察尔汗盐湖的突然形成与地表系统巨变——据介形类研究

ABRUPT FORMATION OF THE CHARHAN SALT LAKE AND THE MEGAEVOLUTION OF THE EARTH SURFACE SYSTEM—ON THE BASIS OF OSTRACODA

本文根据青海省柴达木盆地察尔汗盐湖中６个钻孔岩心介形类的研究，确定了咸水湖相、微咸水湖相、淡水浅湖—湖滨相和池沼相４类介形虫组合，发现该湖区在０．７８ＭａＢＰ以来长期处于寒冷、干燥气候背景下，基本是浅湖—湖滨相环境，只是在末次盛冰期开始时才突然形成盐湖。由于柴达木盆地西部自上新世末即为盐湖，故而盐类矿床沉积中心的迁移是地表系统巨变的反映，即地表径流及大气降水突然减少导致湖泊成盐。

Based on the study on Ostracoda collected from a total of six drilling holes in the Charhan lake area,Qinghai Province,four ostracods assemblages indicative respectively of Saline,brackish,fresh water and swamp facies have been recognized.It was found that since 0.78 Ma B P the area was characterized by a dominance of shallow lake and littoral environment during the long duration of cold,dry climate.The appearance of peat sediments also indicates the Presence of littoral zone at the southeast part of the lake.It was only at the beginning of the last Great Glacial Stage(c.24 ka B P)that the salt lake was abruptly formed.At the west part of the Qaidam Basin the salt deposits have been formed since Late Pliocene.But the lake had undergone some freshening as a result of climatic changes .The extinetion of fresh water or brackish lake was related to the sudden decrease in rainfall and runoff resulting in little or no solution of the salt deposits even in the locene times.So the formation of the Charhan salt lake is thought to be the result of the Earth surface system megaevolution.