【摘要】 有关鄂尔多斯盆地西部晚三叠世的构造属性问题,前人的观点大多认为该时期为(类)前陆盆地,笔者对此提出置疑,主要有3个方面的依据:首先,对西缘汝箕沟、石沟驿和崆峒山地区晚三叠世延长组的3套粗碎屑沉积进行了重新认识。汝箕沟延长组确实为边缘相沉积,但其附近层位板内玄武岩的出现,表明该区晚三叠世为拉张环境下的沉积。最新研究表明,石沟驿地区延长组沉积厚度并不大,不超过1500m。崆峒山砾岩沉积可能受西南部的秦祁造山带影响所致,不能作为盆地西部沉积的代表。其次,通过编制晚三叠世延长组地层等厚图及一系列东西向地层剖面对比,发现该时期以往认为的盆地西部从南至北的巨厚沉降带并不存在。最后,通过地震剖面、平衡剖面和裂变径迹测试数据分析,指出西部现今存在的横山堡后冲构造带和马家滩大型逆冲推覆构造带并未形成于晚三叠世,其最早形成于晚侏罗世。故鄂尔多斯盆地西部晚三叠世构造属性并非为前陆盆地,而是残延克拉通内叠合盆地的组成部分。该认识对盆地西部的油气勘探具有重要意义。更多还原

【Abstract】 Most predecessors held the view that the western Ordos basin was tectonically a foreland basin during the Late Triassic. This paper questions the validity of this view mainly based on the following three lines of evidence. First, three sequences of coarse clastic sediments in the Late Triassic Yanchang Formation in the Rujigou, Shigouyi and Kongdongshan areas on the western margin of the basin were revisited. The Yanchang Formation in the Rujigou area is of marginal facies indeed, but the appearance of intraplate basalt in the horizon nearby suggests that the Yanchang Formation in the area was deposited in an extensional environment during the Late Triassic. Recent study indicates that the Yanchang Formation in the Shigouyi is not very thick, less than 1500 m in thickness. The conglomerate in Kongdongshan is not typical of the sediments in the western part of the basin because it was probably influenced by the Qinling-Qilian orogen to the southwest of the Ordos basin. Secondly, through the compilation of the isopach map of the Late Triassic Yanchang Formation and several E-W-trending stratigraphic correlation sections it is found that a N-S-trending, very thick subsidence belt, as thought previously to be present in the western part of the basin during this period, does not exist. Finally, through the analysis of the seismic profile, balanced cross section and fission track data, the authors think that the present Hengshanbu back-thrust belt and large-scale Majiatan thrust nappe belt did not form in the Late Triassic but in the Late Jurassic. Therefore, tectonically the western Ordos basin was not a foreland basin during the Late Triassic but a component part of a superposed basin in a residual and extended craton.更多还原