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1.
Remote sensing (RS) and geographic information systems (GIS) are very useful for environmental-related studies, particularly in the field of surface water studies such as monitoring of lakes. The Dead Sea is exposed to very high evaporating process with considerable scarcity of water sources, thus leading to a remarkable shrinkage in its water surface area. The lake suffers from dry out due to the negative balance of water cycle during the previous four decades. This paper discusses the application of RS, GIS, and Global Positioning System to estimate the lowering and the shrinkage of Dead Sea water surface over the period 1810–2005. A set of multi-temporal remote sensing images were collected and processed to show the lakes aerial extend shrinkage from 1973 up to 2004. Remote sensing data were used to extract spatial information and to compute the surface areas for Dead Sea for various years. The current study aims at estimating the fluctuation of Dead Sea level over the study period with special emphasis on the environmental impact assessment that includes the degradation level of the Dead Sea. The results indicated that there is a decrease of 20 m in the level of the Dead Sea that has occurred during the study period. Further, the results showed that the water surface area of the Dead Sea has shrunk from 934.26 km2 in 1973 to 640.62 km2 in 2004.  相似文献   

2.
Monitoring the spatiotemporal changes in wetlands and assessing their causal factors is critical for developing robust strategies for the conservation and restoration of these ecologically important ecosystems. In this study, the spatiotemporal changes in the land cover system within a Himalayan wetland and its catchment were assessed and correlated using a time series of satellite, historical, and field data. Significant changes in the spatial extent, water depth, and the land system of the Hokersar wetland were observed from the spatiotemporal analysis of the data from 1969 to 2008. The wetland area has shrunk from 18.75 km2 in 1969 to 13 km2 in 2008 with drastic reduction in the water depth of the wetland. The marshy lands, habitat of the migratory birds, have shrunk from 16.3 km2 in 1969 to 5.62 km2 in 2008 and have been colonized by various other land cover types. The land system and water extent changes within the wetland were related to the spatiotemporal changes in the land cover and hydrometeorological variables at the catchment scale. Significant changes in the forest cover (88.33–55.78 km2), settlement (4.63–15.35 km2), and water bodies (1.75–0.51 km2) were observed in the catchment. It is concluded that the urbanization, deforestation, changes in the hydrologic and climatic conditions, and other land system changes observed in the catchment are the main causes responsible for the depleting wetland extent, water depth, and biodiversity by adversely influencing the hydrologic erosion and other land surface processes in the catchment. All these causes and effects are manifest in the form of deterioration of the water quality, water quantity, the biodiversity changes, and the decreasing migratory bird population in the wetland.  相似文献   

3.
Suspended sediment concentration is a major variable influencing soil erosion and loss, study on which at different spatial scales is of great meaning to understand soil erosion mechanism and sediment transport process. Based on data from 4 sloping surfaces and 7 basins ranging from 0.0003 to 187 km2 in area, the suspended sediment concentration in flood season (SSC) with drainage area is studied. With increasing drainage area on the slope surfaces, the mean suspended sediment concentration in flood season (MSSC) enhances continuously until a peak value of 685 kg m−3 occurs at the whole slope surface No. 7 runoff plot resulting from harder and harder erosion forms downslope. Entering basin systems, the diluted action of subsurface water on the toeslope on MSSC and small water flow power Ω make a minimum MSSC value of 568 kg m−3 occur in the first-order basin system Tuanshangou basin at an area of 0.18 km2, and then from Tuanshangou basin to larger basins, the positive feedback function among drainage density, water flow energy, and hyperconcentrated flow as well as its reduction of settling velocity of coarser particles generates continuously increasing MSSC with drainage area.  相似文献   

4.
The integration of Remote Sensing (RS) and Geographic Information Systems (GIS) constitutes a powerful tool for the evaluation of watershed morphometric parameters. The benefits of this integration include saving time and effort as well as improving the accuracy of the analysis. Moreover, this technique is appropriate for describing the watershed and its streams. In this study, a detailed morphometric analysis of the Wadi Baish catchment area has been performed using the Shuttle Radar Topography Mission (SRTM). The performed morphometric analysis includes linear, areal, and relief aspects. The results of the morphometric analysis reveal that the catchment can be described as of eighth stream order and consists of an area of 4741.07 km2. Additionally, the basin is characterized by a relatively high mean value of bifurcation (4.012), indicative of the scarcity of permeable rocks with high slope in the area. This value of bifurcation ratio is consistent with the high drainage density value of 2.064 km/km2 and confirms the impermeability of the subsurface material and mountainous relief. The hypsometric integral of the catchment is 47.4%, and the erosion integral of the catchment is 52.6%, both were indications of a mature catchment area.  相似文献   

5.
The Dead Sea brine is supersaturated with respect to gypsum (Ω = 1.42). Laboratory experiments and evaluation of historical data show that gypsum nucleation and crystal growth kinetics from Dead Sea brine are both slower in comparison with solutions at a similar degree of supersaturation. The slow kinetics of gypsum precipitation in the Dead Sea brine is mainly attributed to the low solubility of gypsum which is due to the high Ca2+/SO42− molar ratio (115), high salinity (∼280 g/kg) and to Na+ inhibition.Experiments with various clay minerals (montmorillonite, kaolinite) indicate that these minerals do not serve as crystallization seeds. In contrast, calcite and aragonite which contain traces of gypsum impurities do prompt precipitation of gypsum but at a considerable slower rate than with pure gypsum. This implies that transportation inflow of clay minerals, calcite and local crystallization of minerals in the Dead Sea does not prompt significant heterogeneous precipitation of gypsum. Based on historical analyses of the Dead Sea, it is shown that over the last decades, as inflows to the lake decreased and its salinity increased, gypsum continuously precipitated from the brine. The increasing salinity and Ca2+/SO42− ratio, which results from the precipitation of gypsum, lead to even slower kinetics of nucleation and crystal growth, which resulted in an increasing degree of supersaturation with respect to gypsum. Therefore, we predict that as the salinity of the Dead Sea brine continues to increase (accompanied by Dead Sea water level decline), although gypsum will continuously precipitate, the degree of supersaturation will increase furthermore due to progressively slower kinetics.  相似文献   

6.
Lyså, A., Jensen, M. A., Larsen, E., Fredin, O. & Demidov, I. N.* 2010: Ice‐distal landscape and sediment signatures evidencing damming and drainage of large pro‐glacial lakes, northwest Russia. Boreas, Vol. 40, pp. 481–497. 10.1111/j.1502‐3885.2010.00197.x. ISSN 0300‐9483. Sediments from river sections and the morphology of the upper reaches of Severnaya Dvina and Vychegda in northwest Russia show evidence of the existence of large ice‐dammed lakes in the area twice during the Weichselian. During the Late Weichselian, three separate ice‐dammed lakes (LGM lake(s)) existed, the largest one at about 135 m a.s.l. having a volume of about 1510 km3. Stepwise and rapid lake drainage is suggested to have taken place within less than 1000 years. The locations of various passpoints controlled the drainage, and when the lake was at its maximum level water spilled southeastwards into the Volga basin. Later, but before the lake water finally drained into the White Sea, water was routed northeastwards into the southeastern part of the Barents Sea. The oldest lake, the White Sea lake, existed around 67–57 ka ago, slightly in conflict with earlier palaeogeographic reconstructions regarding the chronology. The extent of the lake was constrained by, in addition to the Barents Sea ice‐sheet margin in the north, thresholds in the drainage basin. Later, one threshold was eroded and lowered during the LGM lake drainage. Given a lake level of about 115 m a.s.l., a lake area of about 2.5 × 104 km3 and a water volume of about 4800 km3, the lake drainage northwards and into the ocean probably impacted the ocean circulation.  相似文献   

7.
Based on data from two runoff plots and ten stations in hilly loess region Dalihe drainage basin ranging in area from 0.0006 to 3983 km2 on the Loess Plateau, the relationship between mean annual specific sediment yield (Y s) and drainage area (A) is studied, which is different from those for many other drainage areas of the world, neither at the scale of whole basin nor at local scale on the Loess Plateau. With increasing drainage area, the mean annual specific sediment yield experiences two peak values: the first peak value appears at 0.00408 km2 in area corresponding to the whole slope surface, and the second peak value appears at 96.1 km2 in area. The non-linear variation in the Y s–A can be explained as follows: the first peak value can be explained by the abrupt increase in slope gradient and flow shear stress resulting in highly increased sediment concentration and specific sediment yield. And the second peak value can be explained by the combined influence of flow shear stress and drainage density, represented by dimensionless variable Ω.  相似文献   

8.
 Impact of catchment erosion and the resultant reservoir siltation from a tropical environment is reported here to discuss the effect of a reservoir in the natural degradation of an evergreen-forested segment. While an area of 8.01 km2 has been affected by direct inundation at the full reservoir level, another 2.6 km2 area once under thick forest cover, had also lost its identity over the last 38 years by indirect degradation. This zone mainly falls in the confluence of tributaries, namely Neyyar and Mullayar, with the reservoir. The capacity of the reservoir was found to be reduced by 28.8 Mm3 during this period and the annual average loss is calculated as 0.75 Mm3 (0.71%), indicating the intensity of erosion from the catchment zone. In case the proposed upper dam in the reservoir comes into existence, an additional area of 2.4 km2 from the virgin forest would be submerged and more area would face degradation around the inundated zone. Received: 29 July 1998 · Accepted: 16 November 1998  相似文献   

9.
Ras Banas Peninsula is a large triangular tract of land jutting out into the Red Sea. It extends about 40 km eastward out of the general trend of the Red Sea coast of Egypt, covering an area of about 600 km2. Three sandy spits are jutting out from the main body of the peninsula into the Red Sea, possibly representing relics of structural trends, two of which are located at the western part and the third one is extending from the eastern edge forming a further seaward extension of the main body. A series of isometric and contour maps of the whole area under investigation are provided in digitized visual form of geomorphologic features, landforms and slope configuration. According to difference in relief, the study area can be subdivided into three topographic divisions, namely coastal plain (<50 m), medium-height land (50–150 m) and hinterland (>150 m). Drainage and lineament maps of the drainage networks were prepared from the topographic map and satellite images of the area. The prepared lineament map shows four main trends that control the configuration of the drainage system in the study area. These trends are Aqaba trend (NE–SW to NNE–SSW), Red Sea trend (NW–SE to NNW–SSE), Nubian trend (N–S), and Tethyan trend (E–W). It is clear that the structural trends, lithology and general slope are the main controls of developing parallel and dendritic drainage patterns in the area. Both geomorphology and drainage system configuration have great influences on the land use and natural hazards affecting the peninsula especially torrential floods and sea level fluctuations.  相似文献   

10.
We investigated rates of chemical weathering of volcanic and ophiolitic rocks on Luzon Island, the Philippines. Luzon has a tropical climate and is volcanically and tectonically very active, all factors that should enhance chemical weathering. Seventy-five rivers and streams (10 draining ophiolites, 65 draining volcanic bedrock) and two volcanic hot springs were sampled and analyzed for major elements, alkalinity and 87Sr/86Sr. Cationic fluxes from the volcanic basins are dominated by Ca2+ and Mg2+ and dissolved silica concentrations are high (500-1900 μM). Silica concentrations in streams draining ophiolites are lower (400-900 μM), and the cationic charge is mostly Mg2+. The areally weighted average CO2 export flux from our study area is 3.89 ± 0.21 × 106 mol/km2/yr, or 5.99 ± 0.64 × 106 mol/km2/yr from ophiolites and 3.58 ± 0.23 × 106 mol/km2/yr from volcanic areas (uncertainty given as ±1 standard error, s.e.). This is ∼6-10 times higher than the current best estimate of areally averaged global CO2 export by basalt chemical weathering and ∼2-3 times higher than the current best estimate of CO2 export by basalt chemical weathering in the tropics. Extrapolating our findings to all tropical arcs, we estimate that around one tenth of all atmospheric carbon exported via silicate weathering to the oceans annually is processed in these environments, which amount to ∼1% of the global exorheic drainage area. Chemical weathering of volcanic terranes in the tropics appears to make a disproportionately large impact on the long-term carbon cycle.  相似文献   

11.
Remote sensing data and GIS techniques have been used to compute runoff and soil erosion in the catchment area along the NH-1A between Udhampur and Kud covering an area of approximately 181 km2. Different thematic layers, for example lithology, a landuse and landcover map, geomorphology, a slope map, and a soil-texture map, were generated from these input data. By use of the US Soil Conservation Service curve number method, estimated runoff potential was classified into five levels—very low, low, moderate, high, and very high. Data integration was performed by use of the weighting rating technique, a conventional qualitative method, to give a runoff potential index value. The runoff potential index values were used to delineate the runoff potential zones, namely low, moderate, high, and very high. Annual spatial soil loss estimation was computed using the Morgan–Morgan–Finney mathematical model in conjunction with remote sensing data and GIS techniques. Greater soil erosion was found to occur in the northwestern part of the catchment area. When average soil loss from the catchment area was calculated it was found that a maximum average soil loss of more than 20 t ha−1 occurred in 31 km2 of the catchment area.  相似文献   

12.
A landslide susceptibility map is very important and necessary to efficiently prevent and mitigate the losses brought by natural hazard for a large area. For the purpose of landslide susceptibility analysis for the whole Xiangxi catchment (3,209 km2), Artificial Neural Network (ANN) analysis was applied as the main method. The whole catchment was divided into two parts: the training area and the implementation area. The backwater area (559 km2) of Xiangxi catchment was used as the training area for the ANN method. In the training area the correlations between the landslide distribution and its causative factors, which includes lithology, slope angle, slope curvature and river network, have been analyzed based on the geological map and digital elevation model (DEM). The back-propagation training algorithm in ANN was selected to train the sample data from the training area, which were composed of input data (causative factors) and target output data (landslide occurrence), in order to find the correlations between them. Based on these correlations and input data in the implementation area (causative factors), the network output data were obtained for the implementation area. In the end, a map of landslide susceptibility, which was established by network output data, was presented for Xiangxi catchment. ArcGIS was applied to extract and quantify input information from a DEM for susceptibility analysis and also to present the result visually. As a result, a landslide susceptibility map, in which 70 % of all landslides are rightly classified in the training area (backwater area), was created for Xiangxi catchment.  相似文献   

13.
 The environmental conditions prevailing in the Chicam-Toctina drainage system (approx. 138 km2 in Córdoba, Argentina) are considered representative of a number of catchments in Argentina's Sierras Pampeanas Range. Two groups of ions reflect the sources of dissolved species in the catchment: a) a group (Cl–, SO2– 4, and Na+) which recognizes natural and anthropogenic sources, and which exhibits significant correlations with N– 3 and NO– 2, and b) another group of components (Ca2+, Mg2+, and HCO– 3) which is clearly controlled by carbonate rocks and their waste rock products. In the headwaters, stockpiled marble quarry mining wastes provide a more open system to CO2 gaseous exchange than the outcropping rocks, thus promoting the increase of carbonate dissolution (up to 4.88 g km–2 s–1 during the rainy season). This specific yield was 20% higher than the amount estimated for an area with fewer extended mining activities. The dissolved load delivered by the upper reaches is subjected in the lower drainage area to various processes, mainly controlled by the presence of the city of Alta Gracia (approx. 40,000 inhabitants). In the dry season, due to nutrient inputs supplied by the city, photosynthetic activity plays a major role controlling stream pH. Hence, the high values of calcite saturation indexes and the increase of CaCO3 concentration in bed sediments can be explained by calcite precipitation. Such a process could be accompanied by the coprecipitation on calcium carbonate of low solubility heavy metal carbonates. Received : 17 January 1997 · Accepted : 31 March 1997  相似文献   

14.
The freshwater Lake Kinneret (Sea of Galilee) and the hypersaline Dead Sea are remnant lakes, evolved from ancient water bodies that filled the tectonic depressions along the Dead Sea Transform (DST) during the Neogene-Quartenary periods. We reconstructed the limnological history (level and composition) of Lake Kinneret during the past ∼40,000 years and compared it with the history of the contemporaneous Lake Lisan from the aspect of the regional and global climate history. The lake level reconstruction was achieved through a chronological and sedimentological investigation of exposed sedimentary sections in the Kinnarot basin trenches and cores drilled at the Ohalo II archeological site. Shoreline chronology was established by radiocarbon dating of organic remains and of Melanopsis shells.The major changes in Lake Kinneret level were synchronous with those of the southern Lake Lisan. Both lakes dropped significantly ∼42,000, ∼30,000, 23,800, and 13,000 yr ago and rose ∼39,000, 26,000, 5000, and 1600 yr ago. Between 26,000 and 24,000 yr ago, the lakes merged into a unified water body and lake level achieved its maximum stand of ∼170 m below mean sea level (m bsl). Nevertheless, the fresh and saline water properties of Lake Kinneret and Lake Lisan, respectively, have been preserved throughout the 40,000 years studied. Calcium carbonate was always deposited as calcite in Lake Kinneret and as aragonite in Lake Lisan-Dead Sea, indicating that the Dead Sea brine (which supports aragonite production) never reached or affected Lake Kinneret, even during the period of lake high stand and convergence. The synchronous level fluctuation of lakes Kinneret, Lisan, and the Holocene Dead Sea is consistent with the dominance of the Atlantic-Mediterranean rain system on the catchment of the basin and the regional hydrology. The major drops in Lake Kinneret-Lisan levels coincide with the timing of cold spells in the North Atlantic that caused a shut down of rains in the East Mediterranean and the lakes drainage area.  相似文献   

15.
The Shannon is the longest river in the British Isles (280 km) and drains an area of about 15,530 km2. The source of the river is Shannon Pot, a karst rising in County Cavan, which is one of the most famous springs in Ireland. Water tracer experiments have shown that the rising drains an immediate area of about 12.8 km2 on the slopes of Cuilcagh Mountain, of which about 60% is underlain by limestone. However, two sinks 10–11 km east of the rising and ca. 200 m higher have also been shown to be hydrologically connected during high flow conditions. This suggests that Shannon Pot may once have had a substantially larger catchment area.  相似文献   

16.
《China Geology》2021,4(2):353-363
The environmental change in the wetlands in the southern Mongolian Plateau has important impacts on the environment of North China and even the entire Northeast Asia, from which the global climate change can be understood on a large scale, especially the climate change in the Mongolian Plateau. This study extracted the information on the wetlands from three stages of remote sensing images (also referred to as RS images) of the study area, including Enhanced Thematic Mapper Plus (ETM+) images of 2000, TM images of 2010, and Landsat 8 Operational Land Imager (OLI) images of 2018. As indicated by the extraction results, the area of wetlands decreased from 796.90 km2 of 2000 to 666.24 km2 of 2018 at a rate of 7.26 km2/a. The reduced area is 130.66 km2, which is about 16.4% reduction. And the patch number of wetlands decreased from 731 of 2000 to 316 of 2018 in the study area, approximately 56.8% reduction (415 patches), and the decrease in the area of the wetlands mainly occurred in the northwest endorheic region. In terms of wetland types, the change of the wetlands was dominated by the decrease of lacustrine wetlands, of which the area and patch number decreased by 106.2 km2 and 242, respectively. Furthermore, the area of the lacustrine wetlands decreased at the highest rate of 8.70 km2/a in 2010–2018. From the perspective of spatial distribution, the wetlands in the western part shrunk more notably than those in the eastern part as a whole in the study area. According to local meteorological data, the precipitation gently decreased and the temperature increased (about 1.7°C) from 1975–2018. Overall, the decrease in the area of the wetlands and the temperature rises in the study area were mainly driven by the Mongolian monsoon climate, reduction in precipitation, and human activities.  相似文献   

17.
The Narmada River flows through the Deccan volcanics and transports water and sediments to the adjacent Arabian Sea. In a first-ever attempt, spatial and temporal (annual, seasonal, monthly and daily) variations in water discharge and sediment loads of Narmada River and its tributaries and the probable causes for these variations are discussed. The study has been carried out with data from twenty-two years of daily water discharge at nineteen locations and sediment concentrations data at fourteen locations in the entire Narmada River Basin. Water flow in the river is a major factor influencing sediment loads in the river. The monsoon season, which accounts for 85 to 95% of total annual rainfall in the basin, is the main source of water flow in the river. Almost 85 to 98% of annual sediment loads in the river are transported during the monsoon season (June to November). The average annual sediment flux to the Arabian Sea at Garudeshwar (farthest downstream location) is 34.29×106 t year−1 with a water discharge of 23.57 km3 year−1. These numbers are the latest and revised estimates for Narmada River. Water flow in the river is influenced by rainfall, catchment area and groundwater inputs, whereas rainfall intensity, geology/soil characteristics of the catchment area and presence of reservoirs/dams play a major role in sediment discharge. The largest dam in the basin, namely Sardar Sarovar Dam, traps almost 60–80% of sediments carried by the river before it reaches the Arabian Sea.  相似文献   

18.
Water reservoirs, lakes, and larger basins, including their drainage areas, represent sedimentologically closed to semi-closed denudation-accumulation systems. The mean rates of mechanical denudation, DRme, and clastic sedimentation, SRme, are related by the ratio of the drainage/lake area, Ad/Al. If the latter is known, DRme (or the specific sediment yield SY in t per km2/a) can be calculated from SRme, or vice versa. The best data for modern SY mainly come from the sediment fills of artificial reservoirs. Small drainage areas of mountainous regions show SY values up to two orders of magnitude higher than lowlands and approximately one order higher than larger regions of mixed relief. This is also true of arid to semi-arid zones which often provide approximately as much sediment (SY) as humid temperate and even tropical zones of comparable relief. Lithology and climate (river runoff) also may play some role for SY from catchments of limited size. The importance of these factors is exemplified by perialpine lakes and two East African lakes. Sediment yields gained from some large reservoirs compare well with long-term denudation rates derived from geological studies (e.g., the Tarbela dam reservoir along the Indus River). In many other cases, human activities have raised SY by factors of 2–10, locally up to >100. Artificial reservoirs in mountainous regions with SY in the range of 300–2000?t?per?km2/a tend to become filled within several tens to hundreds of years; some have even shorter lifetimes. Perialpine lakes of the Alps and British Columbia are strongly affected by delta prograding and have lifetimes mostly between 15 and 40?ka. Closed lake systems in deep morphological depressions (Lake Bonneville, Aral Sea, northern Caspian Sea) have a high potential for sediment storage up to the level of spillover and therefore can persist over long time periods. Basins with markedly subsiding basin floors (lakes of the East African rift zone, the southern Caspian Sea, and the Black Sea, both on oceanic crust) can survive for many Ma in the future, despite relatively high terrigenous input.  相似文献   

19.
To develop a technique of implementing global ultra-low density geochemical sampling and as a contribution to the International Geochemical Mapping Program (IGCP Project No. 259), an orientation study in the use of deep (lower-layer) overbank sediments was conducted in Jiangxi Province of Southeast China in 1989–1990. Ninety-four samples were collected at depths of 50 to 120 cm from overbank terraces at an average density of 1 site per 1800 km2. The total area of sampled catchment basins is approximately equivalent to 18% of Jiangxi Province. Most of the samples were collected at outflow sites of catchment basins with areas of 100 to 800 km2. The samples were analyzed for 39 elements.The representativity of wide-spaced lower-layer overbank sediment sampling is discussed from various perspectives; the following features have been observed: (1) Widespaced lower-layer overbank sediment data and the data from China's national geochemical mapping (RGNR) project show similar geochemical patterns for W, Sn, Pb, Cu and Zn. (2) The results of wide-spaced lower-layer overbank sediment sampling demonstrate that catchment basins with areas of 100 to 800 km2 are suitable sample site locations for the global geochemical reference network. (3) Wide-spaced lower-layer overbank sediment sampling is a fast and cost-effective way to identify geochemical provinces and has strategic significance in mineral exploration. (4) There is a significant correlation between the W content of wide-spaced lower-layer overbank sediment samples and the presence of W mineralizations within the catchment basins. (5) The distributions of Ni, Cr and V in wide-spaced lower-layer overbank sediment samples distinctly reveals the boundary between the Yangtze sedimentary platform and the South China Caledonian fold system in Jiangxi Province. (6) Distributions of Rb and Be coincide with the Yanshan granites, which are closely related to the major ore-forming episodes in Jiangxi Province.  相似文献   

20.
The geochemistry of carbonate fault rocks has been examined in two areas of the Arava Fault segment, which forms the major branch of the Dead Sea Transform between the Dead Sea and the Gulf of Aquaba. The role of fluids in faulting deformation in the selected fault segment is remarkably different from observations at other major fault zones. Our data suggest reduced fluid rock interactions in both areas and limited fluid flow. The fault did not act as an important fluid conduit. There are no indications that hydrothermal reactions (cementation, dissolution) did change the strength and behavior of the fault zone, although the two areas show considerable differences with respect to fluid sources and fluid flow. In one area, the investigated calcite mineralization reveals an open fluid system with fluids originating from a variety of sources. Stable isotopes (13C, 18O), strontium isotopes, and trace elements indicate both infiltration of descending (meteoric and/or sea water) and ascending hydrothermal fluids. In the other area, all geochemical data indicate only local (small scale) fluid redistribution. These fluids were derived from the adjacent limestones under nearly closed-system conditions.  相似文献   

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