柴达木盆地第四纪盐湖演化

THE EVOLUTION OF THE QUATERNARY SALT LAKE IN THE QAIDAM BASIN

本文讨论了柴达木盆地第四纪沉积分布及盐矿物产出特征、新构造运动分期及其在区内的表现;指出盆地西部第三系背斜构造带之上分布的四级湖成阶地的形成与距今10万年前发生的新构造运动有关,其分布形态记录了第四纪盐湖演化的历史;结合第四纪沉积分布及盐类沉积特征把盆地第四纪盐湖演化分为4个时期,对应4个盐类沉积阶段。

The Quaternary salt-bearing sediments are of extensive distribution in the Qaidam basin, of which pleistocene saltbearing ones ocour in synclinal depressions around the anticlinal belts composed of Tertiary strata in the west part of the basin, and the greater part of Holocene salt bearing sediments are distributed in the extensive depression in the east part. Five episodes of post-Pliocene neotectonic movements have been recognized, which controlled the evolution and distribution of the salt lakes. The formation of four successive lacustrine terraces found in the anticlinal belts were related to the first to fourth neotectonic movements respectively, approximately during the consecutive time intecvals of 2.00—1.60 Ma, 1.10—0.76 Ma, 0.60—0.30 Ma and 0.16—0.10 Ma respectively. The distribution of such terraces discloses, in a way, the evolutionary history of the Quaternary salt lake region, which may be divided into the following four periods: 1) Pan-lacustrine or flood lake period, from Late Pliocene to the end of Early Pleistocene (before 0.80 Ma), 2) transitional dismembering period of the flood lake, from the end of Early Pleistocene to late Middle Pleistocene (0.8—0.3 Ma), 3) drying period of the paleolake (with further separation of the lake), from late Middle Pleistocene to the end of Late Pleistocene (0.3—0.03 Ma), 4) extint period of the paleolake, since the end of Late Pleistocene (after 0.03 Ma). The corresponding four stages of salt deposition are those of salt accumulation, sodium salt deposition, sodium and magnesium salt deposition and potassium and magnesium salt deposition respectively.