岱海沉积物粒度特征及其古环境意义

GRAIN-SIZE CHARACTERISTICS OF LAKE DAIHAI SEDIMENTS AND ITS PALEAOENVIRONMENT SIGNIFICANCE

处于北方环境敏感带的封闭湖泊岱海 ,其沉积物的粒度特征反映了岱海降水、水动力搬运强度以及湖面水位高低的变化。较为丰富的降水及较强的水动力条件容易沉积成分较粗的陆源碎屑颗粒 ;当湖面较低时 ,缩短了沉积物搬运区与沉积区的距离 ,也容易使沉积物粗颗粒组分增加 ,但仅从平均粒径大小上很难对其沉积作用形式作出判断。通过对岱海沉积物粒度频率曲线的分析 ,讨论了湖泊的几种可能沉积作用 ,区分了正常流水沉积与极端条件下风力作用以及水流与风力作用混合沉积 ,从而揭示了沉积时的古环境特征 ,在岩心 12 .34～ 14.18m段 ,即10 .5 ka前具有低湖面、气候寒冷。

The enclosed Lake Daihai lies in the environment sensitive zone in North China,and the grain size characteristics of its sediments indicate the variations of precipitation,hydrodynamics and the lake level changes.The coarse particles from the terrestrial source are easy to deposit on the conditions of plentiful precipitation and intense hydrodynamics,but the decreasing distance between the transportation and deposition zones during low lake level period is also easy for coarse particles to increase.Thus,it is difficult to determine the deposition environment merely according to mean grain size variations.Based on the analysis of the characteristics of the grain size frequency curves of the lake sediments,some possible major deposition forms are discussed,and fluvial deposition,wind deposition on extreme conditions as well as mixed depositions of fluvial and wind are distinguished.From the results,it is known that typical paleaoenvironment is showed in the interval of 12 34～14 18 m of the core,that is before 10 5 ka,characteristic of a low lake level,cold climate and significant precipitation fluctuations.