In search of sediment deposits from the Limpopo (Delagoa Bight, southern Africa): Deciphering the catchment provenance of coastal sediments

The discrimination of sediment provenance from specific source regions is a crucial prerequisite for the paleoclimatic interpretation of terrigenous sediment archives. The terrigenous material in sediments on the Delagoa Bight near Maputo, Mozambique, has several potential source areas including the Limpopo, Incomati, Matola, and Lusutfu river catchments. While the last three represent a coastal region bordered to the west by the Drakensberg mountains, the Limpopo catchment is much larger and reaches farther into the center of the continent. Due to local current patterns, the sedimentation in the Delagoa Bight is very complex. This may be the reason why previous studies in this area interpreted the origin of sediment bodies only on the basis of seismic profiles. Analytical investigations to the question where which material was/is deposited in the Delagoa Bight, especially the suspension load from the Limpopo River, do not exist. In this study, end-members for the four river catchments were determined based on a selection of aluminium-normalized trace element concentrations in river sediment samples. Relative end-member contribution to core top samples from the shelf, partitioned using a constrained least squares model, and age data of marine surface sediments, indicate a very effective eastward sediment drift, caused by local cyclonic circulation. This strong lee circulation (the Delagoa Bight Eddy) may have meant that hardly any material has been deposited in the eastern and central parts of the bight for ~1000 years. In addition, our results confirm previous studies showing that the majority of Limpopo sediments are dumped onto the eastern flank of the Inharrime Terrace from where material is probably drifted further south under the influence of the Agulhas Current.