{{short description|Movement of the front of a river delta inland over time}} {{About|the geological term related to river deltas|other uses|Retrograde (disambiguation)}}
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, retrogradation is most common: *during periods of sea-level rise which results in marine transgression. This can occur during major periods of global warming and the melting of continental ice sheets. *with extremely low sediment input.
Retrogradation may occur also in carbonate platforms during phases of sea-level rise, when the increment exceeds carbonate inputs from the biological community. In such case there is a landward shift of the reef facies onto preceding back-reef or lagoonal facies, while fore-reef or even basinal facies develop above the preceding reef system.
==See also== *{{annotated link|Progradation}} *{{annotated link|River delta}} *{{annotated link|Aggradation}} *{{annotated link|Marine transgression}} *{{annotated link|Marine regression}} *{{annotated link|Sedimentology}} *{{annotated link|Stratigraphy}} *{{annotated link|Sequence stratigraphy}} *{{annotated link|Sediment transport}}
==References== [http://www.glossary.oilfield.slb.com/Display.cfm?Term=retrogradation Schlumberger Oilfield Glossary]
Category:Sedimentology Category:Stratigraphy
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