广西上泥盆统F-F界线碳同位素的变化特征   总被引：3，自引：0，他引：3  

许冰  顾兆炎  胡滨  李镇梁 《沉积学报》2004,22(4):603-608

发生在晚泥盆世弗拉期(Frasnian)-法门期(Famennian)之交的生物灭绝事件(简称F-F事件)是古生代以来五大生物集群灭绝事件之一,其原因仍含糊不清。碳同位素研究显示,伴随F-F事件全球碳循环发生了显著的变化。但对中国南方F-F事件地层碳同位素变化特征的认识不够,缺乏系统的研究。对广西桂林杨堤上泥盆统灰岩剖面的碳同位素的分析结果表明,在上泥盆统存在两次碳同位素正偏移,分别出现在下rhenana带和F-F的界线,其中,出现在F-F界线的碳同位素正偏移与广西垌村以及欧美和非洲等地的上泥盆统F-F界线附近的碳同位素记录一致,且具有相近的变化幅度。进一步对广西桂林附近的杨堤和垌村剖面F-F界线的碳同位素组成变化模式的分析发现,这次正偏移可能是由多次次级变化组成,与F-F事件中生物的灭绝步骤相似。  相似文献   

多年冻土地基正温输气管道地温场实测及分析     

施瑞  徐震  刘德仁  蒋代军  王旭  胡渊  温智 《冰川冻土》2019,41(4):865-874

我国有多条油气管道位于多年冻土地区,工程问题层出不穷。因输送介质处于正温状态,其所释放热量对管道周围冻土冻融过程有极大影响。为阐明正温管道对多年冻土温度场及冻融特征的影响,基于西部某多年冻土区正温输气管道现场实验,对管道地基温度场进行了为期1年的现场实测。数据分析表明,多年冻土天然上限为1.5~2.0 m;土体融化期及冻结期分别为6-10月、11-次年5月;监测段多年冻土热量收支基本平衡,属于不稳定冻土,在外界热扰动下极易退化;正温输气管道的存在引起了多年冻土的退化且对其温度场有很大影响,水平方向影响范围约1.5 m,管下最大融深可达7.0 m。同时指出了针对处于临界状态的多年冻土,在基于对其全面、深入了解的基础上,越早考虑相关工程建设带来的热扰动对多年冻土的不利影响,则处置难度越低且损失越小。  相似文献   

贵州高原山区正负地形特征及其对人口分布的影响     

罗娅  杨建红  周秋文  周旭  钟九生  胡馨月  高齐云 《世界地理研究》2021,30(1):204-212

正负地形可通过源汇过程对水、土资源进行再分配,影响山区的人口分布。获取正负地形数据,运用6个指标和多元逐步回归法,分析贵州高原山区正负地形特征及其对人口分布的影响。研究表明：①贵州高原山区的正负地形结构异质性明显。蚕食度、深切度、平均粗糙度比、形状指标、匀度指数、破碎度的平均值分别为1.07、371m、1.01、3.40、325和3.34,表明正地形被负地形蚕食明显、切入深度大,正、负地形的粗糙度基本相当,正负地形景观斑块呈现形状不规则、面积不均匀的破碎状态。6个正负地形指标中,匀度指数的变异性最大,变异系数为90.43%;平均粗糙度比的变异性最小,变异系数为1.06%;②贵州高原山区的人口分布不均匀性突出。人口累积达到40%时,累积面积百分比为14%;人口累积达到80%时,累积面积百分比约为50%;③6个正负地形指标中,蚕食度和深切度是影响人口分布的主要因素。蚕食度与人口密度呈正相关关系,深切度与人口密度呈负相关关系。研究成果为研究地形条件的人口影响提供补充,并为贵州高原山区人-地关系协调和土地可持续管理提供参考。  相似文献   

Markov Models for Cross-Covariances     

A. G. Journel 《Mathematical Geology》1999,31(8):955-964

Markov models based on various data screening hypotheses are often used because they reduce the statistical inference burden. In the case of co-located cokriging, the commonly used Markov model results in the cross-covariance being proportional to the primary covariance. Such model is inappropriate in the presence of a smoothly varying secondary variable defined on a much larger volume support than the primary variable. For such cases, an alternative Markov screening hypothesis is proposed that results in a more continuous cross-covariance proportional to the secondary covariance model. A parallel development of both Markov models is presented. A companion paper provides a comparative application to a real data set.  相似文献   

Sedimentary cycle pattern and stacked style of sand-body of the Lower Jurassic Sangonghe Formation in belly of Junggar Basin          下载免费PDF全文

Xu Shu-Mei  Li Meng  Wang Jin-Duo  Ren Xin-Cheng  Chi Xin-Qi  Shu Peng-Cheng  Wang Jie-Qing  Liu Xian 《古地理学报》1999,22(2):221-234

The coarse grain braided river delta in Jurassic Sangonghe Formation of Junggar Basin formed the main Mesozoic reservoir system. At present,there are obvious different opinions on the sedimentary cycle characteristics of Jurassic Sangonghe Formation,and there is a lack of research on the driving mechanisms of sedimentary cyclicity,which leads to a great dispute on the stacked style of sand-bodies. Using 38 wells coring and logging data in the belly of Junggar Basin,based on principles and methods of sedimentology and sedimentary basin analysis,the characteristics of sedimentary cycle in Sangonghe Formation are systematically analyzed. The stacked style and combination rule of sand-bodies are studied in detail within sedimentary cyclic framework. The characteristics of basement subsidence and multi-stage uplifting during the Early Jurassic of Junggar Basin are discussed,so as to clear the driving mechanisms of positive sedimentary cycle. The Sangonghe Formation in the study area is divided into four system tract level positive cycles with no reverse cycle deposition,which reflects the sedimentary characteristics of slow lacustrine transgress and fast lacustrine retrogress. The sand-bodies in the braided river delta front of the Sangonghe Formation show five stacking patterns: Strong erosion of superimposed sand-body by subaqueous distributary channel,weak erosion of superimposed sand-body by subaqueous distributary channel,superimposed river-mouth bar on subaqueous distributary channel,distal bar-blanket sand assemblage,beach bar sand-body. The first cycle is the intermittent distribution of beach bar sand-bodies. The second cycle includes continuous distribution of strong erosion of superimposed sand-body by subaqueous distributary channel,weak erosion of superimposed sand-body by subaqueous distributary channel,and superimposed river-mouth bar on subaqueous distributary channel. The third cycle is composed of relatively continuous distribution of weak erosion of superimposed sand-body by subaqueous distributary channel and distal bar-blanket sand assemblage. The fourth cycle is scattered distribution of beach bar sand-body. It is possible because of the slow subsidence and intermittent rapid uplift of the basement of Junggar Basin that regressive superposition and the scour interface between each sedimentary cycle are formed.  相似文献   

太湖流域排污权交易优化目标模型及方案配置研究     

朱德明  李洁 《湖泊科学》2004,16(Z1):182-187

根据江苏省太湖流域水环境与社会经济特征,建立主要污染物排污权交易优化目标模型;以重点工业污染企业为样本,对排污权交易初始方案实施的预期效果进行定量分析,提出开展排污权交易制度的政策建议.  相似文献   

正循环机械回转钻孔灌注桩在卵石层中的应用     

皮跃进 《福建地质》2009,28(3):250-252

在粒径、密实度较大的卵石层采用正循环机械回转钻进行灌注桩施工,存在钻具类型、合理的泥浆比例和钻探工艺等问题。以西安绕城高速公路谢王立交桥桥桩基工程实践为例,探讨正循环机械回转钻孔灌注桩在卵石层施工工艺等问题。  相似文献   

浙江省沿海陆域与舟山海域地闪回击特征分析     

陈军  孙轶  李京校  张骁  林伟  于梦颖 《气象科技》2022,50(1):139-146

采用2016-2020年浙江省闪电定位资料,利用Access和MATLAB对浙江省陆域、舟山海域地闪回击特征进行分析.结果显示:浙江省陆域年平均地闪回击密度为1.97次·km-2·a-1,正地闪回击密度为0.10次·km-2·a-1,正地闪回击占总地闪回击的5.1％,正地闪回击平均电流强度为42.49 kA,负地闪为3...  相似文献   

一种基于模糊正域类的模糊属性约简方法     

冯楠坪  周磊 《成都信息工程学院学报》2013,28(4):434-439

为了实现模糊信息系统属性约简问题,探讨一种基于正域类的模糊属性约简方法。利用模糊二元相似关系建立模糊相似类的方法,进而定义决策属性关于条件属性的模糊正域类,得到正域类属性的重要度。结果表明:一方面,实现模糊信息系统属性约简;另一方面,通过取不同的相似精度,得到不同属性约简集。  相似文献   

非线性四阶四点边值问题的正解     

田淑杰  孔令彬 《东北石油大学学报》2012,(1):105-110,2

利用锥不动点定理,并结合Green函数性质,证明一类四阶四点边值问题的正解的存在性.  相似文献