太原盆地洪山第四纪剖面的发现

洪山剖面是太原盆地东南边缘一湖积台地上的第四纪中晚期沉积剖面 ,该剖面中的湖相层典型特征是 :质地均一的灰绿、黄绿色粉砂粘土层与含碳酸钙结晶体的沉积层呈互层分布。利用地层连续追踪及铀系测年法分析 ,剖面中的湖相层是在 S5古土壤发育晚期至 S1 古土壤发育早期这一时间段内沉积而成的 ,剖面当时所处的位置正位于太原古湖盆的湖岸地带 ,沉积环境受着气候干湿变化的强烈影响。当气候湿润时 ,湖面升高 ,湖盆扩大 ,剖面点被湖水淹没 ,接受着湖相粉砂粘土层的沉积 ;干旱时 ,湖盆变化则相反 ,剖面点出露气下 ,并因地下水毛管作用的结果在沉积层表面产生碳酸钙结晶体。该剖面的研究结果同时还表明 :由第四纪气候的干湿变化对太原盆地这样大的湖盆 ,只能产生数米的湖面升降波动 ;与构造因素引起的湖盆变化相比 ,这种波动是小幅度的

THE SIGNIFICANCE OF THE HONGSHAN QUATERNARY SECTION IN TAIYUAN BASIN, SHANXI

The Hongshan Quaternary section is located on the Hongshan platform at the southeastern edge of the Taiyuan Basin. It is characterized by grey green and yellow green silty clay beds interbedded with layers of CaCO 3 in the lacustrine sediments. Along the gully up, we can see the layers containing CaCO 3changing into loesses gradually. Using U series to date these CaCO 3, we find that the sediments containing CaCO 3 were formed in consistent with the accumulation of the loesses and lacustrine sediment with that of paleosols. After analyzing all the facts about the section, we draw the preliminary conclusions: 1) the changes in chemical contents in this section result from the change in paleoclimate from 0.50 MaB.P. to 0.13 MaB.P.; in other words, it is the changing paleoclimate that control the development of Taiyuan Basin during this time. 2) the change in paleoclimate can only contribute to the rise and set of lake surface no more than several meters; tectonic uplifts play more important roles in the development of the Taiyuan Basin than the changes of paleoclimate.