It commonly is thought that transgressive or regressive events which may have occurred simultaneously at geographically separated continental margins have been caused by worldwide sea-level rise or fall, respectively. Instead, it will be shown here that these events commonly may be caused by changes in the rates of sea-level rise or fall. The subsidence of an Atlantic-type (passive) margin is modeled here as a platform subsiding about a landward hingeline. The rate of subsidence is greatest at the seaward side of the platform and decreases landward to zero at the hingeline. It appears that the rate of subsidence at the seaward edge of the platform (shelf edge) is greater than the rate at which sea level may possibly rise or fall (excepting sea-level changes due to glaciat on, dessication, flooding of small ocean basins, and other sudden events). Thus, if sea level is falling, the shoreline will move toward that point on the subsiding platform at which the rate of sea-level fall is equal to the rate of subsidence minus the sedimentation rate. If the rate of sea-level fall decreases the shoreline will move landward, if the rate increases the shoreline will migrate seaward. If sea level is rising the shoreline will move to that point where the rate of sea-level rise is equal to the sedimentation rate minus the subsidence rate. Thus, if the rate of sea-level rise decreases the shoreline will move seaward; if the rate increases the shoreline will move landward.

The position of the shoreline also is a function of the sedimentation rate. These relationships have been quantified so that the position of the shoreline and the thickness of the sediments deposited during discrete time intervals may be computed as a function of the rate of sea-level change and the sedimentation rate.