新疆赛里木湖的湖滩岩特征、时代及其对MIS3阶段湖面变化的指示意义

THE FEATURES AND AGES OF LAKE BEACH ROCK AROUND SAYRAM LAKE IN WESTERN TIAN SHAN AND ITS SIGNIFICANCE ON LAKE LEVEL FLUCTUATION DURING THE LAST INTERGLACIAL EPOCH MIS3

在对西天山赛里木湖盆地进行第四纪地质调查与5万填图基础上,发现沿该湖泊的不同湖岸阶地上都不同程度地发育了可指示湖面变化的湖滩岩。水准测量结果表明,典型的湖滩岩最常见于高出现今湖面7.1-9.4 m和33.4-39.4 m的低、高两级湖积台地上。对湖滩岩样品进行岩石学和矿物学研究进一步揭示,湖滩岩主要由内碎屑、藻团块、陆源碎屑、胶结物和填隙物等构成,胶结物主要为亮晶方解石,夹少量文石,表明赛里木湖周边的湖滩岩为典型的方解石胶结砂屑砾屑岩。湖滩岩样品的U系年代测试结果表明,低、高两级台地上的湖滩岩主要形成于距今24.8±1.5 ka至27.6±1.5 ka和55.4±3.8 ka的晚更新世晚期,大致对应末次冰期间冰阶MIS3阶段早期和末期的相对暖湿气候阶段。湖滩岩及其测年结果指示,赛里木湖最近一期最高湖面出现在距今55.4 ka左右末次间冰阶早期,其后由于气候的干旱化,湖面整体处于逐步下降过程,在相对暖湿期间经历了多次湖面相对稳定期并形成湖滩岩。

Lake beach rock is one of the products which can reflect the land and sea interactions, of great significance for studying the ancient lake level fluctuations, lakeshore zone evolution and paleoclimatic change. On the basis of Quaternary geological survey and 1 ： 50000 scale geological mapping for Sayram Lake Basin in western Tianshan, we found lake beach rocks on the different shore terraces, indicating lake level fluctuations. The levelling result showed that the concentration distribution of typical lake beach rock was mainly on the fluvial terraces above the lake level 7. 1 9.4 m and 33.4 -39.7 m. The Petrologic and mineralogical study further showed that the lake beach rocks were mainly composed of intraclast, algal briquette, terrigenous clastic, cement and filler content, etc. , and the cement mainly for the sparry calcite with a small amount of aragonite, which proved that the Sayram Lake beach rocks were typical calcite cementation sand gravel chip rocks. According to the U series dating results of lake beach rock samples, the lake beach rocks on the fluvial terraces were formed from 24.8 ± 1.5 ka to 27.6 ± 1.5 ka and 55.4 ± 3.8 ka, late of the late Pleistocene, roughly corresponding to the relatively warm climate stage of early and late in last glacial interglacial epoch MIS3 stage. The lake beach rocks and dating results indicated that the recent highest level of Sayram Lake appeared in the distance of about 55.4 ka, early in the last interglacial epoch. Due to the subsequent drying climate, the lake level was overall in the process of decline gradually. During the relatively warm moist period, the lake level underwent multiple relatively stable periods, and resulted in lake beach rock formed.