Sedimentation in the modern delta of the River Niger, West Africa

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Oceanographic Abstracts

investigations, carried out by the ~" Rugjer Bogkovid " Institute, Zagreb, are given as an exampic o f such a cooperation. The author stresses a few fundamental points of contact between the laboz~ltories in the littoral region and those in the hinterland, which provide a sound basis for cooperatior~ Viewing the sea from the economic standpoint, i.e. considering it as a source of food, the atrth~ emphasizes the importance, for the fishing industry, of investigations in the field of marine productivit5. A number of scientific disciplines could be embraced, such as the study of the biocycle, the physiology of marine organisms, and immunological investigations of the radiation effect on fertilization and development of such organisms. Additional observations could also be included since marir~,c organisms are an ideal model for the study of actual occurrences. It is also imperative that the spread and effezts of radioactive fall-out should be traced. Modern science cannot detach itscll from the problems of today since the atomic energy is no longer a thing of the future; on the contrar?. it has become an actual fact, and nuclear-propelled ships now range the seas and oceans, nuclear power plants have been built on the shores o f the seas, and spent fuel is deposited in tmderw~e~storage chambers. ALLEN J. R. L., 1964. The Nigerian continental margin: b,)ttom sediments, submav[~: morphology and geological evolution. Mar. Geology, 1 (4): 289-332. Two series of Late Quaternary sediments occur on the surface of the Nigerian continental shclt and slope overlying the Nigerian Coastal Plain geosyncline. The earlier series, the Older Sands, is a quartzose sheet sand which originated at a transgressive strand during the late Pleistocene-earl3 Holocene eustatic rise of the sea. Terraces and rises capped by local ridges occur on its upper surface parallel to shore, which is crossed locally by shallow valleys with channeled floors. The rises with local ridges are interpreted as drowned barrier beach or island complexes, their present depth variation being seen as recording tectonic and compactional subsidence of the continental margin. The later sediments, referred to as the Younger Suite, locally bury the Older Sands very deeply, comprisiug sands near shore, silts in moderate depths and clays in deep water. They have been deposited during the seaward growth of the modern Niger delta. River mouth bars and an inshore terrace and rise are the principal morphological features of the modern continental shelf underlain by the Younger Suite. The continental margin is notched by three submarine canyons and by numerous large and small gullies. It has been an essentially depositional feature since the inception of the Niger Coastal Plain geosyncline in the early Cretaceous. ALLEN J. R. L., 1964. Sedimentation ira the modern delta of the River Niger, Vvesl AfrictL l ~

Detrelopments in Sedimentoh)gy L. M. J, U. Van Straaten, Editor, Elsevier Publishing Co., I : 26--3~L The cycle of deposits present in the modern Niger delta has been built up during a transgression ~I the sea (Late Glacial to earlier Holocene) and a subsequent regression (later Holocene). Quartz sands enriched with glauconite or shell debris were deposited at an advancing strand line during the transgression. The regression o f the sea has been accompanied by the distribution, by x~.avc and current action, of terrigenous sand, silt. clay, and plant debris between the following principa! environments: floodplain, mangrove swamp, estuary, beach with beach-ridges, river mouth bar, delta platform, prodelta slope, open shelf, and continental slope. The lithofacies deposited in thes~ environments overlie the earlier transgressive sands. ALLEN J. R. L., 1965. Coastal geomorphology of eastern Nigeria: beach-ridge barrier island~ and vegetated tidal flats. Geok~gie MUnb. 44 (1): t--21. The visible portion of the Niger delta consists, in eastern Nigeria, of three geomorphotogical units. Behind a chain of barrier islands formed of sand ridges of two types, occurs a broad tidal flat colonised by mangroves and marked by a reticulate drainage pattern. The tidal flat is succeeded inland by ~ forested river floodplain. The tidal flat is also partly in contact with a low terrace formed on I.~t~ Tertiary and possibly Pleistocene sediments. The nature of the barrier islands and the tidal flat is related to the forces at x~ork in the regior~ The mangrove swamp of the eastern delta is growing at the expense of the barrier islands, the floodplain, and the terrace because of erosion in tidal channels. It is suggested that the reticulate drainage pattern o f the tidal flat is due to the stabilising o f deposited sediment by the mangroves and the manner in which these plants grow collectively. The Nigerian barrier complex, situated in the tropics, is compared with the temperate tidal flats of the Dutch coast. The main differences depend on the" contrasted role of plants in the two areas, and thus finally on climate. ALLEN J. R. L., 1965. Sedimentation to the lee of small underwater sandwaves: an experimentai study. J. Geol. 73 (1): 95.~116. Underwater sand waves growing by interaction between a movable sand bed and a fluid flow ~c~¢ simulated in a laboratory flume. Each sand wave advances in step with a flow system involving boundary-layer separation at the wave crest and an induced countercurrent to the wave lee. Four sediment-structure elements result from this flow system, moving simultaneously downstream in the following order: (1) sandwave forests; (2) small-scale asymmetrical ripples fom~ed beneath the countercurrent, pointing toward the sand wave, and overriden by the sand-wave foresets; (3) ar~ erosion hollow where the countercurrent first impinges on the flume bed; and (4)small-scale asymmetrical ripples pointing away from the sand wave and eroded by the downstream advance of the erosion hollow. Foresets, the most important of these four elements, accumulate from a combination