【作者】 杨红梅；

【导师】 王成善；

【作者基本信息】 中国地质大学（北京） ， 古生物学与地层学， 2009， 博士

【摘要】 中新世是青藏高原整体隆升和环境变化的关键时期。可可西里盆地是青藏高原北部最大的陆相新生代沉积盆地,盆地中新世早期发育了分布面积广泛的五道梁组淡水湖相灰岩,表明这里曾经发育了面积巨大的古大湖。将其称为“五道梁古大湖”。五道梁古大湖存在期间恰逢青藏高原的快速隆升关键时期,研究该湖泊的环境演化能够为深入了解青藏隆升与气候环境演化关系提供重要信息。本文选择通天河盆地五道梁组剖面作为研究对象,在该剖面进行系统采样,用沉积学、岩相及相分析及介形虫壳体微量元素和氧碳同位素地球化学等方法研究湖泊的沉积特征及沉积环境的演变。岩石学和岩相学分析结果可知,通天河盆地五道梁组记录了五道梁古大湖由最初的浅湖、演变为盐湖中间有短暂的浅湖环境相间分布,随后水体加深成为深湖环境,之后水体下降成滨湖环境,之后再次成为浅湖后再次加深,最后变浅逐渐加深。反映在通天河盆地区域是位于整个五道梁古大湖由深水向浅水过渡带,使湖泊相变较为频繁的地区。通过对五道梁组中介形虫壳体化石丰度的研究认为五道梁古大湖发育初期湖泊生产力较低,而随着湖泊的扩张和加深,生产力逐渐提高;介形虫壳体氧碳同位素分析结果认为,总体上来讲五道梁古大湖不属于典型的封闭型湖泊;介形虫微量元素地球化学特征反映了从整体上湖水的盐度随着湖泊的发展变小,水温升高。中间有多次盐度和水温的变化。综合五道梁组沉积特征恢复古湖泊的盐度和湖水面的变化特点,反映了23.8～21.8 Ma前该湖泊区域气候由湿润-干旱-暖湿的演化趋势。气候两次明显的变化是区域性事件,可能是同时期青藏高原中部和北部的快速隆升的结果。该研究为进一步了解青藏高原北部的古环境探索了一条新的途径。更多还原

【Abstract】 Early Miocene is the key period of Tibetan Plateau uplift.HXL is the largest nonmarine deposit basin in northern Tibet. Wudaoliang Group greatly distribute in this basin Early Miocene,which shows that large paleolake exist,the paleolake named Wudaoliang paleolake.The study of paleoenvironment evolution of the paleolake will provide more useful information for the relation of Plateau uplift and environment change. Wudaoliang Group in Tongtianhe Basin has been chosen in this paper.The samples has been collected by the numbers.The methods of sedimentology,petrology and geochemistry are used to study the deposit characteristic and paleoenvironment evolution of Wudaoliang Group.The results of petrology and sedimentology show that Wudaoliang Group in Tongtianhe Basin record the development of Wudaoliang paleolake,first is shallow lake environment to a long period saltlake environment ,in which exist a short period of shallow lake environment,and then the depth of the lake increased .After the lake level change shallow again, the depth of the lake increased continuouslyThe preserve condition of ostracod shell show that Wudaoliang Group in Tongtianhe Basin record Wudaoliang paleolake initially paleoproductivity is poor,and then together with the development of the lake, paleoproductivity of the lake rising .The geochemisty of Oxygen and Carbon isotopics of ostracod shell indicate that generally Wudaoliang paleolake is not a typical closed lake. The characteristic of Mg/Ca and Sr/Ca of ostracod shell geochemistry show that the salinity of Wudaoliang paleolake increased followed the development of the lake,at the meantime the temperature of the lake also increased.At the process the salinity and temperature of the lake change many times.Intergration the deposit characteristic of Wudaoliang Group reconstruct the paleosalinity and paleolake level of Wudaoliang paleolake,which reflect that during 23.8-21.8 Ma B.P. the evolution of climate in the area experience the course from west and west to dry ,at last to warm and west .The climate change should be the result of the tectonic reactive after the Tibetan Plateau uplift to denudation and planation. This work explores a new method to study the paleoenvironment in the hinter of the Tibetan Plateau further.更多还原