Abstract: In the light of statistics of the modern delta depositional systems in the world, the depositional systems of downwarped basin deposits are generalized as the fluvial-dalta-lake depositional systems. The paulopost depositional systems may overlie and modify the preceding depositional systems, all of which may contain fluvial-dalta-lake depositional systems. Assuming that the scales of sedimentary basins are constant, the sedimentary base-level falling-progradational processes may give rise to the increase of the proportions of the fluvial deposits in the sedimentary basins while the sedimentary base-level rising-retrogradational processes may bring about the increase of the proportions of the lake deposits in the sedimentary basins. However, the delta deposits may be less variable in proportion and less developed in the sedimentary basins. The total delta area/basin area ratios generally range between 0 and 10%. Therefore, the scales of the deltas tend to depend on those of sedimentary basins. The macroscopic scales of sedimentary basins should be considered in the sedimentary facies analysis.