Structural studies in the Pre-Vindhyan rocks of Rajasthan: A summary of work of the last three decades     

K. Naha  S. Mohanty 《Journal of Earth System Science》1990,99(2):279-290

Multiple deformation in all the Precambrian metamorphic-migmatitic rocks has been reported from Rajasthan during the last three decades. But, whereas the Aravalli Group and the Banded Gneissic Complex show similarity in the style and sequence of structures in all their details, the rocks of the Delhi Group trace a partly independent trend. Isoclinal folds of the first generation (AF₁) in the rocks of the Aravalli Group had gentle westerly plunge prior to later deformations. These folds show reclined, inclined, and upright attitude as a result of coaxial upright folding (AF_la). Superposition of upright folds (AF₂) of varying tightness, with axial plane striking N to NNE, has resulted in interference patterns of diverse types in the scale of maps, and deformation of earlier planar and linear structures in the scale of hand specimens. The structures of the third generation (AF₃) are either open recumbent folds or reclined conjugate folds with axial planes dipping gently towards NE or SW. Structures of the last phase are upright conjugate folds (AF₄) with axial planes striking NNE-SSW and E-W. The Banded Gneissic Complex (BGC) underlies the Aravalli Group with a conglomerate horizon at the contact, especially in southern Rajasthan. But, for a major part of central and southern Rajasthan, migmatites representing BGC show a structural style and sequence identical with those in the Aravalli Group. Migmatization, broadly synkinematic with the AF₁ folding, suggests extensive remobilization of the basement. Very rare relict fabric athwart to and overprinted by structures of AF, generation provide tangible evidence for a basement. Although the structures of later phases in the rocks of the Delhi Group (DF₃ and DF₄) match with the late-phase structures in the Aravalli Group (AF₃ and AF₄), there is a contrast in the structural history of the early stages in the rocks of the two groups. The folds of the first generation in the Delhi Group (DF₁) were recumbent to reclined with gentle plunge towards N to NNE or S to SSW. These were followed by coaxial upright folds of varying tightness (DF₂). Absence of westerly trending AF₁ folds in the Delhi Group, and extreme variation in plunge of the AF₂ folds in contrast with the fairly constant plunge of the DF₂ folds, provide evidence for an angular unconformity between the Aravalli and the Delhi Groups. Depending on the importance of flattening attendant with and following buckling during AF₂ deformation, the lineations of AF₁ generation show different patterns. Where the AF₁ lineations are distributed in circular cones around AF₂ axes because of flexural-slip folding in layered rocks with high viscosity contrast, loci of early lineations indicate that the initial orientation of the AF₁ axes were subhorizontal, trending towards N280°. The orientation of the axial planes of the earlier folds has controlled the development of the later folds. In sectors where the AF, axial planes had N-S strike and gentle dips, or E-W strike with gentle to steep dips, nearly E-W horizontal compression during AF₂ deformation resulted in well-developed AF₂ folds. By contrast, where the AF, axial planes were striking nearly N-S with steep dips, E-W horizontal compression resulted in tightening (flattening) of the already isoclinal AF₁ folds, and probably boudinage structures in some instances, without the development of any AF₂ folds. A similar situation obtains when DF₄ deformation is superposed on earlier structures. Where the dominant S-planes were subhorizontal, N-S compression during DF₄ deformation resulted in either chevron folds with E-W striking axial plane or conjugate folds with axial plane striking NE and NW. In zones with S-planes striking E-W and dipping steeply, the N-S compression resulted in flattening of the earlier folds without development of DF₄ folds.  相似文献   

Defining success in fisheries and conflicts in objectives     

Ray Hilborn 《Marine Policy》2007

The traditional fisheries management objectives of maximizing yield and employment lead to heavily exploited stocks. Many current high-profile disputes arise from conflicting objectives, and the proposed solutions to “the fisheries problem” are primarily particular stakeholders’ efforts to have managers implement their own objectives. I suggest many “failures” are in fact successes for other objectives. Fisheries objectives, as reflected in management actions, are changing. Two current trends are the acceptance of objectives that value less disturbed ecosystems and acceptance of fisheries allocation through dedicated access to improve the fisheries’ economic efficiency. I suggest that increased use of dedicated access will result in more congruent objectives and less conflict.  相似文献   

Anchor deployment for deep water floating offshore equipments   总被引：1，自引：0，他引：1  

O. B. Augusto  B. L. Andrade 《Ocean Engineering》2003,30(5):611-624

In this work a planning methodology for deep water anchor deployment in offshore platforms and floating production systems aiming at operational resources optimization is explored, by minimizing a multi criteria objective function. As an additional advantage provided by the proposed methodology, planning automation is achieved. Planning automation overcomes the traditional way, using a trial error basis. With it, an engineer, using an anchoring software, decides how much work wire and anchoring line must be paid out from both the floating system and the tug boat. Additionally, he decides which horizontal force must be applied to the line, trying to settle the anchor on a previously defined target on the ocean floor.  相似文献   

Estimation of bearing capacity for multiple footings in sand     

Junhwan Lee  Jongwan Eun 《Computers and Geotechnics》2009

In the present study, the effects of multiple-footing configurations in sand on bearing capacity were investigated using field plate load tests and finite element analyses. Both strip and spread footings were considered in the finite element analyses. In each case, different footing distances were applied for the purposes of comparison among all of the results. From these results, it was observed that the load responses of multiple footings are similar to those of the single footing at distances greater than three times the footing width. Design equation and correlation parameters, necessary for quantifying the values of the bearing capacity ratio for the different multiple-footing configuration, were derived. Experimental test results from the literature were selected and used in verifying the proposed method.  相似文献   

基于沉积模式的地震多属性量化沉积微相解释方法——以松辽盆地北部高台子地区泉头组三-四段为例   总被引：2，自引：0，他引：2       下载免费PDF全文

陈树民  沈加刚  宋永忠  张尔华  乔彦国  于兴河  关晓巍 《地质科学》2009,44(2):740-758

本文针对松辽盆地北部扶杨油层赋存的泉头组三.四段河道砂体地震识别问题开展了地震地质综合研究.以高分辨率层序地层学原理和沉积岩石学理论为指导,识别了沉积微相和河道砂体沉积特征,用钻井和地震联合分层对比的方法建立层序地层格架和区域沉积微相展布模式,确定了地震剖面上具有可对比追踪性的四级层序界面.通过地震多属性多元回归与聚类分析拟合含砂率,在沉积模式的指导下对含砂率平面图进行沉积微相解释,确定河道砂体的宅间展布和有利区,经钻探验证说明取得了较好的预测效果.  相似文献   

Stationarity Scores on Training Images for Multipoint Geostatistics   总被引：2，自引：2，他引：0  

Piotr W. Mirowski  Daniel M. Tetzlaff  Roy C. Davies  David S. McCormick  Nneka Williams  Claude Signer 《Mathematical Geosciences》2009,41(4):447-474

This research introduces a novel method to assess the validity of training images used as an input for Multipoint Geostatistics, alternatively called Multiple Point Simulation (MPS). MPS are a family of spatial statistical interpolation algorithms that are used to generate conditional simulations of property fields such as geological facies. They are able to honor absolute “hard” constraints (e.g., borehole data) as well as “soft” constraints (e.g., probability fields derived from seismic data, and rotation and scale). These algorithms require 2D or 3D training images or analogs whose textures represent a spatial arrangement of geological properties that is presumed to be similar to that of a target volume to be modeled. To use the current generation of MPS algorithms, statistically valid training image are required as input. In this context, “statistical validity” includes a requirement of stationarity, so that one can derive from the training image an average template pattern. This research focuses on a practical method to assess stationarity requirements for MPS algorithms, i.e., that statistical density or probability distribution of the quantity shown on the image does not change spatially, and that the image shows repetitive shapes whose orientation and scale are spatially constant. This method employs image-processing techniques based on measures of stationarity of the category distribution, the directional (or orientation) property field and the scale property field of those images. It was successfully tested on a set of two-dimensional images representing geological features and its predictions were compared to actual realizations of MPS algorithms. An extension of the algorithms to 3D images is also proposed. As MPS algorithms are being used increasingly in hydrocarbon reservoir modeling, the methods described should facilitate screening and selection of the input training images.  相似文献   

西部典型地区遥感考古的设想     

李先华周坚华  刘树人姚萌 《地球信息科学学报》2003,5(4):94-96

遥感考古是遥感技术与田野考古的整合 ;本研究将遥感考古和计算机仿真技术与考古相关多学科相结合 ,进行中国西部典型地区重要古遗址所赋存的古地理环境演变及相互关系的研究 ,其主要特点是自然科学与社会科学的交叉渗透和融合 ,典型地区考古实践与遥感考古新理论和高新技术研究的融合。在基础研究方面 ,以中国西部典型遥感考古目标波谱特性、遥感考古的机制、机理 (遥感考古目标微弱信息的提取研究和地下隐藏典型考古目标的遥感信息传递机制研究 )、遥感考古理论体系和技术规范的研究等为主要内容 ;在技术开发方面 ,以研究全谱段、全天候、全天时、多平台的综合对地观测、开发和建立具有全谱段、高分辨率、有一定对地透视能力的、时空多维、多元化信息源的遥感考古信息处理分析体系、典型考古目标的数字仿真和古地理环境的虚拟反演等为特色 ;在应用方面 ,以普查中国西部典型地区古遗址分布、建立中国西部典型地区重要古遗址信息系统 ,找出西部典型地区古遗址时空分布规律 ,以丰富中国西部的文明史等。  相似文献   

塔里木盆地轮南低凸起:一个复式油气聚集区   总被引：36，自引：17，他引：19       下载免费PDF全文

孙龙德  李曰俊 《地质科学》2004,39(2):296-304

轮南低凸起是塔里木盆地塔北隆起上的一个次级构造单元,多年的勘探开发实践表明,该地区具有多个产层、多种油气藏类型和多期油气充注的特点;多种类型的油气藏,垂向上复合叠置,横向上连片成带,共同构成了一个典型的复式油气聚集区。渤海湾盆地油气勘探和研究的实践中总结出来的复式油气聚集区的理论,已经成功地指导了我国东部和南方含油气盆地的勘探,轮南复式油气聚集区的认识,表明该理论在我国西部挤压型含油气盆地也有广泛的应用和发展前景  相似文献   

苏鲁造山带南缘虎山多期次韧性剪切变形特征研究     

潘明宝  陈火根  解国爱  张庆龙  卢华复  陈守矩 《高校地质学报》2004,10(1):62-69

从变形机制、力学性质和变质变形矿物世代研究入手,对江苏东北部苏鲁造山带南缘东海虎山多期叠加剪切带进行的研究表明,该区存在三期韧性剪切变形,第一期为滑脱拆离变形,长英质糜棱岩中形成长石拉伸线理,榴辉岩中形成绿辉石、石榴石分异成分层;第二期变形为韧性逆冲,形成蓝晶石、多硅白云母、黝帘石拉伸线理,在榴辉岩中形成石榴石眼球体;第三期变形为韧脆性逆冲构造,形成长英质S—C糜棱岩,具S—C面理和丝带状石英条带,该结论为建立区域构造变形序列提供了依据。  相似文献   

Multi-scale entropy analysis of Mississippi River flow   总被引：4，自引：3，他引：1  

Zhongwei Li  You-Kuan Zhang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(4):507-512

Multi-scale entropy (MSE) analysis was applied to the long-term (131 years) daily flow rates (Q) of the Mississippi River (MR) to investigate possible change in the complexity of the MR system due to human activities since 1940s. Unlike traditional entropy-based method that calculates entropy at only one single scale, the MSE analysis provided entropies over multiple time scales and thus accounts for multi-scale structures embedded in time series. It is found that the sample entropy (S _E) for Q of the MR and its two components, overland flow (OF) and base flow (BF), generally increase as time scale increases. More importantly, it is found that there have been entropy decreases in Q, OF, and BF over large time scales. In other words, the MR may have been losing its complexity since 1940s. We explain that the possible loss in the complexity of the MR system may be due to the major changes in land use and land cover and soil conservation practices in the MR basin since 1940s.  相似文献