پسروی (علوم زمین)

thumb | right|Scheme describing a retrogradation depositional pattern of coastal (shore or deltaic) sediments: t1-2-3 are consecutive sedimentation times. Ideal lithostratigraphic sections along the depositional system are reported. Retrogradation is the landward change in position of the front of a coastal depositional system (such as a river delta) with time. This occurs when the mass balance of sediment into a delta or a beach system is such that the volume of incoming sediment is less than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion. As a result,