古代西域南道上的若干历史地理问题   总被引：1，自引：0，他引：1  

王北辰 《地理研究》1983,2(3):30-43

本文探讨塔克拉玛干沙漠南沿、和田以东至若羌间的几个历史地理问题。1,历史时期,塔里木盆地南沿上是否有过一条与北方塔里木河相对应的“南河”?笔者认为是没有的。2,自古以来,和田以东的绿洲数目是在逐期增多或是逐期减少?笔者认为是逐期增多。3,历史时期,和田以东出现过几处绿洲城镇废弃和交通路线改线的现象,笔者就其中的安迪尔、且末、尼雅三地的历史演变作了初步探讨。  相似文献   

一万年来白洋淀的扩张与收缩   总被引：5，自引：0，他引：5  

王会昌 《地理研究》1983,2(3):8-18

本文探讨了一万年来的全新世期间,白洋淀兴起、扩张和收缩的变迁过程,恢复了各个发展阶段的古湖淀范围,论述了相应时期的古环境特征,指出了白洋淀令后的演变趋势。  相似文献   

A technical note on seismic microzonation in the central United States     

Zhenming Wang 《Journal of Earth System Science》2008,117(2):749

Microzonation is an effort to evaluate and map potential hazards found in an area, urban area in particular, that could be induced by strong ground shaking during an earthquake. These hazards include: ground motion amplification, liquefaction, and slope failure. The microzonation maps, depicting ground-motion amplification, liquefaction, and landslide potentials, can be produced if the ground motion on bedrock (input) and the site conditions are known. These maps, in combination with ground-motion hazard maps (on bedrock), can be used to develop a variety of hazard mitigation strategies such as seismic risk assessment, emergency response and preparedness, and land-use planning. However, these maps have certain limitations that result from the nature of regional mapping, data limitations, generalization, and computer modeling. These microzonations show that when strong ground shaking occurs, damage is more likely to occur, or be more severe, in the higher hazard areas. The zones shown on the hazard maps should not serve as a substitute for site-specific evaluations.  相似文献   

湖南雪峰山地区沈家垭金矿成矿学及年代学研究   总被引：2，自引：0，他引：2  

陈富文  戴平云  梅玉萍  李华芹  王登红  蔡红 《地质学报》2008,82(7):906-2008-01-30

湘西沈家垭大型金矿是雪峰山地区颇具代表性的金矿床介绍,矿体分布于新元古界板溪群马底驿组第四岩性段中,矿化作用严格受北东东向沃溪和香草湾等深大断裂和唐浒坪复式背斜的联合控制。本次研究获得该矿床含金石英脉RbSr等时线年龄为90.6±3.2Ma,表明成矿作用发生于晚白垩世,成矿作用可能与燕山期区域性大规模的逆冲推覆作用密切相关,矿床成因类型为构造热液型。  相似文献   

广西大厂拉么锌铜多金属矿床成岩成矿作用年代学研究   总被引：20，自引：1，他引：19  

李华芹  王登红  梅玉萍  梁婷  陈振宇  郭春丽  应立娟 《地质学报》2008,82(7):912-2008-01-30

本文对广西大厂矿田拉么矿区内出露的酸性侵入岩和矿石进行了精细的年代学研究,分别获得龙箱盖含斑黑云母花岗岩锆石原位SHRIMP UPb和全岩RbSr等时线年龄为94±4Ma（95%可信度）和98.6±1.9Ma（95%可信度）,矽卡岩成矿期锌铜矿石中石英矿物RbSr等时线年龄为98.6±6Ma（95%可信度）。上述测定结果表明,拉么锌铜多金属矿床的成矿年龄与相关岩体的成岩年龄接近,均形成于早白垩世晚期。  相似文献   

赣南崇义—大余—上犹矿集区不同类型含矿石英中白云母40Ar/39Ar年龄及其地质意义   总被引：14，自引：0，他引：14  

刘善宝  王登红  陈毓川  李建康  应立娟  许建祥  曾载淋 《地质学报》2008,82(7):932-2008-01-30

崇义—大余—上犹矿集区是世界著名的黑钨矿床集中区,本文选择钨锡多金属硫化物石英脉型（柯树岭和漂塘矿床）和锡钨石英脉型（仙鹅塘矿床）3个矿床石英中的白云母开展40Ar/39Ar年代学研究,测得坪年龄分别是：钨锡多金属硫化物石英脉型是 158.9 ± 1.4 Ma（漂塘）、158.8 ± 1.2 Ma（柯树岭）;钨锡石英脉型的是231.4 ± 2.4 Ma（仙鹅塘）,在反等时线图上,其对应的截距年龄分别是158.8 ± 1.6 Ma、158.7 ± 1.9Ma和232.5 ± 2.4 Ma。由此表明,在崇余犹矿集区内存在两个不同成矿时期,即以黑钨矿为主的多金属硫化物石英脉型矿床形成于中侏罗世,集中于160~150Ma之间,与南岭地区钨锡矿床的主成矿期是一致的;而以锡石为主的,并含有大量白钨矿的石英脉型矿床可形成于印支期  相似文献   

Impact of land use covers upon karst processes in a typical Fengcong depression system of Nongla, Guangxi, China   总被引：2，自引：0，他引：2  

Cheng Zhang  Jianguo Pei  Yunqiu Xie  Jianhua Cao  Lanling Wang 《Environmental Geology》2008,55(8):1621-1626

The direction and intensity of karst processes can be deeply affected by soil physical and chemical variations which were resulted from land use. Taking Nongla Fengcong depression area, Mashan County, Guangxi as an example, authors discussed the impact of land use on karst processes based on the data of field limestone tablet. The results showed that the corrosional rates at varied soil depth are quite different. Corrosional rate in woodland and orchard is mostly bigger than 20 mg/a, which is much higher than that in tilled land and shrub. Generally, corrosional rate decreased from orchard, woodland, tilled land, fallow land and shrub successively, in which soil organic matter (OM) and soil pH are two major controlling factors: corrosion process is controlled remarkably by soil OM in woodland and orchard. The higher the organic matter content is and the less the pH value is, the higher the corrosional rate is. Owing to lower organic matter content, the corrosional rate is mainly affected by soil CO₂ in tilled land and shrub.  相似文献   

Correlations between heavy metals and organic carbon extracted by dry oxidation procedure in urban roadside soils   总被引：1，自引：0，他引：1  

Xue Song Wang 《Environmental Geology》2008,54(2):269-273

The organic fraction in soils has a significant influence on heavy metal transport. In this study, the organic carbon content was measured by dry oxidation procedure from 21 Xuzhou urban roadside soils to assess the relationships between the concentrations of heavy metals (Pb, Cu, Zn, and Cr) and the amount of organic carbon. The anthropogenic heavy metals (e.g. Pb, Cu, Zn) were strongly correlated with organic carbon (denoted by C_org−c) extracted by dry oxidation while natural heavy metal (e.g. Cr) showed no correlation to the C_org−c. The anthropogenic heavy metals were also strongly correlated with the amount of the total carbon. These results show that the anthropogenic heavy metals are mainly enriched in the organic matter in the Xuzhou urban roadside soils.  相似文献   

Response of groundwater chemistry to water deliveries in the lower reaches of Tarim River,Northwest China   总被引：2，自引：0，他引：2  

Yongjin Chen  Kefa Zhou  Yaning Chen  Weihong Li  Jiazhen Liu  Tao Wang 《Environmental Geology》2008,53(6):1365-1373

In this paper, we analysed the monitored data from nine groundwater-monitoring transects in the lower reaches of Tarim River during the five times of stream water deliveries to the river transect where the stream flow ceased. The results showed that the groundwater depth in the lower reaches of Tarim River rose from −9.30 m before the conveyances to −8.17 and −6.50 m after the first and second conveyances, −5.81 and −6.00 m after the third and fourth the conveyance, and −4.73 m after the fifth. The horizontal extent of groundwater recharge was gradually enlarged along both sides of the channel of conveyance, i.e., from 250 m in width after the first conveyance to 1,050 m away from the channel after the fourth delivery. With the rising groundwater level, the concentrations of major anions Cl⁻, SO₄²⁻ and cations Ca²⁺, Mg²⁺, Na⁺, as well as total dissolved solids (TDS) in groundwater underwent a significant change. The spatial variations in groundwater chemistry indicated that the groundwater chemistry at the transect near Daxihaizi Reservoir changed earlier than that farther from it. In the same transect, the chemical variations were earlier in the monitoring well close to watercourse than that farther away from the stream. In general, the concentration of the major ions and TDS at each monitoring well increased remarkably when the water delivery started, and decreased with the continued water delivery, and then increased once again at the end of the study period. Hence, the whole study period may be divided into three stages: the initial stage, the intermediate stage and the later stage. According to the three stages of groundwater chemistry reaction to water delivery and the relationships between groundwater chemical properties and groundwater depths, we educe that under the situation of water delivery, the optimum groundwater depth in the lower reaches of the Tarim River should be −5 m.  相似文献   

Natural radioactivity in sediment of Wei River,China   总被引：1，自引：0，他引：1  

Xinwei Lu  Xiaolan Zhang  Fengling Wang 《Environmental Geology》2008,53(7):1475-1481

The concentrations of natural radionuclides in sediment of Wei River of China were measured using γ-ray spectrometry with the aim of estimating the radiation hazard as establishing a database for radioactivity levels of river sediment of China. The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in sediment samples ranged from 10.4 to 39.9 Bq kg⁻¹, 15.3 to 54.8 Bq kg⁻¹ and 514.8 to 1,175.5 Bq kg⁻¹, respectively. The concentrations of these radionuclides were compared with the typical world values and the average activities of Chinese soil and Shaanxi soil. Radium equivalent activity (Ra_eq), external hazard index (H _ex) and representative level index (I _γr) were calculated for the samples to assess the radiation hazards arising due to the use of these sediment samples in the construction of dwellings. All the sediment samples have Ra_eq lower than the limit of 370 Bq kg⁻¹, H _ex less than unity and I _γr close to 1 Bq kg⁻¹. The overall mean outdoor terrestrial gamma dose rate is 64.8 nGy h⁻¹ and the corresponding outdoor annual effective dose is 0.079 mSv. None of the studied location is considered a radiological risk and sediment can be safely used in construction.  相似文献