鄂尔多斯奥陶纪古构造

用野外露头剖面、钻井剖面和地震剖面相结合的研究方法,对鄂尔多斯地区奥陶系213条共长8317 km的地震剖面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,把鄂尔多斯奥陶系划分为10个地层单位,即冶里组、亮甲山组、马家沟一组、马家沟二组、马家沟三组、马家沟四组、马家沟五组、马家沟六组、平凉组和背锅山组,并绘制了它们的等厚图。从这些图可以看出,冶里期和亮甲山期的古构造格局为“一隆三凹”,即西缘凹陷、南缘凹陷和东缘凹陷呈“U”字形包围着一个中部隆起。到马家沟一期至六期,“一隆三凹”的古构造格局仍然基本上保持着,尽管其隆起和凹陷的形状、大小和位置均有所变化。到平凉期,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。到背锅山期,古构造格局为“一隆一凹”,即一个残留的西南缘凹陷位于一个更加庞大的鄂尔多斯隆起的西南缘一隅。到奥陶纪末,鄂尔多斯地区以及整个的华北地台均变为隆起区,从而结束了鄂尔多斯地区隆起与凹陷并存的古构造格局。

PALAEOTECTONICS OF ORDOVICIAN IN ORDOS

The Ordovician in Ordos was identified with a comprehensive method of integrating the outcrop sections, well sections and seismic profiles. Totally 213 pie
ces and 8317 km of seismic profiles were disposed and stratigraphically interpre
tated, which greatly upgraded the interpretation of the seismic profiles. Based
on above achievements, the Ordovician in Ordos was divided into 10 stratigraphi
cal units, i.e. Yeli Formation, Liangjiashan Formation, Majiagou Formation Ⅰ, Majiagou Formation Ⅱ, Majiagou Formation Ⅲ, Majiagou Formation Ⅳ,  Majiagou Formation Ⅴ, Majiagou Formation Ⅵ, Pingliang Formation and Beiguoshan Formation.Their isopach maps were compiled. These maps show that the palaeotectonics
of Yeli Age and Liangjiashan Age was in the style of one uplift and three depressions, i.e. o
ne middle uplift was surrounded by western depression, southern depression and ea
stern depression, which took the shape of “U". The palaeotectonics of Majiagou
Age Ⅰ to Majiagou Age Ⅵ shaped up one uplift and three depressions, although the shape, size and location of uplifts and depressions were changeable. The palaeo tectonics of Pingliang Age was in the shape of one uplift and two depressions, i.e. the enormous Ordos uplift was edged with the western depression and southern depression, which took the shape of “L". The  palaeotectonics of Beiguoshan Age was in the shape of one u
plift and one depression, i.e. the residual southwestern depression was located at the southwestern corner of the more enormous Ordos uplift. At the end of Ordov
ician, the Ordos and the whole North China Platform came into an unified uplift
and the framework of uplifts cooperated with depressions vanished.