可可西里地区中新世湖相叠层石成因及其古气候意义  

THE ORIGIN OF MIOCENE LACUSTRINE STROMATOLITES IN THE HOH XIL AREA AND ITS PALEOCLIMATIC IMPLICATIONS

作　　者：伊海生[1] 林金辉[2] 周恳恳[1] 李军鹏[1] 黄华谷[1] 

机构地区：[1]成都理工大学沉积地质研究院,四川成都610059 [2]成都理工大学材料与化学化工学院,四川成都610059

出　　处：《矿物岩石》2008年第1期106-113,共8页Mineralogy and Petrology

基　　金：国家自然科学基金资助项目(编号:40572077);教育部博士点基金项目(编号:20060616005)

摘　　要：青藏高原北部可可西里地区新发现湖相叠层石,它们集中分布在中新世五道梁群地层中。这些叠层石形态以穹隆状最为常见,局部地区甚至形成叠层石藻丘礁,根据显微镜和扫描电镜观察,其纹层构造和显微结构与现代海洋叠层石和前寒武纪时期的叠层石十分相似。根据对采集的叠层石样品进行微量元素分析、碳氧同位素分析,并与藻团块灰岩、生物碎屑灰岩和泥质灰岩以及少量白云岩进行对比研究,结果表明:叠层石灰岩、藻团块灰岩具有相似的地球化学特点,表现为低Sr/Ba、高Fe/Mn的特点,判断这些叠层石碳酸盐沉积在低盐度湖泊环境,建造叠层石的蓝绿藻生长在滨浅湖地带。它们的δ18O值变化于-6.63‰^-7.63‰之间,接近一般湖相淡水灰岩的范围内,指示入湖水量增加、湖水向淡化方向发展。湖泊中蓝绿藻类繁盛和叠层石的出现指示高湖面湖泛事件,说明青藏高原中新世时期曾出现过气候异常湿润期,这为判别区域气候的干湿变化提供了一个沉积标识。The lacustrine stromatolites in the Miocene Wudaoliang Group were discovered in the Hoh Xil area of northern Tibetan plateau. The stromatolites were commonly dome shaped with occasionally as algal mounds appearance. Their laminated structures and microscopic textures which were similar to modern marine and Precambrian stromatolites were obviously observed by microscope and SEM. The trace element contents and carbon and oxygen isotopic compositions of stromatolitic carbonates were measured and compared with algae limestones, bioclastic limestones,marlstones and dolomites. It was showed that the stromatolitic and algae limestones in this area had similar geochemical characters. The stromatolites were of low Sr/Ba ratios,high Fe/Mn values and were considered to be deposited in low salinity lake environments where stromatolitic structures were constructed by blue-green algae mats in shoreline and shallow lacustrine area. The δ^18O values of these stromatolitic limestones ranged from -6.63‰ to 7. 63‰ and were very close to that of normal freshwater lacustrine limestones. It was indicated that the inflow of lake water and abrupt salinity transition occurred at the time of formation of stromatolite. The appearance of stromatolite horizons imply the blooming growth of blue-green algae during lake expansion and indicated a period of high lake level. It was suggested that stratigraphic horizons of lacustrine stromatolites recorded specific humid climate conditions in northern Tibetan plateau during Miocene and can be used as a sedimentary indicator for regional paleoclimatic events.

关 键 词：叠层石 湖相碳酸盐岩 古气候 干湿变化 新近纪 青藏高原 

分 类 号：P534.621[天文地球—古生物学与地层学]