鄂尔多斯早古生代古构造

PALAEOTECTONICS OF ORDOS IN THE EARLY PALAEOZOIC

用野外露头剖面、钻井剖面和地震剖面相结合的综合研究方法,首先用人工合成记录结合11口井的VSP资料,对鄂尔多斯下古生界进行层位标定.在此基础上,对鄂尔多斯全区下古生界371条共长15683 km的地震剖面进行了重新处理和地层解释,这大大提高了解释精度.以此为基础,把鄂尔多斯下古生界划分为5个地层单位,即寒武系中下部、寒武系中上部及冶里组和亮甲山组、马家沟群下部、马家沟群上部、平凉组和背锅山组,并作出了它们的等厚图.从这些等厚图可以看出:前4个地质时期的古构造格局为“一隆三凹”,即西缘凹陷、南缘凹陷和东缘凹陷(或东部凹陷)呈“U”形从西南东三面包围着一个中部隆起.最后一个地质时期的古构造格局为“一隆二凹”,即西缘凹陷和南缘凹陷呈“L”形镶嵌在一个巨大的鄂尔多斯隆起的西缘和南缘.到奥陶纪末,鄂尔多斯全区以及整个华北地台均变为隆起区,从而结束了鄂尔多斯隆起和凹陷并存的历史.

The Lower Palaeozoic in Ordos were identified with the comprehensive method of integrating the outcrop sections, well sections and seismic profiles, first integrating the synthetic seismograms and the vertical seismic profiles(VSP)of 11 wells. Totally 371 pieces and 15 683 kilometers of seismic profiles were processed and stratigraphically interpretated, which greatly upgraded the interpretation of the seismic profiles . Based on above achievements, the Lower Palaeozoic in Ordos were divided into five stratigraphical units, i. e. Lower and Middle Cambrian, Middle and Upper Cambrian and Lower Ordovician, Lower Ma-jiagou Group, Upper Majiagou Group, and pingliang Formation and Beiguoshan Formation, and their isopach maps were compiled. These maps show that the palaeotectonic pattern of the former four ages was 'one uplift and three depressions', i. e. one middle uplift was surrounded by the western depression, southern depression and eastern depression, which together took the shape of 'U' , and the palaeotectonic pattern of the last age was 'one uplift and two depressions', i.e. the huge Ordos uplift borders on the western depression and southern depression, which together took the shape of 'L' . At the end of the Ordovician the Ordos and the whole North China Platform formed an unified uplift and the framework of uplifts alternating with depressions vanished.