. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography Shelf Sedimentation 131 continent reverses so that the drainage area serving the coast increases. Its sediment load increases and its drainage pattern becomes more integrated. As the gradient of the submarine slope decreases, gravity dispersal becomes less efficient; a sediment prism accumulates, whose upper surface is hy- draulically maintained (graded) at a yet-lesser slope. Gravity dispersal is now confined largely to the continental slope. In zo
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography Shelf Sedimentation 131 continent reverses so that the drainage area serving the coast increases. Its sediment load increases and its drainage pattern becomes more integrated. As the gradient of the submarine slope decreases, gravity dispersal becomes less efficient; a sediment prism accumulates, whose upper surface is hy- draulically maintained (graded) at a yet-lesser slope. Gravity dispersal is now confined largely to the continental slope. In zones where it has been particularly efficient, however, the original gradi- ent is retained in the form of submarine canyons extending back into the prograding shelf (Rona, 1969). With further crustal subsidence, the alloch- thonous regime becomes dominant. Sedimentary grading of the continental margin surface extends into the subaerial zone, as fluvial and estuarine depositional environments. The grading process be- comes largely self-maintaining. As long as the sedi- ment load is adequate, the coastal environments prefilter it for maximum mobility and inject it onto the shelf by means of estuary jets, and shoreface and downdrift bypassing. All parts of the shelf surface are nourished and interact with the hy- draulic regime so as to aggrade to the appropriate depth. Marginal coasts, if possessed of an indepen- dent mechanism of subsidence, may begin a cycle of shelf construction at this stage (Bally, in Isacks et al., 1973). Trailing-edge shelves are most liable to alloch- thonous sedimentary regimes, but these are prob- ably never uniformly developed over great dis- tances. Differential subsidence results in continued integration of the stream net, and the resulting master streams tend to preferentially seek loci of maximum subsidence, where they build deltaic piles beneath surfaces undergoing allochthonous sedi- mentation. Intervening shelf sectors may be suf- ficiently star
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