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1.
为研究兴蒙造山带-华北克拉通地球化学走廊带区域地球化学组成及其横向空间变化,统计分析不同地理单元和五万图幅单元的REE含量并绘制其空间分布折线图.内蒙古半干旱草原土壤中稀土含量较低,与其草原沙土的粘土矿物较少有关;江苏北部冲积平原区的土壤中稀土含量较高,与降雨量存在良好空间对应关系.内蒙古红格尔到河北张家口,土壤与岩石∑REE的比值绝大多数小于1,REE发生贫化;山东章丘到江苏连云港,比值基本大于1,REE发生富集.华北克拉通内蒙地块土壤稀土特征与兴蒙造山带相似,可能受其草原沙土景观的影响.在不同构造单元之间,LREE与HREE亏损与富集的空间分布存在细微差异.结果表明:地理景观,特别是黏土矿物是影响土壤REE含量的重要因素,降雨量与REE存在良好空间对应关系,REE自身的地球化学性质的差异在土壤形成过程中对轻重稀土元素分异具有重要影响.   相似文献   

2.

Detecting subcropping mineralizations but also deeply buried mineralizations is one important goal in geochemical exploration. The identification of useful indicators for mineralization is a difficult task, as mineralization might be influenced by many factors, including location, investigated media and depth. Here, a statistical method is proposed which indicates chemical elements related to mineralization along a transect. Moreover, the method determines the potential area of the deposit along a transect. The identification is based on general additive models (GAMs) for the element concentrations across the spatial coordinate(s). The log-ratios of the GAM fits are taken to compute the curvature, where high and narrow curvature is supposed to indicate the mineralization area. By defining a measure for the quantification of high curvature, the log-ratios can be ranked, and elements can be identified that are indicative of the anomaly patterns.

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3.
The effective lithospheric elastic thickness of the continent is an important parameter for examination of the large-scale structure and analyses of the mechanism of isostatic compensation within the plate, and a parameter standing for the strength of the lithosphere.The Te values along Quanzhou-Heishui,the southeast section of the Arctic Ocean-Eurasian Continent-Pacific Ocean geoscience transect, are estimated by using the coherence technique developed by Forsyth.Studies of the feature of the coher-ence between gravity and topography suggest that at short wavelengths(6.6-100km)for each data box that is used to estimate Te,the plate is strong enough to support topographic loads and gravity and topog-raphy are uncorrelated.At long wavelengths where the plate is deflected by surface and subsurface loads are compensated by the flexure model.Sichuan land-stone with low heat-flow values has high Te values whereas in Ninghua,Datian,land-stone with high heat-flow values has low Te values,which reflects a correlation,low heat-flow values corresponding to high Te values and high heat-flow values corresponding to low Te values.Te values can be divided into two sections:northwest high section and southeast low sec-tion.There is roughly a positive correlation between crustal thickness and effective elastic thickness of the lithosphere.  相似文献   

4.
大陆岩石圈有效弹性厚度（Te）是表示岩石圈强度的参数，计算该参数对研究岩石圈大规模构造，分析大陆板块内的均衡补偿机制有一定意义。利用Forsyth提出的相关技术计算的北冰洋－欧亚大陆－太平洋地学断面东南段自黑水到泉州的Te值，并分析了重力和地形波长的相关性特征，初步认为：计算Te值所选的每个数据块在短波长（6.6-100km)内岩石圈板块的强度足以平衡地形负载，重力和地形不相关；在长波长（100－250km)内，地形及地下负载由弯曲模型补偿，岩石圈板块在地形及地下负载作用下而挠曲。断面通过地段具有较低热流密度值的陆核有较高的Te值，具有较高热流密度值的宁化，大田地区有较低的Te值，反映了较高的热流密度值对应较低的Te值，较低的热流密度值对应较高Te 值的关系，Te可分为南东低值段和北西高值段，地壳厚度大体上与Te值呈正相关关系。  相似文献   

5.
黑河流域生态水文样带调查   总被引：1，自引：0，他引：1  
样带研究是研究全球变化与陆地生态系统关系最有效的途径之一。通过在黑河流域上、中、下游分别确定具有代表性的流域样带和空间网格,系统调查植被、土壤、水文、地貌和气候特征及人类活动和社会经济特征,建立相应的数据库。完善流域整体概念的野外观测试验研究网络,形成以流域为单元、科学问题为导向的生态—水文过程的数据—模拟研究平台,使我国流域生态水文研究进入国际先进行列。  相似文献   

6.
To support the development of protocols for the proposed North American Soil Geochemical Landscapes project, whose objective is to establish baselines for the geochemistry of North American soils, two continental-scale transects across the United States and Canada were sampled in 2004. The sampling employed a spatially stratified random sampling design in order to estimate the variability between 40-km linear sampling units, within them, at sample sites, and due to sample preparation and analytical chemical procedures. The 40-km scale was chosen to be consistent with the density proposed for the continental-scale project. The two transects, north–south (N–S) from northern Manitoba to the USA–Mexico border near El Paso, Texas, and east–west (E–W) from the Virginia shore north of Washington, DC, to north of San Francisco, California, closely following the 38th parallel, have been studied individually. The purpose of this study was to determine if statistically significant systematic spatial variation occurred along the transects. Data for 38 major, minor and trace elements in A- and C-horizon soils where less than 5% of the data were below the detection limit were investigated by Analysis of Variance (ANOVA). A total of 15 elements (K, Na, As, Ba, Be, Ce, La, Mn, Nb, P, Rb, Sb, Th, Tl and W) demonstrated statistically significant (p < 0.05) variability at the between-40-km scale for both horizons along both transects. Only Cu failed to demonstrate significant variability at the between-40-km scale for both soil horizons along both transects.The patterns of relative variability differ by transect and horizon. The N–S transect A-horizon soils show significant between-40-km scale variability for 29 elements, with only 4 elements (Ca, Mg, Pb and Sr) showing in excess of 50% of their variability at the within-40-km and ‘at-site’ scales. In contrast, the C-horizon data demonstrate significant between-40-km scale variability for 26 elements, with 21 having in excess of 50% of their variability at the within-40-km and ‘at-site’ scales. In 36 instances, the ‘at-site’ variability is statistically significant in terms of the sample preparation and analysis variability. It is postulated that this contrast between the A- and C- horizons along the N–S transect, that is dominated by agricultural land uses, is due to the local homogenization of Ap-horizon soils by tillage reducing the ‘at-site’ variability. The spatial variability is distributed similarly between scales for the A- and C-horizon soils of the E–W transect. For all elements, there is significant variability at the within-40-km scale. Notwithstanding this, there is significant between-40-km variability for 28 and 20 of the elements in the A- and C-horizon data, respectively. The differences between the two transects are attributed to (1) geology, the N–S transect runs generally parallel to regional strikes, whereas the E–W transect runs across regional structures and lithologies; and (2) land use, with agricultural tillage dominating along the N–S transect. The spatial analysis of the transect data indicates that continental-scale maps demonstrating statistically significant patterns of geochemical variability may be prepared for many elements from data on soil samples collected on a 40 × 40 km grid or similar sampling designs resulting in a sample density of 1 site per 1600 km2.  相似文献   

7.
Submarine mass-transport deposits are important in many ancient and modern basins. Mass-transport deposits can play a significant role in exploration as reservoir, seal or source units. Although seismic data has advanced the knowledge about these deposits, more outcrop studies are needed to better understand gravity mass flows and predict the properties of their resultant deposits. It is proposed that sufficiently well-exposed outcrops of mass-transport deposits can be divided into three strain-dominant morphodomains: headwall, translational and toe. The outcrops of the Rapanui mass-transport deposit, part of the Lower Mount Messenger Formation in the Taranaki Basin, New Zealand, are exposed along a ca 4 km transect in coastal cliffs that enable the identification of the three morphodomains. The aim of this study is to characterize the stratigraphic and sedimentological nature of the Miocene-age Rapanui mass-transport deposit outcrops and the evolution of its basal shear zone. The basal shear zone of a mass-transport deposit is defined as the stratal zone formed in the interface between the overriding mass flow and the underlying in situ deposits or sea floor. Accordingly, the deformation structures in the Rapanui mass-transport deposit and the basal shear zone were documented in an established spatial framework. Traditional methodologies were used to characterize the sedimentology of the Rapanui mass-transport deposit. Data collected from intrafolial folds, rafted blocks and samples from the Rapanui mass-transport deposit were used to investigate strain and matrix texture evolution, estimate palaeoflow direction, and calculate yield strength and overpressure at time of deposition. Additionally, a one-dimensional numerical model was used to test sedimentation-driven overpressure as probable trigger. This work demonstrates that the basal shear zone, as well as the matrix texture of a mass-transport deposit, can vary spatially as sediments from underlying deposits are entrained during shear-derived mixing. This phenomenon can impact the seal potential of mass-transport deposits and their interaction with fluids in the subsurface.  相似文献   

8.
Errors in Phelps et al. ( 2014 ) arise from: (i) inclusion of the East Texas Basin and basin‐flank formations in a regional stratigraphic transect purported to represent the San Marcos Arch (axis of the Comanche Platform, central and south Texas); and (ii) revision of Edwards Group strata (Person Formation) that ignores well‐documented studies in the subsurface and adjacent outcrops in the Balcones fault zone and Edwards Plateau. Consequently, the Upper Albian Composite Sequence 104–101 of Phelps et al. ( 2014 ) should be revised from one cycle to three and the upper boundary of the Albian Supersequence should be elevated to 99·6 Ma.  相似文献   

9.
中国满洲里－绥芬河地学断面地球化学研究李双林，迟效国，尹冰川，戚长谋（中国科学院地球化学研究所贵阳５５０００２）（长春地质学院．长春１３００６１）关键词地学断面，地球化学分区，地球计学分带，构造演化地学断面的地球化学研究的目的是为了查明断面域地壳一上...  相似文献   

10.
格尔木——额济纳旗地学断面综合研究   总被引：17，自引：0，他引：17  
吴功建 《地质学报》1998,72(4):289-300
格尔木－额济纳旗地学断面从南到北穿过昆仑、祁连和北山３个构造带;在断面中划分出北昆仑－柴达木、中南祁连、北祁连、北山南部和北山北部５个构造地层地体;以及昆仑中央、北宗务隆、中祁连北缘、宽滩山及石板井－小黄山５条地体边界断裂带。断面内地壳厚度约５０￣７０ｋｍ,中南祁连地体地壳厚度最大,显示有山根存在;岩石圈厚度约１４０￣１５０ｋｍ。根据地球卫星及地震反射剖面结构表明：青藏高原为一个单独的岩石圈构造单  相似文献   

11.
We present n-alkane distributions in the soil samples along a transect from Lhasa on the Tibetan Plateau to Bharatpur in Nepal, which covers a large geographical area and a wide range of climatic conditions. These data allow us to assess the significance of n-alkane distributions in different vegetation types and their relationships to temperature and precipitation. In the tropical rainforest and broadleaved forest zones, n-alkanes exhibit a bimodal distribution pattern with dominant homologues around n-C_(31) and n-C_(23). The bimodal distribution of tropical rainforest n-alkanes may be a general pattern because of the presence of many lianas, epiphytic plants, algae and the strong microbial activity and degradation involved in the postdepositional process. In the warm-temperate mixed forest and needle-leaved forest zones, the long-chain alkanes have a pattern of n-C_(31) n-C_(33) n-C_(27). In the alpine shrub and grassland zone, although the most abundant homologue is n-C_(31) , relatively high n-C_(23) concentrations have also been observed in some samples. The statistical results show a good correlation between n-alkane proxies and climatic factors. The average chain length(ACL) values are positively correlated with precipitation and temperature across the transect. The carbon preference index(CPI) values show a negative correlation with temperature and precipitation along a Lhasa–Bharatpur transect. Although there is a positive relationship between ACL and temperature, it is difficult to separate the two climatic variables(temperature and precipitation) because they are well coupled in the monsoon region.  相似文献   

12.
A geotechnical information system (GTIS) was constructed within a spatial geographic information system (GIS) framework to reliably predict geotechnical information and accurately estimate site effects at Gyeongju, an urban area in South Korea. The system was built based on both collected and performed site investigation data in addition to acquired geo-knowledge data. Seismic zoning maps were constructed using the site period (T G) and mean shear wave velocity to a depth of 30 m (V S30), and these maps were presented as a regional strategy to mitigate earthquake-induced risks in the study area. In particular, the T G distribution map indicated the susceptibility to ground motion resonance in periods ranging from 0.2 to 0.5 s and the corresponding seismic vulnerability of buildings with two to five stories. Seismic zonation of site classification according to V S30 values was also performed to determine the site amplification coefficients for seismic design and seismic performance evaluation at any site and administrative subunit in the study area. In addition, we investigated the site effects according to subsurface and surface ground irregularities at Gyeongju by seismic response analyses in time domains based on both two- and three-dimensional spatial finite element models, which were generated using spatial interface coordinates between geotechnical subsurface layers predicted by the GTIS. This practical study verified that spatial GIS-based geotechnical information can be a very useful resource in determining how to best mitigate seismic hazards, particularly in urban areas.  相似文献   

13.
In this study, results of GPR profiling related to mapping of subsurface sedimentary layers at tsunami affected Karaikal beach are presented . A 400 MHz antenna was used for profiling along 262 m stretch of transect from beach to backshore areas with penetration of about 2.0 m depth (50 ns two-way travel time). The velocity analysis was carried out to estimate the depth information along the GPR profile. Based on the significant changes in the reflection amplitude, three different zones are marked and the upper zone is noticed with less moisture compared to other two (saturated) zones. The water table is noticed to vary from 0.5 to 0.75 m depth (12–15 ns) as moving away from the coastline. Buried erosional surface is observed at 1.5 m depth (40–42 ns), which represents the limit up to which the extreme event acted upon. In other words, it is the depth to which the tsunami sediments have been piled up to about 1.5 m thickness. Three field test pits were made along the transect and sedimentary sequences were recorded. The sand layers, especially, heavy mineral layers, recorded in the test pits indicate a positive correlation with the amplitude and velocity changes in the GPR profile. Such interpretation seems to be difficult in the middle zone due to its water saturation condition. But it is fairly clear in the lower zone located just below the erosional surface where the strata is comparatively more compact. The inferences from the GPR profile thus provide a lucid insight to the subsurface sediment sequences of the tsunami sediments in the Karaikal beach.  相似文献   

14.
Significant spatial variability of water fluxes may exist at the water-sediment interface in river channels and has great influence on a variety of water issues. Understanding the complicated flow systems controlling the flux exchanges along an entire river is often limited due to averaging of parameters or the small number of discrete point measurements usually used. This study investigated the spatial pattern of the hyporheic flux exchange across a river transect in China, using the heat tracing approach. This was done with measurements of temperature at high spatial resolution during a 64-h monitoring period and using the data to identify the spatial pattern of the hyporheic exchange flux with the aid of a one-dimensional conduction-advection-dispersion model (VFLUX). The threshold of neutral exchange was considered as 126 L m?2 d?1 in this study and the heat tracing results showed that the change patterns of vertical hyporheic flux varied with buried depth along the river transect; however, the hyporheic flux was not simply controlled by the streambed hydraulic conductivity and water depth in the river transect. Also, lateral flow dominated the hyporheic process within the shallow high-permeability streambed, while the vertical flow was dominant in the deep low-permeability streambed. The spatial pattern of hyporheic exchange across the river transect was naturally controlled by the heterogeneity of the streambed and the bedform of the stream cross-section. Consequently, a two-dimensional conceptual illustration of the hyporheic process across the river transect is proposed, which could be applicable to river transects of similar conditions.  相似文献   

15.
Falling‐stage deltas are predicted by sequence stratigraphic models, yet few reliable criteria are available to diagnose falling‐stage deltaic systems in surface exposures. Recent work on the Upper Cretaceous (Turonian) Ferron Sandstone in the western Henry Mountains Syncline of south‐central Utah has established its environment of deposition as a series of modest‐sized (5 to 20 km wide), probably asymmetrical, mixed‐influence deltas (‘Ferron Notom Delta’) that dispersed sediment eastwards from the rising Sevier orogenic hinterland into the Western Cordilleran Foreland Basin. Analysis of sandstone body stacking patterns in a 67 km long, depositional strike‐parallel (north–south) transect indicates that the growth of successive deltas was strongly forced by synsedimentary growth of a long wavelength (ca 100 km), 50 m amplitude fold structure. Herein, two discrete areas within this transect, superbly exposed in three dimensions, are documented in order to determine the details of stratal stacking patterns in the depositional dip direction, and thereby to assess the stratigraphic context of the Ferron Notom Delta. In the two study areas, dip transects expose facies representing river mouth bar to distal delta front environments over distances of 2 to 4 km. Key stratal packages are clinothems that offlap, downlap, and describe descending regressive trajectories with respective to basal and top datums; they are interpreted as the product of relative sea‐level fall. The vertical extent of clinoforms suggests that deltas prograded into <30 m of water. Furthermore, these deltaic successions preserve abundant evidence of delta front slope failure, growth faulting, and incision and filling of deep (<15 m) slope gullies. Gully fills are composed of chaotic intraformational breccia and/or massive sandstone, and constitute linear, ‘shoestring’ sandbodies in the distal portions of individual palaeodelta systems. They are interpreted to have been cut and filled during the late falling‐stage and lowstand of relative sea‐level cycles. The north–south distribution of the stratal style described above seems to be focused on the flanks of the growth anticline, and so the numerous falling‐stage systems tracts preserved within the Ferron Notom Delta probably owe their origin to synsedimentary structural growth, and the unstable fluid pressure regime that this growth imposed on the sea floor and shallow subsurface.  相似文献   

16.
The purpose of this study is to develop a geostatistical model to evaluate the spatial and depth variability of Standard Penetration Test (SPT) data from Bangalore, India. The database consists of 766 boreholes spread over a 220 km2 area, with several SPT values (N) in each of them. The geostatistical analysis is done for N corrected (N corrected) values. The N corrected value has been corrected for different parameters such as overburden stress, size of the bore hole, type of sampler, hammer energy and length of the connecting rod. The knowledge of the semivariogram of the SPT data is used with kriging theory to estimate the values at points in the subsurface of Bangalore where field measurements are not available. The model is used to compute the variance of estimated data. The model predicts reasonably well the SPT data. The geostatistical model provides valuable results that can be used for seismic hazard analysis, site response and liquefaction studies for the development of microzonation maps. The predicted N values from the developed model can also be used to estimate the subsurface information, allowable bearing pressure of soils and elastic modulus of soils.  相似文献   

17.
Non-steady state deformation and annealing experiments on vein quartz are designed to simulate earthquake-driven episodic deformation in the middle crust. Three types of experiments were carried out using a modified Griggs-type solid medium deformation apparatus. All three start with high stress deformation at a temperature of 400 °C and a constant strain rate of 10− 4 s− 1 (type A), some are followed by annealing in the stability field of α-quartz for 14–15 h at zero nominal differential stress and temperatures of 800–1000 °C (type A + B), or by annealing for 15 h at 900 °C and at a residual stress (type A + C).The quartz samples reveal a very high strength > 2 GPa at a few percent of permanent strain. The microstructures after short-term high stress deformation (type A) record localized brittle and plastic deformation. Statisc annealing (type A + B) results in recrystallisation restricted to the highly damaged zones. The new grains aligned in strings and without crystallographic preferred orientation, indicate nucleation and growth. Annealing at non-hydrostatic conditions (type A + C) results in shear zones that also develop from deformation bands or cracks that formed during the preceding high stress deformation. In this case, however, the recrystallised zone is several grain diameters wide, the grains are elongate, and a marked crystallographic preferred orientation indicates flow by dislocation creep with dynamic recrystallisation. Quartz microstructures identical to those produced in type A + B experiments are observed in cores recovered from Long Valley Exploratory Well in the Quaternary Long Valley Caldera, California, with considerable seismic activity.The experiments demonstrate the behaviour of quartz at coseismic loading (type A) and subsequent static annealing (type A + B) or creep at decaying stress (type A + C) in the middle crust. The experimentally produced microfabrics allow to identify similar processes and conditions in exhumed rocks.  相似文献   

18.
The shear wave velocity (VS) profile based on the dispersive characteristics of fundamental mode of Rayleigh type surface waves indicate underground stiffness change with depth as well as near surface stiffness. The most important utility of shear wave velocity (VS) is to estimate the liquefaction hazard potential of an area particularly in seismically active region. Rayleigh type surface waves were utilized to estimate the velocity (VS) of shallow subsurface covering a depth range of 30–50 m employing multichannel analysis of surface waves. The liquefaction hazard map predicts an approximate percentage of an area that will have surface manifestation of liquefaction during an earth quake. The surface wave data acquired in an earth quake prone region of Jabalpur (Seismic zone III), India, yields a velocity (VS) range of 200–750 m/s corresponding to the subsurface depth of 30–35 m. The results were analyzed for possible liquefaction hazard in the study area and presented here besides the N values.  相似文献   

19.
Dividing a catchment to subcatchment or hillslope scales allows for better scrutiny of the changes in spatial distribution of rainfall, soil attributes and plant cover across the catchment. An instantaneous unit hydrograph model is suggested for simulating runoff hydrographs for complex hillslopes. This model is able to estimate surface and subsurface flows of the catchment based on the Dunne-Black mechanism. For this purpose, a saturation model is used to separate the saturated and unsaturated zones in complex hillslopes. The profile curvatures (concave, straight and convex) and plan shapes (convergent, parallel and divergent) of complex hillslopes are considered, in order to compute the travel time of surface and subsurface flows. The model was used for prediction of the direct runoff hydrograph and subsurface flow hydrograph of Walnut Gulch No. 125 catchment in Arizona (USA). Based on results, the geometry of hillslopes can change the peak of the direct runoff hydrograph up to two-fold, either higher or lower. The divergent hillslopes show higher peaks in comparison with the parallel and convergent hillslopes. The highest and lowest peak flows correspond to divergent-concave and convergent-straight hillslopes, respectively.  相似文献   

20.
Sinkhole collapse is one of the main limitations on the development of karst areas, especially where bedrock is covered by unconsolidated material. Studies of sinkhole formation have shown that sinkholes are likely to develop in cutter (enlarged joint) zones as a result of subterranean erosion by flowing groundwater. Electrical resistivity imaging or tomography (RESTOM) is well suited to mapping sinkholes because of the ability of the technique for detecting resistive features and discriminating subtle resistivity variations. Two-dimensional electrical resistivity tomography surveys were conducted at two sinkhole sites near Cheria city where limestone is covered by about 10 m of clayey soils. A Wenner transect was conducted between the two sinkholes. The electrode spacing was 2 m. The length of transect is about 80 m. The survey results suggest that RESTOM is an ideal geophysical tool to aid in the detection and monitoring of sinkholes and other subsurface cavities.  相似文献   

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