Sequence IV is Pliocene sea-onshore transition grayer, grayish gritstone, siltstone and mudstone and becomes thicker sea facies toward trough.

• 层序IV，为上新统海陆过渡相的灰白、浅灰色砂砾岩、粉砂岩、泥岩，往冲绳海槽方向增厚，变为海相。