Micromorphological Analysis of Coastal Sediments from Willapa Bay, Washington, USA: A Technique for Analysing Inferred Tsunami Deposits     

Aoibheann A. Kilfeather  Jeffrey J. Blackford  Jaap J. M. van der Meer 《Pure and Applied Geophysics》2007,164(2-3):509-525

Tsunami deposits are provisionally distinguished in the field on the basis of anomalous sand horizons, fining-up and fining-landward, coupled with organic-rich, fragmented `backwash' sediments. In this paper, micromorphological features of a sediment sequence previously interpreted as being of tsunami origin are described. These characteristics are shown to be consistent with the macro-scale features used elsewhere, but show additional details not seen in standard stratigraphies, including possible evidence for individual waves, possibly wave-magnitude progression, organic fragment alignment and intraclast microstructures. Although replication and more complete studies are needed, this analysis confirms the identification of a tsunami in Willapa Bay in ca.1700 AD, while demonstrating a widely applicable technique for confirming or refuting possible tsunami deposits.  相似文献   

Long‐term landscape evolution: linking tectonics and surface processes     

Paul Bishop 《地球表面变化过程与地形》2007,32(3):329-365

Research in landscape evolution over millions to tens of millions of years slowed considerably in the mid‐20th century, when Davisian and other approaches to geomorphology were replaced by functional, morphometric and ultimately process‐based approaches. Hack's scheme of dynamic equilibrium in landscape evolution was perhaps the major theoretical contribution to long‐term landscape evolution between the 1950s and about 1990, but it essentially ‘looked back’ to Davis for its springboard to a viewpoint contrary to that of Davis, as did less widely known schemes, such as Crickmay's hypothesis of unequal activity. Since about 1990, the field of long‐term landscape evolution has blossomed again, stimulated by the plate tectonics revolution and its re‐forging of the link between tectonics and topography, and by the development of numerical models that explore the links between tectonic processes and surface processes. This numerical modelling of landscape evolution has been built around formulation of bedrock river processes and slope processes, and has mostly focused on high‐elevation passive continental margins and convergent zones; these models now routinely include flexural and denudational isostasy. Major breakthroughs in analytical and geochronological techniques have been of profound relevance to all of the above. Low‐temperature thermochronology, and in particular apatite fission track analysis and (U–Th)/He analysis in apatite, have enabled rates of rock uplift and denudational exhumation from relatively shallow crustal depths (up to about 4 km) to be determined directly from, in effect, rock hand specimens. In a few situations, (U–Th)/He analysis has been used to determine the antiquity of major, long‐wavelength topography. Cosmogenic isotope analysis has enabled the determination of the ‘ages’ of bedrock and sedimentary surfaces, and/or the rates of denudation of these surfaces. These latter advances represent in some ways a ‘holy grail’ in geomorphology in that they enable determination of ‘dates and rates’ of geomorphological processes directly from rock surfaces. The increasing availability of analytical techniques such as cosmogenic isotope analysis should mean that much larger data sets become possible and lead to more sophisticated analyses, such as probability density functions (PDFs) of cosmogenic ages and even of cosmogenic isotope concentrations (CICs). PDFs of isotope concentrations must be a function of catchment area geomorphology (including tectonics) and it is at least theoretically possible to infer aspects of source area geomorphology and geomorphological processes from PDFs of CICs in sediments (‘detrital CICs’). Thus it may be possible to use PDFs of detrital CICs in basin sediments as a tool to infer aspects of the sediments' source area geomorphology and tectonics, complementing the standard sedimentological textural and compositional approaches to such issues. One of the most stimulating of recent conceptual advances has followed the considerations of the relationships between tectonics, climate and surface processes and especially the recognition of the importance of denudational isostasy in driving rock uplift (i.e. in driving tectonics and crustal processes). Attention has been focused very directly on surface processes and on the ways in which they may ‘drive’ rock uplift and thus even influence sub‐surface crustal conditions, such as pressure and temperature. Consequently, the broader geoscience communities are looking to geomorphologists to provide more detailed information on rates and processes of bedrock channel incision, as well as on catchment responses to such bedrock channel processes. More sophisticated numerical models of processes in bedrock channels and on their flanking hillslopes are required. In current numerical models of long‐term evolution of hillslopes and interfluves, for example, the simple dependency on slope of both the fluvial and hillslope components of these models means that a Davisian‐type of landscape evolution characterized by slope lowering is inevitably ‘confirmed’ by the models. In numerical modelling, the next advances will require better parameterized algorithms for hillslope processes, and more sophisticated formulations of bedrock channel incision processes, incorporating, for example, the effects of sediment shielding of the bed. Such increasing sophistication must be matched by careful assessment and testing of model outputs using pre‐established criteria and tests. Confirmation by these more sophisticated Davisian‐type numerical models of slope lowering under conditions of tectonic stability (no active rock uplift), and of constant slope angle and steady‐state landscape under conditions of ongoing rock uplift, will indicate that the Davis and Hack models are not mutually exclusive. A Hack‐type model (or a variant of it, incorporating slope adjustment to rock strength rather than to regolith strength) will apply to active settings where there is sufficient stream power and/or sediment flux for channels to incise at the rate of rock uplift. Post‐orogenic settings of decreased (or zero) active rock uplift would be characterized by a Davisian scheme of declining slope angles and non‐steady‐state (or transient) landscapes. Such post‐orogenic landscapes deserve much more attention than they have received of late, not least because the intriguing questions they pose about the preservation of ancient landscapes were hinted at in passing in the 1960s and have recently re‐surfaced. As we begin to ask again some of the grand questions that lay at the heart of geomorphology in its earliest days, large‐scale geomorphology is on the threshold of another ‘golden’ era to match that of the first half of the 20th century, when cyclical approaches underpinned virtually all geomorphological work. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Geology and geochemistry of the Bingdaban ophiolitic mélange in the boundary fault zone on the northern Central Tianshan Belt, and its tectonic implications     

DONG YunPeng  ZHANG GuoWei  ZHOU DingWu  LUO JinHai  ZHANG ChengLi  XIA LinQi  XU XueYi  LI XiangMin 《中国科学D辑(英文版)》2007,50(1)

  相似文献   

GPS测时在电力系统中的应用   总被引：3，自引：0，他引：3  

聂桂根  刘经南 《武汉大学学报(信息科学版)》2002,27(2):153-157

介绍了利用GPS测时及时间传递的几种方式，详细地讨论了GPS用在电压相角测量，输电线路故障定位以及线路网损和电能结算系统几个方面的应用原理，设计出应用的方案，并得到部分结果。  相似文献   

吉林省海沟金矿断裂地球化学预测研究   总被引：4，自引：0，他引：4  

孙岳  雷时斌等 《地质与勘探》2002,38(3):23-27

在总结海沟矿区控矿断裂构造几何形态学，动力学，运动学和地球化学特征基础上，应用数学模拟和GIS图层分析技术，综合分析研究断裂构造控矿规律和金矿成矿地球化学行为，初步建立了断裂构造地球化学定位预测模型。并对矿区主要赋矿构造-28号矿体深部及外围进行打矿预测。  相似文献   

文峪金矿矿床成因讨论   总被引：3，自引：1，他引：3       下载免费PDF全文

王铁军  樊秉鸿  关康  陈新帮  贺永利  刘军  梁斌祥  王建民 《地质找矿论丛》2002,17(2):85-91

流体包裹体测温表明 ,文峪金矿成矿温度 180～ 45 0℃ ,为中高温热液。成矿压力 1.0×10 5～ 1.4× 10 5k Pa,根据静岩压力推算的成矿深度为 3.6～ 5 .2 km。包裹体盐度特征显示出成矿场内流体以深源流体为主 ,混合的地表渗透水所占比例约 10 %～ 15 %。文峪金矿成矿过程中导致矿质沉淀的主要因素是温度下降及由此导致的 CO2 - H2 O不混溶现象。文峪及小秦岭地区金矿床的成矿热液来源于与文峪花岗岩同源演化的深部岩浆热液。金矿的成矿时代为中生代中晚期  相似文献   

吐哈盆地十红滩铀矿床地质特征及控矿因素分析   总被引：1，自引：0，他引：1  

李保侠 《华东地质学院学报》2002,25(4):292-300

叙述了吐哈盆地地质概况；十红滩铀矿区找矿目的层地质和砂体特征；重点对层间氧化带的纵横展布规律、地球化学分带性及前锋与铀矿化的关系作了阐述；对十红滩铀矿床南、北矿带的空间分布、形态、规模、物质成分、铀存在形式及南、北矿带差异做了研究。通过分析，最后得出十红滩铀矿床控矿因素是层间氧化带、鼻状隆起（南矿带）和北西向断裂构造（北矿带）、同时说明了局部铀矿化产出的决定因素。  相似文献   

青藏高原中部北北东向深部负磁异常带的成因及其意义   总被引：7，自引：6，他引：7  

周伏洪  姚正煦  刘振军  张永军 《物探与化探》2002,26(1):12-16

根据最新测量获得的青藏高原中西部航磁异常图 ,经不同高度向上延拓后 ,发现在测区东部 ,即青藏高原中部自柴达木向西南延伸的广大地区 ,出现一条极为明显的北北东向负磁异常带。从对航磁区域场的分析 ,并结合人工地震、重力计算莫霍面深度、热水活动、最新火山岩活动、地貌特征和天然地震活动等多种资料的解释 ,认为负异常带是由于深部热流沿北北东向上升引起局部岩浆熔融 ,使上地壳下部具有较高的地温 ,导致磁性层底部消磁作用的结果。与此同时也加快了青藏高原隆升的幅度 ,为高原形成和演化的研究提供了新的证据  相似文献   

甚低频电磁法在某萤石矿勘查中的应用   总被引：6，自引：0，他引：6  

白大明  关继东  苏来柱 《物探与化探》2002,26(1):39-41

内蒙古海力敏萤石矿属热液脉型,萤石—石英矿受花岗岩体内NW向断裂破碎带控制。矿区开展了甚低频电磁法找矿勘查研究,在已知矿体上测得明显的甚低频电磁异常,证实了该方法对寻找此类萤石矿床的有效性。在不易识别开采的掩盖区,所测甚低频电磁异常显示控矿断裂带仍存在,极可能赋存萤石矿体。  相似文献   

On Continent-Continent Point-Collision and Ultrahigh-Pressure Metamorphism   总被引：4，自引：0，他引：4  

DONG Shuwen  Chinese Academy of Geological Sciences  Baiwanzhuang Ro  Beijing WU Hongling  LIU Xiaochun  XUE Huaimin Institute of Geomechanics  Chinese Academy of Geological Sciences  Beijing Fei Zhenbi 《《地质学报》英文版》2002,76(1):69-80

Up to now it is known that almost all ultrahigh-pressure (UHP) metamorphism of non-impact origin occurred in continent-continent collisional orogenic belt, as has been evidenced by many outcrops in the eastern hemisphere. UHP metamorphic rocks are represented by coesite- and diamond-bearing eclogites and eclogite facies metamorphic rocks formed at 650-800℃ and 2.6-3.5 GPa, and most of the protoliths of UHP rocks are volcanic-sedimentary sequences of continental crust. From these it may be deduced that deep subduction of continental crust may have occurred. However, UHP rocks are exposed on the surface or occur near the surface now, which implies that they have been exhumed from great depths. The mechanism of deep subduction of continental crust and subsequent exhumation has been a hot topic of the research on continental dynamics, but there are divergent views. The focus of the dispute is how deep continental crust is subducted so that UHP rocks can be formed and what mechanism causes it to be subducte  相似文献