鄂尔多斯盆地南部岐山地区上奥陶统平凉组深水沉积特征及古地理分析

岐山地区上奥陶统平凉组是一套颜色较深的泥岩、粉砂岩、泥质灰岩，夹有薄层斑脱岩的沉积岩系，与上覆和下伏地层在岩石类型、沉积环境和形成的构造背景方面都有明显的差别。研究平凉组的沉积特征，分析其形成环境和构造背景，对于揭示鄂尔多斯盆地晚奥陶世的古地理、古气候、古构造都具有重要的理论意义。通过剖面测制和镜下鉴定，对平凉组的地层学、岩石学和沉积相进行了精细研究。结果表明，平凉组按照岩石组合学特征可以分为3个旋回。第一旋回以泥岩和砂岩为主，灰岩相对较少，沉积作用以浊流沉积和砂质等深流、泥质等深流沉积为主；第二旋回泥岩和灰岩所占比例大致相等，沉积作用为泥质等深流和灰质等深流沉积；第三旋回以砂泥岩为主，少量灰岩，属于砂质等深流为主，少量灰质等深流，浊流沉积不发育。平凉组沉积作用及沉积特征表明，晚奥陶世，华北陆块南缘发生大规模裂陷，结束陆表海沉积，盆地的南部边缘形成大陆斜坡。

Deep-water Sedimentary Characteristics and Paleogeographic Analysis of the Pingliang Formation in Qishan Area,Southern Ordos Basin

The Pingliang Formation in Qishan area is composed of dark mudstone, siltstone and argillaceous limestone with imbedded thin layered bentonites. There are obvious differences between the Pingliang Formation and its overlying as well as underlying strata on rock type, sedimentary environment and tectonic background. The research on sedimentary characteristics, tectonic background and formation environment has theoretical significance for revealing Late Ordovician paleogeography, paleoclimate and paleotectonics in the Ordos Basin. Based on profile measurement and microscopic identification, the stratigraphy, petrology and sedimentary facies of the Pingliang Formation have been studied in detail. All of these results indicate that the Pingliang Formation can be divided into three sedimentary cycles according to the petrological features. The first sedimentary cycle mainly consists of mudstone and sandstone with relatively small quantity of limestone. The sedimentary facies are mainly composed of turbidite deposition, arenarious contour current and argillaceous contour current deposits. In the second sedimentary cycle, the proportion between mudstone and limestone is similar. The sedimentary facies are mainly composed of argillaceous contour current deposits and cinereal contour current deposits. The third cycle comprises mainly sandstone and mudstone with small amount of limestone. The sedimentary facies are mainly composed of arenarious contour current with a small amount of cinereal contour current deposits.