摘要：

在对鄂尔多斯盆地目的层段总体资料了解的基础上，对盆地南部4个露头剖面、18口井岩心的砂岩进行了切片分析，根据长石含量变化和其他岩矿特征、测井曲线与岩石组合特征、连井剖面以及露头沉积相分析，明确了山西组—下石盒子组盒8段沉积物在盆地南部的汇水区位置。“汇水区”指搬运南北物源沉积物的流水汇聚区，它大体上是南北物源沉积物分布的分界区、大致呈东西向分布。汇水区南北的长石含量存在明显差异。提出了在汇水区局部又存在南北物源沉积“交互区”的认识，“交互区”指南北物源沉积物抵达汇水区并在局部地段发生交互的地区，它是南北物源沉积物的连通区。交互区位于汇水区并分隔汇水区。在盒8段交互区发现了还原条件下形成的早期成岩矿物——菱铁矿结核。盆地南部山西期—盒8沉积期的沉积古地理受南部和北部物源沉积物的双重影响，连井剖面显示汇水区南北沉积相带具有对称分布的特征，其沉积单元和相带包括：（1）汇水区，含3个交互区；（2）汇水区南缘三角洲相带，含来自南部物源的3个三角洲；（3）汇水区北缘三角洲相带，含来自北部物源的4～5个三角洲；（4）与南、北三角洲相带过渡的河流相带。在上述认识的基础上，绘制了研究区目的层段沉积模式图。

Abstract:

Previous studies have not determined the location of the catchment area of the Shanxi Formation and Member 8 of Xiashihezi Formation sediments in the Ordos Basin derived  from north and south provenaces. Thinsection analyses of sandstones from 4 outcrops and cores for 18 wells in the southern basin have been carried out in this study on the basis of understanding of the general data of the studied stratigraphic intervals in the Ordos Basin. The location of catchment area for the  sediments of the Shanxi Formation and Member 8 of Xiashihezi Formation is defined in the southern Ordos Basin based on the changes of feldspar content and other lithological characters，the characteristics of log curves and rock assemblages，and the facies analyses of across well profiles and outcrops. The “catchment area” refers the area where the rivers transporting the sediments from north and south provenances merge and it is the bordering area which separates the
earlyderived sediments from the north to the south. It lies roughly in eastwest direction. There are obvious differences in feldspar content between the north and south sides of the catchment area. It is put forward that there are “intersection parts” of sediments from the north and south in local places of the catchment area. The “intersection parts” mean the areas where the sediments from the north and south meet and intersect with each other，which are the connecting places of the sediments from the north and south. The intersection parts are located in the catchment area and separate  it into different parts. The siderite nodules formed in the early diagenetic stage under reduction conditions were found in the intersection parts of the Member 8 of Xiashihezi Formation. The palaeogeography of the southern basin during the deposition of the Shanxi Formation and Member 8 of Xiashihezi Formation was controlled by  sediments from both the north and south. The acrosswell sections show that the sedimentary facies belts have a symmetrical distribution on the north and south sides of the catchment area. The sedimentary units and facies belts include:1)the catchment area，with three intersection parts; 2)the delta facies belt on the south margin of the catchment area，including 3 deltas from the south provenance; 3)the delta facies belt on the north margin of the catchment area，including 45deltas from the north provenance; 4)the fluvial facies belts which are the transitional belts of north and south deltas. The depositional model for  the studied intervals in the study area in Ordos Basin is proposed.