The Provenance of Terrigenous Components in Marine Sediments Along the East Coast of Southern Africa

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2018-07, Vol.19 (7), p.1946-1962
• Main Authors: Hahn, Annette, Miller, Charlotte, Andó, Sergio, Bouimetarhan, Ilham, Cawthra, Hayley C., Garzanti, Eduardo, Green, Andrew N., Radeff, Giuditta, Schefuß, Enno, Zabel, Matthias
• Format: Article
• Language: English
• Subjects: Agulhas Current; Archives; biomarkers; Components; Composition; Continental shelves; elemental composition; Environmental changes; Environmental gradient; Erosion; Flood deposits; Fluvial deposits; Fluvial sediments; Heavy minerals; Lipids; Marine sediment cores; Marine sediments; mineralogy; Ocean currents; Pollen; Provenance; Regions; River banks; River mouth; River mouths; Riverbanks; Sediment; sediment provenance; Sediments; Soil; Temporal variations; Terrigenous sediments
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2017GC007228

Terrestrial signals in marine sediment archives are often used for paleoclimatic reconstructions. It is therefore important to know the origin of the different terrestrial sedimentary components. The proximity to a river mouth is often the key location to determine the source. Especially in regions with strong ocean currents, such an assumption might, however, lead to considerable misinterpretations. To investigate the source of various terrigenous sediment fractions in southeastern Africa, a region with strong sediment redistribution, we have performed an extensive comparison between terrestrial material (pollen, plant lipids, detrital modes, and heavy minerals as well as bulk inorganic geochemical composition) from potential source regions and the same components in the adjacent coastal and continental shelf sediments. Onshore the proxy‐indicators reflect small‐scale diversity in sampling locations and associated environments (riverbank sediments, flood deposits, suspension loads, and soils). Nevertheless, the overall trends reflect significant environmental gradients along a SW to NE transect. We note a general comparability of the studied parameters between the continental and marine sediments regardless of their specific differences in transport and depositional characteristics. We propose that the influence of the Agulhas Current affects sediment deposition and distribution only seaward of the midshelf and that pockets of sediment remain preserved in the lee of coastal protrusions where they are protected from erosion. This study provides the essential prerequisite to allow the attribution of temporal variations of compositional changes in marine sediment cores to environmental changes in southeastern Africa. Key Points Elemental, petrographic, and mineralogical composition reflects the different catchment geology from sedimentary rocks to metamorphic/igneous assemblages A shift from a Mediterranean/mountain shrubland vegetation to subtropical grasslands/savanna is reflected by plant wax δ13C and pollen assemblages Plant wax δD signatures are indicative of increasing rainfall amounts on a south to north, subtropical to tropical transect