鄂尔多斯盆地延长组砂岩中石盐成因探讨

Genesis of halite in sandstone of Yanchang formation in Ordos basin

石盐的形成是高盐度水介质环境出现的标志。鄂尔多斯盆地延长组为一套淡水河湖三角洲沉积,现今砂岩地层水矿化度为10~80 g/L,远未达到石盐饱和时的浓度(360 g/L),但是砂岩孔隙中局部可见石盐晶体,它的出现与沉积环境和成岩环境均不匹配。通过对延长组砂岩中石盐充填特征的分析认为,延长组的部分砂岩过于致密,获得的砂岩岩芯孔隙中的流体无法大量渗出,在岩芯运输和保存阶段孔隙流体挥发浓缩,在局部地方形成石盐晶体,它是样品采集与处理过程中的产物,不能据此推测沉积或成岩环境。

Halite formation is the symbol of high salinity water environment.Yanchang Formation of Ordos Basin is a freshwater lacustrine delta deposition.The sandstone salinity of formation water is 10~80 g/l which is far from reaching the saturation concentration of halite(360 g/L),but locally little halite occurs in sandstone pores.There is contradiction between the emerging of halite and the environment of sedimentary and diagenesis.The analysis of the characteristics of halite in sandstone of Yanchang formation indicates that the halite arises in the period of core transport and preservation.The fluid can not seep out of pores of sandstone which is too dense.The halite which precipitates from pore fluid of sandstone by evaporation,cannot be used to predict the environment of sedimentary and diagenesis.