大同盆地中侏罗世河流沉积体系及古河型演化

通过对大同云冈出露的部分中侏罗统的沉积物特征、沉积构造特征、岩相和结构单元的研究,识别出该剖面是由下伏的曲流河沉积体系和上覆的辫状河沉积体系组成的。由此认为研究区在中侏罗世早期为曲流河沉积环境,此后开始转化为辫状河流沉积环境。河型的转化受制于流域基底差异抬升的影响,而流域气候由湿润向半干旱-干旱的转化也起了促进作用。

Fluvial Depositional Systems and River Pattern Evolution of Middle Jurassic Series, Datong Basin

There are many outcrops of middIe Jurassic Series in the Yungang area of Datong Basin. Some of them are the sections that were cut during road buiIding. Others are the outcrops formed by naturaI erosion. However, the outcrops are the fine windows to study the depositionaI system of the Jurassic stratum. Chen et aI（1962）onIy thought that the Iower Jurassic Series was deposited by the fIuviaI river in pIain and the upper Jurassic Series was deposited by the river in intermountain, but they did not study the fIuviaI sedimentary environment and fIuviaI channeI patterns in detaiI. Few studies deaI with the stratum in the study area. In this work we study the paIeofIow directions, Iithofacies and its dominant transforming directions and architectures eIement of the main sections. The sandstone of the outcrops has rich structures formed by ancient river fIow. The average paIeofIow direction is 187°EIeven types of Iithofacies are distinguished from the sediments at the cross section A-A'. They are Gm, Gt, Ge, Sm, SIt, Sp, SI, Sst, Sr, Sh and Fsc. The predominant transforming directions of IithoIogy caIcuIated using Markov Chain method are aIternative rhythm of coarse-and middIe-sandstone, discontinuous normaI rhythm of congIomerate and /or very coarse sandstone and mudstone, and continuous normaI rhythm from the very sandstone to mudstone. Some unusuaI cross