Variations of geochemical compositions and the paleoclimatic significance of a loess-soil sequence from Garzê County of western Sichuan Province, China

The West Sichuan Plateau is located in the southeast margin of the Tibetan Plateau, where the climate is mainly influenced by the Indian southwest summer monsoon and the Tibetan Plateau monsoon. In this study, detailed geochemical analysis has been carried out on Ganzisi loess-paleosol sequence in Ganzê County of western Sichuan Province. The results indicate that Ganzê loess and paleosol have experienced the incipient stage of chemical weathering in dust source regions, characterized by the decomposition of plagioclase which caused the depletion of mobile elements Na and Ca. The post-depositional chemical weathering is characterized by carbonate dissolution and oxidation of Fe2＋. The variations of some geochemical indexes （such as CIA values, Na/K and Fe2＋/ Fe3＋ ratios） in Ganzisi loess-paleosol sequence indicate a gradually decreased chemical weathering intensity in the dust source regions and deposition areas since 1.15 Ma BP consistent with the general increase of global ice volume, reflecting that the arid trend since 1.15 Ma BP in the southeast Tibetan Plateau is a regional response to the global climate change. The geochemical indexes in this section also reveal an obvious drying step occurred at about 250 ka BP in this region. We interpret this drying step as a result of decreased influence of the Indian southwest summer monsoon. This decrease in monsoon moisture is probably attributable to the uplift of the southeast margin of the Tibetan Plateau at about 250 ka BP.     

遥感技术在全国第一次河流湖泊普查中的应用

河流湖泊是水体环境的主要形式,是生活用水、生产用水、生态用水的重要来源,对社会经济的发展起着至关重要的作用.遥感技术为全国第一次河湖普查提供了重要的技术支撑,本次河流湖泊普查涉及到的遥感影像数据为中巴地球资源卫星(CBERS)数据及2.5m高空间分辨率影像.为全面查清我国湖泊数量、分布等基本情况,本文对全国第一次河湖清查阶段中利用CBERS数据进行湖泊对象清查进行了介绍;并着重讨论了ENVI\IDL环境下CBERS数据批处理模式的建立及应用,为同类CBERS数据的大范围、大批量数据应用提供一定的参考和依据;同时,全国1:5万分幅2.5m高空间分辨率影像作为重要的河流水系现势性检查数据,本文对利用此数据进行1:5万DLG数字水系的合理性检查进行了探讨,并利用ENVI\IDL实现了全国水系的自动化检查;作为水系复核工作中的有效工具,增强了河流水系提取的现势性,提高了河流水系的精度,实现了水系提取数据精度源于并高于1:5万DLG数字水系的目的.