. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography MODELS OF SHELF SEDIMENTATION 315 Channtl (C-F). Cloyey silt and silly cloy (C) - coortt gr Sond | (M) ~ madium V (F) - fin* gr 1VF)- vtry fin* gr. FIGURE 4. Schematic illustration of the depositional environ- ments and sedimentary Jacies of the Niger Delta and Niger shelf. Progressive size sorting of sediment results in a decrease in grain size through successive depositional environments in a seaward direction. From Allen (1970a). tidal jet, and b
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography MODELS OF SHELF SEDIMENTATION 315 Channtl (C-F). Cloyey silt and silly cloy (C) - coortt gr Sond | (M) ~ madium V (F) - fin* gr 1VF)- vtry fin* gr. FIGURE 4. Schematic illustration of the depositional environ- ments and sedimentary Jacies of the Niger Delta and Niger shelf. Progressive size sorting of sediment results in a decrease in grain size through successive depositional environments in a seaward direction. From Allen (1970a). tidal jet, and be entrained into the shelf dispersal sys- tem. The shoreface behaves more nearly as a sediment trap, and bypassing occurs primarily through river mouths. The Niger-Benue delta system is one of the best studied examples of differential sediment bypassing through a prograding, deltaic environment (Allen, 1964, 1970a). The Niger-Benue river system delivers about X 106 m3 of bed load sediment and about 16 X 106 m3 of suspended sediment (Allen, 1964) to its delta each year. During peak discharge from September to May, average flow velocities range from 50 to 135 cm sec, and gravel as well as sand is in violent trans- port. During low stages, flow velocities decrease to 37 to 82 cm sec, enough to transport sand and silt. In the higher part of the flood plain, the Niger is braided; in the rest the Niger shows large meanders (Fig. 4). During high stages, levees are overtopped, crevasse develops, and bottom lands are flooded. Gravel and coarse sand are deposited as a substratum of braid bars and meander point bars, respectively, and are veneered with a top stratum of overbank clays. Silt undergoes temporary deposition in levees in the lower flood plain but these tend to be undermined, so that their deposits reenter the transport system. Thus the flood plain environment serves as a skewed bandpass filter, with preferential bypassing of the medium and finer grades, preferential entrap
Size: 1796px × 1392px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionamericana, booksponsorlyrasismemb
