Study On The Paleohydrogeology Evolution Of The Shule River Alluvial Fan Oasis In Holocene

Shule River Alluvial Fan Oasis can be referred as an ideal object for investigation of the ecological system evolution of Alluvial Fan Oasis, especially the natural oasis,restricted usually by hydrological environment and climate change in the arid Hexi Corridor,Gansu Province,in the Late Quaternary.The thesis mainly deals with the Holocene variation of ecological-hydrological environment of Shule River Alluvial Fan Oasis based on the project of evolution of environment and hydrological system 50ka.B.P in Shule River Alluvial Fan Oasis in Gansu "subsidized by CNSF. Through field geological and environmental observations and sampling, quartz OSL dating, organic carbon ¹⁴C dating, as well as analysis of TOC,grain size and Pollen assemblage of the samples from ten sediment profiles in front fine grain sediment zone of the Shule River Fan, the results obtained as follows:(1)The vegetation evolution history on Shule River Alluvial Fan and circumjacent since about 13 ka B.P. could be divided into 6 phases: about 12.1-13.1ka, a sparse coniferous and broadleaf trees - shrub grassland, cold and wet climate; 9.2-12.1ka, shrub grassland, temperature rising but precipitation and humidity getting down; 5.8-9.2ka, sparse forest with the most flourish shrub grassland under the optimal climate; 4.3-5.8ka, coniferous and broadleaf mixed forests -shrub grassland, temperature rising slightly and getting dry; 4.3-2.8ka, grass vegetation and climate became more dry; 2.8-2.3ka, coniferous forests -shrub grassland, precipitation and temperature getting down, but a higher relative humidity.(2)The detail survey of the spatial distributing relationships between different sedimentary facies and groundwater overflow zones show that the swamp mud-silt or mud-sand sediment with lot of life-form remains could be treated as an indicator of groundwater spilling belt. The spatial locations of groundwater spilling belt in the alluvial fan during Holocene have been sketched, and shifts shown that it was obviously taken place by 3 times (in 1.5-1.9ka, 2.9-3.5ka and 6.4-12.8ka B.P. respectively) according to the OSL ages, ¹⁴C ages and locations of the swamp layers along sediment sequences at more than 20 sites.(3)On the basis of self-checking coarse grain quartz OSL dating results and of the contrast with the ¹⁴C dating results, the preparing and measurment program of the quartz OSL dating were improved for the sediment samples which have lots of cutting grains and little content of quartz grains.