The middle oil-member is characterized by medium-sized sandstone and pebbled sandstone, with fair sorting and subangular sphaericity.Rock types mainly were feldspar debris sandstone.

中油组积中砂岩和含砾中砂岩，粒整体较粗，分选性较好，磨圆棱角状为，岩石类型为长石岩屑砂岩。