progradation

Progradation is the net outward growth of a coastline or delta front resulting from the accumulation of sediment at the shore that extends the land into the sea. In sedimentary geology, it occurs when sediment supply exceeds the rate at which accommodation space is created by sea-level change, subsidence, or tectonic influences. Relative sea-level fall or ongoing subsidence can create space for new deposits, enabling the shoreline to advance seaward.

Progradational coastlines commonly develop as river-borne sands and silts are deposited at the coast or delta front, building outward lobes and strandplains. The resulting deposits include deltas with multiple lobes, beach and dune systems, and prograded deltaic wedges. Progradation produces characteristic seaward-dipping clinoforms and onlapping, downlapping, or progradational stacking patterns in outcrops and seismic reflectors.

The phenomenon has important implications for sedimentary geology and natural resources. Prograded shoreline sequences can host reservoir-quality sands in deltaic and strandplain settings and influence groundwater flow and coastal management. Progradation is contrasted with retrogradation, in which the shoreline migrates landward as accommodation exceeds sediment supply, and with aggradation, where vertical build-up occurs in place rather than a net shoreline shift.