秦岭太白盆地黄土地层发育时的古环境

PALEOENVIROMENT DURING DEVELOPMENT OF THE LOESS STRATA IN TAIBAI BASIN OF QINLING MOUNAIN

太白盆地黄土地层厚１６ｍ左右．发育有两层红褐色古土壤。化学分析与微结构鉴定表明该盆地黄土中的古土壤为ＦｅＯ３与Ａｌ２Ｏ３迁移深度大但无聚集的棕壤．并已成为明显的风化无，发育时的年平均降水量在１０００ｍｍ以上．太白盆地黄土中ＣａＣＯ３含量少，发育有淀积型的光性定向粘土．表明黄土地层发育时的降水量也在６００ｍｍ以上。该盆地黄土地层发育在距今约２０多万年前．指示从这一时期开始，中国黄土搬运高度已超过２０００ｍ。微结构的观察还表明，光性定向粘土不仅可用于降水量的研究，也可用于指示温度的相对高低．

By field investgation, two weathering crusts haVe been asscertained in the loess of Middle Pleistocene inTaibai Basin. On the basis of chemical composition and microtexture of paleosols, the paleosols in the loessin Taibai Basin have been determined as brown soils in which the accumulation of Fe2O3 and Al2O3 did not occur and the mean annual rainfall was above 1000 mm, when they developed. There is a little of CaCO3 in loessin the area and there is some optical oriented clay film that belong to illuvial type, which indicates the meanannual rainfall was more than 600mm. when the loess develope in the area.Accrding to coparing the paleosols in Taibai Basin with the paleosols in loess Plateau, we know that thedevelopmental age of the loess in Taibai Basin is more than 200000 years before present, which indicates thetransported height of the loess was above 2000m at that time.The material obtained by optical observation show that oriented clay film not only can be used in restoring rainfall, but also can used in restoring relative temperature.