对青藏高原东北部风成砂-古土壤序列泽库剖面(ZK剖面)常量元素氧化物含量及其比值进行分析,结合14C测年,揭示其常量元素地球化学特征,探讨了青藏高原东北部全新世环境演变。结果表明:(1)剖面沉积物的化学组成以SiO2、Al2O3、CaO为主,其中SiO2和CaO的标准差较高,对气候变化较为敏感。(2)自剖面底部向上SiO2含量和残积系数呈现先减少后增加的趋势,高值指示冷干的气候意义,CaO含量和退碱系数则相反,高值指示温湿的气候意义。(3)9.4 ka BP以来青藏高原东北部的气候经历了由温湿向冷干的转变过程,可划分为9.4~4.2 ka BP气候温湿期和4.2 ka BP至今气候冷干期;其中在6.6~6.2 ka BP、2.4~2.0 ka BP和1.7~1.5 ka BP存在次一级的气候波动。
在分析常量元素氧化物含量及其比值的基础上,结合14C测年,对共和盆地马四剖面风成沉积序列进行研究,重建了12 cal ka BP以来共和盆地成壤环境演变过程。结果表明:(1)剖面常量元素氧化物以SiO2、Al2O3为主,元素含量SiO2>Al2O3>Fe2O3>MgO>CaO>Na2O>K2O;(2)12 cal ka BP以来区域成壤环境大致经历了凉干-温润-冷干-凉润-凉干-温湿-凉干7个阶段,即11.98 cal ka BP以前区域气候凉干,风沙活动频繁,成壤作用较弱;11.98~9.75 cal ka BP气候温润,但波动频繁,成壤环境不稳定;9.75~8.09 cal ka BP气候冷干,风沙活动强,成壤作用最弱;8.09~4.78 cal ka BP气候适宜,成壤作用强;4.78~2.90 cal ka BP气候凉干,成壤环境较弱;2.90~0.67 cal ka BP气候转暖期,气候温湿,成壤作用达到最强;0.67 cal ka BP至今气候凉干,成壤作用较弱。
以青藏高原东北部泽库剖面(ZK)风成沉积物为研究对象,利用CM-5分光测色计测定了169个样品的色度参数红度(a^(*))、黄度(b^(*))、亮度(L^(*))并计算饱和度(C^(*))和色调角(h^(*)),在分析风成沉积物各色度参数变化特征的基础上,辅以磁化率、粒度敏感指数(SC/D)、Si O_(2)及Fe_(2)O_(3)含量等指标对青藏高原东北部9.4 ka以来的环境演变进行探讨。研究结果表明:(1)色度参数a^(*)、L^(*)自剖面底部向上呈先增大后减小的变化特征,h^(*)则自下而上先减小后增大。(2)色度参数可作为青藏高原东北部重建古气候的有效代用指标,a^(*)和L^(*)高值指示温湿环境,h^(*)高值指示冷干环境;各色度参数指示环境的敏感性有差异,但均对气候突变反应较为灵敏,可用于判断气候突变的典型冷暖事件。(3)9.4 ka以来青藏高原东北部的环境整体呈现为由温湿向冷干发展的态势,可分为两大阶段。9480~4290 a BP的温湿期,气候整体呈现向温湿方向发展的趋势,表现为较温湿→温湿→较温湿的波动;4290 a BP至今的冷干期,气候整体不断向冷干方向发展,表现为温干→温润→凉润→冷干的变化。
本文以共和盆地马四剖面古风成砂-古土壤沉积序列为研究对象,利用CM-5分光测色计获得土壤色度参数亮度(L^(*))、红度(a^(*))及黄度(b^(*))值,分析色度参数的变化特征,结合Fe2O3、有机质及利用磁化率重建的温度、降水量指标探讨色度参数的古气候意义,重建12 cal ka BP以来共和盆地的气候演变过程。结果表明:(1)色度参数L^(*)、a^(*)、b^(*)均值在剖面中整体表现出古风成砂层高于古土壤层的特征, a^(*)/b^(*)与之相反;(2)色度参数可作为有效的气候代用指标重建古气候,b^(*)及a^(*)/b^(*)对气候转变反应敏感,b^(*)高值指示气候冷干,b^(*)低值指示气候温湿,a^(*)/b^(*)高值代表气候温湿, a^(*)/b^(*)低值代表气候冷干。L^(*)、a^(*)在此区域对气候的响应具有一定的局限性;(3) 12 cal ka BP以来共和盆地马四剖面色度揭示的气候演变可划分为7个阶段,表现出冷干-温湿旋回的变化特征。
The circum-lake zone of the Qinghai Lake is one of the most serious regions of desertification on the Qinghai-Tibetan Plateau. Based on Remote Sensing （RS） and Geographical Information System （GIS） techniques, the four sets of remote sensing images acquired in 1976, 1987, 1995, and 2006 were selected to conduct thematic information extraction in 14,300 km2 of land in the circum-lake zone using the Earth Resource Data Analysis System （ERDAS） image and information processing function. In the meantime the off-site interpretation and filed check-correction methods were used to recon- struct the temporal-spatial dynamic changes and differentiation patterns of land desertification in the circum-lake zone in the past 30 years, and based on this, the developmental trend of land desertification in the next 20 years was predicted. The results of the study show that in the past 30 years land desertification in the region experienced a continuous fluctuation between rapid- and slow-development processes in time, while in space it exhibited a few small patchy distributions or sporadic distributions in many places while at the same time, four large sand-dominated distributions stood out and evolved into a circum-lake belt differentiation pattern with a lakeside dike as the connecting line. Due to the integrated effects of climate changes, human activities and artificial rehabilitation, land desertification area in the region in the next 20 years will exhibit an increasing trend in the first 15 years and then increase at a slower rate, and afterward occur in a reverse, decreasing trend.
