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.

油组主要沉积砂岩和砂岩，粒整体较，性较好，磨圆以次棱角状为主，岩石类型为长石岩屑砂岩。