Geoarchaeology at Gi, a middle stone age and later stone age site in the Northwest Kalahari

Journal

of Archaeological

Science 1983,10,181-197

Geoarchaeology at Gi, a Middle Stone Age and Later Stone Age Site in the Northwest Kalahari David M. Helgren” and Alison S. Brooksb Gi with sealed middle stone age and later stone age occurrences is located in the Dobe Valley along the Botswana-Namibia border. The phases of middle stone age settlement were linked to a semiarid streamway during the early Upper Pleistocene. A major humid interval followed, when a large lake was ponded in the Dobe Valley. Later stone age settlement appeared after this lake disappeared and was replaced by a mosaic of pans (ephemeral lakes). Subsequently, another period of humid environment favoured another valley-wide lake during the late Upper Pleistocene. Later stone age settlement resumed when this second lake deteriorated into the modern pan terrains of the Dobe Valley. In total, the Gi beds record multiple environmental changes both more humid and more arid than present during the Upper Pleistocene and Holocene, as well as a variable array of adaptive opportunities for prehistoric settlement. BOTSWANA ARCHAEOLOGY, QUATERNARY ENVIRONMENTS, PALAEO LAKES, RIVER TERRACES, PANS, MIDDLE STONE AGE, LATER STONE AGE. Keywords:

Introduction Palaeolithic archaeological research has only proceded slowly in the Kalahari basin, and the region is poorly known compared with other areas of southern Africa (for summary, see Sampson, 1974). Persistent deposition throughout the basin has left few exposures, and exploration has been hampered by logistic difficulties. Furthermore, archaeological materials may not be abundant in the Kalahari. Modern climatic and edaphic limitations on water resources probably have been typical through much of the Quaternary and the region, like today, may often have been near or beyond the frontier of settlement. Archaeological residues seem most frequent along the basin margins, where pre-Cenozoic bedrocks outcrop and surface waters are more reliable. However,

sites with good preservation remain rare. Gil is a sealed, stratified middle stone age and later stone age locality in the northwest 1 Kung San orthography is simplified here by omitting the clicks. Gi is # Gi; Kung is !Kung, Kangwa is !Kangwa; Xaixai is /Xai/xai; Goshe is !Goshe; Xabi is !Xabi; Kubi is !Kubi; Twihaba is /Twihaba. Lee (1979, Figure 3.2) labelled # Gi as # Din. # is an alveolar click, ! an alveopalatal click, and / a dental click. aDepartment of Geography, University of Miami, Coral Gables, Florida 33124, U.S.A. bDepartment of Anthropology, George Washington University, Washington D.C. 20052, U.S.A. 181 0305-4403/83/020181+17

$03.00/O

@ 1983 Academic Press Inc. (London) Limited

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182

BOTSWANA

NAMIBIA

I

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AND A. S. BROOKS

IGom-

I

2:1-E .

,

2?OE

Tsau. “,“I*.

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Figure 1. Northwest Kalahari.

Kalahari. The site is within the modern Kung San landscape about 700 m east of the Botswana-Namibia border and at an elevation of about 1100 m (c. 19” 37’S; 21” Ol’E, Figure 1). Gi is along the shore of a small pan (ephemeral lake) of the same name. The archaeological materials are stratified in relict pan, lacustrine, and fluvial sediments. The site was discovered and first excavated by John Yellen in 1969-70 (Yellen, 1971), and the geology was briefly examined by A. B. A. Brink in 1970. Extensive excavations were conducted in 1975, 1976, and 1977 (by A.S.B.). Site geology and geomorphic context were studied in 1977 (by D.M.H.), followed by field re-evaluation during 1980. Gi is an important site because it provides historic context for the modern San population, preserves important palaeo-environmental data, and is the only systematically excavated middle stone age site in the surrounding quarter million square kilometres. Northwest Kalahari Landscapes Terrains of the northwest Kalahari are dominated by veneers of relict eolian sands, often shaped into long, northwest-trending longitudinal dunes (Grove, 1969). Individual dune crests stand 15 to 30 m high and may extend for tens of kilometres. The interdune valleys (molapos or dums) serve as the lowest order, ephemeral drainageways. Bedrocks occasionally protrude through the sands, creating isolated hills and ridges, such as the Aha or Twihaba Hills. East of the dunes are the relict and modern marsh terrains of the inland Okavango Delta. Westward, the sand veneer only thins near the central highland of Namibia. Gi is within the broad Dobe Valley, to the north of the Aha Hills (Figure 2). The rounded ridges of these hills reach an absolute elevation of 1255 m, standing up to 150 m

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GI

-.I DOBE

VALLEY AND !KANGWADUM

Figure 2. Dobe Valley and Kangwadum.

above the surrounding plains. Exposed Aha bedrocks are later Precambrian limestones, marbles, and dolomites of Damaran affinities. Beds tend to be thin (
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1975-76 submerged much of the Dobe Valley. At that time many pans coalesced; water stood up to a meter deep on some pan interfluves; and small streams connected the pans to the Kangwadum. The temperature regime is typical of higher altitude, subtropical, semiarid regions. Apart from rainy periods diurnal temperature variation is usually more than 20 “C; summer maxima are between 30 “C and 40 “C, and nightly light frosts are frequent during the three winter months. The vegetation response to this climate is a dense, tall-tree savanna on rocky substrates and a more open, savanna grassland on thick, sandy soils (see Lee, 1979, pp. 92-98). However, the freely drained, relict dunes and karstic bedrocks seem to guarantee continuing edaphic drought, and severely restrict the availability of surface waters. From this perspective the modern Kung San environment with only limited water resources, yet abundant vegetation, is an inappropriate environmental model for upper Pleistocene, hunter-gatherer adaptation in landscapes with greater water availability. Geology

of the Gi Beds

The Dobe Valley is about 7 km wide and 18 km long, extending from 8 km west of the Namibia boundary fence to beyond the village of Xabi in the east (see Figure 2). There are no natural exposures in this valley, and the Gi excavations provide the most informative sedimentary record. Test excavations elsewhere in the valley provided supplementary detail, and can be correlated readily to the Gi deposits. Compared to the extensive sand sheets that dominate the northwest Kalahari, the Dobe Valley has only limited sands. This appears to be an artifact of the original depositional pattern of these sands, which were deflated from an ancient Okavango basin, probably during the first major episode of regional aridity in the later Cenozoic. Initial sand deposition certainly predates any evidence of human settlement in the region. When these sands were mobilized, the Dobe Valley was sheltered to the lee of the Aha Hills and only a small volume of sand reached the valley. Correspondingly thick sands bank against the Ahas north of Xaixai. LANDSAT imagery also indicates that the Dobe Valley is centered in an arcuate graben in the Aha limestones and basement complex. The regional bedrock structure is poorly known, due to the thick cover sands. Terrains in the Dobe Valley today are dominated by outcrops of Pleistocene, lacustrine limestones which, in turn, support discontinuous veneers of relict, at least partly autochthonus grey and white sands, as well as the dark sandy mucks of the modern pan basins. Local relief within the valley is less than 3 m. Most prominent are enigmatic, calcrete ridges, apparently with cores of resistant bedrocks of the Aha limestone sequence. The grey and white sands are scattered across the valley floor as both thin veneers and relict, amorphous dunes, particularly on pan interfluves. Also providing relief are low “pan terraces” such as at the Gi excavation area. At Xabi there is a low mound of relict spring tufa. The valley margins are only subtly marked. To the south are low-angle slopes veneered by red sands and calcretes leading into the Ahas. On the north near Dobe pan, grey sands become widespread and the valley merges gradually with the first relict dune ridge, which is probably supported by an unseen platform. Eastward the valley funnels gently toward the Kangwadum. Gi pan is about 1.5 m deep and relatively circular, measuring about 100 m across at 2 In this report “calcrete” is used in a non-genetic sense, and refers to any horizon dominated by calcium carbonate and sometimes including mixtures of silica cements. In the Gi region this designation includes lacustrine limestones, fluvial and spring tufas, as well as pedogenic calcretes. The term “silcrete” refers to a number of calcrete facies which have substantial SiO, replacement of carbonates; petrologies vary from opaline masses to variably cemented sandstones and quartzites.

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the modern high water mark. The early dry-season diameter is about 70 m. During the later 1960s and earlier 1970s the pan dried to small waterholes by June and was dry by August. Modern sediment dynamism around Gi pan is dominated by the activities of large herds of domestic cattle watered at the pan. They have badly overgrazed the surrounding vegetation, overturned cobble-grade blocks of limestone, and seem to be carrying important amounts of mud away on their legs (see also Alison, 1899). These herds have appeared in the Dobe region only in the last 25 years. Surficial sediment transport by fluvial processes is inhibited by low gradients, and noteworthy washing of pebble-grade clasts is only obvious on the 4’ slopes along the eroded pan edge. The excavation area is on a low pan terrace preserved along the southeast shore (Brooks & Yellen, 1979). This terrace marks a relict filling of the pan basin to about 2 m above the modern pan bottom, and is composed of Unit 1 and 2A sediments in the excavation area. The excavations exposed nearly 270 m2, to varying depths. The composite stratigraphy is illustrated in Figure 3, and is described in Table 1. The car&m Unit 1 is a black colluvial Dan-filling which is vertisolic in the lowest areas. Thk’u& includes later stone age debris. In the non-vertisolic areas this unit is

1A 1B 2A 2B

Figure 3. Sedimentary profile at Gi (schematic).

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Table 1. Lithostratigraphya

at GZ

Unit l-Black colluvialpanflling. The capping Unit 1A is 8 to 35 cm thick, massive to subangular blocky, uncemented, pH 8.0, black (N2, 1OYR 2.5/l), clayey silt sand (52% sand/27*5!/, silt/20.5% clay; sample 434), which in lower and wetter areas has been altered to a vertic, clayey silt sand (37.5/3 1*5/3 1; sample 425) with a well-developed cracking network. Included are dispersed but well stratified sand to cobble-grade, subrounded to angular clasts of derived calcrete. Unit 1 includes later stone age material throughout. #425: P-25.0 parts/million; K-1200 parts/million; Zn-6.6 parts/million; OM-6.9%; HCl solubles-45’$& #434: P-12.5 parts/million; K-330 parts/million; Zn-O.4 parts/million; OM--+l%; HCl solubles -39%. Unit IB. Beneath the vertic facies of Unit 1A is 7-10 cm, unconsolidated, weakly vertically structured, light grey (2.5Y 6*5/l) sandy silt clay (24/2%5/47*5; sample 426). Calcrete clasts are less common in the vertic zones. #426: P-13.1 parts/million; K-1400 parts/million; Zn-1.6 parts/million; OM-2.2%; HCl solubles-57%. Contact between Units 1 and 2 is a clear and usually abrupt unconformity, with undulations varying with the Unit 2 facies beneath.

which tends to be smooth

Unit Z-Later stone age lake andpan beds. This unit varies from 10 to 60 cm thick and consists of (A) a capping zone of unconsolidated pan sediments and valley colluvia, (B) a medial zone of lacustrine limestone and (C) a basal zone of unconsolidated pan sediments and valley colluvia. Later stone age material is present in zones (A) and (C). Unit 2A is O-40 cm, massive to platey structured, uncemented, pH 8.3, light grey (IOYR 6/l) to white (2.5Y.8/1) sandy clay silt (14.5/50/35*5; sample 427). The variably cemented areas are a laminated, contemporary ( ?) “ground-water calcrete”, 5 to 10 cm thick. The zone includes 10 to 60 cm-wide, fluvially stratified channel fillings as well as dispersed, sand to cobble-grade, subrounded to angular clasts of derived calcrete. Unit 2A includes later stone age material throughout, and rare 15 cm wedges of grey (IOYR S/l), massive, silty sand (71/22/g; sample 451) occupation soils. Parts of 2A are corroded fragments from 2B. #441: P-75 parts/million; K-265 parts/million; Zn-0~14 parts/million; OM-1.5%; HCl solubles -75%. Unit 2B is 5 to 40 cm thick, light grey to white (IOYR), massive, indurated limestone with mesocrystalline and cryptocrystalline facies and veins of silica cements (HCl solubles-92%; insoluble residue texture 43/36.5/20*5; sample 437). Continuing weathering of Unit 2B is producing angular to subangular cobbles as well as bulbous concretionary surfaces at the base of the unit. Unit 2C is 0 to 40 cm thick, variably cemented, white (2*5Y 9/l) silty sand (sample 436 HCl insoluble residue) and light grey (5Y 6/l) clayey silt sand (sample 448 HCl insoluble residue) with horizontal stratification suggesting both colluvial and alluvial deposition. HCl solubles vary from 80% to 90% and the unit includes widespread sand to cobble-grade, subrounded to angular clasts of calCrete, both derived laterally and from the units above and below. Contact to Unit 3 is an abrupt, wavy unconformity bulbous irregularities on the surface of Unit 3.

with relief provided

by microsolution

cavities and

Unit 3-Post middle stone age limestone. This unit is 20 to 60 cm thick, massive indurated, light brownish grey (IOYR 6/2) to white (IOYR), lacustrine limestone with mesocrystaline and cryptocrystalline facies as well as veins of secondary silica (sample 449; 90% HCl solubles). Contact to Unit 4 is an abrupt and broken unconformity off at the contact.

with cobbles of the Unit 3 limestone breaking

Unit I-Middle stone age alluvia and colluvia. This unit is 50 to 15 cm thick and consists of inhomogeneous, culturally altered valley-floor colluvia and alluvia. One facies is an unconsolidated, irregularly stratified, calcrete pebble to cobble-grade (subrounded to angular) conglomerate with a matrix of light grey (5Y 7/l) sandy clay silt (sample 438), pH 8.1. Another facies is a consolidated, massive to very coarse subangular blocky irregularly stratified, grey (10YR 6/l) silty sand (sample 445), with dis-

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Table 1 (cont.) persed pebbles of derived calcrete, pH 7.6. Another facies is massive to very coarse angular blocky, weakly consolidated, white (5Y 8-9/2) clayey silt sand (64/20/16; sample 499) with secondary carbonate plasmas and dispersed calcrete pebbles. The darker facies are richer in cultural materials. These facies are more prominent near the top of the unit, where a tendency toward greater rounding in the derived calcrete fragments was noted. Modern roots reach this horizon as do insect burrows. #438: P-14.2 parts/million; K-170 parts/million; Zn-0.45 parts/million; OM-1.0%; HCl solubles-70%. #445: P-22.0 -53%.

parts/million;

K-124

parts/million;

2n-4.4

parts/million;

OM-1

.S%; HCl solubles

Contact to Unit 5 is a gradual to abrupt unconformity. Unit S-Uncemented alluvia. This unit’is up to 75 cm thick and consists of inhomogeneous fluvially cross-bedded, uncemented, white and grey sands with gravels of calcrete, quartz and cherts and reworked, culturally fiaked fragments of probable middle stone age affinities. Contact to Unit 6 is an abrupt, erosional unconformity. Unit 6-A “Kalahari conglomerate”. Only the surface of indurated, pebble to cobble-grade conglomerate with a white “calcrete/silcrete” matrix was intersected. a Descriptions and methods follow Helgren (1979, Appendix A), where colors are on dry samples, horizon descriptions are from Soil Survey Staff (1975), and textural designations are from Link (1966). The divide between silt and sand is 0.063 mm, and textures were determined by the hydrometer method. The soil chemistry analyses were completed by Jim Quick at the Agricultural Extension Service Soil Laboratory, University of California, Davis (protocol of December, 1969). Table 2. GZ radiocarbon dates” Level Unit 1A

No. SI-4098 SI-409 1A SI-4091C

Unit 2B Unit 3 Unit 4

X-4090 SI-4647 SI-4089 SI-4648 SI-4097 SI-4094 SI-4095

a Dates provided Laboratory.

Apparent radiocarbon years before present

Material charcoal carbonaceous soil coarser than 125 microns carbonaceous soil finer than 125 microns limestone limestone limestone limestone ostrich egg shell ostrich egg shell ostrich egg shell

by Robert

Stuckenrath,

Smithsonian

110*50 495f45 810&60 23,980&590 22,250&290 10,255&80 31,47oi-1,010 > 42,000 >40,000 > 43,000 Radiation

Biology

conspicuously horizontally stratified, yet poorly sorted with subrounded pebbles and cobbles of white, derived calcrete, dispersed in the dominant dark sandy facies. These areas include filled and active animal burrows with 1 to 8 cm diameters. In the finer textured vertisolic areas the crack networks are open much of the year to pebble-grade and finer debris, dropped or washed on to the surface. Also, large and small fragments could be tread into the unit when wet, and net downward motion of fragments would seem possible. No obvious stone or artifact lines were discovered at the unit’s base; however statistical summaries of artifact depths show the highest concentrations in the

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lowest 20 cm. The very dark sediments of Unit 1 are characteristic of the pans in the Dobe Valley. The removal of most of this filling from the Gi basin has exposed limestones and related rubbles of Unit 2 and particularly Unit 3 around the pan. However pans near Gi, such as Kubi, typically preserve proportionately much more of this sediment, suggesting that recent grazing pressure has been geomorphically more significant near Gi. Sedimentation of Unit 1 seems compatible with a climatic environment similar to recent wet years. Unit 2 is a complex of light colored pan sediments and lacustrine deposits. Units 2A and 2C are similar, largely uncemented, pan-margin alluvia and colluvia with sandy and silty facies as well as rubble conglomerates. Unit 2B is a lacustrine limestone. Later stone age debris is present in Unit 2A and Unit 2C. Sediments in Units 2A and 2C are consistently well-stratified in detail, but textures vary quickly across the excavated area, indicating micro-topographic complexity during deposition. Discontinuous, darker toned lenses were discovered at the base of both 2A and 2C. In Unit 2A are animal burrows with 1 to 12 cm diameters filled with sediments derived from Unit 1. These were found in more than 40% of the 4 m2 excavation squares. Unit 2A also includes a presumably contemporary, “ground water calcrete” which undulates across the lowest part of the excavation area. Units 2A and 2C suggest long-lasting pan margin environments more arid than today when both less organic matter was being produced in the Dobe Valley and organic matter in surficial sediments was oxidizing more readily. Gi pan was a very ephemeral water resource. Perhaps equivalent to Units 2A and 2C are the low, relict dunes on nearby pan intertluves. The lacustrine limestone of Unit 2B is one of the two widespread “calcretes” near Gi pan. Facies near Gi include algal mats as well as slump diamictites with pebble-grade clasts. Unit 2B indicates a broad, up to 4 m-deep lake of relatively fresh water along at least the southern side of the Dobe Valley. An environment substantially moister than today is implied by 2B. The opportunities for human settlement and adaptation were then very different from today. Unit 3 is another lacustrine limestone, which is the principal surface outcrop along the Dobe Valley. Facies near Gi also include algal mats and subaqueous slump facies. This relatively fresh lake was at least 4 m deep, and limestone/calcrete veneers on the shoulders of the modern Dobe Valley suggest a water depth of up to 9 m. Again, settlement along the valley bottom would have been impossible. Unit 4, the horizon with middle stone age residues, is dominated by partly anthropogenie valley-floor colluvial and alluvial sediments resting on the clearly alluvial sediments of Unit 5. Unit 4 sediments include abundant derived carbonate clasts, suggesting a semiarid environment with high-magnitude rainfalls washing debris into the site area. The darker facies, which are particularly abundant near the top of the unit, suggest moist areas where oxidation of organic matter was inhibited. Artifacts and teeth from Unit 4 ate locally cemented into the sole of Unit 3. Unit 5 verifies a stream passing the Gi area before the contemporary pan topography was established, after deposition of Unit 3. The setting for middle stone age settlement during accumulation of Unit 4 therefore is along the margin of a recently dried river channel, and perhaps focused on the water resources of an ephemeral pool in the valley bottom. A regional environment similar to zones 2A and 2C and somewhat more arid than present is the central theme of Unit 4. Unit 6 is an indurated conglomerate, separated from Unit 5 by an erosional hiatus. Wells in the Dobe area intersect similarly indurated horizons and suggest thicknesses of up to 6 m and a dominance of sandy facies. Interestingly the geomorphic and climatic dynamism recorded at Gi in Dobe Valley may have been paralleled by only minor geomorphic changes and gradual vegetation transitions in the dune and molapo country to the north, and the sand veneered Ahas to the south. Pollen samples from the Gi

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excavation have proved too fragmentary to be informative (E. M. van Zindern Bakker, 1981, pers. comm.). An explicit climatic interpretation for Units 3, 4, and 5 at Gi is clouded by signs of subtle tectonic dynamism in the region. In particular the Unit 3 limestone signifies appearance of a major lake, which only could be a response to a surplus of precipitation over evaporation. Yet the lake appeared so quickly that fragile archaeological materials were preserved in Unit 4. This only seems explicable by an abrupt climatic change, perhaps accompanied by gentle tectonic re-shaping of the Dobe Valley that may have contributed to ponding of the river valley and perhaps effected hydrogeological changes at depth. Wayland (1944) recorded an ethnographic earthquake report near Twihaba (Drotsky’s Cave), where Cooke (1975) has mapped low-displacement, normal faults of Pleistocene age. While the regional bedrock shapes remain poorly known, photogeology of joints and lineaments in the Ahas suggests that this massif is the crest of a regional north to northeast-trending arch, which may have intermittently ponded drainages from the Namibian highlands since post-Karoo times. Unfortunately detailed topographic maps, let alone basic geophysical data, are not yet available for this part of Botswana. Similarly the morphology and hydrogeology of the bedrock threshold between the Dobe Valley and Kangwadum is poorly known. Only a steepening valley slope was noted on many ground traverses east of Xabi. Archaeological Stratigraphy

and Dating of the Gi Beds

The stone tools at Gi are made primarily from cherts, chalcedonies and silcretes, as well as quartzite and flint pebbles. Unit 1 contains abundant later stone age lithic materials and, in the top 5 cm of deposit, also pottery fragments and rare iron items, reflecting contacts with both Europeans and Bantu speakers. This “microlithic” industry is marked by many crescents, primarily simple, and by pointed bladelets, backed or steeply retouched on both sides (see Figure 4). Al so included are a series of perforators and burins, together with a small number of scrapers and a wide range of retouched flakes and blades. The artifact patterning varies from isolated pieces to several concentrations. The most impressive features are several pits, three of which penetrate Unit 3 limestones in the northwest corner of the excavation (Brooks & Yellen, 1979; Brooks et al., 1980.. These may be pit traps, hunting blinds, or the remains of wells. The pits contained large mammal mandibles, horn cores, bone points or arrow foreshafts, and ostrich-egg-shell beads, in addition to a variety of microlithic tools, primarily crescents. No potsherds or metal items were recovered from the pits. Macro-botanical fragments are poorly preserved in Unit 1, and zoological remains, while abundant, consist mainly of ostrich eggshell and long bone fragments, snail shell, and a few diagnostic teeth, A further interpretive problem of Unit 1 is the continuing upward and downward mobility of small fragments, which is to be expected due to vertisolic processes, bioturbation and cultural activities. Such vertical mobility seems typical of both sandy and muddy unconsolidated substrates in the region (see Wilmsen, 1980; Yellen, 1977). The artifacts from Unit 1 were introduced to the site terrain both during and after sedimentation of the unit and, no doubt, were affected by these mixing opportunities. However, each of the sediment volumes with artifacts appears substantially discrete, bounded by volumes of sediment without artifacts. In this sense the artifacts in each concentration can be associated with each other and a general disposal behaviour. There is no evidence of important lateral movement of the artifacts after abandonment. The pattern of artifact dispersal in Unit 1 suggests several clusters characterized by significantly different tool percentages, perhaps reflecting different activity areas and

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-_ >. *.*. k!i

‘. -. .\-. i I:.\ ;.,1 I’/,’ ,’,’

fg?

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5 CENTIMETERS

a

Figure 4. Gi nos l-7: Units 1 and 2a. 1 Duckbill scraper; 2 small scraper; 3 bifacially worked scraper; 4 truncated blade (incomplete crescent); 5, 6, 7 crescents. Nos 8-14: Unit 2c. 8 small scraper; 9 small scraper; quartzite; 10 small core; 11 notched flake; 12 small retouched blade; 13 small retouched blade, LSA-type chert ; 14 bifacially retouched side-scraper on blade, broken, LSA-type chert. All artifacts made on cryptocrystalline rocks unless noted otherwise. Backed edges shown x 2 scale, Nos 12 and 13 shown approx. x 1.8 normal scale indicated.

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occupation episodes. Two hearths, one within a specially prepared pit, were located well back from the modern pan margin and associated with particularly dense artifact scatters. The patterning of debris and its relationship to excavated features is markedly different from that in either short-term or longer-term dry season camps of the modern Kung (Brooks, 1980; Brooks et al., “in press”). However the debris patterning is closely analogous to historic accounts, recent observations, and excavations of ambush structures near watering points. Thus the artifacts in Unit 1 apparently record brief visits to a hunting venue and water source, and do not indicate a settlement locality. Radiocarbon dates from Unit 1 suggest limited age. However, the dates seem to refer to an isolated occupation and a soil humus mixture dominated by relatively modern components. The archeological materials could span several millenia. On the one hand the stone implements compare to historic traditions in the region. On the other, the assortment of finished tool types suggests an affinity of the entire unit 1 later stone age complex with the “Coastal Wilton”, which was established before the middle Holocene in the Cape (Brooks & Yellen, 1979; Sampson, 1974). All in all, Unit 1 seems to signal micro- and meso-environments similar to the present, as well as resource patterning and adaptive strategies much like the immediate ancestors of the Kung San. Perhaps Gi has been a specialized hunting locality for several millenia. The later stone age materials from Unit 2A are not yet fully evaluated, but they do not appear to differ in any major way from the Unit 1 material. Bilaterally backed bladelets and microblade cores seem slightly more common in Unit 2, but this impression may not be statistically significant. Artifact densities tended to be highest at the base of the unit. As in Unit 1, discrete concentrations with differing artifact frequencies were noted, but fauna1 remains were limited to small bone fragments and rare teeth. Excavations at Gi inadvertently focused in areas were 2C sediments were absent, apparently due to erosion into the pan basin before the 2B lake appeared. Less than 4 m2 were excavated outside Yellen’s 1970 test trench. Consequently the artifact content of 2C is not fully known. The artifacts discovered are considered here to be of later stone age affinity, but they do have middle stone age aspects. Of about 25 pieces with some retouch, about one-fifth are of a size, shape and material comparable to the middle stone age horizons of Unit 4, while the rest consist of small chunks, little scrapers and retouched and backed blades (see Figure 4). No microliths were recovered in the small sample, which is significant compared to Units 1 and 2A. Radiocarbon assays on the inorganic limestone of Unit 2B verify an Upper Pleistocene age for this lake, and suggest an Upper Pleistocene age for all of Unit 2. Analyses of radiocarbon dates on inorganic carbonates from the southern Kalahari, where modern carbon contamination also is a persistent problem (Butzer et al., 19‘18), suggest these must be viewed as minimum ages, that may be 25% to 50% too young. By implication, Unit 2A may span much of oxygen-isotype Stage 2, and Unit 2B may be late Stage 3 or earliest Stage 2, i.e., earlier than the last glacial maximum of the Northern Hemisphere (for chronologies see Shackleton & Opdyke, 1973, 1976). Unit 2C apparently represents isotope Stage 3, suggesting that the artifactual vestiges from this horizon deserve renewed field investigation. The Unit 3 lacustrine limestone contains a few pieces, all of middle stone age type, cemented into the base of the unit and constituting about 4% of the total middle stone age sample. Although the dates on Unit 3 are inconsistent, the Unit 2B dates suggest that the 31,000 bp assay is most relevant. As with Unit 2B, inorganic carbonate dates this old are no more than minimum values and may be substantially too young. Unit 4 is the horizon with residues of middle stone age activities. While the basic sediments are interstratified valley-floor alluvia and colluvia, there is no evidence of important fluvial sorting or abrasion. Localized, dense concentrations of artifacts and

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Figure 5. Gi Unit 4. 1 Unifacial point; 2 unifacial point, reduced base: 3 partially bifacial point; 4 bifacial point; 5 side and end-scraper, quatzite; 6 side-scraper; 7 convergent side-scaper, quartzite; 8 denticulate; 9 unifacial foliate; denticulate type, quartzite; 10 retouched blade; 11 core, disc type; 12 disc. All artifacts made on cryptocrystalline rocks unless noted otherwise.

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teeth, separated both vertically and horizontally by zones with relatively little debris, may relate to distinct episodes of artifact and food waste disposal. The principal middle stone age tool types are bifacially and unifacially retouched, small to medium-sized (average length: 42 mm) pointed forms, which consitute about 25% of the retouched sample (see Figure 5). Also numerous are side- and end-scrapers, notched scrapers, and denticulates, which comprise another 20% of the retouched sample. The closest analogous site is Redcliff in Zimbabwe (see Sampson, 1974, “Bambata complex”). The collection suggests a significant degree of curation, with evidence of resharpening and some recycling of the formalized pieces into new shapes. The re-use of pieces implies a shortage of good quality cherts and chalcedonies, which comprise over 80% of the raw materials. Quartizites and quartz constitute the rest of the sample. An abundant mammalian fauna accompanies the middle stone age lithic assemblage and includes over 1000 teeth and fragments as well as several hundred bone fragments. The collection includes three extinct species: giant zebra (Equus capensis), giant buffalo (Pelorovis antiquus), and a giant alcelaphine, probably Megalotragus prisms (identifications by R. G. Welbourne, names following Klein, 1980). The dominant elements in the fauma are zebra (both the giant zebra and Burchell’s zebra: Equus burchelli), and warthog (Phacochoerus aethiopicus). Modern forms of these species are all extremely difficult to hunt. The Kung consider a pack of good hunting dogs absolutely essential to a warthog hunt, while zebra are frequently the object of a food taboo, both in the Kung area and in the central Kalahari (Silberbauer, 1981). When zebra are hunted today, it is usually from horseback. Klein (1979) has commented on the difficulty of hunting warthog and on its rarity in the middle stone age sites of the Cape Province. It is possible that taking of warthog and zebra was possible only through an ambush strategy, and Gi may have provided such a venue. Less than 20% of the proven middle stone age deposit has been excavated. The abundant teeth and lesser number of relatively fragile bones and ostrich egg shell fragments suggest repeated, relatively intense, yet brief occupations over no more than several centuries. The radiocarbon dates on ostrich eggshell from Unit 4 are infinite. By extrapolation from Units 2 and 3, the middle stone age settlement at Gi probably dates to early IsO Stage 4 or perhaps late Stage 5. In any event the abrupt transition from Unit 4 to Unit 3 suggests the terrestial record of one of several sudden climatic changes during the early Upper Pleistocene indicated in the oceanic oxygen-isotope chronologies. Unit 5 includes derived somewhat rolled materials of probable middle stone age affinities. Unit 6 is indurated; however some exposed cobbles suggested early stone age flake-scars. Unfortunately none could be retrieved. Unit 6 may represent much of the Middle Pleistocene of the region. Kangawadum Alluvial Fills and Terraces The Gi beds are paralleled downslope by a complex of alluvial fills and terraces along the Kangwadum. A composite cross-section above a knob of schist basement is illustrated in Figure 6. The most informative area is marked as Goshe West on Figure 2. The high terrace on Figure 6 is nearly continuous along the Kangwa valley. Fill A is a calcreted gravel lag of relatively rounded, pebbles and small cobbles. It presumably represents a secondarily calcified, alluvial residue of the first episode of drainage breaching the longitudinal dune landscape. No comparable deposits or terraces are known in the Dobe Valley. The absence of artifacts suggests an early Pleistocene, minimum age. A major episode of valley incision followed calcretion of Fill A and is most likely related to tectonic steepening of the valley below Kangwa as well as occasional, at least moderately semihumid environments. However accurate assessment awaits better data

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ALLUVIAL FILLSAND TERRACES ALONG THE !KANGWADUM

+4m

B -

Early

C -

Middle

Stone

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E -

Late

Stone

Age

G -

Late

Stone

Age

Stone

Figure 6. Alluvial fills and terraces along the Kangwadum Bedrock is a knob of schist.

Age

(schematic).

on bedrock morphologies and reliable topographic maps. Fill B, signalling another important episode of stream discharge is a calcreted, alluvial conglomerate. It is apparently equivalent to Unit 6 at Gi, and yielded a small early stone age hand-axe fashioned in white quartzite as well as a large bifacially worked disc of the same material. Fills C, E, and G are uncemented sandy valley-fills with local conglomeratic lenses along bedrock .outcrops. They signal environments more arid than today, when the valleyway was choked by sandy debris from the surrounding dune landscape. Fills C and E have residues of calcic entisols or inceptisols on their surfaces, which probably formed during more semihumid environments when valley incision was underway. Facies development as well as archaeological associations appear to correlate Fill C with Units 4 and 5 at Gi, Fill E with Unit 2C at Gi, and Fill G with either Unit 2A or Unit 1 at Gi. Fills D and F along the Kangwadum are locally discontinuous, spring and channel tufas, recording episodes of large-scale discharge from the Aha karstic reservoir which served to incise earlier fills and to deposit limestone. They verify environments significantly more humid than at present that can be correlated to the lacustrine phases (Unit 3 and 2B) at Gi. Fill D is particularly well developed around the large springs of the Kangwa valley, such as Karuwe. Fills F and G can be traced nearly continuously from Goshe West into the Dobe Valley past Xabi (Figure 2). The incision of Fill G compares with incision of the Gi pan terrace, and suggests a recent change in land-use as the prime explanation. As noted above, subtle tectonism may be a factor in the Gi sedimentary record. However, the closely compatible cut-and-fill chronology in the adjacent Kangwa Valley is dominated by changing patterns of sediment supply and ground-water discharge.

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Climate change must be suggested as the dominant variable in regional geomorphic dynamism during the upper Quaternary. The closest analogues to the Kangwa valley fills and terraces are Xaixaidum features near Twihaba described by Cook (1975). Unfortunately, correlation is not immediate; apparently the river valleys do not share the same sediment supply and tectonic histories in detail. Cooke’s major late Pleistocene wet phase and channel tufas (“calcrete”) probably correlate to Unit 2B at Gi, but further correlations would require reinvestigation with a search for more informative outcrops.

Summary of Dobe Valley Palaeo-landscapes and Adaptive Opportunities

The Gi depositional suite and the Kangwadum alluvial fills and terraces verify regionally significant environmental changes. Even accommodating the effects of continuing, lowgrade tectonism, the repeated appearance and disappearance of valley-wide lakes near Gi and rivers in the Kangwa valley are significant, and certainly were no less so for hominid adaptation and settlement during these intervals. No doubt water availability has been the crucial settlement variable in this landscape of pervasive edaphic drought. The basal conglomerate at Gi (Unit 6), the equivalent cemented and mainly alluvial sands exposed in wells near Dobe, as well as the Fill B conglomerate near Goshe West, probably are the residue of many environments both more arid and more humid than today, during the middle and perhaps early Pleistocene. The regional landscape of longitudinal dunes was already in place, but the pan morphologies of the modern Dobe Valley had not yet been established. Instead, several streamways coursed the Dobe Valley, connecting it directly to the Kangwa. One can envision Acheulian settlement moving eastward out of the better-watered Namibian highlands into the Dobe region during more humid intervals and retreating westward during arid intervals. The uncemented alluvia and middle stone age occupation debris (Units 4 and 5) at Gi signal a semiarid environment during the earlier Upper Pleistocene, coinciding with the last interval of important channels passing through the Dobe Valley into the Kangwadum. Middle stone age people focused on Dobe Valley for water resources along the ephemeral channelway, and the abundant, large mammalian fauna verifies a productive regional biomass. The first valley-wide lake (Unit 3 at Gi) drove middle stone age settlement to the valley margins, if not further afield. No middle stone age settlement later than Gi has been discovered around the Dobe Valley, even though this lake and the related humid regional environment may have persisted for several millenia. An initial later stone age settlement at Gi followed desiccation of the lake. As the lake dried, a landscape of pans was established in a Dobe Valley more arid than today (Unit 2C). Settlement was again terminated at Gi when another lake expanded to fill the valley floor (Unit 2B). Later stone age people visited Gi when this lake also dried out and the pan landscape returned. Arid environments recorded at this time (Gi Unit 2A) may span much of the last, glacial maximum of the northern hemisphere. Still later, a more semiarid landscape, similar to that of today, became prevalent. Initially sedimentation was slow (Gi Unit lB), but the phytomass later increased, producing more organic matter in the Dobe Valley; eventually relatively humic sediments were washed into the pan basins (Unit 1A). Still more recently the modern pan basin was eroded at Gi. Gi’s isolation sets it off as a nearly unique point of archaeological information in the northwest Kalahari. The full significance and regional context of the site can only be assessed when further archaeological and palaeoenvironmental data become available for this region.

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Acknowledgements This research was supported by N.S.F. Grants SOC 75-14227 and BNS 76-19633 (to A.S.B.) and a Junior Faculty Fellowship from the University of California (to D.M.H.). Robert Stuckenrath of Smithsonian Radiation Biology Laboratory kindly provided the quality radiocarbon assays. E. M. van Zinderen Bakker searched the Gi sediments for productive pollen samples. More than 80 sediment samples were analysed in the Geomorphology Laboratory of the University of California. This research would have been impossible without the cooperation and assistance of the Gi excavation team and the many people who live in the Dobe Valley. Figures 1, 2, 3 and 6 were drafted by Jeff Murphree at the University of Miami, and Figures 4 and 5 were illustrated in Washington, D.C. by Patricia Cutts, who drew the artifacts from Units 4 and 2C, and by Michael Srnka, who drew the artifacts from Units 1 and 2A.

References Alison, M. S. (1899). On the origin of pans. Transactions Geological Survey of South Africa 4, 159-161. Brooks, A. S. & Yellen, J. E. (1979). Archeological excavations at #Gi: A preliminary report on the first two field seasons. Botswana Notes and Records 9, 21-30. Brooks, A. S., Crowell, A. L. & Yellen, J. E. (1980). #Gi: A stone age archaeological site in the northern Kalahari Desert, Botswana. In (Leakey, R. E. & Ogot, B. A., Eds) Proceedings of the 8th Panafrican Congress of Prehistory and Quaternary Studies (1977). Nairobi: T. I. L. L. M. I. F. A. P., pp. 304-309. Brooks, A. S., Gelburd, D. E. & Yellen, J. E. (in press). Food production and culture change among the !Kung San: implications for prehistoric research. In Clark, J. & S. Brandt, Eds, Causes and Consequencesof Food Production in Africa, University of California Press. Butzer, K. W., Stuckenrath, R., Bruzewicz, A. J. & Helgren, D. M. (1978). Late Cenozoic paleoclimates of the Gaap Escarpment, Kalahari Margin, South Africa. Quaternary Research 10, 310-339. Cooke, H. J. (1975). The palaeoclimatic significance of caves and adjacent landforms in western Ngamiland, Botswana. Geographica Journal 141,430-444. Grove, A. T. (1969). Landforms and climatic change in the Kalahari and Ngamiland. Geographical Journal 135, 191-212. Helgren, D. M. (1979). Rivers of diamonds: An alluvial history of the lower Vaal Basin, South Africa. Chicago: University of Chicago, Department of Geography Research Series NO. 185. Klein, R. G. (1979). Stone Age exploitation of animals in Southern Africa, American Scientist 67, 151-160. Klein, R. G. (1980). Environmental and ecological implications of large mammals from Upper Pleistocene and Holocene sites in southern Africa. Annals of the South African Museum 81, 222-283. Lee, R. G. (1979). The !Kung San: Men, women, and work in a foraging society. New York: Cambridge University Press. Link, A. G. (1966). Textual classification of sediments. Sedimentology 7, 249-254. Sampson, C. G. (1974). The Stone Age archeology of southern Africa. New York: Academic Press. Shackleton, N. J. & Opdyke, N. D. (1973). Oxygen-isotope and paleomagnetic stratigraphy of Equatorial Pacific Core V28-238: oxygen isotope temperatures and ice volumes on a lo6 and lo6 year scale. Quaternary Research 3, 35-55. Shackleton, N. J. & Opdyke, N. D. (1976). Oxygen-isotope and paleomagnetic stratigraphy of Pacific core V28-239. Late Pliocene to latest Pleistocene. Memoirs Geological Society of America 145, 449-464. Silberbauer, G. B. (1981). Hunter and Habitat in the Central Kalahari Desert. New York: Cambridge University Press.

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Soil Survey Staff (1975), Soil Taxonomy. Washington: Soil Conservation Service, U.S.D.A., Agricultural Handbook No. 436. Wayland, E. J. (1944). Drodsky’s cave. Geographical Journal 103, 230-233. Wilmsen, E. N. (1980). Prehistoric and historic antecedents of a contemporary Ngamiland community. Botswana Notes and Records 10, 5-l 8. Yellen, J. E. (1971). Archeological investigations in Western Ngamiland. Botswana Notes and Records 3, 276.

Yellen. J. E. (1977). Archeological

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