Abstract
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.
Highlights
The Fynbos and Succulent Karoo Biomes, located at the southern tip of Africa, are biodiversity hotspots with a high level of endemism
In areas where the granite outcrops values were used, the elevation above Mean Sea Level were extracted from the 90 m shuttle radar topography mission (SRTM) data
The current study suggests a terminal Oligocene-early Miocene age for the distal, seaward margin of the Elandsfontyn Formation
Summary
The Fynbos and Succulent Karoo Biomes, located at the southern tip of Africa, are biodiversity hotspots with a high level of endemism. The most species- and endemic-rich parts of Fynbos are associated with winter-rainfall, rough topography, oligotrophic soils and recurrent fire (Cowling and Lombard, 2002; Goldblatt and Manning, 2002; Verboom et al., 2015). Fynbos climates are underpinned by cyclonic winter rainfall, which in concert with cold currents of the Benguela Upwelling System, are controlled by the South Atlantic Anticyclone as it migrates northward in winter (Tyson, 1999). To the north the anticyclone prevents monsoonal rainfall, resulting in drier conditions with karroid vegetation. The establishment of this climatic framework is pertinent to the spread and diversification of the Fynbos Biome (Linder, 2003), which is hypothesised to have emerged during the Miocene, leading to the demise of drought- and fire-intolerant forests (Linder et al, 1992; Linder and Verboom, 2015). Given the widespread diversification of Fynbos lineages as early as the Oligocene (Linder, 2005), it has been suggested that a Proto-Fynbos biome may have been associated with skeletal soils of the Cape Fold Belt and sandplains of the lowlands during a cooler and drier period with enhanced seasonality, probably the late Eocene-early Oligocene (Linder and Verboom, 2015)
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