Marine regression is a geologic event in which areas of the seafloor are exposed above sea level, thus changing the coastline and the corresponding increase in the surface area of emerged land.
Regressions can be caused by an actual drop in sea level that may be caused by glaciation, or by a rise in the earth’s crust caused by tectonic movements, or by subsidence of the ocean floor related to episodes of subduction of the earth’s crust during ongoing plate tectonic movements.