. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 128 Continental Margins case of the North American Atlantic Shelf in that there is less preservation of nearshore depositional patterns. As a consequence of the intensity of the hydraulic climate, there is less on shelf storage (category 3) and more material in transit. NIGER SHELF: STORM DOMINATED AUTOCHTHONOUS REGIME General. A very different regime of shelf sedi- mentation, and probably one more representative of the allochthonous regimes that ha
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 128 Continental Margins case of the North American Atlantic Shelf in that there is less preservation of nearshore depositional patterns. As a consequence of the intensity of the hydraulic climate, there is less on shelf storage (category 3) and more material in transit. NIGER SHELF: STORM DOMINATED AUTOCHTHONOUS REGIME General. A very different regime of shelf sedi- mentation, and probably one more representative of the allochthonous regimes that have built the broad constructional shelves of continental margins, is that of the Niger delta, as described by Allen (1964). The hydraulic climate of the Niger Shelf is probably most nearly analogous to that of the Central Atlantic Shelf, in that storm flow is more significant than tidal flow in driving shelf sedimentation. The shelf is dominated by the great arcuate Niger delta (Fig. 13), a concentric assemblage of terrestrial and transitional depositional environments that filter and modify the sediment load of the Niger River, before bypassing it to the Niger Shelf. Such a delta is by no means a prerequisite for allochthonous sedimentation, although the correlation between major river mouths and allochthonous sedimenta- tion is probably higher in the present period of relatively rapid transgression than during the slow transgressions of the past. Differential Bypassing in the Deltaic Environments. The Niger-Benue river system delivers about X 106 m3 of bed-load sediment and about 16 X 106 m3 of suspended sediment (Allen, 1965) 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 are in violent transport. During low stages, flow velocities de- crease to 37 to 82 cm/sec, enough to transport sand and silt. In the higher part of the floodplain, the Niger is braided; in the remainde
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