Progradation of a clastic continental-margin sediment wedge onto attenuated continental or oceanic crust is characterized by load-induced crustal subsidence and a predictable internal structural and depositional architecture. The prograding wedge has one free surface, characterized by a very low but nonetheless unstable slope. Here, sandy, normally consolidated sediment is deposited on top of an underconsolidated mud-rich

End_Page 2044------------------------------

foundation. The combination of large scale, morphology, and undercompaction make continental-margin sequences prime sites for syndepositional gravitational tectonics, including gravity gliding, gravity spreading, and diapirism.

Strain regimes reflect the focus of tensional stress along the continental margin and of compressive stress at the toe of the slope. A belt of active, listric normal faults defines the contemporary shelf margin, producing a structurally defined shelf edge/upper slope depocenter. In contrast, the lower slope is a compressional tectonic terrane characterized by uplift, folding, and overthrusting.

Major prograding clastic margins, such as the Gulf Coast Cenozoic wedge or the Niger delta, contain one or more principal depocenters where deltaic headlands prograde to the contemporary shelf edge, feeding sediment directly onto portions of the continental slope. Marginal to such headlands, submarine canyon systems may act as pipelines, funneling large amounts of sediment across the outer shelf, down the slope, and onto the abyssal plain in front of the offlap wedge. Eustatic sea level changes may temporally or locally affect depositional and erosional patterns, but are commonly masked or overwhelmed by regional intraplate tectonic events and extrabasinal controls on rate and location of sediment transport into the basin.

End_of_Article - Last_Page 2045------------