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71.
松辽分水岭东段白土山组成因与时代 总被引:3,自引:1,他引:3
综合考虑松辽分水岭东段地区白土山组的地层分布、沉积特征、地貌部位及第四纪以来松辽分水岭的演化过程、松辽水系的变迁,认为其为河流冲积物,形成时代为早更新世早期。 相似文献
72.
73.
海河平原地下水资源可持续利用前景评价 总被引:7,自引:0,他引:7
本文通过综合分析海河平原地下水资源盈余量以及建立典型三级区平原开采系数与地下水水位下降速率、地面沉降速率的关系,分析了各三级区平原依靠环境容量可扩大开采量,根据疏干时限性评价指标对海河平原地下水的开采潜力进行了评价,客观展现了维持现状开采条件下研究区地下水资源可持续利用的暗淡前景。 相似文献
74.
采用一系列温和的化学降解法对松辽盆地南部嫩江组烃源岩的干酪根进行连续的选择性化学降解,并对不同降解产物进行色谱—同位素比值质谱分析。研究表明碱性水解和脱硫产物以一元脂肪酸和正构烷烃为主,其中正构烷烃碳同位素分布曲线呈现一定的“负倾”(即随碳数增加呈现逐渐贫13C)趋势;一元脂肪酸以C16和C18为主,具有明显的偶碳优势,与同碳数的正构烷烃具有相似的碳同位素组成。氧化产物则以一元脂肪酸和α,ω 二元脂肪酸为主,一元脂肪酸低碳数部分呈现“负倾”趋势,高碳数部分则呈现“正倾”的趋势;α,ω 二元脂肪酸与低碳数的一元脂肪酸具有相似的分布,表明它们可能具有相同的母源。对比研究表明JL 30抽提物中正构烷烃可能存在混源的影响,其碳同位素组成是多源混合的结果。 相似文献
75.
María Gabriela García Ondra Sracek Diego Sebastián Fernández Margarita del Valle Hidalgo 《Environmental Geology》2007,52(7):1261-1275
The concentration of arsenic measured in groundwater from three aquifers in the study area located in the Eastern Tucuman
province, Argentina, mostly depends on the lithology, but the spatial and temporal variations of concentrations seem to be
also controlled by pH changes, climatic factors, and human perturbations. The highest concentrations of As (more than 1,000 μg
L−1) were found in the shallow aquifer, made of As-rich loess, while the lowest concentrations were measured in the deep confined
aquifer, consisting of alternating layers of alluvial sands/gravels and clays. Intermediate values were measured in the semiconfined
aquifer made of the fluvial sediments deposited in the Salí River valley, that alternate in the upper part of the sedimentary
sequence with layers of loess. Because most of As in the loess is considered to be adsorbed onto Fe-oxyhydroxide coatings,
the increase of pH in the flow direction (west-east) leads to increasing arsenic concentrations towards the eastern border
of the study area. The decomposition of organic wastes poured into the Salí River or associated with local and diffuse sources
of contamination in the eastern part of the study area depletes dissolved oxygen, which leads to the reductive dissolution
of Fe and Mn oxyhydroxides, and to the subsequent release of the adsorbed and co-precipitated As. This process mainly affects
shallow groundwater and the upper part of the semiconfined aquifer. Geochemical and hydrological data also suggest that rising
water table levels at the end of the wet season may also lead to reductive dissolution of As-rich Fe oxyhydroxides in the
shallow aquifer. 相似文献
76.
Origin and stratigraphy of phreatomagmatic deposits at the Pleistocene Sinker Butte Volcano, Western Snake River Plain, Idaho 总被引:1,自引:3,他引:1
Brittany D. Brand Craig M. White 《Journal of Volcanology and Geothermal Research》2007,160(3-4):319-339
Sinker Butte is the erosional remnant of a very large basaltic tuff cone of middle Pleistocene age located at the southern edge of the western Snake River Plain. Phreatomagmatic tephras are exposed in complete sections up to 100 m thick in the walls of the Snake River Canyon, creating an unusual opportunity to study the deposits produced by this volcano through its entire sequence of explosive eruptions. The main objectives of the study were to determine the overall evolution of the Sinker Butte volcano while focusing particularly on the tephras produced by its phreatomagmatic eruptions. Toward this end, twenty-three detailed stratigraphic sections ranging from 20 to 100 m thick were examined and measured in canyon walls exposing tephras deposited around 180° of the circumference of the volcano.Three main rock units are recognized in canyon walls at Sinker Butte: a lower sequence composed of numerous thin basaltic lava flows, an intermediate sequence of phreatomagmatic tephras, and a capping sequence of welded basaltic spatter and more lava flows. We subdivide the phreatomagmatic deposits into two main parts, a series of reworked, mostly subaqueously deposited tephras and a more voluminous sequence of overlying subaerial surge and fall deposits. Most of the reworked deposits are gray in color and exhibit features such as channel scour and fill, planar-stratification, high and low angle cross-stratification, trough cross-stratification, and Bouma-turbidite sequences consistent with their being deposited in shallow standing water or in braided streams. The overlying subaerial deposits are commonly brown or orange in color due to palagonitization. They display a wide variety of bedding types and sedimentary structures consistent with deposition by base surges, wet to dry pyroclastic fall events, and water saturated debris flows.Proximal sections through the subaerial tephras exhibit large regressive cross-strata, planar bedding, and bomb sags suggesting deposition by wet base surges and tephra fallout. Medial and distal deposits consist of a thick sequence of well-bedded tephras; however, the cross-stratified base-surge deposits are thinner and interbedded within the fallout deposits. The average wavelength and amplitude of the cross strata continue to decrease with distance from the vent. These bedded surge and fall deposits grade upward into dominantly fall deposits containing 75–95% juvenile vesiculated clasts and localized layers of welded spatter, indicating a greatly reduced water-melt ratio. Overlying these “dryer” deposits are massive tuff breccias that were probably deposited as water saturated debris flows (lahars). The first appearance of rounded river gravels in these massive tuff breccias indicates downward coring of the diatreme and entrainment of country rock from lower in the stratigraphic section. The “wetter” nature of these deposits suggests a renewed source of external water. The massive deposits grade upward into wet fallout tephras and the phreatomagmatic sequence ends with a dry scoria fall deposit overlain by welded spatter and lava flows.Field observations and two new 40Ar–39Ar incremental heating dates suggest the succession of lavas and tephra deposits exposed in this part of the Snake River canyon may all have been erupted from a closely related complex of vents at Sinker Butte. We propose that initial eruptions of lava flows built a small shield edifice that dammed or disrupted the flow of the ancestral Snake River. The shift from effusive to explosive eruptions occurred when the surface water or rising ground water gained access to the vent. As the river cut a new channel around the lava dam, water levels dropped and the volcano returned to an effusive style of eruption. 相似文献
77.
东北平原西部沙地近10年的沙质荒漠化 总被引:35,自引:0,他引:35
东北平原西部沙地位于欧亚大陆中纬度巨型沙带的东部边缘,为我国沙质荒漠化土地的东缘,是我国自然环境最好的沙区,随着经济的发展,生态环境遭到严重破坏,沙质荒漠化景观日益明显,尤其是南部的科尔沁沙地,沙质荒漠化已十分严重,已经超过与其相邻的西部环境条件更差的沙区,利用RS和GIS,根据NOAA/AVHRR数据建立的沙质荒漠化监测指标,对东北平原西部沙地沙质荒膜化现代过程进行了动态监测,在此基础上利用TM数据对沙质荒漠化的发展方式与成因进行了深入的探讨,并有针对性地提出了区域沙质荒漠化的防治对策。 相似文献
78.
The west sandy land of the Northeast China Plain is located in the eastern huge sandy belt of mid-latitude in Eurasia and the eastern fringe of desertified land with best bio-climatic conditions in China. Over-extensive regional development has made the desertified landscape very obvious, especially in Horqin Sandy Land where desertification is more serious than that in Hushandake Sandy Land with worse bio-climatic conditions. There were some researches on the desertification in western No… 相似文献
79.
依据松辽盆地深部地震资料 ,分析了深部地震反射特征及深部层圈结构特征。应用“非对称伸展作用”理论 ,通过对深部层圈结构、基底构造特征、侏罗系断陷构造格局的综合分析 ,建立了松辽盆地北部的盆地成因模式。从该模式可看出 ,基底滑脱拆离断层控制了侏罗系断陷的发育。 相似文献
80.