首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Fan-Delta,Braid Delta and the Classification of Delta Systems   总被引：7，自引：0，他引：7  
This paper mainly discusses the origin and deposhional features of fan-deltas and braid deltas. Fan-del-tas are storm discharge-dominated, while braid deltas are usually flashy flood-dominated. The two types ofdelta, like common deltas, were reworked by marine processes. Delta systems are classified into nine deltatypes on the basis of the subaerial depositional processes and the nature of marine reworking. Fan-deltas and braid deltas are of great significance for petroleum exploration. In divergent-marginforeland and intraplate rift-subsided basin settings fan-deltas often form combination traps for petroleum ac-cumulation.  相似文献   

2.
Water resources system is composed of natural water subsystem and social water subsystem. And it is a complicated large system, which contains certain regional background, as well as specific framework, function and dynamic balance. The evaluation of the water resources system needs the viewpoint of sustainable development and the measurement according to water resources system carrying capacity, which holds the meaning of both water resources carrying capacity and water environment carrying capacity. The Changjiang River Delta is a very important area in China. As the local water resources are concerned, the Delta is an area lack of water as a matter of fact. The water resources system of the Delta experiences a long, intricate and degenerate period. The lack of water due to resources shortage in the 1950＇s was converted to that due to water quality from the 1980＇s. Furthermore, the status of water shortage sharpens gradually. The representations are summarized as follows： firstly, the discharge amount of wastewater and polluted water is large all along. Secondly, the pollution status of rivers, which involve the Changjiang River, the Grand Canal, the rivers in cities and the rivers in small towns and villages, is noticeable. Thirdly, water quality of Taihu Lake is worth of more attention. Therefore, the countermeasures on the reconditioning and regulating of water resources system in the Delta demands the following new strategies, such as to treat the rivers, the lakes and the seas as one overall system, to improve, harmonize and counterpoise water resources system carrying capacity, to implement the integrated management of water resources, which means the integrated management of drainage area along with the regional area, especially the integrated management of city water, and to carry on water saving and scientific use so as to increase the efficiency of water use, and so on.  相似文献   

3.
Persistent organic pollutants （POPs） are semi-volatile chemicals that are toxic to wildlife and human. Typical POPs include most organochlorine pesticides （OCPs）, polycyclic aromatic hydrocarbons （PAHs）, polychlorobiphenyls （PCBs）, polybrominated biphenyl ethers （PBDEs）, etc. Most POPs are hydrophobic, capable of accumulating and existing for a long time in the sediments. Well preserved, laminated sediment layers hence can serve as archives for POP pollution history in the sediment pool. Rapid economic growth has taken place since the early 1980s in most parts of China, of which the Yangtze River Delta, the Pearl River Delta and the Pan-Bohai Bay took the lead. Along with the brilliant regional economic development, the environmental quality has been severely deteriorated. For a more sustainable economic and social development, it is of vital need to understand the relationship between regional economic development and environmental pollution.  相似文献   

4.
The Yangtze River Delta Region is one of the most important economic development areas in China. In the process of its industrialization and urbanization, a great deal of wastewater is poured into rivers, lakes and coasts. Researches on contamination and bioavailability of heavy metals can help us to assess the ecological risks in the aquatic environment of the Yangtze River Delta. The samples were collected from three environmental compartments including the Yangtze River, Taihu Lake, and the south coast of Jiangsu. The concentrations of heavy metals were determined by ICP-MS. Metal speciation was determined by the sequential extraction procedure modified based on Tessier＇s scheme. Among the seven elements of Cu, Pb, Zn, Cr, Cd, Co, Ni detected, the contents of Cr, Zn did not vary significantly, while Cd and Pb varied significantly. Compared to the background values （loess in the basement）, all metals detected except Co, Cr exceeded the background level. Cd had the greatest exceeding values, reaching 2 to 7 times. Ni and Pb were followed. The contents of Zn were comparatively high in lake sediments, especially in the lake bays. Ni was enriched in fiver sediments and Cu was highest in sediments from the Yangtze River estuary. Cd and Pb were concentrated in the coastal sediments. Comparatively, in space, Cr was associated with the carbonate fractions in the bay of lake. Cu-bound Fe-Mn oxides and Ni in residual form were highest in the open lake. In the river environment, Fe/Mn oxide-bound Pb, exchangeable Cd were the highest fractions. In the estuary environment, Pb and Zn bound carbonates, Cd-bound Fe-Mn oxides are the largest fractions. Cd in the exchangeable fraction, Cu-bound Fe-Mn oxides had the larger proportions in the coast. In general, the bioavailability of Cu and Cd were high in lake environment, the available Pb, Cd were remarked in river environment, and Pb and Zn were easily assimilated by creatures in estuary.  相似文献   

5.
Liu  Baoyin  Siu  Yim Ling  Mitchell  Gordon  Xu  Wei 《Natural Hazards》2013,69(3):2039-2055
Natural Hazards - In recent years, greater attention has been given to advancing the theory and practice of assessing risk from multiple hazards. Most approaches calculate multi-hazard risk by...  相似文献   

6.
Point bars are well developed on the Yellow River delta, among which the Shengli I point bar is the most typical. The point bar, being about 4 km in length and several tens to more than 100 meters in width, is located on the south side of the Shengli Bridge in Kenli County, Dongying, Shandong. It is a typical fine-grained point bar with silt, which is predominant, some clay and minor plant debris and clay boulders. The Shengli I point bar has complicated 3-D structures. Firstly, in a plane view, it comprises mainly eight sedimentary units, bar edge, bar ridge, bar platform, bar plain, bar channel, bar gully, bar pond and bar bay, developing side by side and superimposed one by one in a complex way. Secondly, its vertical structures are very complex due to the partial superimposition of the 8 sedimentary units. Besides hydatogenesis, very intensive wind erosion, eolian, ice and meltwater actions are also visible on the Shengli I point bar. The complex form is made even more complicated because of the abo  相似文献   

7.
The leaching processes along the flow path and over abstraction of the alluvial aquifer, the principal aquifer in delta Tokar, by the agricultural and domestic sectors and natural factors, have led to its salinization which may be due to interaction between geological formations and adjacent brackish and saline water bodies as well as seawater transgression. The main objectives of this study are to assess the hydrochemical characteristics of the groundwater and to delineate the locations and the sources of aquifer salinization. Water samples in the project area were chemically analyzed for major cations and anions at the laboratory by the standard analytical procedures. Chemical data and water level measurements were manipulated using GIS techniques for hydro chemical and flow direction maps and piper diagram for chemical facies and SPSS software for statistical analyses such as basic statistics (mean and standard deviation) and Spearman’s correlation matrix. The general flow direction of the groundwater is from Southwest towards East and Northeast. The hydraulic gradient is relatively steeper at the apex of the delta (0.06) and amounts to 0.005 at the distal part of the delta. The average transmissivity value of the water bearing formations was found to be about 4.5?×?103 m2/s, whereas, the storage coefficient was about 0.28. A hydrochemical study identified the locations and the sources of aquifer salinization and delineated their areas of influence. The investigation indicates that the aquifer water quality is significantly modified as groundwater flows from the southwestern parts of the study area, where the aquifer receives its water by lateral underflow from Khor Baraka flood plain, to the central and northeastern parts, with few exceptions of scattered anomalous concentration pockets in the deltaic plain. Significant correlation between TDS and/or EC with the major components of Na+, Cl?, and SO 4 ?2 ions is an indication of seawater influence on the groundwater salinity. Moreover, Cl?, SO 4 2? , and Na+ are predominant ions followed by Ca2+ and HCO 3 ? . Hence, four types of groundwater can be chemically distinguished: Na–Ca–SO4–Cl– facies, Na–Cl–SO4–HCO3– facies, Na–Ca–Mg–SO4–Cl–HCO3 facies, and Na–Ca–Mg–Cl–SO4 facies. The processes that govern changes in groundwater composition as revealed by chemical and statistical analyses are mainly associated with over-abstraction, biodegradation, marine intrusions, and carbonate saturation.  相似文献   

8.
The wetlands of the Okavango Delta accommodate a multitude of ecosystems with a large diversity in fauna and flora. They not only provide the traditional livelihood of the local communities but are also the basis of a tourism industry that generates substantial revenue for the whole of Botswana. For the global community, the wetlands retain a tremendous pool of biodiversity. As the upstream states Angola and Namibia are developing, however, changes in the use of the water of the Okavango River and in the ecological status of the wetlands are to be expected. To predict these impacts, the hydrology of the Delta has to be understood. This article reviews scientific work done for that purpose, focussing on the hydrological modelling of surface water and groundwater. Research providing input data to hydrological models is also presented. It relies heavily on all types of remote sensing. The history of hydrologic models of the Delta is retraced from the early box models to state-of-the-art distributed hydrological models. The knowledge gained from hydrological models and its relevance for the management of the Delta are discussed.  相似文献   

9.
An assessment was carried out on the pollution impact potentials of drilling waste generated from wells X and Y in “Eden Field,” offshore Niger Delta. Eleven samples each were collected from well X (8 treated and 3 untreated cuttings) and well Y (6 treated cuttings and 5 spent muds). The samples were subjected to three separate analyses, namely, oil-on-cutting analysis using Dean and Stark reflux method, heavy metal analysis using atomic absorption spectrophotometer (Unicam 929), and toxicity test analysis using bioassay procedure on test organisms such as Desmoscaris trispinosa and Palaemonetes africanus all in attempt to detect their pollution potential. The results showed that the oil-on-cutting analysis for the well X samples was between 15.8 and 17.5 % for unwashed cuttings and between 4.6 and 5.1 % for washed cuttings, while that for well Y samples was between 3.49 and 4.27 % for washed cuttings and 1.69 to 2.59 % for the drill mud samples. The heavy metal analysis on the wells X and Y samples showed absence of mercury, cadmium concentration ranged from 0.52 to 0.99 mg/kg for well X and from 0.69 to 0.78 mg/kg for well Y samples. The result of the toxicity test of samples from well X on D. trispinosa showed that 96-h LC50 occurred at 9800 to 10,900 mg/l for the washed drill cutting and 6200 to 6700 mg/l for the unwashed drill cuttings. On the other hand, the toxicity test on P. africanus indicated more resistant to the toxicity of the drill cuttings as 96-h LC50 was achieved at higher concentrations. At 96-h exposure, the concentration that killed 50 % of the test organism (LC50) occurred at 14,000 to 16,900 mg/l for the washed cuttings and 10,300 to 11,350 mg/l for the unwashed cuttings. Similarly, the 96-h LC50 was achieved on washed drill cuttings from well Y at concentrations of 9800 to 10,400 mg/l using D. tripinosa and 11,600 to 17,200 mg/l using P. africanus. The study has shown that oil-on-cutting content, heavy metal concentrations, and toxicity level did not indicate any major risk to the environment as the treatment and cleaning of the drilling wastes on the rig helped in reducing the concentration of all the contaminants in compliance with the regulatory limits.  相似文献   

10.
《中国地球化学学报》2006,25(B08):79-79
  相似文献   

11.
Changes in water temperatures caused by climate change in California’s Sacramento–San Joaquin Delta will affect the ecosystem through physiological rates of fishes and invertebrates. This study presents statistical models that can be used to forecast water temperature within the Delta as a response to atmospheric conditions. The daily average model performed well (R 2 values greater than 0.93 during verification periods) for all stations within the Delta and San Francisco Bay provided there was at least 1 year of calibration data. To provide long-term projections of Delta water temperature, we forced the model with downscaled data from climate scenarios. Based on these projections, the ecological implications for the delta smelt, a key species, were assessed based on temperature thresholds. The model forecasts increases in the number of days above temperatures causing high mortality (especially along the Sacramento River) and a shift in thermal conditions for spawning to earlier in the year.  相似文献   

12.
This study deals with the relationship between sea-level changes and paleoclimatic fluctuations based on the analysis of stratigraphy, grain sizes, palynology, and radiometric dating of the Yellow River delta since the Late Pleistocene. Evidence from the sedimentary record, grain sizes, and pollen provides a paleoenvironmental history of the Late Pleistocene from the boreholes of the delta. Based on a combination of grain-size analysis with lithological studies, marine deposit units contain the intervals of 13.85–16.9, 18.5–19.69, 27.9–34.8, 36.4–37.2, 48.4–51.6, and 54.1–55.9 m, and transitional facies units contain the intervals of 10.25–13.85, 16.9–18.5, 19.69–27.9, 34.8–36.4, 37.2–48.4, 51.6–54.1, and 55.9–60 m, compared with fluvial(terrestrial facies) deposit units(3.36–10.25 m). Based on pollen analysis and pollen assemblages, there were three warm-wet periods from 9.1–0.16 ka BP, 16.1–60 ka BP, and 90.1–94.6 ka BP From the top to the bottom of the borehole, the paleoclimate has an evident fluctuation: warm and moist(Holocene Optimum) —cool and dry(Younger Dryas Event)—mild semi cool—cool and dry—warm and moist. There were three warm-wet periods from 9.1–0.16 ka BP, 16.1–60 ka BP, and 90.1–94.6 ka BP, corresponding to the Holocene Optimum stage, MIS 3, and MIS 5, respectively. The warm period allowed monsoonal evergreen and broadleaved deciduous forests that corresponded to Holocene hypsithermal climatic conditions and the Late Pleistocene climatic Optimum. Three warm-wet periods occurred in marine deposit units from 9.1–0.16 ka BP, 60.1–16.1 ka BP, and 94.6–90.1 ka BP. These periods correspond to the Cangzhou transgression, Xianxian transgression, and Huanghua transgression, respectively. From 90.1–60.1 ka BP, 17.5–9.1 ka BP, and 0. 16 ka BP–1855 AD, three dry and cold phases are recognized. The phases indicate the fluvial(flood plain) sedimentary environment, corresponding to cooler and mild dry periods based on palynological results and grain-size distribution.  相似文献   

13.
Quantitative rock physics analyses were used to determine the lithology and pore fluid of a reservoir in the Niger Delta. Inaccurate prediction of lithology and pore fluid results in the inaccurate determination of other petrophysical properties and parameters such as porosity, permeability, and net pay. This research is to predict lithology and pore fluid using rock physics analysis. However, reservoir zones were also predicted. Density, compressional wave velocity, and shear wave velocity logs were used as input to calculate elastic parameters such as velocity ratio, Poisson’s ratio, and bulk modulus. The calculated velocity ratio log was used to differentiate between sand and shale. Poisson’s ratio and velocity ratio using Goodway interpretation template were carried out and used to delineate pore fluid content, gas sand, oil sand, and sandstone formation from crossplot analysis.  相似文献   

14.
Short-term sedimentation patterns were evaluated from August 1992 to May 1993 in different wetland habitats characteristic of the Rhône Delta, including impounded and seasonally-dry saline Arthrocnemum marshes, brackish Juncus, Phragmites, and Scirpus riverine wetlands directly connected to the Rhône River, and Arthrocnemum-dominated marine marshes influenced by the Mediterranean. Short-term sedimentation was measured as sediment accumulation on paper filters which had been placed on the soil surface for several weeks. Total sedimentation and material lost on ignition was significantly related to individual sampling periods, reflecting the importance of short-term processes. High sedimentation at riverine sites (up to 22 g m?2 d?1) was related to a combination of river stage and wind events. Marine and impounded wetlands of the Rhône Delta experienced low sedimentation throughout the period of study. Sedimentation rates averaged over the study period were 0.8 g m?2 d?1, 1.8 g m?2 d?1, and 5.4 g m?2 d?1 for marine, impounded, and riverine sites, respectively. Percent material lost on ignition was low in all habitats (average 15%) and followed a seasonal trend with a minimum in late fall and winter (1%). Soil percent organic matter was also low in the top several centimeters (13%), suggesting that inorganic sedimentation is very important for accretion on these wetland surfaces. Coastal flooding was not a significant mechanism for sedimentation in the marine sites during the period of study. Sedimentation is an important factor in elevation change, and this study shows that impounded habitats, the most common “natural environment“ left in the delta, may become vulnerable to sea-level rise in the future if management practices continue to isolate these wetlands from riverine sources of sediment.  相似文献   

15.
The BOCIM method (bottleneck-focused continuous improvement) has been designed to support the optimum adaptation of a local water resources management depending on regional conditions to ensure a sustainable supply of water. Being an interdisciplinary approach, the BOCIM method tries to take into account all the factors affecting the water supply. Geared to solving water problems, it is used to: identify and solve whatever the core problem happens to be in a regional water system by applying the bottleneck-concentrated strategy (Mewes in Orell Füssli Management, 112 p, 2000); replace the fragmented project-based approach with continuous improvement; run a management system-orientated quality management standard (e.g. ISO 9001).  相似文献   

16.
Encasingboxisoneofthebasicproblemsincom putinggeometry .ItiswidelyusedinmanyengineeringapplicationssuchasimageprocessingpatternrecognitionandCAD .Theproblemofcomputingthemin arearect angleencasingboxforclosedcontourisaspecialcaseofencasingboxproblem .Thisproblemisinvestigatedforpracticalapplication ,especiallyindesigningpath ,colli siondetectionandreal timeroaming (Day ,1988;PreprataandShamos ,1985 ) .ThecommonapproachisAABB (axis alignedboundingboxes)whenfindingrectangleencasingboxnow ,wh…  相似文献   

17.
  相似文献   

18.
Net to gross (NTG) is an important parameter in evaluating the volumes of hydrocarbon in place (VHIP) in reservoirs, and proper evaluation of this parameter will lead to significant accuracy in the estimated reserves. The use of conventional petrophysical log evaluations often does not provide sufficient resolution for net sand analysis of reservoirs, especially in laminated reservoir rocks. The uncertainties associated with log-derived net-to-gross estimates arise from the petrophysical shale volume (V sh) cutoffs used in deriving the net sand count over a reservoir interval. One way of improving the net-to-gross estimates is by using a model that calibrates log-derived net to gross to a core equivalent, which is the more accurate representation of net sand counts. In this study, a model for calibrating log-derived net to gross to a core equivalent based on genetic units and facies associations of reservoir rocks in three wells (wells 7, 36, and K008) was established. Ultraviolet core photographs show a good contrast between hydrocarbon-stained sandstones and shales, and combining it with white light-slabbed core images facilitated a manual net sand count of the core photographs on a bed-by-bed basis. Petrophysical shale volume (V sh) cutoff derived from two volumes of shale indicators was applied to generate net sand counts, which were used to get log-derived net-to-gross values. Then, the net to gross from core images and petrophysical clay volume (V sh) analysis were compared by facies associations, and this comparison yielded a reliable core-calibrated net-to-gross model, which reduces the uncertainties in net-to-gross values estimated from V sh cutoffs. The results show that for the distributary channel sands, net to gross derived using V sh cutoff results in an underestimation of net to gross by about 6–10 % when compared with the core-calibrated net to gross, while for the upper shoreface units, V sh cutoff overestimates net to gross by about 7–10 % when compared to its core-calibrated equivalent.  相似文献   

19.
Nonhydrolyzable carbon （NHC） and black carbon （BC） were measured upon treatments with the HCl/HF/trifluoroacetic acid method, and with the combustion method at 375 ℃, respectively in three contaminated soils from the urban area of Guangzhou and twenty-two bulk and size-fractionated sediments from the Pearl River Delta and Estuary, China. The isolated NHC and BC fractions were also characterized using elementary analysis, radiocarbon accelerated mass spectroscopy （AMS）, solid state ^13C cross-polarization and magic angle spinning unclear magnetic resonance spectroscopy （^13C-CP/MAS NMR）, Fourier transformed infrared spectroscopy （FTIR）, and Raman microspectrometry. The results showed that the NHC and BC accounted for 25.6%-84.7 % and 4.14%-17.3%, respectively, of the total organic carbon （OC） with averages of 51.9% and 11.2% in the soils and sediments. For the less contaminated, low OC fiver and estuary sediments （WR and C08）, the OC and NHC concentrations increased with decreasing particle size.  相似文献   

20.
The Hammerhead Delta–Deepwater Fold-Thrust Belt is located in the Ceduna Sub-Basin of the Bight Basin, offshore southern Australia. It is synonymous with the Hammerhead Supersequence and consists of three, Campanian to Maastrichtian, deltaic sediment packages. The Hammerhead Delta–Deepwater Fold-Thrust Belt is a short-lived gravity-gliding system that exhibits a distinctive spoon-shape in cross-section. The system detaches on a master horizon at the top of the Tiger Formation. Finite Element Method based two-dimensional restorations show that the Hammerhead Delta–Deepwater Fold-Thrust Belt is a near-balanced system with near equal amounts of up-dip extension and down-dip compression. Overall, there is only 2.4% additional extension in the Hammerhead Delta–Deepwater Fold-Thrust Belt. This near-balanced system is unusual in comparison with other passive margin Delta–Deepwater fold-thrust belts, which generally demonstrate large amounts of extension compared with shortening, due to the regional-scale progradational nature of the systems. The results suggest that sediment input to the Hammerhead Delta–Deepwater Fold-Thrust Belt was not sufficient to result in the regional-scale progradation of fault activity and that the sediment supply shutdown before the system could develop in an extensive passive margin Delta–Deepwater fold-thrust belt, hence demonstrating that it is sediment supply that drives ongoing gravitational deformation in Delta–Deepwater fold-thrust belts and not slope gradient.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号