杭州湾南岸平原海蚀地貌的发现及意义     

李长安  王伟  侯红星  祝晓松  孙永辉 《地质论评》2022,68(1):287-292

杭州湾南岸是我国近代海岸线变化最大的海岸带之一.前人曾利用史料、遥感、土地利用等手段对这一带岸线的变化进行过大量的研究.最近,笔者等在慈溪市滨海平原中距海岸线2～3 km的二座孤山—伏龙山和海王山发现了海蚀崖、海蚀沟、海蚀穴等海蚀地貌,从而提供了对历史海岸线位置有明确指示意义的地质地貌证据.分析认为此乃20世纪60年代...  相似文献   

土壤表面划痕与颗粒碰撞磨蚀实验研究   总被引：1，自引：0，他引：1  

贾晓鹏  王海兵 《中国沙漠》2009,29(2):219-222

在沙漠地区,风蚀作用可以导致土壤表面破碎,土壤表面的性质不同,破碎的程度也不尽相同。划痕方法在测量土壤表面的比研磨能量上具有较好的效果,使用通用微型摩擦计(UMT)测量沙土、沙壤土、粉沙壤土、壤土,粉沙粘壤土和粉沙粘土6种不同土壤类型的土壤表面相对磨蚀能量和相对表面硬度,发现土壤表面相对硬度对土壤表面相对磨蚀能量有很大的影响。对沙土,沙壤土、粉沙壤土、壤土、粉沙粘壤土和粉沙粘土6种不同类型的土壤表面进行了颗粒碰撞磨蚀试验,结果表明,土壤表面的碰撞磨蚀速率与碰撞颗粒速度的平方成正比、土壤平均颗粒大小的2.6次方成正比,而与土壤表面相对磨蚀能量的1.5次方成反比,与土壤相对硬度的1.7次方成反比。  相似文献   

菱刈矿床矿脉群形成的构造环境     

《地质与资源》1995,4(2):153-160

本文主要介绍菱刈矿床矿脉的赋存状态、裂隙体系分析、矿脉群赋存的构造环境。菱刈矿床属脉状浅成热液型金银矿床。矿床成因与裂隙系统的形成关系密切。矿脉群大致位于基底岩石(四万十层群)隆起的中央部位。  相似文献   

Sediment transport in high‐speed flows over a fixed bed: 2. Particle impacts and abrasion prediction          下载免费PDF全文

Christian Auel  Ismail Albayrak  Tetsuya Sumi  Robert M. Boes 《地球表面变化过程与地形》2017,42(9):1384-1396

Single bed load particle impacts were experimentally investigated in supercritical open channel flow over a fixed planar bed of low relative roughness height simulating high‐gradient non‐alluvial mountain streams as well as hydraulic structures. Particle impact characteristics (impact velocity, impact angle, Stokes number, restitution and dynamic friction coefficients) were determined for a wide range of hydraulic parameters and particle properties. Particle impact velocity scaled with the particle velocity, and the vertical particle impact velocity increased with excess transport stage. Particle impact and rebound angles were low and decreased with transport stage. Analysis of the particle impacts with the bed revealed almost no viscous damping effects with high normal restitution coefficients exceeding unity. The normal and resultant Stokes numbers were high and above critical thresholds for viscous damping. These results are attributed to the coherent turbulent structures near the wall region, i.e. bursting motion with ejection and sweep events responsible for turbulence generation and particle transport. The tangential restitution coefficients were slightly below unity and the dynamic friction coefficients were lower than for alluvial bed data, revealing that only a small amount of horizontal energy was transferred to the bed. The abrasion prediction model formed by Sklar and Dietrich in 2004 was revised based on the new equations on vertical impact velocity and hop length covering various bed configurations. The abrasion coefficient k_v was found to be vary around k_v ~ 10⁵ for hard materials (tensile strength f_t > 1 MPa), one order of magnitude lower than the value assumed so far for Sklar and Dietrich's model. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

A worldwide correlation for exponential bed particle size variation in subaerial aqueous flows     

P. H. Morris  D. J. Williams 《地球表面变化过程与地形》1999,24(9):835-847

The particle size of the bed sediments in or on many natural streams, alluvial fans, laboratory flumes, irrigation canals and mine waste deltas varies exponentially with distance along the stream. A plot of the available worldwide exponential bed particle size diminution coefficient data against stream length is presented which shows that all the data lie within a single narrow band extending over virtually the whole range of stream lengths and bed sediment particle sizes found on Earth. This correlation applies to both natural and artificial flows with both sand and gravel beds, irrespective of either the solids concentration or whether normal or reverse sorting occurs. This strongly suggests that there are common mechanisms underlying the exponential diminution of bed particles in subaerial aqueous flows of all kinds. Thus existing models of sorting and abrasion applicable to some such flows may be applicable to others. A comparison of exponential laboratory abrasion and field diminution coefficients suggests that abrasion is unlikely to be significant in gravel and sand bed streams shorter than about 10 km to 100 km, and about 500 km, respectively. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

The effects of particle breakage and abrasion on the magnetic properties of two soils     

R. H. Crockford  J. M. Olley 《水文研究》1998,12(9):1495-1505

As mineral magnetism is used as a tracer for sourcing river and dam sediments, changes in the magnetic properties that may occur during transport between the source and sink must be considered. Abrasion and breakage of particles will occur during transport. These processes were examined in simulation experiments with a granitic and a sedimentary soil. The effects of these processes on the magnetic properties of a granitic and a sedimentary soil were examined using a simulated breakage/abrasion experiment. Breakage and/or abrasion had substantial effects on the magnetic properties of both soils. All particle sizes were affected, but the magnitude varied through the size range of derived particles. The major effect was on the concentration of magnetic minerals, with differences between the concentrations in particle sizes of the original material and those generated by the experiments being as much as 20 times. The effect on the granite soil was to reduce the concentrations, i.e. derived material was less than original material; whereas for the sedimentary soil the derived particles had higher concentrations. The effect on magnetic grain size, as indicated by the magnetic ratios, was less than the effect on the mass magnetic properties, but still substantial for some ratios for some sizes. © 1998 John Wiley & Sons, Ltd.  相似文献   

钝顶螺旋藻藻胆体的稳定性研究   总被引：1，自引：0，他引：1  

张熙颖  刘鲁宁  陈秀兰  张玉忠  周百成 《海洋科学》2004,28(8):38-42

根据室温荧光发射光谱表征 ,研究了藻胆蛋白浓度、离子强度、pH和葡聚糖等因素对钝顶螺旋藻(Spirulinaplatensis)藻胆体的稳定性的影响。藻胆蛋白浓度为0.6～1.2g/L时 ,钝顶螺旋藻藻胆体的室温荧光发射峰在676～681nm之间 ,此时藻胆体的稳定性强 ,不易解离。在低离子强度(<0.75mol/L)条件下 ,钝顶螺旋藻藻胆体易解离 ,解离速度随离子强度的递减而加快。钝顶螺旋藻藻胆体在 pH7时稳定 ,而在 pH5,6,8,9时只有轻微解离 ,表明藻胆体在较宽的 pH范围内保持相对稳定。在钝顶螺旋藻藻胆体溶液中加入10%的葡聚糖 ,保存30d后藻胆体依然保持完整 ,说明葡聚糖对藻胆体的稳定性有保护作用  相似文献   

Abrasion-derived sediments under intensified winds at the latest Pleistocene leading edge of the advancing Sinai-Negev erg     

Yehouda Enzel  Rivka Amit  Onn Crouvi  Naomi Porat 《Quaternary Research》2010,74(1):121-482

Quaternary desert loess and sandstone-loessite relationships in the geological record raise questions regarding causes and mechanisms of silt formation and accretion. In the northern Sinai-Negev desert carbonate terrain, only sand abrasion in active erg could have produced the large quantities of quartzo-feldspathic silts constituting the late Quaternary northwestern Negev loess. In the continuum of source (medium to fine sand of dunes) to sink (silts in loess) the very fine sand is unaccounted for in the record. This weakens the sand abrasion model of silt formation as a global process. Here, we demonstrate that, as predicted by experiments, abrasion by advancing dunes generated large quantities of very fine sand (60-110 μm) deposited within the dune field and in close proximity downwind. This very fine sand was generated 13-11 ka, possibly synchronous with the Younger Dryas under gusty sand/dust storms in the southeastern Mediterranean and specifically in the northern Sinai-Negev erg. These very fine sands were washed down slope and filled small basins blocked by the advancing dunes; outside these sampling basins it is difficult to identify these sands as a distinct product. We conclude that ergs are mega-grinders of sand into very fine sand and silt under windy Quaternary and ancient aeolian desert environments.  相似文献   

Transport and dispersal of organic debris (peat blocks) in upland fluvial systems     

Martin Evans  Jeff Warburton 《地球表面变化过程与地形》2001,26(10):1087-1102

This paper assesses the mechanisms and pathways by which peat blocks are eroded and transported in upland fluvial systems. Observations and experiments from the north Pennines (UK) have been carried out on two contrasting river systems. Mapping of peat block distributions and appraisal of reach‐based sediment budgets clearly demonstrates that macro‐size peat is an important stream load component. In small streams block sizes can approximate the channel width and much of the peat is transported overbank. Local ‘peat jams’ and associated mineral deposition may provide an important component of channel storage. In larger systems peat blocks rapidly move down‐channel and undergo frequent exchanges between bed and bank storage. Results of peat block tracing using painted blocks indicate that once submerged, blocks of all sizes are easily transported and blocks break down rapidly by abrasion. Vegetation and bars play an important role in trapping mobile peat. In smaller streams large block transport is limited by channel jams. Smaller blocks are transported overbank but exhibit little evidence of downstream fining. In larger rivers peat blocks are more actively sorted and show downstream reduction in size from source. A simple model relating peat block diameter (D_p) to average flow depth (d) suggests three limiting transport conditions: flotation (D_p < d), rolling (d < D_p > d/2) and deposition (D_p > d/2). Experiments demonstrate that peat block transport occurs largely by rolling and floating and the transport mechanism is probably controlled by relative flow depth (d/D_p ratio). Transport velocity varies with transport mechanism (rolling is the slowest mode) and transport lengths increase as flow depth increases. Abrasion rates vary with the transport mechanism. Rolling produces greater abrasion rates and more rounded blocks. Abrasion rates vary from 0 to 10 g m^?1 for blocks ranging in mass from 10 to 6000 g. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

The factors influencing the abrasion efficiency of saltating grains on a clay‐crusted playa     

Christopher A. Houser  William G. Nickling 《地球表面变化过程与地形》2001,26(5):491-505

The entrainment and subsequent transport of PM₁₀ (particulate matter <10 µm) has become an important and challenging focus of research for both scientific and practical applications. Arid and semi‐arid environments are important sources for the atmospheric loading of PM₁₀, although the emission of this material is often limited by surface crusts. It has been suggested that the primary mechanisms through which PM₁₀ is released from a crusted surface are abrasion by saltating grains or disturbance by agricultural and recreational activities. To examine the importance of saltation abrasion in the emission of PM₁₀, a series of field wind tunnel tests were conducted on a clay‐crusted surface near Desert Wells, Arizona. In a previous part of this study it was found that the emission rate varies linearly with the saltation transport rate, although there can be considerable variation in this relationship. This paper more closely examines the source of the variability in the abrasion efficiency, the amount of PM₁₀ emitted by a given quantity of saltating grains. The abrasion efficiency was found to vary with the susceptibility of the surface to abrasion, the ability of the sand to abrade that surface and the availability of material with a caliper size <10 µm within the crust. Specifically, the results of the study show that the abrasion efficiency is related to the crust strength, the amount of surface disturbance and the velocity of the saltating grains. It is concluded that the spatial and temporal variability of these controls on the abrasion efficiency imposes severe contextual limitations on experimentally derived models, and can make theoretical models too complex and impractical to be of use. Copyright­© 2001 John Wiley & Sons, Ltd.  相似文献