鄂尔多斯盆地镇原地区长8油层组古盐度分析

根据黏土矿物X射线衍射分析和微量元素分析结果,应用Adams公式与Couch公式,对鄂尔多斯盆地镇原地区上三叠统延长组长8油层组沉积期的湖盆水体古盐度进行定量计算。由于受到伊蒙混层转化的影响,利用Couch公式计算出的盐度可能偏低,而Adams公式计算结果更加符合长8沉积时期浅水三角洲沉积体系的湖水盐度的平面规律。研究表明:镇原地区长8油层组沉积期湖盆水体具半咸水—咸水的性质,盐度从北东和北西2个方向往湖盆中央及东南方逐渐升高。盐度值较高的区域为相对闭塞的湖湾和湖盆中心的半深湖区。平面上,古盐度顺河流入注湖盆的方向逐渐降低。根据古盐度变化恢复了古地理。较高盐度的水体在早成岩阶段有利于绿泥石环边胶结和浊沸石形成,前者有利于原生粒间孔隙保存,后者有利于溶蚀形成丰富的次生溶孔。

Analysis of paleosalinity from Member 8 oil layer of Yanchang Formation in Zhenyuan area,Ordos Basin,China

Based on the analysis of X-ray diffraction analysis and the trace elements of clay minerals, the authors use the Adams Formula and Couch Formula quantitatively calculate and restore the water paleosalinity of the basin in Member 8 oil layer sedimentary period of Yanchang Formation in Zhenyuan area,Ordos Basin.Due to the mutual transformation of illite and laumontite,the calculated palaeosalinity by the Couch Formula may be low.And the result by the Adams Formula is more in line with the law of the paleosalinity of the shallow water deltaic depositional system in Member 8 sedimentary period.The research finds that the lacustrine water body has properties of brackish water and saline water during the deposition of Member 8 of Yanchang Formation in Zhenyuan area.And the salinity increases gradually from the northeast and northwest to the centre of the lake and the southeast.The semi deep lake in the relatively occlusion bay and the central area have higher salinity values.The paleosalinity reduces gradually with the river flowing into lakes abd basins on plane.This paper recovers the ancient geography according to the change of paleosalinity,and also verifies that the high salinity water is conducive to the formation of chlorite rim cementation and laumontite in the early diagenetic stage.The former is conducive to the preservation of primary intergranular pores,and the latter is conducive to the formation of rich secondary pores by corrosion.