progradational

Progradational describes a mode of sediment deposition in which the active depositional margin advances seaward due to ongoing sediment supply. In coastal and deltaic settings, progradation occurs when sediment delivered to the coast accumulates at the shoreline faster than space is created in the basin, causing the shoreline or delta front to grow outward and the depositional wedge to extend seaward.

In stratigraphy, progradational sequences are stacked deposits that exhibit outward growth of the deposit over time. These sequences often show landward thinning and basinward downlap of beds, and may feature foreset beds dipping toward the basin. Progradation is commonly associated with periods of relatively low relative sea level or high sediment supply and can be facilitated by tectonic subsidence that maintains accommodation for new sediment.

Common environments include river-dominated deltas and other shoreline-dominated deltaic or shelf-margin systems where substantial sediment input drives outward expansion of the depositional margin. Progradational intervals are typically considered in contrast to retrogradation, where the shoreline migrates landward due to rising sea level or reduced sediment supply, and to aggradation, where vertical buildup occurs without significant shoreline shift.

Economic significance may arise because progradational sequences can create stratigraphic architectures that influence reservoir connectivity and trap development in deltaic and shelf systems. Related concepts include retrogradation, aggradation, clinoforms, and sequence stratigraphy.