Donghe sandstone in Akekule

composed of mud-pebbly sandstone

well sorted(medium-to)fine-grained sandstones

siltstone and mudstone

is a normal sequence with a complete transgressive-regressive cycle

the top and bottom of which are defined by unconformities

i.e.

type Ⅰsequence boundaries.Donghe sandstone can evidently be divided

from bottom to top

into lowstand system tract

transgressive system tract and highstand system tract.As the lowstand system tract is subaerial fluvial deposit

it is underdeveloped in the basin with limited distribution.The transgressive system tract is mainly composed of shore deposit controlled by tide.A series of shallowing and fining upward parasequences constitute the retrograding parasequence group.The parasequences gradually change upward from subtidal sandbar in the lower part to intertidal sand flat

mixed sand and mud flat

and mud flat.The highstand system tract is mainly distributed in the upper Donghe sandstone.Duing the continuous deposition of Donghe sandstone

the inshore sea water circulated smoothly and(unimpededly)after the largest marine flooding surface was reached

leading to the formation of wave-controlled shore deposition system with wave action as the main geologic agent

which is mainly characterized by grayish white(medium-to)fine-grained sandstone. They constitute the characteristic "Donghe sandstone".