Marine transgression

A marine transgression is a geologic event where sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding.

Sedimentary facies changes may indicate transgressions and regressions and are often easily identified because of the unique conditions required to deposit each type of sediment.

Fine-grained sediments however, such as silt and carbonate muds, are deposited further offshore, in deeper, lower energy waters.

[1] Thus, a transgression reveals itself in the sedimentary column when there is a change from nearshore facies (such as sandstone) to offshore ones (such as marl), from the oldest to the youngest rocks.

Lateral changes in facies are also important; a well-marked transgression sequence in an area where an epeiric sea was deep may be only partially further away, where the water was shallow.