重庆老龙洞地下河不同部位水体、表层沉积物有机氯农药含量及组成研究

为研究重庆老龙洞地下河不同部位水体、表层沉积物有机氯农药分布特征,用气相色谱-微池电子捕获检测器(GC-μECD)分析了样品中OCPs含量。结果表明:研究区水样、表层沉积物中OCPs检出率均为100 %,其浓度在时间上存在季节差异,水体中OCPs、DDTs、HCHs含量丰水期小于枯水期,而在表层沉积物中则表现为OCPs、HCHs丰水期大于枯水期,DDTs丰水期小于枯水期;在空间上则表现为水体中有机氯农药总体下游大于上游,而沉积物中则与之相反。通过对比可知,岩溶洞穴环境由于缺乏光照,空气流动缓慢,生物活动不频繁,使水体中的HCHs不易降解,沉积物中的HCHs不易重新释放而浓度高于洞外。枯水期由于洞内流速较小且变幅不大,水体中的DDTs大量沉积因而其浓度低于洞口,而丰水期洞口因受大量雨水的稀释作用DDTs反而低于洞内的含量;洞内沉积物中的DDTs则因洞内环境恒定不易重新释放和枯水期水体中的大量沉积而一直高于洞外。洞穴环境、不同污水汇入对水体中DDTs和表层沉积物中DDTs、HCHs的组成结构均有不同程度的影响,而对水体中HCHs的组成结构影响不大。此外,地下河不同部位污染源的输入对有机氯污染物的组成结构也有影响。与国内外水体及表层沉积物中HCHs、DDTs相比较,研究区水体、表层沉积物中HCHs、DDTs浓度分别处于中等和偏高水平。      

A strike‐slip core complex from the Najd fault system,Arabian shield

Metamorphic core complexes are usually thought to be associated with regional crustal extension and crustal thinning, where deep crustal material is exhumed along gently dipping normal shear zones oblique to the regional extension direction. We present a new mechanism whereby metamorphic core complexes can be exhumed along crustal‐scale strike‐slip fault systems that accommodated crustal shortening. The Qazaz metamorphic dome in Saudi Arabia was exhumed along a gently dipping jog in a crustal‐scale vertical strike‐slip fault zone that caused more than 25 km of exhumation of lower crustal rocks by 30 km of lateral motion. Subsequently, the complex was transected by a branch of the strike‐slip fault zone, and the segments were separated by another 30 km of lateral motion. Strike‐slip core complexes like the Qazaz Dome may be common and may have an important local effect on crustal strength.     

Relative Sea Level Changes in Maldives and Vulnerability of Land Due to Abnormal Coastal Inundation

Oceanic Islands in the Pacific and Indian Oceans have extremely small land areas, usually less than 500 km2, with maximum height about 4 m above sea level. The Republic of Maldives is an independent island nation in the Indian Ocean south of Sri Lanka which stretches vertically in the Indian Ocean from 07° 06'N - 0° 42'S. The land area of this island country is about 300 km2, and none of Maldives' 1190 islands has an elevation more than 3 m above sea level. In fact the Maldives has the distinction of being the flattest country on earth, making it extremely vulnerable to the effects of global warming. Of the south Asian countries, the Maldives is the most vulnerable nation, facing severe consequences as a result of global warming and sea level rise (SLR). Because of their obvious vulnerability to SLR, the Government of Maldives is very much concerned about climate change. As global warming and the related SLR is an important integrated environmental issue, the need of the hour is to monitor and assess these changes. The present article deals mainly with the analysis of the tidal and Sea Surface Temperature (SST) data observed at Male and Gan stations along the Maldives coast in the northern and southern hemispheres, respectively. The objective of the analysis is to study the trends of these parameters. Trend analysis is also performed on the corresponding air temperature data of both stations. The results show that Maldives coastal sea level is rising in the same way (rising trend) as the global sea level. The mean tidal level at Male has shown an increasing trend of about 4.1 mm/year.Similarly at Gan, near the equator,it has registered a positive trend of about 3.9 mm/year.Sea level variations are the manifestations of various changes that are taking place in the Ocean-Atmosphere system. Therefore, the variations in SST and air temperature are intimately linked to sea level rise. It is found that SST and air temperature have also registered an increasing trend at both stations. The evidence of rising trends suggest that careful future monitoring of these parameters is very much required. Tropical cyclones normally do not affect the Maldives coast. However, due to its isolated location, the long fetches in association with swells generated by storms, that originated in the far south have resulted in flooding. Thus the rising rate of sea level with high waves and flat topography have increased the risk of flooding and increased the rate of erosion and alteration of beaches.     

Depositional facies of the subsurface Neogene Surma Group in the Sylhet Trough of the Bengal Basin,Bangladesh: record of tidal sedimentation

The Bengal Basin, in the north-eastern part of the Indian subcontinent, contains a thick (± 22 km) early Cretaceous-Holocene sedimentary succession. The Neogene succession in the Sylhet Trough of the basin reaches a thickness of more than 6 km of which the Surma Group contains important sandstone reservoirs. Lithologically, the group consists of a succession of alternating shales, siltstones, sandy shales and sandstones, with minor conglomerates. This research work is a sedimentological analysis of the subsurface Neogene succession encountered in the petroleum exploration wells in the Sylhet Trough of the Bengal Basin. Detailed lithologic logs of the cores, based on considering texture and sedimentary structure, permit a subdivision into eight lithofacies, e.g., a shale-dominated facies, interbedded fine sandstones and mudstones, ripple-laminated sandstones, parallel-laminated sandstones, massive sandstones, cross-bedded sandstones, cross-bedded sandstones with pebble/granule lag and conglomerates. Characteristic sedimentary structures of the Surma Group, such as flaser-, wavy- and lenticular-bedding, bipolarity of ripple cross-stratification, evenly laminated sand/silt-streaked shales, reactivation surfaces within cross-bedded sandstone sets, mud-drapes on foreset laminae and herringbone cross-stratification as well as small-scale vertical sequences (several fining-upward cycles) are diagnostic for tidal influence. On the basis of the lithofacies associations and prograding character of the deposits revealed from the electrofacies associations, the Surma Group sediments have been interpreted as representing deposits of tide-dominated deltaic depositional setting.     

Clay mineralogy of the pleistocene soil horizon in Barind Tract, Bangladesh

Pleistocene red soil horizons were exposed in different areas of the Barind Tract in north-west Bangladesh. X-ray diffractions of twenty seven samples from different depths of these soil horizons revealed that the soil horizons consisted of kaolinite, illite and chrysotile with significant amount of opal-CT. Samples from Maddhapara, Bogra, and Nachole contain kaolinite, illite, quartz and opal-CT, and the samples from Kantabari contain chrysotile instead of kaolinite. Clay mineral compositions of different soil horizons indicated two different types of clay assemblages, viz. (a) illitekaolinite and (b) illite-chrysotile. In the village of Kantabari, illite-chrysotile clay mineral assemblage indicate that soil horizons were formed under low temperatures with alkaline and reducing conditions. However, other soil horizons of illite-kaolinite clay mineral assemblage indicate that soils were possibly formed under humid, temperate and welldrained conditions. These two soil horizons were formed under different geochemical, geomorphological and climatic conditions from different parent materials. Scanning Electron Microscopy photographs showing the presence of glass shards and no opal-A were found using XRD, suggesting that the opal-A might not be a precursor to opal-CT in the red soil horizon of the study area. This opal-CT along with the general lack of fossils and presence of glass shards was indicative of a volcanogenic rather than biogenic origin for the Opal-CT in the study area, and X-ray fluorescence data reveals higher percentages of silica which is comparable to the Toba Ash of Toba Caldera, Indonesia of about 75,000 B.P.     

Petrology of the prehistoric lavas and dyke of the Barren Island,Andaman Sea,Indian Ocean

Although Barren Island (Andaman Sea, Indian Ocean) witnessed several volcanic eruptions during historic times, the eruptions that led to the formation of this volcanic island occurred mainly during prehistoric times. It is still active and currently in the fumarolic stage. Its volcanic evolution appears to be characterized by a constructive phase with the piling up of lava flows and scoria deposits and Strombolian activities, followed by a sudden collapse of the main cone. Deposits of a possible caldera-forming eruption were not recognized earlier. After a period of peri-calderic hydromagmatic activity, whose deposits presently mantle inner and outer caldera walls, a new phase of intracalderic Vulcanian activities took place. A prominent dyke in the SE inner side of the caldera wall was recognized. Petrographically the lava flows and dyke are similar but they differ in their chemical composition (viz., SiO₂, MgO, Ni, Cr) significantly. Similarity in major, minor and trace element composition (viz., K/La, K/Nb, K/Rb, K/Ti ratios) of these rocks together with Chondrite normalized trace element (Rb, Ba, Sr, P, Zr, Ti and Nb) and REE (La, Ce, Nd and Y) patterns of the Barren Island prehistoric lava flows and dyke and low-K lavas of Sunda Arc indicates that Barren Island must have evolved from a source similar to that of Sunda Arc lavas during the Quaternary Period.     

Petrographical and geochemical signatures of Jurassic rocks of Chari Formation,Western India: implications for provenance and tectonic setting

The sandstones of the Ridge and Athleta members of Chari Formation (Callovian-Oxfordian) exposed at Jara have been analyzed for their petrographical and geochemical studies. Texturally, these sandstones are medium to coarse grained, poorly to well sorted, sub-angular to sub-rounded, and show low to medium sphericity. These sandstones were derived from a mixed provenance including granites, granite-gneisses, low and high-grade metamorphic, and some basic rocks of Aravalli range and Nagarparkar massif. The petrofacies analysis reveals that these sandstones belong to the continental block and recycled orogen tectonic regime. The studied sandstones are modified by paleoclimate, distance of transport, and diagenesis. Mineralogically and geochemically, sandstones are classified as quartzarenite, subarkose, arkose, sublithic arenite, and wacke, respectively. The A-CN-K ternary plot and CIA, CIW, PIA, and ICV values suggest that the similar source rocks suffered moderate to high chemical weathering under a hot-humid climate in an acidic environment with higher \({\text{P}}_{{{\text{CO}}_{ 2} }}\). Generally good to strong correlations between Al₂O₃ and other oxides in these sediments indicate clay mineral control. The K₂O/Na₂O versus SiO₂ diagram indicates that the studied samples occupy passive margin fields but the SiO₂/Al₂O₃ versus K₂O/Na₂O plot suggests that the Athleta Sandstone and Ridge Sandstone fall within the passive margin field, while Ridge Shale falls within the active continental margin field.     

Questioning the water wars rationale: a case study of the Indus Waters Treaty

The water wars rationale predicts that countries will wage war to safeguard their access to water resources, especially if there is water scarcity, competitive use and the countries are enemies due to a wider conflict. Following this argument, India and Pakistan should have fought a war over the Indus basin instead of negotiating the 1960 Indus Waters Treaty. In explaining this Indo–Pakistan cooperation which is specifically over water, the critical feature that emerges is that through cooperation the countries were able to safeguard their long–term water supply. In other words, cooperation is water rational. Using the Indus basin experience, the underlying logic of the water wars rationale is questioned, in particular, the use of public statements by key decisionmakers as evidence of future water wars and is shown to be wanting.     

Impact assessment due to rural electrification in hill tract of Bangladesh for sustainable development

Environmental impact assessment (EIA) of any project is essential for understanding the sustainability of the project. For sustainable development of hill tracts, electricity is inseparable. Like other parts of Bangladesh hill tracts districts felt increasing demand of electricity. In this paper an attempt has been taken to present the existing environmental condition and analysis the future environmental condition after implementation of project. Electrification will extend the length of the active day. Electrification will improve security (people’s perception of safety and security) at the region. The elements of the project identified as components for analysis are chosen based on DOE’s guideline. The study showed that 87% people say that they feel safer at night since being electrified. Impacts are classified on the basis of EPA’s scaling and DOE, university’s teachers, NGOs expert’s opinions. Value more than 10 is classified significantly affected element of the project. In this paper advantages and disadvantages of the Electrification Project has been presented.     

Unplanned urbanization: Assessment through calculation of environmental degradation index

Urbanization is an inevitable phenomena for the country like Bangladesh. The push and pull factors help to migrate people from rural area to urban area. As a result haphazard and unplanned urbanization create environmental degradation. Survey data reveals that inadequate solid waste disposal services, lack of adequate public water supply, traffic congestion, water logging, air pollution, noise pollution, hill cutting are the main problems in the city area. Concentration of dust as well as SOx, NOx exceeded the allowable limit at the selected points. Groundwater level of Sylhet city has a considerable lowering over the last few decades. It has lowered from 3380 mm below ground in 1982 to 7880 mm below ground. Sylhet is located in highly seismic risk zone but most of the buildings and other structures in this area are constructed without considering earthquake risk. Environmental degradation index was calculated based on economical condition of the country.