. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography J^^y 6' â LLOCHTHONOUS PATTERNS OF SEDIMENTATION 339 YOUNGER SUITE COARSEST GRADE FINE SAND AND COARSER VERY FINE SAND CLEAN VC. SILT CLAYEY SILT SILTY CLAY 5°. OLDER SANDS V. COARSE SAND COARSE SAND MEDIUM SAND FINE SAND VERY FINE SAND FIGURE 30. Distribution of sediments on the Niger shelf. Young suite is of allochthonous origin; older suite of autochthonous sand is exposed in nondepositional windows. From Allen (1964). by bottom wave surge. Bott
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography J^^y 6' â LLOCHTHONOUS PATTERNS OF SEDIMENTATION 339 YOUNGER SUITE COARSEST GRADE FINE SAND AND COARSER VERY FINE SAND CLEAN VC. SILT CLAYEY SILT SILTY CLAY 5°. OLDER SANDS V. COARSE SAND COARSE SAND MEDIUM SAND FINE SAND VERY FINE SAND FIGURE 30. Distribution of sediments on the Niger shelf. Young suite is of allochthonous origin; older suite of autochthonous sand is exposed in nondepositional windows. From Allen (1964). by bottom wave surge. Bottom turbidities ranged from 50 mg 1 during the flood to 4 to 6 mg 1 during the next winter, but were at no time dense enough to drive density currents. Drake et al.'s study suggests that the transport of sus- pended sediment across shelves undergoing allochthon- ous sediment action starts with introduction by a river jet, and continues with deposition, resuspension, and intervals of diffusion and advection by coastal currents in a near-bottom nepheloid layer. Depositional Patterns on Allochthonous Shelves Fine sediments deposited on allochthonous shelves may occur as a seaward-thinning sheet (Fig. 30), or as a series of strips of fine sand or mud oriented generally parallel to the shoreline, see Figs. 31 and 32 (see also Venkatarathnam, 1968; McMaster and Lachance, 1969; and Niino and Emery, 1966). On shelves of equant or irregular dimensions, shelf sectors surfaced by far- traveled, fine-grained sediment may be more irregular in shape (Niino and Emery, 1966; McManus et al., 1969; Knebel and Creager, 1973). Such allochthonous deposits tend to be separated by, or to enclose, nondepositional "windows" in which relatively coarse autochthonous sands are exposed. The disposition of these strips and sheets of allochthonous sediment is generally meaningful in terms of what is known of regional circulation patterns. Locally, the strips may underlie turbid, brackish water pl
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