The Sebei gasfield is the largest biogas accumulation found in China and many reservoirs and seal rocks superposed on a syndepositional anticline in Quaternary. The biogas charging and dissipating process and its distribution have been a research focus for many years. The authors suggest a diffusing and accumulating model for the biogas, as they find that the shallower the gas producer, the more methane in the biogas, and the lighter stable carbon isotope composition of methane. Based on the diffusing model, diffused biogas is quantitatively estimated for each potential sandy reservoir in the gasfield, and the gas charging quantity for the sandy reservoir is also calculated by the diffused gas quantity plus gas reserve in-place. A ratio of diffusing quantity to charging quantity is postulated to describe biogas accumulating state in a sandy reservoir, if the ratio is less than 0.6, the reservoir forms a good gas-pool and high-production layer in the gasfield, which often occurs in the reservoirs deeper than 900 m; if the ratio is greater than 0.6, a few gas accumulated in the reservoir, which frequently exists in the reservoirs shallower than 900 m. Therefore, a biogas accumulation model is built up as lateral direct charging from gas source for the sands deeper than 900 m and indirect charging from lower gas-bearing sands by diffusion at depth shallower than 900 m. With this charging and diffusion quantitative model, the authors conducted re-evaluation on each wildcat in the central area of the Qaidam Basin, and found many commercial biogas layers.
Based on investigations of the Zhongwei Nanshan aeolian section situated in the southeastern margin of Tengger Dcsert, carbon-14 and TL (thermoluminescence) dating results and paleoclimatic proxies such as magnetic susceptibility and grain size, we inferred that the northwestern margin of East Asian monsoon region experienced abrupt climatic changes during the last deglaciation. Six oscillation events were identified: Oldest Dryas, Belling, Older Dryas, AllerФd, lntra-AllerФd Cold Period (1ACP) and Younger Dryas (YD). The summer monsoon was weaker during Oldest Dryas and Younger Dryas when the winter monsoon was stronger. However, during the B/A (BФlling/AllerФd) period, the summer monsoon strengthened, reflected by magnetic susceptibility, when the winter monsoon also became strong, which is different from the paleoclimatic pattern established in the East Asian monsoon region. Furthermore,the summer monsoon was nearly in phase with the climate changes inferred from the oxygen isotopic records of Greenland ice cores. It could be speculated that the variations of the sea ice cover in the high latitudes of the North Hemisphere affected the high pressure of Asian continent and the changes of the winter monsoon inland. On the other hand,the sea ice cover variations might have indirectly caused the occurrence of ENSO events that has tightly been related to the summer monsoon in northwest margin of East Asian monsoon region. 相似文献
Invasive smooth cordgrass (Spartina alterniflora, hereafter Spartina) has been expanding rapidly in the estuarine wetlands at Chongming Dongtan (East China) at the expense of native sea-bulrush (Scirpus mariqueter, hereafter Scirpus) and common reed (Phragmites australis, hereafter Phragmites). To examine the potential impacts of the Spartina invasion on bird diversity, we compared the abundance and species richness of birds in habitats created by Spartina, Phragmites, Spartina mixed with Phragmites, Scirpus, and the bare intertidal zone at Chongming Dongtan in spring 2008. Most birds were recorded in the native habitats, with songbirds and breeding birds being most abundant in the Phragmites habitats, and waterbirds and migrants being most abundant in the Scirpus habitats and bare intertidal zone. Both species number and population densities of birds were lower in the exotic Spartina habitats than in the other four habitats. Although some songbirds and breeding birds used the Spartina-invaded habitats, and even preferred Spartina-invaded habitats to Scirpus habitats and bare intertidal zone, their densities were lower in the Spartina-invaded habitats than in the native Phragmites habitats. This might have resulted from the dense Spartina stands restricting bird movement and providing insufficient useable food for most birds. We conclude that the spread of exotic Spartina has negative impacts on local bird communities. Because Chongming Dongtan is an important stopover site for energy replenishment of shorebirds in the East Asian–Australasian Flyway, urgent measures are needed to control further spread of Spartina and to restore the native habitats for birds. 相似文献
Based on Hagget's theory of spatial structure,researches on the nodes and field of tourist origins to Huang-cheng Village in Shanxi Province of China have been explored.Nodal hierarchy structure of tourist origins is analyzed with cluster analysis and the gravity model.And field of tourist origins is analyzed with attraction radius index(R)and geography concentration index(G).In the field analysis,R and G of Huangcheng Village are compared with Xidi Village that is a world heritage located in Huangshan City of Anhui Province in China.According to comparison of loca-tions of two areas,influential factors for field area of Huangcheng Village are identified.It is concluded that:1)cluster analysis and gravity model can be complementary methods to each other for nodal hierarchy structure analysis of tour-ist origins;and 2)as far as location is concerned,the weak intensity effect of tourism resources in the tourist region is a major cause for explaining why tourist origins to Huangcheng Village are mainly its neighboring areas.Moreover,it is suggested that the regional effect of tourist resources should be regarded as a component of destination attractiveness when applying gravity model. 相似文献
The competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain. Most of recent studies have attributed terrace formation to climatic changes and held that, even in tectonically active settings, climate variations control cycles of terrace planation and abandonment. Based on field investigations of loess-paleosol sequences, magnetostratigraphy and optically stimulated luminescence (OSL) dating, we develop a new chronology for a spectacular flight of terraces along the Yellow River near Lanzhou, China over past 1.24 Ma. All the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads, suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates. However, the ages of terraces cluster in two relatively short time periods (1.24–0.86 Ma and 0.13 Ma – present). During the intervening time between 0.86 Ma and 0.13 Ma, terraces either did not form or were not preserved. We suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation/preservation. Thus, our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision. 相似文献