Retrogradation is the landward change in position of the front of a
river delta
A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creat ...
with time. This occurs when the
mass balance of sediment into the delta is such that the
volume
Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...
of incoming
sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
is less than the volume of the delta that is lost through
subsidence
Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...
,
sea-level rise, and/or
erosion
Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...
. As a result, retrogradation is most common:
*during periods of
sea-level rise which results in
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. Transgressions can be caused by the land sinking or by the ocean basins filling with water ...
. This can occur during major periods of
global warming
Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...
and the melting of continental
ice sheets.
*with extremely low sediment input.
See also
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ReferencesSchlumberger Oilfield Glossary
Sedimentology
Stratigraphy
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