Alluvial Terraces of the Lower Vaal River, South Africa: a Reappraisal and Reinvestigation1
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ALLUVIAL TERRACES OF THE LOWER VAAL RIVER, SOUTH AFRICA: A REAPPRAISAL AND REINVESTIGATION1 KARL W. BUTZER, DAVID M. HELGREN, G. J. FOCK, AND ROBERT STUCKENRATH Departments of Anthropology and Geography, University of Chicago; Department of Geography, University of Chicago, 60637; McGregor Memorial Museum, P.O. Box 316, Kimberley, South Africa; and Smithsonian Radiation Biology Laboratory, Rockville, Maryland ABSTRACT The alluvial terraces of the Lower Vaal River, South Africa, are well known for their unique strati- graphic record of the Pleistocene period and as the focus of an apparent Acheulian sequence. Recent field examination indicates that this terrace suite is both more complex and more systematic than previously understood, extending downstream from the classical study area at Windsorton and Barkly West to the Orange-Vaal confluence. An expanded stratigraphic framework for the late Pliocene to early Pleistocene Older Gravels is described, while major subdivisions for the Younger Gravels (with Middle Pleistocene fauna and Acheulian occurrences) are proposed. A new late Pleistocene to Holocene lithostratigraphic en- tity, the Riverton Formation (with five members), is defined. Finally, problems of paleoenvironmental interpretation are discussed. INTRODUCTION Butzer 1973a), no excavations of Acheulian In the 1940s southern Africa seemed to sites south of the Zambezi have been fully offer one of the best-known Pleistocene en- reported. The earlier work in southern vironmental and cultural successions of Africa was, for its time, excellent yet inten- the continent. However, in the last three sive reinvestigation of nearly all the early decades conceptual developments and dis- and mid-Pleistocene deposits seems to be coveries elsewhere have placed the South needed. African record in a backwater position. The One of the foremost study areas of early early and mid-Pleistocene time range is now and mid-Pleistocene environments and cul- relatively poorly understood from either the tures in South Africa has been the lower stratigraphic/environmental point of view Vaal River Basin. Here the Vaal and its (see, e.g., Flint 1959; Cooke 1967) or the tributaries have created complex terrace archeological one (see Cole 1961; Mason forms that provide an intermittent alluvial 1962, 1967). The study of this period in history spanning all of the Pleistocene. South Africa does not compare well with Since the Interior Plateau of southern Af- current information on the Rift Valley in rica has been subject to extensive erosion East Africa, where the discoveries at through most of the Cenozoic, the "Vaal Olduvai, along the eastern shores of Lake Gravels" comprise one of the few moderate- Rudolf, and in the lower Omo Basin have ly large areas of Pleistocene deposition. In proved so rewarding. The South African addition, the Vaal Gravels contain mam- australopithecine deposits and faunas stand malian fossils and Acheulian artifacts in in stratigraphic isolation, with the regional several of the younger alluvial units. implications of their paleoenvironmental in- The Vaal River gravels were "discov- ferences controversial (see Butzer 1971b; ered" in the early 1870s by diamond-dig- 1971c, p. 427-432; 1973d). With the ex- gers, whose relentless search for alluvial ception of Amanzi Springs (Deacon 1970; diamonds over the succeeding 100 years pitted most of the occurrences of the Vaal 1 Manuscript received September 11, 1972; re- Gravels into a cratered landscape. Such vised December 15, 1972. gravels can be readily traced at intervals [JOURNAL OF GEOLOGY, 1973, Vol. 81, p. 341-362] from the Vaal-Orange confluence upstream © 1973 by the University of Chicago. All rights reserved. for 280 km to Windsorton, beyond which 341 This content downloaded from 128.83.56.173 on Tue, 18 Jul 2017 14:18:25 UTC All use subject to http://about.jstor.org/terms 342 K. W. BUTZER, D. M. HELGREN, G. J. FOCK, AND R. STUCKENRATH exposures become few and sporadic. The sented here are based on sedimentological most productive gravels, between Barkly analysis of over 75 samples, involving hy- West and Windsorton, yielded fossils and drometer and wet-sieve determinations, artifacts in sufficient quantity to attract the Chittick calcium carbonate readings, pre- attention of Du Toit (1907, 1907-1908) at liminary quartz-grain micromorphology, pH the turn of the century, leading to closer values, and further, selective chemical tests. scientific investigation since the mid-1930s. This work is primarily associated with GENERAL GEOMORPHOLOGY OF THE Sdhnge et al. (1937), Cooke (1947, 1949), VAAL BASIN Breuil et al. (1948), and Van Riet Lowe The Vaal River rises on the High Veld (1952). Huzayyin (1941) drew attention Plateau of the southeastern Transvaal and to the importance of the Vaal Gravels, and eastern Orange Free State, an area of un- Zeuner (1958 [1945], 1959 [1946]) suc- dulating plains at 1,400-1,800-m elevation cessfully introduced the Vaal sequence into and formed primarily by shales and sand- the secondary literature of the northern stones of the Karroo System. Along the sub- hemisphere. After this first impetus for sequent section of its 1,350-km course to study passed, reservations, modifications, join the Orange River at 957-m elevation and even negative evaluations began to ap- near Douglas, the Vaal generally cuts below pear for the established terrace sequence Karroo shales, tillites, and diabase intru- (Maarleveld 1960; Partridge and Brink sions ("dolerite") into Precambrian quartz- 1967), the paleoclimatic interpretation ites, dolomites, andesitic lavas ("diabase"), (Flint 1959; Cooke 1967; Bond 1967; and granite. Beyond the grain of the com- Partridge and Brink 1967; Butzer 1971a, plex Precambrian structures of the Vaal's 1973d), and the archeological record itself superimposed course between Vereeniging (Cole 1961; Mason 1962, 1967). and the Vredefort Dome, the valley broad- As a result of these much-needed, pri- ens out onto the lower planation surface marily negative, reassessments, the Vaal ofse- the Middle Veld, an irregular plain stud- quence is now widely regarded with equivo- ded by hills and mountains of resistant cation. Meanwhile, ongoing geochronologi- igneous rocks. cal, paleoenvironmental, and archeological The beveled nature of the Veld surfaces, work elsewhere in eastern and southern gently cutting across the strata of the Kar- Africa continues to emphasize the potential roo System, was first emphasized by Davis importance of the Vaal Gravels for eluci- (1906), who interpreted it as a peneplained dating both environmental history and pre- landscape studded with monadnocks. Dixey historic subsistence patterns during the (1938) went further and interpreted the early and mid-Pleistocene time range. High Veld "peneplain" as part of a mid- Following brief reconnaissance in 1969 Tertiary erosional surface claimed to be al- and 1970, a reinvestigation was begun by most ubiquitous for the African continent. Butzer in 1971 with further detailed studies King (1963, p. 226-229; 1968, p. 271- (D.M.H.) currently underway. The pur- 274), on the other hand, considers the High pose of this paper is to review critically Veld to be part of an "extreme" planation the available evidence, both from the older surface, resulting from pedimentation pro- literature and particularly as gained in the cesses whereby subhorizontal plains are cut field since 1969. Whereas our interpretation when extremely broad, coalescent pedi- of the older erosional forms and deposition- ments remove upland interfluves. Like al features remains to be completed, study Dixey, King (1968, chap. 9) postulates a of the late Pleistocene and Holocene se- sequence of universal erosional cycles that quence now allows the definition of a new deserve consideration in discussing the evo- lithostratigraphic entity. The results pre- lution of the Vaal Valley: This content downloaded from 128.83.56.173 on Tue, 18 Jul 2017 14:18:25 UTC All use subject to http://about.jstor.org/terms ALLUVIAL TERRACES OF THE LOWER VAAL RIVER, SOUTH AFRICA 343 1. "Gondwana" Planation Surface, cut dur- interior watersheds were possibly uparched. ing the Late Triassic and Jurassic across the Deep dissection and headward cutting of the Stormberg basalts (Karroo System) and now coastal rivers into the escarpment has con- forming residuals along the crests of the Vaal tinued into the present, without significantly watershed. affecting the exceptionally low gradients of the 2. "Post-Gondwana" dissection, with cutting river courses (e.g., 6.5:10,000 in the case of the of incipient surfaces in valley heads below the Vaal) of the interior plateaus. "Gondwana" Surface. These Early Cretaceous readjustments adjacent to the upwarped Dra- The High Veld surface has been tenta- kensberg were followed by further tectonic tively dis- approximated in figure 1 by attempt- turbances along the Great Escarpment. ing to reconcile the 1:250,000 topographic 3. "African" Landsurface, cut across the maps with King's small-scale outline map High Veld during the time span of the Late (King 1968, fig. 119). Elevation of this Cretaceous to mid-Cenozoic. surface rises gradually from 1,200 m in the 4. Two cycles of pediplanation, in response Kimberley region to nearly 2,000 m at the to repeated epeirogenic uplift in Miocene and watershed of the Great Escarpment. In gen- again in Pliocene times, cutting the broad val- ley-side and tributary pediments of the Lower eral, the High Veld constitutes an impres- Vaal Middle Veld. sive planation surface. Nonetheless, it is 5. The Pleistocene stage was set by reeleva- disturbing that some sectors, such as the tion of the Great Escarpment while the old Gaap Plateau on Precambrian dolomites, FIG. 1.-The Vaal and upper Orange Drainage, with High Veld planation surface and gravel occur- rences. In part modified after DuToit (1907), SShnge et al. (1937), Cooke (1947), and King (1968). This content downloaded from 128.83.56.173 on Tue, 18 Jul 2017 14:18:25 UTC All use subject to http://about.jstor.org/terms 344 K. W. BUTZER, D. M. HELGREN, G.