陕北红碱淖沉积物粒度特征所揭示的环境变化

Environmental Changes Deduced from Grain-size Characteristics of the Sediments from Hongjiannao Lake,Shaanxi Province

通过沉积物粒度参数，对陕西红碱淖近几十年以来的湖泊演化和区域环境变化进行了探讨。沉积岩芯下部样品粒度组成呈双峰特征，据此可以分辨沉积物中湖相和风成组分。结果表明红碱淖形成于1928年，成湖初期流域风沙发育，其中1936年、1939年和1941年发生了三次强沙尘暴事件；1952～1960年为湖泊快速扩张时期，系人为改造使入湖地表径流在短时间内快速增强所致；1960年以后，红碱淖演化为稳定深湖环境，湖区降水增多，风沙发生的频率和强度大大降低，沉积物粒度频率分布曲线也演变为单峰形态。20世纪90年代中期以来，该湖水面有下降趋势。红碱淖粒度参数特征较好地反映了湖泊演化历史、区域风沙强度变化以及人类活动特征。

On the basis of analyzing grain-size proxies, the evolution history of Hongjiannao Lake for the past 80 yrs. is discussed in this article. Grain-size distribution of the samples from the lower part of the sedimentary core is characterized by the ＂double-peak＂ feature, which enables us to distinguish the aeolian materials from the lacustrine sediments. It＇s revealed that Hongjiannao Lake formed in about 1928 A.D. and in its initial stage sandstorms were prevalent with three extremes took place in 1936 A. D. , 1939 A.D. and 1941 A. D.. During 1952～1960 A. D. , the lake expanded greatly , due to the sharp increase of inflow waters to the lake as a result of the channelled-off water from the around swamp caused by human beings. Hongjiannao Lake has remained a higher water level since 1960s and the frequency and intensity of sandstorms have reduced a lot with the ＂double-peak＂ feature of the grain-size frequency curve changing into the ＂single-peak＂ feature. The water level of Hongjia.nnao Lake has been holding a dropping trend since 1950s. The lake evolution history as well as the paleosandstorm characteristics and the anthropogenic activities are perfectly inferred from the study of grain-size proxies.