TRANSGRESSION, MARINE

Flooding of the land by the sea; a relative rise in sea level. Evidence of a [Page 1108]marine transgression in sedimentary deposits may be preserved as marine deposits (e.g. marine band) overlying non-marine ones, an upward deepening of facies or, in the deposits of terrestrial environments, a change in facies type or facies architecture. A surface of marine transgression is termed a flooding surface in sequence stratigraphy.

A marine transgression may be caused by one or several of the following factors: (1) a eustatic sealevel rise (i.e. absolute sea-level change, a mechanism of allocyclic change); (2) an increase in the rate of tectonic subsidence (a relative sea-level change, an allocyclic change) or (3) a decrease in sediment supply (relative sea-level change), which could be attributed to an allocyclic change (e.g. climatic change in the source area) or an autocyclic change (e.g. abandonment of a delta lobe due to avulsion). One of the challenges for modern sedimentology is to clarify the complex relationships between these controlling factors in the geological record.

[See alsoeustasy, highstand, regression, marine, sea-level change, sea-level rise]