South Africa - Inkaba.org

Climate/sealevel fluctuations along the Southern
African West Coast: regional and global context
D Roberts 1
1. Council for Geoscience, South Africa, droberts@gescience.org.za
ABSTRACT
Long term global trends in Cenozoic climatic/oceanographic evolution are mediated by fundamental
geological processes such as the changing configuration of landmasses. These in turn have major
impacts on ecosystems at all scales. However, the underlying forces driving some global trends remain
obscure. Whereas the Oligocene lowstand can be attributed to the final separation of Gondwana
landmasses allowing free flow of the Antarctic Circumpolar Current, neither the subsequent Early-
Middle Miocene recovery, nor the early Piocene warm period have obvious main causes.
Superimposed on these fundamental (global) trends are regional events such as tectonism, which
impinge on local climate and relative sea levels. The South African west and southern coasts form an
ideal field laboratory for studying late Cenozoic climatic/oceanographic histories because of the
extremely rich palaeorecord contained in the onshore littoral and fluvio-estuarine deposits, as
represented in a large number of well studied sites. The manner and extent to which they link with the
regional and global record may illuminate some of these important issues. In particular, many new
dates of major events based on palaeontology, radiometric methods, palaeomagnetics and luminescence
have provided fresh insights into the chronological sequence of events. Regionally, the southern
African subcontinent represents a passive intraplate, trailing edge setting, which is also removed from
glacial influence and has experienced no Cenozoic volcanic activity. Rates of vertical crustal motion
are consequently low and late Cenozoic shoreline datums chiefly reflect glacio-eustatic sea level
history. The tectonic stability of this region is therefore highly favourable for the study of glacioeustatic
sea level fluctuations. However, some authors have suggested otherwise, positing that the
region has undergone sharp and asymetric periodic uplift in the Neogene and the evidence cited for this
viewpoint is critically reviewed. This paper is essentially a critical review of the literature, but includes
some unpublished novel observations.
Keywords: Sea level; climate; late Cenozoic; southern Africa; chronology
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