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991.
本文把油气藏上方划分为五个地球化学带。通过对地壳中含量较高的变价元素铁的分析,认为在过渡带Ⅲ_1中将富集成岩磁铁矿,在还原柱与围岩的接触面上存在过剩电位差,可将其等效为双电层.成岩磁铁矿产生弱磁异常,双电层引起自然电位异常。从而把磁法和自然电场法直接找油气的理论统一为变价元素铁在不同的环境下所发生的物理化学作用上。利用简单的几何形体代表各地球化学带建立了磁模型,把双电层等效成电偶层建立了自电模型,最后对玉门某构造上磁异常和自电异常进行了解释. 相似文献
992.
S. LLANA-FÚNEZ K. H. BRODIE E. H. RUTTER J. C. ARKWRIGHT 《Journal of Metamorphic Geology》2007,25(4):423-438
A series of dehydration experiments was carried out on both intact rock and cold-pressed powdered samples of serpentinite at temperatures in the range 535–610 °C, 100–170 °C above the onset of the breakdown temperature of 435 °C. Pore water pressures near 120 MPa were servo-controlled using a pore volumometer that also allowed dehydration reaction progress to be monitored through measurement of the amount of evolved water. Effective hydrostatic confining pressures were varied between 0 and 113 MPa. The reaction rate of intact specimens of initially near-zero porosity was constant up to 50–80% reaction progress at any given temperature, but decreased progressively as transformation approached completion. Water expulsion rates were not substantially affected by elevation of effective pressures that remained insufficient to cause major pore collapse. An Arrhenius relation links reaction rate to temperature with an activation enthalpy of 429 ± 201 and 521 ± 52 kJ mol−1 for powdered and intact specimens, respectively. Microstructural study of intact specimens showed extensive nucleation beginning at pre-existing cracks, veins and grain boundaries, and progressing into the interior of the lizardite grains. Extrapolation of these data towards equilibrium temperature provides an upper bound on the kinetics of this reaction in nature. 相似文献
993.
A high-resolution, biostratigraphic (calcareous nannofossils, calpionellids), chemostratigraphic (C-isotope) and cyclostratigraphic (magnetic susceptibility) study was performed on the marl–limestone alternations of the Upper Berriasian–Valanginian Orpierre section, deposited in the hemipelagic setting of the Vocontian Basin (SE France). The main aims of this study were to detect orbital forcing, to estimate the duration of the Valanginian “Weissert” episode, and to discuss the palaeoenvironmental implications. Detailed calcareous nannofossil biochronology allowed the recognition of Upper Berriasian–Lower Hauterivian biohorizons. The general trends of the δ13C curve and the major positive C-isotope excursion (amplitude of 1.8‰) recorded at the Orpierre section are very similar to those found in other sections worldwide. Spectral analysis applied on high-resolution magnetic susceptibility (MS) variations coupled with frequency ratio method reveals a strong cyclic pattern related to the Earth's orbital parameters (precession, obliquity and eccentricity). The prominent 405 kyr eccentricity cycle in the MS signal and has been used as a geochronometer to time calibrate the section. The duration of the Weissert episode was estimated as 2.08 Myr. This duration is coherent with those obtained from the Umbria Marche Basin (∼2.3 Myr) and from the Angles section (∼2.14 Myr). Durations of more than 2 Myr suggest that a long perturbation in the dynamic of the global carbon cycle that is not compatible with the rapid and intense volcanic activity. Our cyclostratigraphic study indicates a minimal duration of 4.29 Myr for the Valanginian stage. The comparison between the MS signal at Orpierre and the spectral gamma-ray signal recently obtained in two composite sections of the Vocontian Basin allows to propose a revised duration for the Valanginian stage of 4.695 Myr instead of 5.08 Myr. 相似文献
994.
The present study deals with the application of analytical hierarchy process to prepare landslide hazard risk map of the Shivkhola Watershed applying remote sensing and geographic information system (GIS). Firstly, to integrate all the required thematic data layers and to prepare landslide susceptibility map, prioritised class rating value and prioritised factor rating value were obtained by developing couple-comparing matrix with a reasonable consistency and with the help of MATLAB software after Saaty. Three important risk factor/element maps, that is, weighted land use/land cover map, road contributing area map and settlement density map, were developed and their weighted linear combination was performed to prepare landslide risk exposure map. Then by integrating landslide susceptibility map and landslide risk exposure map, a classification was incorporated on ARC GIS Platform to prepare landslide hazard risk map. To evaluate the validity of the landslide hazard risk map, probability/chance of landslide hazard risk event has been estimated by means of frequency ratio between landslide hazard risk area (%) and number of risk events (%) for each landslide hazard risk class. Finally, an accuracy assessment was also made on ERDAS Imagine (8.5) which depicts that the classification accuracy of the landslide hazard risk map was 92.89 with overall Kappa statistics of 0.8929. 相似文献
995.
996.
Vijendra Kumar Pandey 《自然地理学》2013,34(6):510-536
Landslides are frequent natural disasters in mountainous regions, particularly in the Himalayas in India during the southwest monsoon season. Although scientific study of landslides has been in progress for years, no significant achievement has been made to preclude landsliding and allay disasters. This research was undertaken to understand the areal distribution of landslides based on geological formations and geomorphological processes, and to provide more precise information regarding slope instability and mechanisms of failure. After completing a landslide inventory, prepared through field investigation and satellite image analysis, 493 landslides, comprising 131 investigated in the field and 362 identified from satellite imagery, were identified and mapped. The areal distribution of these landslides shows that sites more prone to landsliding have moderate to steep slopes, the lithology of the Lesser Himalayan formations, and excavations for road corridors. Landslide susceptibility zones were delineated for the area using the weight-of-evidence method on the basis of the frequency and distribution of landslides. Weights of selected variables were computed on the basis of severity of triggering factors. The accuracy of landslide susceptibility zones, calculated statistically (R2 = .93), suggests high accuracy of the model for predicting landsliding in the area. 相似文献
997.
Integrated Water Resource Management (IWRM) becomes increasingly important in arid watersheds, where water resources are
scarce and demands are rising under increased population pressure. In this case study, we present the results from the Elqui Valley
in Chile, where water resources are shared between agriculture, mining operations, hydropower generation and drinking water for
nearby cities. An IWRM model was applied to visualize water resources distribution in the catchment and determine irrigation and
water use efficiencies. After calibration with observed surface and groundwater measurements, the model showed large differences
in efficiencies between different irrigation sectors. Most notably, irrigation sectors with the highest irrigation security, i.e.,
higher water rights per hectare, were characterized with lower water use efficiencies. Frequent water deficits were present in sectors
downstream of the main reservoir, which was related to limited water rights per hectare, lower irrigation efficiencies and
higher water demands due to larger agricultural areas. In subsequent scenario analyses, the model was used to evaluate the impact
of improved irrigation and water use efficiencies in these downstream sectors, to confirm an important reduction in water deficits,
except for drought years when surface water resources are insufficient. In a third scenario, groundwater resources were allowed to
compensate for water deficits, effectively reducing these in most irrigation sectors, especially during droughts. Expansion of the
current agricultural area by 37% was evaluated, as a future scenario, and was found to be unsustainable, as aquifer levels are lowered
to such levels that make annual recharge insufficient. 相似文献
998.
The Changbai Mountains,located in the temperate monsoon climate zone of East Asia,is an ideal loca-tion for the research on timberline response to global changes.In this study,the topsoils were collected from different vertical vegetation zones on the northern slope of the Changbai Mountains,Northeast China in August 2009,and phytoliths in the soil samples were extracted by using wet oxidation method and identified with Motic 2.0 microscope in laboratory.The results show that phytoliths are abundant in the ... 相似文献
999.
DONG Jin WANG Yong ZHANG ShiHong CHI ZhenQing YAO PeiYi & ZHAO ZhiLi 《中国科学:地球科学(英文版)》2012,(9):1494-1503
Spatial variations in lake sediments are a product of their depositional heterogeneities.To better correlate synchronous strata in Huangqihai Lake,two sections were excavated from the lake-center and the lake-shore.The study involved detailed lithology,mineralogy,and rock magnetic analysis.The results show that the frequency-dependent susceptibility,which is related to the content of super-paramagnetic minerals,is relatively easy to contrast between the two sections.However,mass susceptibility and saturation isothermal remanence,which are related to the content of total magnetic minerals,are difficult to contrast.A possible reason for this difference is that small-particle super-paramagnetic minerals are formed mainly during pedogenic processes,which correlates well with climate change and avoids the effects of local factors when corrections are made at the whole-lake scale.Both sections can be divided into three stages,which appear to be well correlated with previous results obtained through other environmental proxies. 相似文献
1000.