顶积层 前积层 底积层 pset Distributary channel Lake Foreset beds Bottomset eas (a Prograding delta-1 FIGURE 4.16 (a)Internal structure of the simplest type of prograding delta (b)A small delta in which bottomset, foreset, and topset beds are visible顶积层 前积层 底积层 Prograding delta-1