鄂尔多斯盆地西部奥陶纪岩相古地理特征

Petrofacies Paleogeographic Characteristics in Ordovician Period of Western Ordos Basin

鄂尔多斯盆地西部处于鄂尔多斯地块与阿拉善地块、秦祁褶皱带之间，经历了多阶段沉积演化，构造变形复杂，岩相古地理重建困难。本文通过大量地表露头和钻井剖面观察，采用盆地构造和盆地沉积充填相结合分析的方法，将鄂尔多斯盆地西部划分出2大沉积体系7个沉积-构造单元，认为奥陶纪岩相古地理总格局为“海陆并存、台地斜坡海槽（盆地）相邻过渡，台地中有坪和滩，斜坡海槽（盆地）中有扇”。指出桌子山期以台地相沉积为主，克里摩里-平凉期以斜坡-海槽（盆地）沉积为主，背锅山期海退隆升。经历了拗陷→裂陷→闭合回返一个完整的海水进退旋回。

Through massive observation of outcrops and drilling profiles, western Ondos basin is divided into 7 sedimentary-tectonic units in 2 sedimentary systems, by using an analysis method of combining the basin structure with the basin sedimentary filling. The overall petrofacies palaeogeographic pattern in Ordovieian Period is considered to be ＂the sea and land coexists; the tableland-slope-trough （basin） neighboring transition; the tableland contains plateau and stream bed; the slope-trough （basin） has the fan＂. It is pointed out that the table-facies deposition is dominated at the Zhuozishan Age. Slope-trough （basin） deposition is dominated at Kelimoli - Pingliang Age. At Beiguoshan Age, marine regression and land rise occur. From depression to crackdown and dosed return, a complete cycle of marine progression and regression is experienced.