青藏高原晚新生代湖泊地质环境与成盐成藏作用

摘要

青藏高原湖泊演化是地质构造和气候环境变化共同作用的产物.湖泊沉积既是地质环境记录器,又是盐类和油气战略资源.但是,以往在高原内部还缺乏连续完整的高分辨率的长达1~2 km的湖芯.本项目在柴达木东、西部获取1~2 km 5支系统的岩芯,取得丰富的高原沉积盆地新纪录.将本轮工作的年代学结果与最新的国际标准相对比,建立了柴达木盆地较精确的磁性地层年代框架.通过柴达木钻孔剖面冷、暖相盐类矿物环境指标研究,从2 Ma BP开始断续出现冷相矿物至今,柴达木盆地西部共出现31个冷系列,这与国外冰期研究结果相近.通过对钻孔沉积速率和粒度的研究,尝试对青藏高原隆升的几个阶段进行划分.对盆地盐沉积的综合研究,首次发现在盆地中部存在古大气环流的明显界限和成盐突变带.在该线以北,反映冷湿期盐沉积的西风优势区,在该区西侧2 Ma出现冷相盐沉积,向东侧渐变至0.72 Ma出现冷相盐沉积；而在该分界线以南,0.048 Ma才突然出现盐沉积.提出在高山深盆背景下多级盐盆迁聚成钾观点,进一步完善陆相成钾理论.本轮工作还在柴达木盆地西部发现富钾卤水的新型矿层.%The evolution of the lakes in the Tibetan plateau is dominated by the change of both the geological structure and the climate. Thus the lacustrine sediments can serve as a good recorder for both the past geological events and the climate change. Besides, the lacustrine sediments are strategic resources for salts, oils and gas. However, there had been no high resolution successive drilling core from the lacustrine sediments in the QT plateau that could reach a length of 1~2 km before this work. Since the beginning of this century, the authors have systematically collected 5 drilling cores with lengths of 1~2 km from the east and west Qaidam basin, and have obtained unprecedented rich information concerning the geological and climatic history of the Tibetan Plateau from these sedimentary cores. Through comparing the chronologic results with the latest international standard, a more precise model of magnetostratigraphy was established. Based on studying the cold, warm and eurythermal saline minerals in Qaidam basin, the authors found 31 series of cold events since 2 Ma BP. From that time Qaidam basin began to intermittently appear cold events. The time of cold events is close to the chronologic data of Cenozic Global Glaciation. The uplift of the Tibetan Plateau was tentatively divided into several stages according to the study of the deposition rate and the particle size. At the first time, the authors found that there was a demarcation line in the middle of Qaidam basin, which was not only the boundary of paleo-atmospheric circulations but also the boundary of salt formation. The westerly wind inclined area located to the north of the investigated line reflects salt deposits in the cold-wet climate period. To the west of the study area, the cold saline sediments occurred after 2 Ma, whereas they gradually crystallized into cold saline deposits at 0.72 Ma;in contrast, the saline sedimentary period started at 0.048 Ma in the south part of the boundary. The point of view is put forward in this paper that potassium was concentrated by the transportation of the multi-stage salt basin lying in the high mountain-deep basin environment, and this viewpoint can further improve the theory of potassium formation in continental facies. A new potash-rich brine horizon was found by the authors in the western Qaidam basin.