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1.
Cryogenic structure (patterns made by ice inclusions) in seasonally frozen and permafrost-af-fected soils result from ice formation during freezing. Analysis of cryogenic structures in soils is essential to our understanding of the cryogenic processes in soils and to formulating land use management interpretations. When soils freeze, the freezing front moves downward and attracts water moving upward resulting in mainly horizontal lenticular ice formation. Platy and lenticular soil structures form between ice lenses in upper active layer. The reticular soil structure usually forms above the permafrost table caused by freeze-back of the permafrost. The upward freeze-back resulted in platy soil structure and the volume changes following the annual freeze-thaw cycle resulted in vertical cracks. The combined result is an ice-net formation with mineral soils embedded in the ice net. The upper permafrost layer that used to be a part of the active layer has an ice content exceeding 50% due to repeated freeze-thaw cycles over time. The mineral soils appear in blocks embedded in an ice matrix. The permafrost layer that never experienced the freeze-thaw cycle often consists of alternate layers of thin ice lens and frozen soils with extreme hard consistence and has relatively lower ice content than the ice-rich layer of the upper permafrost. Ice contents and thaw settling potentials associated with each cryogenic structure should be considered in engineering and land use interpretations.  相似文献   

2.
The active layer is the top layer of permafrost soils that thaws during the summer season due to increased ambient temperatures and solar radiation inputs. This layer is important because almost all biological activity takes place there luring the summer. The depth of active layer thaw is influenced by climatic conditions. Vegetation has also been found to have a strong impact on active layer thaw, because it can intercept incoming radiation, thereby insulating the soil from ambient conditions. In order to look at the role of vegetation and climate on active layer thaw, we measured thaw depth and the Normalized Difference Vegetation Index (NDVI; a proxy for aboveground plant biomass) along a latitudinal temperature gradient in arctic Alaska and Canada. At each site several measurements of thaw and NDVI were taken in areas with high amounts of vegetation and areas with little to no vegetation. Results show that the warmest regions, which had the greatest levels of NDVI, had relatively shallow thaw depths, and the coldest regions, which had the lowest levels of NDVI, also had relatively shallow thaw depths. The intermediate regions, which had moderate levels of NDVI and air temperature, had the greatest depth of thaw. These results indicate that temperature and vegetation interact to control the depth of the active layer across a range of arctic ecosystems. By developing a relationship to explain thaw depth through NDVI and temperature or latitude, the possibility exists to extrapolate thaw depth over large scales via remote sensing applications.  相似文献   

3.
In order to study the deep geoelectrical structure and the regional geological structure and detect potential oil and gas areas in Qiangtang basin in northern Xizang (Tibet), 222 MT soundings were conducted along three N - S MT profiles across the basin .The MT results indicate that the south and north parts of the Qiangtang basin have a good contrast in the deep electrical structure . In the south Qiangtang , there are generally two high conductivity layers in the crust . The first is at a depth of about 10-25 km and possesses a resistivity of about 10-80 Ωm . The second, the high conductivity layer in the lower crust, is at a depth of about 40-70 km with 3- 50 Ωm . In the north Qiangtang , there is generally one high conductivity layer . It is at a depth of about 10-30 km and the resistivity is about 1-60 Ωm . The thickness of the second high conductivity layer in both the south Qiangtang and the Bangong-Nujiang suture is much greater than that of the first . The thickness of the lithosphere is abou  相似文献   

4.
青藏高原多年冻土区地温监测结果分析   总被引：6，自引：0，他引：6  
王绍令  赵新民 《冰川冻土》1999,21(4):351-356
Ground temperatures monitored at four observation sites in permafrost regions on the Tibetan Plateau was analyzed. It was found that the ground temperature at the depth of 12～20 m increased 0.2～0.4 K and the permafrost thickness decreased 4～5 m from the base in Xidatan Site from 1975 to 1989; and the ground temperature at the depth of 6～15 m increased 0.2～0.4 K in Kunlun Pass Site from 1982 to 1997. Contrast observations show that a sand cover, 15～20 cm in depth, can result in a ground temperature decrease of 0.1～ 0.2 K in MS66 Site; and a removal of vegetation can result in a ground temperature decrease of some 0.2 K in Hoh Xil Site. The monitor demonstrates that many factors that control permafrost developing have duality, e.g., sand and vegetation are able to increase or decrease the ground temperature. These factors, in conjunction with permafrost behaviour, play different roles under different conditions. Therefore, it is necessary to study, understand and evaluate permafrost and its engineering geological properties taking the viewpoint of dynamic variation.  相似文献   

5.
<正>The Tazhong paleouplift is divided into the upper and the lower structural layers,bounded by the unconformity surface at the top of the Ordovician carbonate rock.The reservoirs in the two layers from different parts vary in number,type and reserves,but the mechanism was rarely researched before.Therefore,an explanation of the mechanism will promote petroleum exploration in Tazhong paleouplift.After studying the evolution and reservoir distribution of the Tazhong paleouplift,it is concluded that the evolution hi late Caledonian,late Hercynian and Himalayan periods resulted in the upper and the lower structural layers.It is also defined that in the upper structural layer,structural and stratigraphic overlap reservoirs are developed at the top and the upper part of the paleouplift,which are dominated by oil reservoirs,while for the lower structural layer,lithological reservoirs are developed in the lower part of the paleouplift,which are dominated by gas reservoirs,and more reserves are discovered in the lower structural layer than the upper. Through a comparative analysis of accumulation conditions of the upper and the lower structural layers,the mechanism of enrichment differences is clearly explained.The reservoir and seal conditions of the lower structural layer are better than those of the upper layer,which is the reason why more reservoirs have been found in the former.The differences in the carrier system types,trap types and charging periods between the upper and the lower structural layers lead to differences in the reservoir types and distribution.An accumulation model is established for the Tazhong paleouplift.For the upper structural layer,the structural reservoirs and the stratigraphic overlap reservoirs are formed at the upper part of the paleouplift,while for the lower structural layer,the weathering crust reservoirs are formed at the top,the reef-flat reservoirs are formed on the lateral margin,the karst and inside reservoirs are formed in the lower part of the paleouplift.  相似文献   

6.
Arsenic pollution of groundwater has become a serious health problem in several regions of the world. Wuyuan County located in the central part of the Hetao Plain, Inner Mongolia, is one of the most severely arsenic polluted areas. Peoples of the county have used groundwater of shallow （12-25 m） tube-well as drinking water. The groundwater is Na-HCO3 and Na-Cl type on the piper plots and aligns with steady Ca ： Mg ratio on cation diagram. The arsenic content in the water is more than 0.2 mg/L and the highest value reaches up to 0.52 mg/L. Drilling data show that Holocene sediments are divided into three zones on the basis of their color appearances; brown, grey and dark gray zones. The strata from 2m to 9-14m under the surface are mainly composed of clay and silt which are impermeable layers. The grey and dark grey zones composed of sand underlie the impermeable bed and the condition of their zones is reductive. At the depth of 30 m near the bottom of drilling, ORP of the groundwater is -300- -400 mV. The dark grey sand changes to yellow in color under the atmosphere. Under reducing environment, the color returns to its original dark grey. The characteristic color is due to amorphous or low-crystalline Fe sulfide coating sand grains. The sediments are of fluvial origin by the Yellow River. The arsenic content in the sediments is rich in fine-grained part and its values are more than 20 mg/kg in clay layer. The highest is 38 mg/kg. X-ray diffraction and macroscopic observation show that the clay layer is made of minerals such as chlorite and illite and contains high quantities of organic matter.  相似文献   

7.
《地学前缘(英文版)》2019,10(6):2135-2145
In fractured reservoirs characterized by low matrix permeability,fracture networks control the main fluid flow paths.However,in layered reservoirs,the vertical extension of fractures is often restricted to single layers.In this study,we explored the effect of changing marl/shale thickness on fracture extension using comprehensive field data and numerical modeling.The field data were sampled from coastal exposures of Liassic limestone-marl/shale alternations in Wales and Somerset(Bristol Channel Basin,UK).The vertical fracture traces of more than 4000 fractures were mapped in detail.Six sections were selected to represent a variety of layer thicknesses.Besides the field data also thin sections were analyzed.Numerical models of fracture extension in a two-layer limestone-marl system were based on field data and laboratory measurements of Young's moduli.The modeled principal stress magnitude σ_3 along the lithological contact was used as an indication for fracture extension through marls.Field data exhibit good correlation(R~2=0.76) between fracture extension and marl thickness,the thicker the marl layer the fewer fractures propagate through.The model results show that almost no tensile stress reaches the top of the marl layer when the marls are thicker than 30 cm.For marls that are less than 20 cm,the propagation of stress is more dependent on the stiffness of the marls.The higher the contrast between limestone and marl stiffness the lower the stress that is transmitted into the marl layer.In both model experiments and field data the critical marl thickness for fracture extension is ca.15-20 cm.This quantification of critical marl thicknesses can be used to improve predictions of fracture networks and permeability in layered rocks.Up-or downsampling methods often ignore spatially continuous impermeable layers with thicknesses that are under the detection limit of seismic data.However,ignoring these layers can lead to overestimates of the overall permeability.Therefore,the understanding of how fractures propagate and terminate through impermeable layers will help to improve the characterization of conventional reservoirs.  相似文献   

8.
A preliminary organic geochemical study shows that the sulphide ores from the hydrothermal deposit of the Okinawa Trough are generally low in the total organic carbon and extremely low in the soluble organic matter. In the aliphatic hydrocarbon fraction, the n-alkanes range from C15 to C35, with usual maxima in the middle n-C20 region and strong odd-carbon number predominance when n > C25 (CPI = 1.2). The dominant analog in the aromatic fraction is phenanthrene, a polynuclear aromatic hydrocarbon, which provides evidence for hydrothermal activity. The organic matter derived mainly from marine planktonic and terrigenous vascular plants is entrapped in a high-temperature regime such as an active chimney and cooled quickly in the sulphide ores on the seafloor. Organic matter and sulphides are definitely products of a high-temperature alteration. The biomarker compounds indicate that the ores are formed under low Eh and pH conditions-a reducing to anoxic environment, which is favourable for sulphates to be  相似文献   

9.
As the globally largest area covered by high altitudinal permafrost, the Qinghai-Tibet Plateau may contribute substantially to atmospheric CH4 budget when global warming. Preliminary observations on CH4 emission at Qingshuihe from November 5 to 14, 1995 show that alpine grassland may be a small source for atmospheric CH4 during early winter. The emission rates of CH4 from moist grassland surface varied from-16. 1 to 23. 9 μg. m-2h-1, with an average of 1. 82 μg. m-2h-1. Emission rates of CH4 from water surface of Qingshuihe River were from -21. 0 to 37. 1 μg. m-2h-1, with an average of 1. 56 μg. m-2h-1. The emission rates of CH at 30 to 200 cm in depth ranged from-69. 0 to 36. 0 μg. m-2h-1, with the average rate at these depths varying from -2. 15 to 2. 04 μg' m-2h-1. The mean emission rates of CH4 in the active layer and permafrost indicate the lower part of active layer tends to release CH4, CH4 is absorbed at low rates in the middle section and in the vicinity of permafrost table, and net fluxes of CH4 is emitted from the soils in the upper part. During the observation periods, the methane concentrations in static chambers and emission rates of grassland and water surface displayed noticeable diurnal variations. The water/ice content may play important role in the spatial variations of methane emission rates. The emission rates of methane is weakly correlated with the ground temperatures at sampling depths and air temperatures. The observed emission rates of methane from the comparatively dry and sandy grassland soils are quite low compared with that observed in the permafrost regions in the high latitudes.  相似文献   

10.
正Objective The gas hydrates in the permafrost region of Qilian Mountain are characterized by low latitude,thin thickness,shallow burial depth,abundant coal seams,high contents of heavy hydrocarbons and multiple sets of source rocks.Up to date,the source of gas or the main source rocks of the Muli gas hydrates have remained  相似文献   

11.
积雪对多年冻土活动层和近地表的热状态具有重要影响。然而,积雪对祁连山区黑河上游地区多年冻土热状态的影响机制尚不清楚,迫切需要可靠的野外观测数据进行定量研究。基于两个典型野外监测站点2012—2019年观测数据,分析积雪对表面能量平衡、5 cm地表热通量及活动层热状态的影响。结果表明：厚度约21 cm的积雪在秋冬季对活动层具有保温作用;2013—2018年,俄博岭（EB）和野牛沟（PT1）监测场,活动层厚度分别为61~86 cm和159~164 cm,平均活动层厚度分别为74.2 cm和162.1 cm。受积雪影响,相隔两年（2015—2017年）的活动层厚度变化达25 cm。定量分析了祁连山积雪对多年冻土热状态的影响,为未来祁连山相关研究提供重要资料。  相似文献   

12.
青藏高原西大滩多年冻土活动层土壤性状与地表植被的关系   总被引：12，自引：11，他引：1  
以青藏高原多年冻土区北界的西大滩为研究基点, 选取多年冻土不同退化阶段的两个样地, 对植被分布特征、 冻土活动层和土壤特性等进行调查监测, 同时分析不同活动层状态下土壤水热、 养分和地表植被特征变化及相互间的作用关系. 结果表明: 西大滩地区的植被以浅根系植物为主, 0~10 cm的表层土壤中地下生物量约占地下生物总量的63%和62.2%之多. 在气候条件基本一致的情况下, 多年冻土的存在情况及活动层土壤水热状况对植被生态系统的演变起决定性作用. 高地表植被覆盖下的冻土土壤水热调节能力强, 有助于延缓冻土退化过程. 西大滩土壤全氮、 碱解氮、 速效钾与有机质含量密切相关, 含量随冻土退化明显减少, 且随土层深度的变化曲线表现为相同的趋势. 土壤表层养分和速效养分受冻土退化程度的影响较大.  相似文献   

13.
上新世湖相纹泥及其环境信息与时间标尺记录   总被引：6，自引：3，他引：3       下载免费PDF全文
纹泥反映了湖相沉积物中特有的沉积韵律,是气候的季节变化和年际变化的产物。山西榆社张村地区上新世晚期的湖心相沉积中发育了极为完好的纹泥剖面。纹泥深浅相间形成清晰的纹理,分别代表夏秋和冬春。一深一浅组成一对,代表一年。纹泥层的单层厚度平均为0．12～0．25mm／条,薄者＜0．1mm／条,厚者可达0．3mm／条。暗色纹泥层的厚度大于浅色纹泥层。暗色纹泥的有机质含量丰富,木本植物孢粉占优势,同时CaO的含量低;浅色纹泥恰好相反。湖相纹泥具有建立高分辨率时间标尺和环境演化序列的特殊优越条件。  相似文献   

14.
受气温变化影响,浅层冻土滑坡失稳涉及水分的固液相态转换,是一个复杂的水热力耦合过程。为揭示气温变化对多年冻土斜坡稳定性的影响,基于冻土水热力耦合数值模型,模拟了2020—2024年青海省多年冻土区斜坡水热力演化过程。研究结果表明:水分迁移速率呈周期性变化,每年5—10月活动层融化程度高,总体积含水率变化趋势显著;夏季多年冻土上限以下的高含冰量土层融化产生厚度约15 cm的富水层,孔隙水压难以消散;4年间多年冻土上限下移10.4 cm,导致活动层和富水层的厚度增大,上覆融土下滑力增大、抗滑力减小,土体抗剪强度进一步下降;活动层土体每年产生数厘米冻胀融沉变形,抗剪强度不断劣化,坡脚处最容易形成薄弱带。  相似文献   

15.
祁连山区黑河上游俄博岭多年冻土区活动层碳储量研究   总被引：2，自引：2，他引：0  
为了探索在全球气候变化背景下多年冻土区碳储量现状, 通过野外实地勘探和室内实验, 对黑河上游俄博岭多年冻土区地貌特征及不同海拔活动层内的碳储量进行考察和估算. 结果表明: 黑河上游俄博岭冰缘现象显著, 土壤季节冻融过程活跃, 且活动层中碳储量丰富. 在研究区约2.5×106 m2 的范围内, 活动层平均厚度约为1.1 m, 活动层土壤有机质平均含量约为72.1%, 碳储量估算约为1.57 Mt C. 活动层不同深度处有机质含量呈现不同的变化规律. 随着活动层深度增加, 土壤有机质的含量逐渐降低, 在多年冻土上限附近有机质含量较高. 另外, 活动层有机质含量随着海拔和土壤含水量的不同而变化, 同时多年冻土区微地形和地质条件也对有机质含量具有重要的影响.  相似文献   

16.
活动层含水量是表征多年冻土区气候、水文和生态过程的关键参数。长期以来,由于受多年冻土区活动层水分实测样点数量稀少的限制,各类基于遥感反演、模式模拟乃至数据融合和同化等手段生产的土壤水分空间数据均存在着较大的误差。2020年10—11月在青藏高原腹地（沱沱河源区）测定了 1 072组活动层土壤含水量数据并进行分析,探讨了该时段该区域活动层土壤水分的空间差异,并与全球陆面数据同化系统数据产品（GLDAS-Noah）和欧洲中期天气预报中心发布的第五代再分析资料（ERA5-Land）进行了对比分析。结果表明,在该区域平均厚度为2.72 m的活动层内,土壤质量含水量（总含水量）约为14.0%,活动层土壤含水量与植被发育情况存在正相关关系。除高寒沼泽草甸类型外,高寒草甸与高寒草原类型的活动层含水量随深度的增加呈现出先减小后增大的变化趋势。不同坡位类型的活动层含水量呈上坡位>下坡位>中坡位>平坡位,阳坡水分高于阴坡且两者活动层剖面水分变化相似。多年冻土区浅表层0~350 cm深度范围内的土壤含水量大于区内融区同深度的土壤含水量,两者土壤剖面水分分布均呈现出先增大后减小再增大的特征。该区域的GLDAS-Noah同化水分产品与实测数据对比的误差在10%以内,比ERA5-Land再分析土壤水分数据更为准确,但两种数据产品对土壤剖面上的水分垂直分布情况描述均与实测数据有较大差异。该研究结果可以为数据同化系统的模式冻融参数化方案优化及遥感水分产品研发提供科学依据。  相似文献   

17.
杨成松  程国栋 《冰川冻土》2011,33(3):461-468
对1961-2100年IPCC气候模拟与预测结果进行降尺度处理,得到铁路沿线空间分辨率为1km、时间分辨率为1h的大气边界条件.对铁路和公路沿线钻孔资料在垂直和水平两个方向进行空间差值处理,得到水平1 km、垂直0.1m分辨率的沿线地下含水（冰）量的二维分布,作为初始条件.考虑气候模型预测误差和空间格网内地形的变化,以...  相似文献   

18.
Engineering geological problems of thaw-settlement and frost-heave occur frequently along the Qinghai–Xizang (Tibet) Highway (QXH) line and produce an adverse impact on roadbed stability. Eight monitoring sites were established along the QXH to investigate the engineering geological characteristics and environmental process of permafrost, including the upper and lower boundary of the active layer under the natural surface, the seasonal freeze–thaw depth under the asphalt pavement, the permafrost table temperature and roadbed stability. The investigation results show that the active layer thickness and permafrost table temperature under an asphalt pavement are higher than under a natural surface due to the absorption heat and reduced evaporation capability of the asphalt pavement. The implication for highway design and construction in permafrost areas are discussed.  相似文献   

19.
为了研究马衔山多年冻土区和非多年冻土区土壤微生物碳氮、土壤酶活性的差异,选取多年冻土区、季节冻土区和交界区为对象,分析了0~30 cm土层微生物碳氮和转化酶、脲酶、中性磷酸酶、淀粉酶、过氧化氢酶、多酚氧化酶酶活性不同季节的变化特征。结果表明：全氮、总有机碳、微生物量碳氮与多数土壤酶之间呈显著相关关系。在不同区域,土壤微生物碳氮均在0~10 cm含量最高,10~20 cm次之,20~30 cm最低。土壤微生物碳氮在生长季表现为含量逐渐增加,但是多年冻土区与季节冻土区差异不大。土壤酶活性在深度方面表现与微生物碳氮含量变化一致。土壤酶并无的季节变化规律。在多年冻土区,转化酶、多酚氧化酶和磷酸酶活性明显高于非多年冻土区。本研究表明,尽管多年冻土区的植被和土壤总有机碳明显高于非多年冻土区,其土壤微生物碳氮含量相当,且一些土壤酶活性也相当。说明非多年冻土区土壤的生物地球化学相对强度较大。因此,多年冻土退化后可能会导致生态系统的退化。  相似文献   

20.
青藏高原多年冻土活动层厚度对气候变化的响应   总被引：12，自引：8，他引：4  
活动层厚度变化将会对多年冻土区生态系统、地气间能水平衡和碳循环等产生重要影响。利用Stefan公式模拟了1981-2010年青藏高原多年冻土区活动层厚度的分布和空间变化特征。结果表明：多年冻土区活动层厚度平均为2.39 m,活动层厚度在羌塘盆地最小,在多年冻土区边缘、祁连山、西昆仑山、念青唐古拉山活动层厚度较大。在气候变化条件下,青藏高原多年冻土区活动层厚度呈整体增大趋势,在1981-2010年,活动层厚度的变化量为-1.54~2.24 m,变化率为-5.90~10.13 cm·a-1,平均每年变化1.29 cm。活动层增厚趋势与年平均气温增大的趋势基本一致,这说明气候变化对活动层厚度变化有很大的影响。  相似文献   

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