Variability of Holocene to Late Pleistocene Zambezi riverine sedimentation at the upper continental slope off Mozambique, 15°–21°S
Large rivers on continental margins play an important role as interfaces between land and ocean sedimentation. In many cases the modes and history of sediment dispersal, and the final deposition of the impressive volumes of terrigenous matter in the deep ocean remain poorly constrained by detailed sedimentary observations. The Zambezi River, by far the largest river of southeast Africa, discharges into the narrow, funnel-shaped Mozambique Strait between Africa and Madagascar. Here, we study the distribution of lithic grain sizes and major bulk fractions of biogenic and abiogenic components in core tops and long sediment cores off the Zambezi River, spanning the past ~. 60,000. years of the central and northern Mozambique continental margin. Due to the particular current regime, the modern Mozambique margin shows distinct sedimentation patterns not seen off most rivers of comparable size. Deposition is largely free of hiatuses, with high accumulation rates of fine-grained material, and only minor signs of erosion or sediment winnowing. Zambezi riverine detritus dominates the sedimentary facies between 20°S and 17°S from below the shelf break down to 2000. m water depth. However, a considerable fraction at present high sea level is deposited not directly downstream the Zambezi River mouth, but is dispersed to the northeast by along-shore transport, opposite to the mean flow within the Mozambique Strait. As a consequence, downslope transport today is highly unfocused and a canyon system at the upper slope is only poorly developed. We suggest that most of the riverine matter leaves the continental shelf ~. 200. km to the northeast of the present river mouth. Sediments took a more direct, chanellized path during the last glacial period of lowered sea level, which was confirmed by the reconstruction of Holocene and Late Glacial sedimentation rates in the area. In this regard, the Zambezi River-Margin sedimentary system stands for a margin with considerable temporal and spatial variabilities in downslope deposition on glacial-to-interglacial timescales. © 2011 Elsevier B.V.