Palaeoenvironments during a terminal Oligocene or early Miocene transgression in a fluvial system at the southwestern tip of Africa

• Published in: Global and planetary change 2017-03, Vol.150, p.1-23
• Main Authors: Roberts, D.L., Neumann, F.H., Cawthra, H.C., Carr, A.S., Scott, L., Durugbo, E.U., Humphries, M.S., Cowling, R.M., Bamford, M.K., Musekiwa, C., MacHutchon, M.
• Format: Article
• Language: English
• Subjects: 3D landscape reconstruction; Biostratigraphy; Coastal environment; Marine transgression; Palaeoecology; Southern Africa; Terminal Oligocene/early Miocene
• ISSN: 0921-8181; 1872-6364
• DOI: 10.1016/j.gloplacha.2017.01.007

A multi-proxy study of an offshore core in Saldanha Bay (South Africa) provides new insights into fluvial deposition, ecosystems, phytogeography and sea-level history during the late Paleogene-early Neogene. Offshore seismic data reveal bedrock topography, and provide evidence of relative sea levels as low as −100m during the Oligocene. 3D landscape reconstruction reveals hills, plains and an anastomosing river system. A Chattian or early Miocene age for the sediments is inferred from dinoflagellate taxa Distatodinium craterum, Chiropteridium lobospinosum, Homotryblium plectilum and Impagidinium paradoxum. The subtropical forest revealed by palynology includes lianas and vines, evergreen trees, palms and ferns, implying higher water availability than today, probably reduced seasonal drought and stronger summer rainfall. From topography, sedimentology and palynology we reconstruct Podocarpaceae-dominated forests, Proto-Fynbos, and swamp/riparian forests with palms and other angiosperms. Rhizophoraceae present the first South African evidence of Palaeogene/Neogene mangroves. Subtropical woodland-thicket with Combretaceae and Brachystegia (Peregrinipollis nigericus) probably developed on coastal plains. Some of the last remaining Gondwana elements on the sub-continent, e.g., Araucariaceae, are recorded. Charred particles signal fires prior to the onset of summer dry climate at the Cape. Marine and terrestrial palynomorphs, together with organic and inorganic geochemical proxy data, suggest a gradual glacio-eustatic transgression. The data shed light on Southern Hemisphere biogeography and regional climatic conditions at the Palaeogene-Neogene transition. The proliferation of the vegetation is partly ascribed to changes in South Atlantic oceanographic circulation, linked to the closure of the Central American Seaway and the onset of the Benguela Current ~14Ma. [Display omitted] •First palaeoecological record from terrestrial Chattian-Burdigalian of South Africa•First fossil evidence of mangroves at the southwestern coast of Africa•Seismic and proxy data reflect changes in fluvial systems during transgression.•Evidence for fire & fire-prone vegetation (fynbos) prior to summer dry climate onset