The extension variation of the depressions in the Bohai basin clearly suggests that the basin was experienced Eocene and Oligocene extension cycles, and the latter involves two subcycles.

• 渤海盆地中各坳陷在早第三纪各阶段拉张量表明,盆地经历了始新世与渐新世的拉张旋回,而渐新世的拉张旋回又可分为两个亚旋回,在时空上,拉张活动具很大的不均衡性。