysis. The following conclusions have been made based on the block theory analysis results, which are closer to the reality: (1) The final MSSA range between 30° and 47°, 44° and 70°, 47° and 69° for cut slope dip directions of 20–30°, 105–210°, and 270–355°, respectively; (2) For cut slope dip directions of 20–30°, 200–210° and 275–315°, wide ranges of values have been obtained for the final MSSA reflecting the influence of variability of fracture orientations on MSSA; (3) Apart from the region R-d-1 for slope dip directions in the range 20–30°, rest of the regions at the dam site seem to be stable for slope angles less than 40°. Detailed comparisons are given between the kinematic and block theory analyses covering both the theoretical concepts and application results. Also a brief comparison is included between the laboratory and in situ discontinuity shear strength results.  相似文献   

三维网络结构岩体力学架构与展望     

陈剑平 《工程地质学报》2022,30(1):21-36

三维网络结构岩体力学是岩体力学的一个分支。根据笔者20余年对裂隙岩体研究的心得,阐述了三维网络结构岩体力学的主要特点、研究对象,基本架构、主要研究内容与未来的展望。将岩体结构控制论归结为材料强度控制、结构类型控制、渗流通道控制和几何边界控制4个方面。技术层面的主要内容包括三维RQD估算、岩体表征单元估算技术、结构块体搜索技术、定向投影岩体结构面三维连通率估算技术以及岩体三维渗径搜索技术等。理论层面主要由球面投影理论、概率统计理论、随机动力学、几何拓扑理论、块体理论、非线性系统理论和裂隙岩体多尺度等效结构模型等构成。强调足量的随机不连续面地质信息的原位统计取样是三维网络结构岩体力学的基础,岩体随机不连续面三维网络数值模拟技术是三维网络结构岩体力学的核心技术。  相似文献   

Coupled HM analysis using zero‐thickness interface elements with double nodes. Part I: Theoretical model     

J. M. Segura  I. Carol 《国际地质力学数值与分析法杂志》2008,32(18):2083-2101

In recent years, the authors have proposed a new double‐node zero‐thickness interface element for diffusion analysis via the finite element method (FEM) (Int. J. Numer. Anal. Meth. Geomech. 2004; 28 (9): 947–962). In the present paper, that formulation is combined with an existing mechanical formulation in order to obtain a fully coupled hydro‐mechanical (or HM) model applicable to fractured/fracturing geomaterials. Each element (continuum or interface) is formulated in terms of the displacements (u) and the fluid pressure (p) at the nodes. After assembly, a particular expression of the traditional ‘u–p’ system of coupled equations is obtained, which is highly non‐linear due to the strong dependence between the permeability and the aperture of discontinuities. The formulation is valid for both pre‐existing and developing discontinuities by using the appropriate constitutive model that relates effective stresses to relative displacements in the interface. The system of coupled equations is solved following two different numerical approaches: staggered and fully coupled. In the latter, the Newton–Raphson method is used, and it is shown that the Jacobian matrix becomes non‐symmetric due to the dependence of the discontinuity permeability on the aperture. In the part II companion paper (Int. J. Numer. Anal. Meth. Geomech. 2008; DOI: 10.1002/nag.730 ), the formulation proposed is verified and illustrated with some application examples. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献