摘要
文章记述了云南龙街盆地龙街组湖相粉砂层的特征、形成环境及地层时代,并讨论了龙街粉砂层和泥石流堆积的相变关系及其发育规律。对广布于龙街盆地的红土风化壳的化学性质、类型、时代及其所反映的气候环境进行了分析。在此基础上着重讨论了龙街盆地自中—晚更新世以来的湖盆变迁、沉积规律及气候环境特征。
This paper deals wkh the Late Pleistocene lacustrine sedimentary facies and red clay weathering mantle of Longjie Basin, Yunnan Province, and discusses their features and the development of the basin in Pleistocene. The Longjie Basin is situated on the conflunce of Jinshajiang River and Longchuanjiang River in the north part of Yuanmou Basin. The height of basin is about 950—1 000m, it is a long and narrow graben basin. The lacustrine fluvial and debris flow deposits, as well as red clay weathering mantle are well developed in the basin. This area is under the control of the subtropical high pressure zone, the effect of Fohn is distinct. The climate is hot and dry. The physical and chemical weathering of rock was very intense. The Longjie formation is widespread in the basin. This formation consists of silt and claycysilt, its colour varies from grey to greyish-white, hence forming a uniform silt layer, where stable and large horizonal beddings and laminated clayey silt are well developed. The thickness is about 130m. It is a typical sediments of deep-lake facies. During the end of the Mid-Pleistocene or the beginning of the Late-Pleistocene, the Yuanmou fault began to reactivate, the Longjie Basin was downfauhed and covered with water, and the lacustrine sediments were deposited. In addition, the red clay weathering mantle is widespread on the top of the hills within and along the margin of the Longjie Basin. A lot of dark-brown manganese-iron nodules, and mantle are scattered on the surface of the red clay. White calcareous concretion beds are developed at the bottom of the red clay. The chemical elements of the red clay are: SiO_2 62—64%, Al_2O_3 16%. The ratio of SiO_2/Al_2O_3 varies from 6.5 to 6.7. The characteristics mentioned above indicate that the red clay belongs to the weatl ring mantle of the calcium-rich silicon-aluminium-ferrite type. The age of the red clay weathering mantle is Late Pleistocene to Holocene. Therefore, the paleoclimate in this region in Late Pleistocene was hot and dry.
出处
《第四纪研究》
CAS
CSCD
1992年第3期216-223,共8页
Quaternary Sciences
