鄂尔多斯盆地西缘晚古生代层序地层划分

LATE PALAEOZOIC SEQUENCE STRATIGRAPHIC DIVISION OF THE WESTERN FRINGE OF E’ERDUOSI BASIN

鄂尔多斯盆地西缘上古生界地层发育较全,沉积巨厚,是最有前景的天然气勘探层系。根据露头、钻井、测井和地震资料综合分析,在上古生界识别出了4种类型的层序界面,划分5个层序12个体系域。在此基础上通过剖面相分析,编制地层、砂岩厚度和含砂率等图件,结合古构造背景,采用优势相作图法,重塑了岩相古地理。认为该区经历了裂陷海湾、陆表海和内陆拗陷充填3 大沉积发展阶段,岩相古地理由裂陷海湾—陆表海碳酸盐岩台地—三角洲复合沉积体系逐渐演变为三角洲—河流沉积体系,最终被河流—湖泊沉积体系取代,指出砂岩分布受控于沉积环境。从而为寻找有利相带,部署钻井提供了地质依据。

The Upper Paleozoic along the western fringe of E'erduosi Basin is the most perspective formation for gas exploration in the basin, being completely developed with a great thickness. Through comprehensively analyzing the data on outcrop observation, drilling, log and seismic exploration, it was indicated that there are 4 sequence interfaces, 5 sequence and 12 system domains in Upper Paleozoic. On the basis of the section facies analysis and the working-out of these contour maps as formation thickness, sand-stone thickness and sand content, etc., the lithofacies and paleogeography were reestablished by use of dominant facies mapping method in combination with palaeotectonic setting. It was considered that three sedimentary developing stages, i. e. rift-sag gulf, epicontinental sea and inland depression filling, had been suffered in the region; and the lithofacies and paleogeography changed from the rift-sag gulf - epicontinental carbonate platform - delta compound deposit system to the delta - fluvial deposit system, then to the fluvial-lacustrine deposit system. Finally, it is pointed out in the paper that the distribution of sandstones is controlled by sedimentary environments, thus providing a geological basis for surveying the favourable facies zones to deploy exploration wells.