On the basis of sedimentary rhythmic characteristics from lake delta of the Triassic Yanchang Series in North Shaanxi

some petrogenetic units were selected

the paragenetic relationship of the units were found out through mathematical statistics

and the relation-ship was induced to be a vertical sequential correlatograph.According to the thickness statistics of the petrogenetic units

the vertical model of the lake delta was established.The model shows that the lake deltaic sediments are characterized by the development of dis-tributary channel sandbodies belonging to constructive delta resulted mainly by river.