老挝万象地区的侏罗系

THE JURASSIC SYSTEM IN THE VIENTIANE AREA OF LAOS

为了解老挝万象含盐盆地的形成与演化历史,在老挝万象平原钾镁盐矿勘查项目中,对该地区进行了区域地质调查。老挝万象地区的侏罗系为一套夹少量碳酸盐岩的红色陆源碎屑沉积,由上到下可划分为班辛黑组、南舍组、南立组;该地层的介形类分属Gomphocythere-Darwinula组合、Darwinula sarytirmenensi-Darwinula magnca组合,叶肢介属滇南古渔乡叶肢介动物群,腹足类具中侏罗世陆生动物群特征;本区侏罗系为一套以湖泊沉积为主的河湖相沉积,构成一个完整的Ⅲ级层序,可划分出低水位体系域、湖侵体系域、凝缩期沉积及高水位体系域。这3个组的岩石地层、生物地层及年代地层特征,可与我国滇西地区的漾江组、花开左组相对比。

In order to understand the formation and evolution history of the Vientiane salt-bearing basin of Laos, we have carried out a regional geological survey of this area in the project of K-Mg salt deposit exploration of the Vientiane Plain of Laos. According to the investigation, the Jurassic in Vientiane area of Laos is represented by a set of red terrigenous clastic deposit with minor carbonate rocks. It can be divided into, in descending order, the Banxinhei Formation （J2bh）, Nanshe Formation （J1-2ns） and Nanli Formation （Jlnl）. The ostracod faunas in the Jurassic succesions of the Vientiane area belong to the Gomphocythere-Darwinula assemblage and Darwinula sarytirmenensi-Darwinula magna assemblage. The conchostracan fossils belong to Palaeolimnadia diannanensis fauna. The gastropod fossils are characteristics of middle Jurassic terrestrial faunas. The Jurassic in this area consists of a set of fluvial-lacustrine sediments （dominated by lacustrine sediments）, which form a complete third-order sequence with recognizable of low water-table system, lake transgression system, condensation sediment, and high water-table system. The lithostratigraphic, biostratigraphic and chronostratigraphic characteristics of these formations can be compared with the Yangjiang Formation （J1y） and Huakaizuo Formation （J2h） in West Yunnan of China.