The lower sedimentary of Yixian Formation show form basin margin to centre three facies coexistence paleogeography characteristics of planar, linear and relatively quiescence water mass depositions.

• 义县组底部沉积相表现了该盆地边缘向中心横向上的洪（冲）扇、季节性河流和湖泊沉积的三相发育的古地理特征。