USGS Open-File Report 94-023
Some Manifestations Of Pliocene Warming In Southern Africa
- L. Scott
- University of the Orange Free State, Bloemfontein, South Africa
- T. C. Partridge
- Transvaal Museum, Pretoria, South Africa
Pliocene vegetation types in southern Africa, especially those of the
Middle Pliocene, are not well documented. They can be reconstructed in
part on the basis of palynological data from the interior and the western
coastal and offshore regions. Pollen spectra from marine deposits off the
northern Namibian coast (van Zinderen Bakker, 1984) which can broadly be
assigned to the middle Pliocene, contain relatively prominent
Chenopodiaceae pollen, and are interpreted here as reflecting a tropical
climate, possibly associated with more intense evaporation. Early
Pliocene pollen accompanying fauna from the Varswater Formation at
Langebaanweg, in the "Mediterranean" southwestern Cape Province, indicates
that swampy conditions existed in a fynbos (macchia) environment, with a
suggestion of slightly more tropical characteristics than at present
(Scott, in press). Middle- to late-Pliocene (ca. 3 Myr) cave breccias at
Makapansgat in the interior of the subcontinent (Cadman and Rayner, 1989),
and a coprolite from these layers (this report), contain "Bushveld" pollen
types, but exotic Pinus contaminants suggest that the spectra were
probably derived from the modern environment. Pollen from terminal
Pliocene to early Pleistocene travertines in the Sterkfontein and
Kromdraai sites of the highveld grassland region, tentatively indicates
open Protea savanna at that time. In comparison with older strata from
Sterkfontein, these deposits contain a fauna indicative of relatively open
vegetation (Vrba 1985). It can be assumed therefore, that the preceding
mid-Pliocene vegetation contained denser woodland, although there are no
independent palynological data to support this.
Geomorphological and sedimentological data provide independent support for
some of these conclusions and provide further insights into the amplitude
and timing of Pliocene changes in the subcontinent. High marine terraces
at elevations up to 90 m are associated with an extensive terrestrial
fauna at Langebaanweg on the western Cape coast, and provide important
proxy evidence of early - mid Pliocene deglaciation. The upper terraces
of the Vaal River contain sparse Pliocene fossils; their massive gravel
armoring is indicative of semi-arid alluviation, probably towards the end
of the Gauss chron. At about the same time a shift is evident within the
hominid-bearing cave deposits of the interior from sub aqueous
accumulation to of predominantly fine clastic sediments to an influx of
courser colluvial elements under the influence of episodic sheetfloods.
Major carapaces of the Ghaap escarpment, which accumulated between 2.4 Myr
and the middle Pleistocene can also be linked to cycles of spring activity
under semi-arid climatic conditions. In sum, a growing body of evidence
is coming to hand which documents an important shift from relatively warm,
mesic conditions during the Pliocene to the recurrent cool, relatively dry
cycles which typified much of the Quaternary.
References
- Cadman, A. and Rayner, R.J., 1989, Climate change and the appearance of Australopithecus africanus in the Makapansgat sediments: Journal of Human Evolution, v. 18, p. 107-113.
- Scott, L., in press, Pollen Evidence for vegetation and climate change in southern Africa during the Neogene and Quaternary: Proceedings of Conference on Paleoclimate and Evolution, Airlie, Virginia, submitted to Yale University Press.
- van Zinderen Bakker, E.M., 1984, Palynological evidence for Late Cenozoic arid conditions along the Namibia coast from Holes 532 and 530A, Leg 75, Deep Sea Drilling Project: Initial Reports of the Deep Sea Drilling Project v. 75, p. 763-768.
- Vrba, E.S., 1985, Early hominids in southern Africa--updated observations on chronological and ecological background, in, Tobias, P. H., ed., Hominid Evolution: Alan R. Liss, New York, p. 195-200 .
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