Tertiary environmental changes along the south-western African coast

Coetzee, J. A.
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Bernard Price Institute for Palaeontological Research
Evidence for major vegetation and climatic changes during the Tertiary in the south-western Cape has been obtained from a number of sites. The palynomorph assemblages indicate in general an alternation of relatively cool temperate forests with two periods of subtropical - tropical palm-dominated vegetation from the Late Oligocene/ Early Miocene to the Pliocene when many of the taxa became extinct. Subsequently, strong development of macchia vegetation took place. These changes can be correlated with some palaeogeographic data and the major temperature changes of the Southern Ocean indicated in the palaeotemperature curve of Shackleton and Kennett (1975) which reflects the longterm progressive cooling of the earth since the Eocene/Oligocene boundary. The two subtropical- tropical periods can probably be related to the respective Early and Middle Miocene pan-African faunas of Arrisdrift and Luderitz and could coincide with the two warmest periods of the Miocene at 19 My and 14 My ago. The end of the Miocene witnessed the maximum build-up of the Antarctic icesheet and the substantial increase of the upwelling in the Benguela Current. This resulted in the initiation of the aridification of the present Namib desert, the extermination of the palm vegetation and the provincialism of the coastal molluscs. The important drop in temperature which reached its maximum about 3,5 My ago in the Pliocene could have exterminated the surviving elements of the last of the temperate Tertiary forests. The progressive aridity of the continent resulted in the spread of savannas, the evolution of the Alcelaphini and Antelopini and the change to regional vertebrate faunas. The increasing summer aridity in the southwestern Cape led to the strong development of the macchia vegetation.
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cimatic change; Tertiary; Africa