SPECIFIC DEGRADATION OF WATERSHEDS     

Boubacar KANE Pierre Y. JULIEN 《国际泥沙研究》2007,22(2):114-119

An extensive database of reservoir sedimentation surveys throughout continental United States is compiled and analyzed to determine specific degradation SD relationships as function of mean annual rainfall R, drainage area A, and watershed slope S. The database contains 1463 field measurements and specific degradation relationships are defined as function of A, R and S. Weak trends and significant variability in the data are noticeable. Specific degradation measurements are log normally distributed with respect to R, A, and S and 95% confidence intervals are determined accordingly. The accuracy of the predictions does not significantly increase as more independent variables are added to the regression analyses.  相似文献   

Triassic mid-oceanic sedimentation in Panthalassa Ocean: Sambosan accretionary complex, Japan     

Tetsuji  Onoue  Hiroyoshi  Sano 《Island Arc》2007,16(1):173-190

Abstract   The Sambosan accretionary complex of southwest Japan was formed during the uppermost Jurassic to lowermost Cretaceous and consists of basaltic rocks, carbonates and siliceous rocks. The Sambosan oceanic rocks were grouped into four stratigraphic successions: (i) Middle Upper Triassic basaltic rock; (ii) Upper Triassic shallow-water limestone; (iii) limestone breccia; and (iv) Middle Middle Triassic to lower Upper Jurassic siliceous rock successions. The basaltic rocks have a geochemical affinity with oceanic island basalt of a normal hotspot origin. The shallow-water limestone, limestone breccia, and siliceous rock successions are interpreted to be sediments on the seamount-top, upper seamount-flank and surrounding ocean floor, respectively. Deposition of the radiolarian chert of the siliceous rock succession took place on the ocean floor in Late Anisian and continued until Middle Jurassic. Oceanic island basalt was erupted to form a seamount by an intraplate volcanism in Late Carnian. Late Triassic shallow-water carbonate sedimentation occurred at the top of this seamount. Accumulation of the radiolarian chert was temporally replaced by Late Carnian to Early Norian deep-water pelagic carbonate sedimentation. Biotic association and lithologic properties of the pelagic carbonates suggest that an enormous production and accumulation of calcareous planktonic biotas occurred in an open-ocean realm of the Panthalassa Ocean in Late Carnian through Early Norian. Upper Norian ribbon chert of the siliceous rock succession contains thin beds of limestone breccia displaced from the shallow-water buildup resting upon the seamount. The shallow-water limestone and siliceous rock successions are nearly coeval with one another and are laterally linked by displaced carbonates in the siliceous rock succession.  相似文献   

The fate of inorganic colloidal particles in Lake Brienz     

Vincent Chanudet  Montserrat Filella 《Aquatic Sciences - Research Across Boundaries》2007,69(2):199-211

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Impact of natural reforestation on floodplain sedimentation in the Dragonja basin,SW Slovenia   总被引：4，自引：0，他引：4  

S. D. Keesstra 《地球表面变化过程与地形》2007,32(1):49-65

Changes in floodplain sediment dynamics have profound effects on riverine habitats and riparian biodiversity. Depopulation due to socio‐economic changes in the Dragonja catchment (91 km²) in southwestern Slovenia resulted in the abandonment of agricultural fields, followed by natural reforestation since 1945. This profoundly changed the water and sediment supply to the streams, as well as floodplain sediment deposition. This paper presents a reconstruction of the development of the Dragonja floodplain due to these land use changes during the last 60 years. The reconstruction is based on dating of floodplain sediments using ¹³⁷Cs profiles, measurement of actual sedimentation rates using artificial grass sedimentation mats, and linking this information to the present‐day hydrological behaviour of the river. The sedimentation mats showed that floodplain sedimentation was restricted to peak flows of considerable magnitude. Due to the reforestation, the return period of such high flows increased from 0·31 year in the period 1960–1985 to 0·81 year between 1986 and 2003, with commensurate changes in sedimentation rates. At the 1·5 m river terrace (formed about 60 years ago), ¹³⁷Cs‐based sedimentation rates (1960–1986) were roughly twice the rates inferred from the artificial grass mats (2001–2003). This finding matches the increase in the return period for larger peak events during the 1986–2003 period, which caused fewer major inundations at this level. Conversely, sedimentation rates determined for the lowest terrace at 0·5 m were similar for both techniques (and periods) because the return periods of the peak events responsible for sediment deposition at this lower level did not change much over the period 1986–2003. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

陆气相互作用及陆面模式的研究进展   总被引：20，自引：2，他引：20  

陈海山  孙照渤 《南京气象学院学报》2002,25(2):277-288

较为全面地回顾了有关陆气相互作用的研究进展及陆面模式的发展现状，结合近年来开展的有关陆气相互作用的20多个大型国际研究计划和目前国内外具有代表性的陆面模式，分析了当前陆气相互作用及陆面模式研究中存在并有待进一步解决的问题，探讨了未来陆面模式的发展趋势。  相似文献   

Fault propagation and climatic control of sedimentation on the Ghoubbet Rift Floor: insights from the Tadjouraden cruise in the western Gulf of Aden     

L. Audin  I. Manighetti  P. Tapponnier  F. Métivier  E. Jacques  P. Huchon 《Geophysical Journal International》2001,144(2):391-413

A detailed geophysical survey of the Ghoubbet Al Kharab (Djibouti) clarifies the small-scale morphology of the last submerged rift segment of the propagating Aden ridge before it enters the Afar depression. The bathymetry reveals a system of antithetic normal faults striking N130°E, roughly aligned with those active along the Asal rift. The 3.5 kHz sub-bottom profiler shows how the faults cut distinct layers within the recent, up to 60 m thick, sediment cover on the floor of the basin. A large volcanic structure, in the centre of the basin, the 'Ghoubbet' volcano, separates two sedimentary flats. The organization of volcanism and the planform of faulting, with en echelon subrifts along the entire Asal–Ghoubbet rift, appear to confirm the westward propagation of this segment of the plate boundary. Faults throughout the rift have been active continuously for the last 8400 yr, but certain sediment layers show different offsets. The varying offsets of these layers, dated from cores previously retrieved in the southern basin, imply Holocene vertical slip rates of 0.3–1.4 mm yr⁻¹ and indicate a major decrease in sedimentation rate after about 6000 yr BP, and a redistribution of sediments in the deepest troughs during the period that preceded that change.  相似文献   

The world''s large lake basins as denudation-accumulation systems and implications for their lifetimes     

Matthias Hinderer  Gerhard Einsele 《Journal of Paleolimnology》2001,26(4):355-372

The mechanical denudation rates of 81 large lake basins (lake area > 500 km²) were determined from long-term river loads and erosion maps. Using the drainage area/lake area ratios the mean sedimentation rates of the lakes were calculated for a porosity of 0.3. The mean sedimentation rates of different lake types vary between 0.1 mm/a (glacial lakes, lowland) and 5.4 mm/a (mostly sag basin lakes). The calculated lifetimes of the lakes are based on the lake volumes and mean sedimentation rates, assuming steady-state conditions and solely clastic material. On average, glacial lakes in highlands and fault-related lakes show the shortest lifetimes (c. 70 ka), glacial lakes in lowlands and rift lakes have the longest lifetimes (c. 1 Ma). Some lakes remain unfilled for very long time spans due to rapid subsidence of their basin floors. The calculated lifetimes are compared with those derived from sediment core studies. Most core studies indicate lower mechanical sedimentation rates than the calculated ones because a major part of the incoming sediment is trapped in deltas. However, a number of lakes (e.g., the Great Lakes of North America) show the opposite tendency which is largely caused by extensive shoreline erosion and resuspension. The lifetimes of large glacial lakes often exceed the duration of interglacials. Hence, their lifetimes are restricted by glaciation and not by sediment infill. Rift lakes persist for long time periods which exceed the calculated lifetimes in some cases. Time-dependent subsidence, basin extension, as well as the impact of climate change are briefly described.  相似文献   

Cherts from the Yangla copper deposit, western Yunnan Province: geochemical characteristics and relationship with massive sulfide mineralization   总被引：4，自引：0，他引：4  

PAN Jiayong  ZHANG Qian  MA Dongsheng  Li Chaoyang 《中国科学D辑(英文版)》2001,44(3):237-244

Four layers of cherts were found for the first time in the Yangla copper deposit, western Yunnan Province. The cherts possessed the following geochemical characteristics: 1 Low TiO₂ and Al₂O₃ contents, but high ore-forming element (e.g. Cu, Au, Ag) contents; 2 low total REE contents and clear negative Eu anomalies when normalized to chondrite similar to the REE contents and distribution patterns of associated massive sulfide ores; 3 silicon isotopic compositions of cherts in the Yangla deposit being the same as cherts and geyserite of hot-water sedimentary origin; 4 lead and sulfur isotopic compositions of cherts in the Yangla deposit being similar to those of the massive sulfide ores in the Yangla deposit; 5 Rb-Sr isochron age of cherts from the Yangla deposit being identical with that of host strata. Hence, we conclude that the cherts in the Yangla deposit are of hot-water sedimentary origin, which have a close relationship with the massive sulfide ores. The discovery of hydrothermal cherts from the Yangla copper deposit provides further evidence for the hydrothermal exhalative origin of the massive sulfide deposits.  相似文献   

某住宅楼的地基加固与纠偏     

刘善国  殷友东 《化工矿产地质》2001,23(2):125-127

面对连云港市新浦区软土地基上施工的某住宅楼 ,施工时由于对北楼部分桩出现的缩颈及断裂未能妥善处理 ,造成楼房北倾的问题。经协商 ,及时采取了旋喷桩加固法加固北楼基础 :采用沉降法(切桩 )、纠偏 (使各承台均匀、协调、沉降 )、接桩、固封等措施 ,效果良好。  相似文献   

粤北大沟谷热水沉积钠长石岩岩石化学及稀土元素   总被引：3，自引：0，他引：3  

梁华英  王秀璋  程景平 《沉积学报》2001,19(3):415-420

大沟谷含金钠长石岩带上为层状下为脉状产于震旦系乐昌峡群片岩中,主要由钠长石岩及碳酸盐岩组成。钠长石岩多为块状及条带状构造。钠长石岩和片岩化学成分不同,钠长石岩相对富集Al₂ O₃ 、TiO₂ 、MnO、Na₂O、P₂O₅,而贫Fe₂O₃ 、FeO、MgO、CaO、K₂ O。在主要氧化物组成的直角坐标图上,钠长石岩和片岩位于不同的区域及具不同的变化趋势。钠长石岩稀土元素含量较低,在 12.5 6× 10 -6～ 5 5.6 6× 10 -6之间,具较低的La/Yb(1.82～ 6.42 )、La/Sm(0.96～ 2.99)、Gd/Yb(0.99～ 2.71)比值,较大的δEu异常范围 (0.41～ 0.8),弱的δCe异常。钠长石岩地质产状特征及稀土元素特征表明其主要是热水沉积形成的。  相似文献