. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography B. BEACH DETACHMENT. C. CYCLIC SPIT PROGRADATION FIGURE 21. Barrier formation with spit-building dominant. As a rugged coast passes from stillstand to transgression, a mature configuration is replaced by a transient state of mainland beach detachment, then by a quasi-steady state regime of cyclic spit building. This diagram also illustrates the relationship between the concepts of coastal equilibrium and coastal climax, since it consists of Johnson'
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography B. BEACH DETACHMENT. C. CYCLIC SPIT PROGRADATION FIGURE 21. Barrier formation with spit-building dominant. As a rugged coast passes from stillstand to transgression, a mature configuration is replaced by a transient state of mainland beach detachment, then by a quasi-steady state regime of cyclic spit building. This diagram also illustrates the relationship between the concepts of coastal equilibrium and coastal climax, since it consists of Johnson's (1919) stages of coastal maturity—portrayed in reverse sequence! the barrier. As the loop of the barrier into the bay becomes extreme, sediment supply from headlands is liable to capture by secondary spits formed during storms. These may prograde out toward the drowned valley thalweg until capacity is again exceeded and their tips are stabilized, further movement being limited to retreat coupled with that of the headland to which they are attached. Finally the survival of primary barriers on such a coast would be limited by the tendency of submerging headlands to form islands. A spit tied to a promontory that becomes an island can retreat no further if a drowned tributary valley lies landward of it, but must instead be overstepped. The few unequivocal examples of trans- gressed barriers on the shelf floor appear to be over- stepped, rock-tied spits (Nevesskii, 1969; McMaster and Garrison, 1967). On the other hand, transgression of a coast of very subdued relief, such as is the case for most coastal plains, would tend to promote mainland beach detachment at the expense of spit formation, given initial conditions of a straight coast (Fig. 22). The depth of water in which detached bay mouth barriers would be built would be less, because the relief would be less. The upper, ero- sional zone of the shoreface (Fig. 10/1) would be more likely to extend down into the pre-Recent sub
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