选择位于季风边缘区的吉兰泰盐湖为研究对象,利用OSL和14C测年手段重建湖面波动历史,探讨盐湖形成年代与环境变化过程。通过大范围的野外调查发现,在该湖泊南部地区发育高于现代干盐滩9 m的湖滨砂沉积,上覆风成砂沉积,其中湖滨沉积物的OSL年代为6.7 ka BP前后,表明当时该湖泊处于浅水状态,此后湖水经历了快速的下降过程。对于盐湖中心剖面点盐层之下粘土层的14C测年显示,在5 500 aBP以来,集聚大量的石膏、芒硝和石盐等蒸发盐类,该湖泊进入成盐期。通过区域对比发现,吉兰泰湖面快速下降阶段与季风边缘区中全新世干旱事件发生时间相对应。研究认为,吉兰泰盐类矿物的开始沉积,反映了中全新世阿拉善高原区域环境的突然变化,可能指示着5.5 Cal ka BP前后干旱事件的发生。 相似文献
This paper presents a method of geomorphologic regionalization for Xinjiang, with the use of Srtm-DEM (resolution 90 m) and
TM images for 1990 (resolution 30 m). After interpretation and classification of geomorphologic types, the present research
focuses on the qualitative and quantitative distribution of different geomorphologic types based on geographical grid analysis.
Then, by using system clustering analysis method, geomorphologic types are grouped into divisions. The resulting geomorphologic
regionalization hierarchy of Xinjiang includes three levels, i.e., macro-landform divisions, medium-landform divisions, and
micro-landform divisions, containing 6, 23 and 200 types, respectively. This method makes it possible to digitally delimit
geomorphologic regions. Comparison and verification show that the spatial precision of the boundaries of geomorphologic subareas
in Xinjiang is very high. 相似文献
Understanding how the transpiration of this vegetation type responds to environmental stress is important for determining the wa-ter-balance dynamics of the riparian ecosystem threatened by groundwater depletion. Transpiration and sap flow were measured using the heat-pulse technique. The results were then projected up to the stand level to investigate the stand’s water-use in relation to climate forcing in the desert riparian forest in an extreme arid region. This study took place from April through October 2003 and from May through October 2004. The experimental site was selected in the Populus euphratica Forest Reserve (101o10’ E, 41o59’ N) in Ejina county, in the lower Heihe River basin, China. The sapwood area was used as a scalar to extrapolate the stand-water consumption from the whole trees’ water consumption measured by the heat-pulse velocity recorder (HPVR). Scale transferring from a series of individual trees to a stand was done according to the existing natural variations between trees under given environmental conditions. The application of the biometric parameters available from individual tree and stand levels was proved suitable for this purpose. A significant correlation between the sapwood area and tree diameter at breast height (DBH) was found. The prediction model is well fitted by the power model. On the basis of the prediction model, the sapwood area can be cal-culated by DBH. The sap-flow density can then be used to extrapolate the stand-water use by means of a series of mathematical models. 相似文献
Understanding the changes in streamflow and associated driving forces is crucial for formulating a sustainable regional water
resources management strategy in the environmentally fragile karst area of the southwest China. This study investigates the
spatio-temporal changes in streamflow of the Guizhou region and their linkage with meteorological influences using the Mann–Kendall
trend analysis, singular-spectrum analysis (SSA), Lepage test, and flow duration curves (FDCs). The results demonstrate that:
(1) the streamflow in the flood-season (June–August) during 1956–2000 increased significantly (confidence level ≥95%) in most
catchments, closely consistent with the distinct increasing trend of annual rainfall over wet-seasons. The timings of abrupt
change for streamflow in most catchments are found to occur at 1986; (2) streamflow in the Guizhou region experiences significant
seasonal changes prior/posterior to 1986, and in most catchments the coefficient of variation of monthly streamflow increases;
(3) spatial changes in streamflow indicate that monthly streamflow in the north-west decreases but increases in other parts;
(4) the spatial high- and low-flow map (Q5 and Q95) reveals an increase in the extremely large streamflow in the five eastern catchments but a decrease in the extremely low
streamflow in the four eastern catchments and three western catchments during 1987–2000. An increase in streamflow, particularly
extreme flows, during the flood season would increase the risk of extreme flood events, while a decrease in streamflow in
the dry season is not beneficial to vegetation restoration in this ecologically fragile region. 相似文献
The devastating MS8.0 Wenchuan earthquake ruptured two large parallel thrust faults along the middle segment of the Longmenshan thrust belt. Preseismic and postseismic leveling data indicated the hanging wall of the YingxiuBeichuan-Nanba thrust fault mainly presented coseismic uplift with respect to the reference point at Pingwu county town, and the observed maximum uplift of 4.7 m is located at Beichuan county (Qushan town) which is about 100 m west of the fault scarp. The foot wall of the Yingxiu-Beichuan-Nanba thrust fault mainly showed subsidence with maximum subsidence of 0.6 m near the rupture. By employing a listric dislocation model, we found that the fault geometry model of exponential dip angle δ= 88°?×1-exp(-9/h) with depth of 18 km and uniform thrust-slip of 5.6 m could fit the observed coseismic vertical deformation very well, which verifies the listric thrust model of the Longmenshan orogenic zone.
A 400 km-long wide-angle seismic experiment along Lianxian-Gangkou profile in South China was carried out to study contact relationship between southeast continental margin of Yangtze block and northwest continental margin of Cathaysia block. We reconstructed crustal wide-angle reflection structure by the depth-domain pre-stack migration and the crustal velocity model constructed from the traveltime fitting. The wide-angle reflection section shows different reflection (from crystalline basement and Moho) pattern beneath the Yangtze and Cathaysia blocks, and suggests the Wuchuan-Sihui fault is the boundary between them. A cluster of well-developed reflections on Moho and in its underlying topmost mantle probably comes from alternative thin layers, which may be seismic signature of strong interaction between crust and mantle in the tectonic environment of lithosphere extension. 相似文献