鄂尔多斯盆地延安组层序地层格架与煤层形成

研究鄂尔多斯盆地延安组的煤层发育特征，首先建立延安组等时的层序地层格架，进而分析可容空间变化对煤层形成的控制作用。通过分析野外露头、钻孔、测井等资料，识别延安组中发育的关键层序地层界面，将延安组划分为3个三级层序；层序由低位正常湖退、湖侵、高位正常湖退和强迫湖退4个体系域组成，并建立了全盆地范围等时的层序地层格架。研究发现:在等时层序地层格架中，煤层主要发育在层序I、层序Ⅱ湖侵和高位正常湖退体系域的中、晚期和层序Ⅲ的湖侵体系域的晚期；在区域上，盆地北部地势较为平坦，发育中等厚度、区域稳定性较好的煤层,盆地南部发育稳定性较差的厚-巨厚煤层；从滨湖平原到三角洲平原再到河流泛滥平原，厚煤层从位于四级基准面上升半旋回的底部逐渐过渡到中上部。综上可知，不同沉积区可容空间增加速率与泥炭堆积速率达到平衡的位置不同，厚煤层主要发育在二者近似处于平衡状态的位置，并且发育随着沉积相带变化有规律地迁移。

Sequence Stratigraphic Framework and Coal Formation of Yan’an Formation in Ordos Basin

In order to research the coal bearing features of Yan’an Formation in Ordos basin, the isochronous stratigraphic framework is established, then the controlling effect of accommodation space changes to coal formation can be analyzed. By analyzing the outcrops, boreholes, logging curves, the typical sequence stratigraphy boundaries were recognized. The Yan’an Formation are divided into 3 third-order sequences, and each of them are composed of lowstand normal regression systems tract, lake transgressive systems tract, highstand normal regression system tracts, and forced regression systems tract. The thick coals mainly developed in the middle and late periods of the lake transgressive systems tract and highstand normal regression system tract. In north part of the basin, the mid-thick and stable coal seams developed on the flat landform. And in south part of the basin, thick-mega and unstable coal seams developed. From the lakeshore plain to delta plain to flood plain of river, the thick coal seams located in the bottom to middle upper part of the fourth base level uprising cycle gradually. It can be concluded that, in different sedimentary area, position of the balance between accommodation space changes rate and peat accumulation rate was different, and the thick coal beds mainly developed at the balance position. The development of thick coal beds migrated following the sedimentary changes.