. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography A LLOCHTHON OLS PATTERNS OF SEDIMENTATION 343. KILOMETRES 0 100 100 FROM AXIS OF SYMMETRY -ACROSS DELTA FIGURE 36. Grain size in relation to sedimentary environments in Siger Delta area. In subaerial delta, all grades present are shown. In offshore part of delta, coarsest grade in near- surface layers is projected onto vertical plane perpendicular to axis of delta symmetry. From Allen (1964). (1972) have described grain-size gradients in Briston Bay
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography A LLOCHTHON OLS PATTERNS OF SEDIMENTATION 343. KILOMETRES 0 100 100 FROM AXIS OF SYMMETRY -ACROSS DELTA FIGURE 36. Grain size in relation to sedimentary environments in Siger Delta area. In subaerial delta, all grades present are shown. In offshore part of delta, coarsest grade in near- surface layers is projected onto vertical plane perpendicular to axis of delta symmetry. From Allen (1964). (1972) have described grain-size gradients in Briston Bay of the Bering Sea that are more nearly related to the iso- baths than to the prevailing currents. They consider the textural gradients to be the consequence of wave surge diffusion (Fig. 37). The operative mechanism would be progressive sorting during the seaward diffusion of sedi- ment. In this process, sediment that drifts seaward into deeper water during a transport event is likely to leave its coarsest fraction behind when reentrained. because of the weaker nature of deep-water wave surge (see dis- cussion of progressive sorting. Chapter 10. p. 162. Stratigraphy of Allochthonous Shelves The tenfold reduction in the rate of eustatic sea-level rise experienced between 4000 and 7000 years ago (Milliman and Emery. 1968) has resulted in a shift from autochthonous to allochthonous regimes in a number of shelf sectors (Curray. 1964). River mouths servicing such shelves have equilibrated with their tidal prisms. and have begun to bypass fine sediment in quantities sufficient to result in deposition on the shelf surface. Two characteristic stratigraphies have resulted, which may be correlated with the transport schemes illustrated in Figs. 3a and 3c. Where the shift in the balance between the rate of sedimentation and the rate of sea-level rise has not been adequate to cause coastal progradation, the coast has continued to undergo erosional shoreface retreat, or has approached stil
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