Abstract: The analysis of the relation of A/S ratio to development of sand bodies in shortterm and middleterm baselevel cycles shows that shortterm cycle sequences with A1、A2 and C2 structural types are the most favorable for sand bodies development, the top and bottom of various grade sequence boundaries are favorable position for sand bodies with good reservoir property, and middle part of various grade cycle sequences is the position of muddy cap and barrier beds. With consideration of contradiction between the classification scheme of individual strata based on sequence boundaries of baselevel cycle and the fourgrade traditional reservoir division scheme, it is suggested that fourgrade division scheme of sandbodies and reservoirs is bounded by muddy cap and barrier beds deposited during various grade flooding, and strides across sequence boundary. The reservoir series, reservoir suite, composite reservoir, and single reservoir are related to longterm, middleterm, shortterm, and suppershortterm baselevel cycles respectively. This scheme is conformed to the divisional principle of pool development series, and is more operable in practical use.

Key words: highresolution sequence stratigraphy, baselevel cycle, sand body, barrier bed, reservoir division