. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography rrr^TTT777T7. LAGOONAL DEPOSITS FIGURE 2 3. Contrasting sand budgets of a barrier built (A) on a gentle submarine gradient as in Fig. 22, and (B) on a steep submarine gradient as in Fig. 21. In (A), zone of shoreface erosion penetrates to Pre-Recent substrate, which becomes "income" for barrier nourishment. In (B) the barrier may only "borrow" from its own "capital" through shoreface erosion, and the heavy ex- penditure
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography rrr^TTT777T7. LAGOONAL DEPOSITS FIGURE 2 3. Contrasting sand budgets of a barrier built (A) on a gentle submarine gradient as in Fig. 22, and (B) on a steep submarine gradient as in Fig. 21. In (A), zone of shoreface erosion penetrates to Pre-Recent substrate, which becomes "income" for barrier nourishment. In (B) the barrier may only "borrow" from its own "capital" through shoreface erosion, and the heavy ex- penditure involved in paving the shelf with sand during barrier retreat may "bankrupt" the retreating barrier, which must either accelerate its retreat or be overstepped. In either case shoreface continuity is liable to be broken, resulting in cyclic spit building. downdrift coast becomes sediment starved. The mud flat erodes back and a beach ridge formed of the coarse sediment is thrown up by storm high tide. Todd (1968) has stressed the role of estuary mouths and inlets in the localization of chenier plains. He notes that littoral cur- rents updrift of the inlet tend to decelerate during ebb tide because of a reduction of the coastwise pressure gradient by the ebb jet, resulting in sediment deposition. Littoral currents in the same locality are accelerated by proximity of the inlet during flood tide, but fine sediment deposited requires a greater velocity for erosion than for deposition, and in any case has already compacted. Hence chenier plains tend to be localized on the muddy, updrift sides of tidal inlets. Downdrift of the inlet, the coast may instead be starved for fines as a result of sea- ward transport or "dynamic diversion" of the littoral current by the ebb jet, and the littoral sand deposits have more nearly the character of a beach ridge sequence. Otvos (1969) recognizes the role of inlets in localizing deposition, but notes that chenier deposition goe
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