16
Journal of Archaeological Science (1996) 23, 7–22 Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana L. H. Robbins and M. L. Murphy Department of Anthropology, Michigan State University, East Lansing, MI 48824, U.S.A. N. J. Stevens Department of Anthropology, Suny Stony Brook, NY 11794-4364, U.S.A. G. A. Brook and A. H. Ivester Department of Geography, University of Georgia, Athens, GA 30602, U.S.A. K. A. Haberyan Department of Biology, Troy State University, Troy, AL 36082, U.S.A. R. G. Klein Department of Anthropology, Stanford University, Stanford, CA 94305-2145, U.S.A. R. Milo Department of Anthropology, University of Chicago, Chicago, IL 60637, U.S.A. K. M. Stewart Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario, Canada D. G. Matthiesen Department of Zoology, University of Florida, Gainsville, FL 32611, U.S.A. A. J. Winkler Shuler Museum of Paleontology, Southern Methodist University, Dallas, TX 75275, U.S.A. (Received 23 February 1994, revised manuscript accepted 11 August 1994) Test excavations conducted at Drotsky’s Cave have provided important new information on the paleoenvironment and archaeology of the western Kalahari desert during the late and terminal Pleistocene. An occupation layer dated to the terminal Pleistocene was rich in Late Stone Age artefacts, pieces of ostrich egg shell, the remains of carnivorous bullfrogs, springhare, and other fauna. A detailed sediment study, along with the evidence of Angoni vlei rat, climbing mouse, an aquatic Xenopus frog, and side neck turtle confirms that conditions were for the most part, substantially more moist than at present between approximately 30,000 and 11,000 years ago. Analysis of a diatom assemblage dated to the terminal Pleistocene implies that the currently dry Gcwihaba Valley was most likely flowing for much of the year. Our evidence supports findings made at other localities in the Kalahari documenting the existence of especially moist conditions during the terminal Pleistocene. ? 1996 Academic Press Limited Keywords: DROTSKY’S CAVE, SOUTHERN AFRICAN PREHISTORY, TERMINAL PLEISTOCENE/HOLOCENE CLIMATE CHANGE, KALAHARI DESERT. 7 0305-4403/96/010007+16 $12.00/0 ? 1996 Academic Press Limited

Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

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Page 1: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

Journal of Archaeological Science (1996) 23, 7–22

Paleoenvironment and Archaeology of Drotsky’s Cave:Western Kalahari Desert, Botswana

L. H. Robbins and M. L. Murphy

Department of Anthropology, Michigan State University, East Lansing, MI 48824, U.S.A.

N. J. Stevens

Department of Anthropology, Suny Stony Brook, NY 11794-4364, U.S.A.

G. A. Brook and A. H. Ivester

Department of Geography, University of Georgia, Athens, GA 30602, U.S.A.

K. A. Haberyan

Department of Biology, Troy State University, Troy, AL 36082, U.S.A.

R. G. Klein

Department of Anthropology, Stanford University, Stanford, CA 94305-2145, U.S.A.

R. Milo

Department of Anthropology, University of Chicago, Chicago, IL 60637, U.S.A.

K. M. Stewart

Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario, Canada

D. G. Matthiesen

Department of Zoology, University of Florida, Gainsville, FL 32611, U.S.A.

A. J. Winkler

Shuler Museum of Paleontology, Southern Methodist University, Dallas, TX 75275, U.S.A.

(Received 23 February 1994, revised manuscript accepted 11 August 1994)

Test excavations conducted at Drotsky’s Cave have provided important new information on the paleoenvironment andarchaeology of the western Kalahari desert during the late and terminal Pleistocene. An occupation layer dated to theterminal Pleistocene was rich in Late Stone Age artefacts, pieces of ostrich egg shell, the remains of carnivorousbullfrogs, springhare, and other fauna. A detailed sediment study, along with the evidence of Angoni vlei rat, climbingmouse, an aquatic Xenopus frog, and side neck turtle confirms that conditions were for the most part, substantiallymore moist than at present between approximately 30,000 and 11,000 years ago. Analysis of a diatom assemblage datedto the terminal Pleistocene implies that the currently dry Gcwihaba Valley was most likely flowing for much of the year.Our evidence supports findings made at other localities in the Kalahari documenting the existence of especially moistconditions during the terminal Pleistocene. ? 1996 Academic Press Limited

Keywords: DROTSKY’S CAVE, SOUTHERN AFRICAN PREHISTORY, TERMINALPLEISTOCENE/HOLOCENE CLIMATE CHANGE, KALAHARI DESERT.

70305-4403/96/010007+16 $12.00/0 ? 1996 Academic Press Limited

Page 2: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

Introduction

N atural rock shelters and caves with long paleo-environmental and Stone Age archaeologicalsequences are relatively rare in the Kalahari in

comparison to neighbouring areas of Zimbabwe andSouth Africa. For this reason our overall knowledge ofpaleoenvironments and Stone Age archaeology in theKalahari is generally based on composite views drawnfrom various open sites, which often lack stratigraphy,or are surface sites, rather than from single localitieswith deep deposits. In fact, major rock shelter excava-tions have only been carried out at the Depression andWhite Paintings sites in the Tsodilo Hills and the onlyexcavated caves are the lower Male Hill Cave atTsodilo and Drotsky’s Cave located in the GcwihabaHills (Robbins, 1990; Robbins & Campbell, 1989;Robbins, 1991; Campbell & Robbins, 1993; Yellen,Brooks, Stuckenrath & Welbourne, 1987; Pickford,1990), (Figure 1).In 1969, John Yellen, accompanied by a group of

!Kung San from the Dobe area, conducted archaeo-logical research in the northeast entry chamber ofDrotsky’s Cave (Figure 2). He excavated a series

of four 5 ft square test pits (Yellen et al., 1987). One ofthe test pits (A) yielded 61 stone artefacts as well asnumerous pieces of ostrich egg shell, fauna and char-coal. The artefacts were found between 28 and 40 in.below a datum that was established at the base of theletter Y in Drotsky’s name, which was carved byMartinus Drotsky into the side of a large boulderin the entry chamber in 1932. (Drotsky’s name wasstill clearly visible when we visited the cave in1991). Charcoal recovered from 31 in. below thisdatum in square A yielded a radiocarbon date of12,200&150 . This represented the first discovery ofin situ terminal Pleistocene archaeological material inthe western Kalahari, and as such was important to thebasic question of the length of time Khoisan ancestorshad lived in the area. The other excavation unitsapparently did not yield artefacts.Over 90% of the lithic material recovered by Yellen

was débitage, mainly consisting of silcrete. The absenceof microliths and lack of evidence of blade technologysuggested that the Drotsky’s cave area was part ofthe ‘‘non-microlithic’’ complex described by Deacon(1984) for interior parts of southern Africa during theterminal Pleistocene/early Holocene.

Drotsky'sCave

OrangeR.

25°S

EtoshaPan

Botswana

30°S

20°S

35°S

Namibia

Windhoek

5

4

32 1

8

95

6 10

Gaborone

Africa

Molopo R

. Johannesburg

Swaziland

LesothoDurban

South Africa

Cape Town

5000

km

Figure 1. Southern African locality map.

8 L. H. Robbins et al.

Page 3: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

Yellen also noted that his !Kung San field assistantsreported traditions of using the cave to obtain honey,but they did not camp in it. Finally, it was suggested onthe basis of faunal remains that a ‘‘generalist’’ strategyof food procurement was likely, similar to thatethnographically observed among the !Kung.

1991 ResearchDrotsky’s Cave is in the dolomite marbles of theGcwihaba Hills, that consist of six outcrops straddlingthe now dry Gcwihaba Valley. The hills are sur-rounded by low, longitudinal sand dunes, alignedWNW–ESE, that have been stabilized by vegetation.Drotsky’s Cave is confined within one of the hills, thewest-facing slope of which is a steep rocky face wherethe two entrances to the cave are located (Cooke &Baillieul, 1974). The present climate of the area issemiarid. Annual precipitation at Maun 230 km east,Ghanzi 200 km south, and Shakawe 150 km north is491, 401, and 520 mm respectively and occurs almostexclusively in the Austral summer months. The firstpaleoenvironmental investigations at the cave werebegun in 1972, and over the past 20 years the cave hasbeen an extremely valuable source of paleoenviron-

mental data for the Ngamiland region (Cooke, 1975;Grey & Cooke, 1977; Cooke & Verhagen, 1977; Cooke& Verstappen, 1984; Shaw & Cooke, 1986).Following the encouragement of Yellen, another test

pit was excavated at Drotsky’s Cave in 1991. We hopedto enlarge the artefact and faunal sample by sieving,which was not done in the original study. The ultimateaim of our work at Drotsky’s Cave is to provide a database that can be compared to ongoing multidisci-plinary research into the paleoenvironment and pre-history of the Tsodilo Hills, which are located about125 km to the north (Robbins, Murphy, Stewart,Campbell & Brook, 1994).Our test pit, limited to 1 m2, was located next to

Yellen’s pit D not far from the rear wall of the entrychamber. Figures 2 and 3 show the location andstratigraphy of our test pit. This pit was excavated to adepth of 130 cm below the surface, or 186 cm below thedatum used by Yellen. The base of the deposit has notyet been established and there may well be deeperoccupation levels. The sediments consist largely ofKalahari sand described in detail below. The moststriking result of our excavation was the discovery of acontinuous layer of charcoal between 50 and 80 cmbelow the surface (Figure 3). This charcoal layer was

Figure 2. Drotsky’s Cave: view of northeast entry chamber showing 1991 test pit and remnants of pit D.

Paleoenvironment and Archaeology of Drotsky’s Cave 9

Page 4: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

also quite clearly the main artefact and faunal layerrevealed by the excavations. The base of the charcoallayer was marked by a white/grey ash zone, underlainby a red fire-oxidized area. Levelling from the datumused by Yellen established that the top and base of thischarcoal layer correspond closely to the two charcoallayers discovered by Yellen and his pit D; (i.e. the topof Yellen’s upper layer matches the top of our layerand the bottom of ours matches the bottom of hislower layer.)The charcoal layer’s general nature and shape

suggests to us that it did not correspond to a singlehearth, but may, instead, represent intensive super-imposed fires. The charcoal was exceptionally well-preserved with many pieces measuring about 4 cm.Some pieces had sub-pointed and rounded ends sug-gestive of deliberate cutting, but inspection by apaleoethnobotanist did not reveal cut-marks or otherdefinite evidence of work (K. Egan, pers. comm.).

DatesThe following radiocarbon dates were obtained fromthe 1991 test pit:(1) Between 20 and 30 cm below the surface (dispersedcharcoal scatter found in sand) dates to 5470&90 (Beta 50162);(2) 50 cm (top of the above-mentioned charcoal layer)dates to 11,240&60 (Beta 50163);(3) Between 70 and 80 cm (base of the charcoal layer)dates to 12,450&80 (Beta 47862).

Deposits between 80 and 130 cm yielded very littlecharcoal and have not been radiocarbon dated. Esti-mated ages for the deposits beneath the charcoal layerwill be presented below in a discussion of thesediments.The above dates reveal that Drotsky’s Cave was

utilized over an extensive period. However, the mainartefact and charcoal bearing deposits between 50 and80 cm appear to have accumulated over approximately1200 years. Although the date obtained from the baseof the charcoal-rich layer is in remarkably good agree-ment with Yellen’s date, it should be noted that hisdated charcoal sample from Square A was recoveredfrom approximately 47 cm above our sample in termsof our comparative measurements to the site datum(the Y in Drotsky’s name). This difference may resultfrom sloping deposits, greater buildup of depositstoward the entrance, or other unknown factors. What-ever the case may have been, the similarity in the datessuggests that terminal Pleistocene material is widelydistributed in the entrance area of the cave. As will beshown, it is significant that the terminal Pleistocenedates are in close agreement with the age of calcreterecovered from the Gcwihaba Valley within 2 km ofthe cave. The calcrete contains fresh water diatomswhich suggest significant stream flow at the time theywere deposited.

ArtefactsLate Stone Age artefacts from Drotsky’s Cave arediscussed below relative to the terminal Pleistocenecharcoal layer. Most of the interpretations are tentativeuntil extensive systematic excavations are conducted.Although detailed reports on the fauna follow thediscussion of the artefacts, we refer to some of thegeneral information on the fauna in the artefactdiscussion for the purpose of enhancing the culturalinterpretation.

The deposits above the charcoal layer (0–50 cm):Casual use of the cave during the Holocene

Nothing was found in the excavation of the first 50 cmthat was clearly indicative of an occupation surface,nor was there a concentration of material suggestingthat the cave was used as an actual camp. In fact, verylittle cultural material or fauna was recovered from anyof the individual 10 cm levels above the charcoal layer.For this reason, we present an overview of the infor-mation while the specific lithic data by levels is shownin Table 1.It may be significant, given the current interest in the

issue of the degree of contact between early Iron Agepeoples and Kalahari foragers, that no potsherds orother traces of contact with Iron Age peoples werefound in the uppermost deposits (Wilmsen & Denbow,1990). This lack of early Iron Age material might

1m

cm

0

100

50

Red/brown sand

Red/brown sand

Light brown sand

Ash lensRed oxidized sand

Calcite layer

Grey/brown/black sand

130

Figure 3. Drotsky’s Cave: cross section of the east face of the 1991test pit.

10 L. H. Robbins et al.

Page 5: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

support the view that foraging peoples in the interior ofthe Kalahari were little influenced by Iron Age peoples.However, this negative evidence could easily be aproduct of the small area excavated and/or a situationwhere only a few people, who rarely lost or discardedtheir tools or belongings, used the cave.Fifty one stone artefacts were recovered in the upper

50 cm, of which 33 were made from the locally avail-able travertine (flowstone). This casual use of theflowstone in the cave is suggestive of an ‘‘expedient’’technology, which would be in keeping with the inter-pretation of brief visits by a few individuals for honeycollecting as mentioned by Yellen et al. (1987).Noteworthy finds included an edge damaged chert

flake from the dated 20–30 cm level, along with a chertburin and chert scaper from the 40–50 cm level. Thelatter two finds were the only retouched tools found inthe entire upper 50 cm. The source of the chert isunknown, but is most likely not local.In addition to the stone artefacts, there were two

ostrich eggshell beads and 11 unburned ostrich eggshell fragments. Other signs of human activity includedthree mongongo nut shell fragments found in the10–20 cm level. Yellen et al. (1987) mention the pres-ence of mongongo groves in the area and that thesewere exploited by the !Kung. Elsewhere (Robbins,1990), we have shown that mongongo nuts, an impor-tant staple food of the San, have been exploited since atleast the early Holocene in the western Kalahari.

The Terminal Pleistocene charcoal layer (50–80 cm):intensive use of the cave

There was a substantial increase in cultural remains inthe charcoal layers, especially in chert artefacts andfauna (Table 1). The increase in artefacts and bones,mainly of large African bullfrogs, together with anabundance of large, burned ostrich eggshell fragmentswithin the dense charcoal layer, represents a significantchange in the pattern of human use of Drotsky’s Cave.Both fauna and other paleoenviromental data, dis-

cussed in detail later, reveal that it was substantially

wetter in the Drotsky’s Cave area during the lateterminal Pleistocene, with stream flow in the GcwihabaValley possibly for lengthy periods during the year.The setting certainly was very different in comparisonto today. We suggest that the nearby Gcwihaba Riverand valley were being systematically exploited and thatthe mouth of the cave was inhabited as a camp.We recovered 146 pieces of debitage (56 were chert),

six cores (five were chert), 10 retouched pieces (eightwere chert) and eight with edge damage that mostlikely resulted from use. In addition, there was afragment of what is most likely a cobble-sized grind-stone. The debitage included 58 side struck flakes(55·2% of the total from the charcoal layer) and 47 endstruck flakes (44·8%). Although the retouched toolsdid not include any backed microliths, the presenceof well-made chert bladelets and four cores with nega-tive bladelet scars clearly demonstrates the use of asophisticated microlithic technology in the terminalPleistocene (Figure 4). This interpretation contrastswith Yellen’s speculation that Drotsky’s Cave was partof the non-microlithic tradition of the interior ofsouthern Africa (Yellen et al., 1987).Unfortunately, the lack of diagnostic tools prevents

any close comparison with any of the well-knownterminal Pleistocene assemblages from southernAfrica, but in a general way, it may represent the endof the late Pleistocene microlithic period describedby Deacon (1984). These late Pleistocene microlithicassemblages are recognized archaeologically by ‘‘thesystematic production of small bladelets from stan-dardized single-platform bladelet cores and by theoccurrence in some quantity of bipolar cores that havesometimes been so reduced by flaking that they areclassed as . . . scaled pieces’’ (Deacon, 1984: 227). Insuch assemblages the frequency of formal tools is lessthan 1% of the total, and in general, they are lessstandardized than those found in Holocene assem-blages. This characteristic of terminal Pleistoceneassemblages may explain why comparatively few for-mal tools were found in the charcoal layer. Other lateand terminal Pleistocene samples from the western

Table 1. Stone artefacts from the 1991 test excavations at Drotsky’s Cave

cm Débitage Cores Edge damage Scraper Notch Burin Bifacial pt Miscellaneous Total

0–10 3 2 510–20 8 820–30 7 2 930–40 19 1 1 2140–50 15 1550–60 82 4 1 2 1 1 9160–70 49 2 3 2 1 5770–80 15 1 1680–90 1 190–100 2 2100–110 10 10110–120 2 2120–130 3 3

Note: The raw materials for all levels in the test pit include travertine (47%), chert (27%), chalcedony (1%), quartz (14%), and silcrete/other(10%).

Paleoenvironment and Archaeology of Drotsky’s Cave 11

Page 6: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

Kalahari include assemblages from Gi, an open-airpan margin site near Dobe, and the Tsodilo HillsDepression and White Paintings Shelters. Interestingly,the artefact assemblage recovered from levels datedto between 10,900&420 and 13,060&280 at theDepression shelter, the same approximate period as theDrotsky’s Cave charcoal layer, is similar to the lithicmaterial from the charcoal layer in that very fewretouched tools occur (Robbins, 1990). Further re-search at Drotsky’s Cave may confirm whether thesame tradition of artefacts was widely distributed inthe western Kalahari during the terminal Pleistocene.The charcoal layer also included two ostrich eggshell

beads and 197 ostrich eggshell fragments, of which 53were burned. As mentioned above, similar large piecesof ostrich eggshell were recovered by Yellen, but mostof them were not burned. It is interesting that largepieces of unworked and unburned ostrich eggshell werealso common in terminal/late Pleistocene levels at theTsodilo Hills White Paintings Shelter. As far as we candetermine, the ostrich eggshells at Drotsky’s Cave werenot being used to manufacture beads. Other sites wherebeads were being made, such as the more recent levelsat White Paintings Shelter, clearly show evidence of thestages of manufacture in terms of overall shapechanges, edge grinding and the drilling of holes.Although ostrich egg shells are also used as canteens,

the charring of the eggs most likely indicates that theeggs were being cooked, but we are uncertain about themethod of cooking. Hitchcock (pers. comm.) describeshow Kalahari San pour the contents of the egg into apot or pan in order to cook it. Presumably, latePleistocene peoples in the Kalahari lacked containerswhich could be placed directly over a fire to cook eggs.However, some recent observations may be pertinent.In 1992, one of us (Robbins) noticed San youths atTsodilo cooking chicken eggs directly on smoldering

coals by wrapping the eggs in wet dung. Whethersimilar methods were used in the past for cookingostrich eggs is, of course, unknown.Judging from the rest of the fauna described below,

it appears as if the terminal Pleistocene inhabitants ofthe cave had a reasonably varied diet, including a rangeof small to medium mammals, tortoises, birds (includ-ing ostrich eggs), and bullfrogs. The comparativeabundance of ostrich eggs and bullfrogs in the charcoallayer hints that the diet had some specialized aspects toit as well.

The deposits below the charcoal layer (80–130 cm):casual use of the cave

The story of the human use of the cave, as suggested byour test pit, once again shifts to a pattern of casualusage consistent with the ethnographic observationsreported by Yellen et al. (1987). The marked concen-tration of artefacts, and animal remains that werelikely to have been used as food, is no longer evident,and is replaced by bones of rodents and birds that aremost likely the result of owl predation and othernatural factors.Artefacts were rarely found, but include 18 pieces of

probable débitage, of which 15 were in flowstone ortravertine. A small grindstone was recovered from the110–120 cm level. There was no chert and formalretouched tools were lacking. However, we did recover20 ostrich eggshell fragments, one of which wasburned, and two ostrich eggshell beads (Figure 3).The presence of the beads, below the terminal

Pleistocene dated levels, confirms that one of thestandard items of decoration used by people in theKalahari has ancient roots that extend at least tothe late Pleistocene. While the overall collection ofbeads recovered from all levels of our excavation at

Figure 4. Drotsky’s Cave artefacts. Upper row-chert bladelet core and chert/silcrete bladelets from the charcoal layer; lower row-chert hollowscraper and chert utilized flake from the charcoal layer, ostrich egg shell beads from 10–20, 90–100 and 100–110 cm. Photo by Susan Eyde.

12 L. H. Robbins et al.

Page 7: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

Drotsky’s Cave is limited to six specimens, it is inter-esting to observe that the size of the beads increases atthe base of the deposits. Bead diameter is as follows:0–10 cm level is 4·6 mm, 10–20 cm is 4·3 mm, 50–60 cmis 4·6 mm, 60–70 cm is 4·2 mm, 90–100 cm is 5·3 mm,100–110 cm is 5·5 mm. This increase in size in theoldest deposits is the opposite to size trends observedat more recent sites in Namibia where there are largersamples (Jacobson, 1987).

FaunaFaunal remains were well-preserved and, as alreadynoted, included mammals, birds, amphibians and rep-tiles. We present the basic analysis below in the form ofindividual specialist reports. Some general commentsare offered as an interpretive ‘‘preview’’ to the reports.There were no fish and this lack could be seen as

paleoecological evidence that the Gcwihaba River wasnot connected to fish-bearing waters such as theOkavango Delta, which was larger during the wetterperiods of the late Pleistocene. On the other hand, itcould be that the occupants of the cave did not catch oreat fish, even though they quite clearly utilized theriver. We think that this interpretation is unlikely giventhe prevalence of catfish remains found at the TsodiloWhite Paintings Shelter throughout the Late StoneAge (Robbins et al., 1994).At present, leopards and hyaenas occasionally visit

the cave. In the past such predators could have beenresponsible for the introduction of some of the bovidremains as well as the single equid bone that was foundbelow the charcoal/main occupation layer. The hyaenabones found above and below the charcoal layer couldrepresent natural deaths of these animals.As will be shown, the majority of the birds and

rodents, with the exception of springhares, were recov-ered from below the charcoal layer in the levels thathad little cultural material. Most of them probablyrepresent natural deaths. In great contrast, 88% of thespringhare elements, an important food animal forthe ethnographically observed San, along with themajority of the macromammals and bullfrogs, wererecovered from the charcoal layer. Most of theseanimals were likely food refuse or, in a few cases,notably the fox and caracal or serval, could have beenexploited for furs.

Macromammals

The macromammals are listed in Table 2. As far as weknow, all the species occurred in the area historically.Small sample size may explain the absence of lechwe(Kobus leche), reedbuck (Redunca arundinum), or otherwetland mammals that are represented in late/terminalPleistocene layers in the Tsodilo Hills. Samplingerror may also account for the absence of blesbok(Damaliscus dorcas) which Yellen et al. (1987) reported

from the previous excavation at Drotsky’s Cave. If thisidentification was correct, it could imply a time whenthe environs of Drotsky’s Cave were grassier, sinceblesbok is a grassland species that was restricted toSouth Africa historically. A possible expansion ofhighveld-type grassland northwards has been inferredfrom the presence of blesbok in the late Pleistocenelayers of Redcliff Cave, Zimbabwe (Cruz-Uribe, 1983).Small sample size almost certainly does not explain therelative abundance of springhare, which are also com-mon at the White Paintings Site in the Tsodilo Hillsand in later Stone Age rock shelters in the northernCape Province of South Africa, on the southern mar-gin of the Kalahari (Klein, 1979). The archaeologicaldata imply that springhare were as important to pre-historic Kalahari hunter–gatherers as they were to the!Kung and other historic San groups (Lee, 1979).Sampling bias is also unlikely to explain the relativeabundance of small and small–medium antelope,which similarly dominate Later Stone Age samples atTsodilo, in Namibia, and on the southern Kalaharimargin (Cruz-Uribe & Klein, 1983; Klein, 1979). Therelative abundance of smaller antelope at so many sitesprobably reflects their live abundance nearby and therelative ease with which they could be transportedfrom kill sites to camp sites.

Micromammals: Rodentia

The rodent remains from Drotsky’s Cave include aminimum of eight genera (Table 3). With the exceptionof the springhares, discussed above under macro-mammals because of their large size (up to 4 kg),rodent specimens were most common in the lower partof the section (100–130 cm). Most of the rodent re-mains (springhares are a likely exception) were prob-ably deposited as food refuse by non-human predators,in particular by owls as regurgitated pellets. The rodentbones are well preserved and evidence of digestion andtransport is rare. Most specimens are nearly intact:long bones are usually missing only the very proximaland/or distal ends, teeth are often present in the alveoli,and many mandibles are essentially complete exceptfor the ascending rami. In addition, all the identifiabletaxa are almost exclusively nocturnal and all (forwhom the predators are known) are known prey forowls, in particular the barn and grass owls. Asdiscussed below, bones of what is most likely barnowl (0–10 cm and 70–80 cm) and also other raptors(70–80, 100–110, 120–130 cm) have been recoveredfrom Drotsky’s Cave.As was previously noted, springhares found in the

greatest abundance in the terminal Pleistocene char-coal layer from 50 to 80 cm are reasoned to have beenan important food resource. The fat mouse is alsoconsidered a delicacy by indigenous African people (deGraaff, 1981), but this genus may only be present at110–120 cm, and it is not found in the units (50–80 cm)where occupation was most evident.

Paleoenvironment and Archaeology of Drotsky’s Cave 13

Page 8: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

Table2.Macromammalsfrom

the1991testexcavationsatDrotsky’sCave

Taxon

0–10cm

10–20

cm30–40

cm40–50

cm50–60

cm60–70

cm70–80

cm80–90

cm90–100

cm100–110

cm110–120

cm120–130

cmAll

Pedetescapensis(Springhare)

——

1/1

1/1

21/2

4/1

4/1

——

1/1

1/1

—33/2

Otocyonmegalotisorvulpeschama(Fox)

——

1/1

——

1/1

——

——

——

2/1

Viverridaegen.etsp.indet.(Indeterminatemongoose)

——

——

1/1

——

——

——

—1/1

HyaenabrunneaorCrocutacrocuta(Hyaena)

1/1

——

——

——

——

——

1/1

2/1

Felisservalorcaracal(caracalorserval)

——

——

4/1

——

——

——

—4/1

Equusburchelli(Plainszebra)

——

——

——

——

——

1/1

—1/1

DicerosbicornisorCeratotherium

simum

(Rhinoceros)

——

——

—1/1

——

——

——

1/1

Tragelaphusstrepsiceros(Greaterkudu)

—2/1

——

——

——

——

——

2/1

Sylvicapragrimmia(Grayduiker)

—1/1

—1/1

1/1

——

—.

——

—1/1

4/1

Raphiceruscampestris(Steenbok)

1/1

1/1

Bovids—

general

Small(e.g.steenbok)

—1/1

——

12/1

4/1

1/1

——

——

—18/2

Smallmedium(e.g.grayduiker,springbok)

—1/1

—1/1

1/1

1/1

——

——

—1/1

5/1

Largemedium(e.g.greaterkudu,hartebeest)

—2/1

—1/1

1/1

2/1

1/1

1/1

——

—1/1

9/1

Largebovid(e.g.eland,bu

ffalo)

——

——

——

——

——

——

Note:Thelargermammalspeciesfoundinsuccessive10cm

spitsinthe1991excavationsatDrotsky’sCave.ThenumberbeforetheslashineachcaseistheNum

berofIdentifiedSpecimens

(NISP).ThenumberafterwardsistheMinimum

Num

berofIndividuals(MNI)from

whichthespecimensmusthavecome.Mostofthebonescomefrom

acharcoallayer50–80cm

below

thesurface,whichaccumulatedbetweenroughly12,500and11,000radiocarbonyearsago.

Table3.Rodents(micromammals)from

the1991testexcavationsatDrotsky’sCave

Taxon

0–10cm

10–20

cm20–30

cm30–40

cm40–50

cm50–60

cm60–70

cm70–80

cm80–90

cm90–100

cm100–110

cm110–120

cm120–130

cmAll

Mystromyalbicaudatus(white-tailedrat)

——

——

——

——

——

—2/1

3/2

5/3

Gerbilluruspaeba(Hairy-footedgerbil)

——

1/1

——

1/1

——

——

—3/1

1/1

6/4

Tateracf.T.leucogaster(Bushveldgerbil)

——

——

—1/1

——

——

——

—1/1

Tateracf.T.brantsii(Highveldgerbil)

1/1

——

——

—1/1

5/7

——

34/13

11/5

20/7

72/34

Taterasp.

1/1

—2/1

——

——

2/2

——

1/1

3/3

1/1

10/9

Dendromussp.(Clim

bing

mouse)

——

——

——

——

——

——

1/1

1/1

Steatomyssp.(Fatmouse)orMalacothrixsp.

(Large-earedmouse)

——

——

——

——

——

—2/2

—2/2

Otomyscf.O.angoniensis(Angonivleirat)

——

——

——

—3/3

——

5/2

12/4

3/2

23/11

Muridae

——

2/1

——

——

——

——

——

2/1

Unidentifiedmuroids

——

——

——

—1/1

——

1/1

2/2

4/3

8/7

Note:Alloftheidentifiablefaunathatwasrecoveredisreportedwiththeexceptionoftheremainsofbatsandinsectivores.Thebatremainsarealmostcertainlytheresultofnaturaldeaths.

Batsareabundantatpresentinthecave.

14 L. H. Robbins et al.

Page 9: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

The rodents found at Drotsky’s Cave represent twomain ecological niches. The majority (hairy-foooted,Highveld, and Bushveld gerbils, and springhare, to-gether comprising 80% of the total number of speci-mens identifiable to genus) can be characterized asinhabitants of dry, open areas with light vegetationcover and sandy soils. The fat mouse may also befound in this environment, but the large-eared mouseprefers harder ground. The other important ecologicalniche represented is a more heavily vegetated areaalong a major water source such as a river. This nicheis suggested by the Angoni vlei rat and the climbingmouse. The recovery of the latter taxa supports otherevidence (e.g. from calcrete samples) indicating theformer presence of a river in the Gcwihaba Valleybelow the cave. If owls deposited the remains of thevlei rats in the cave, we can estimate from the range ofthe modern barn owl that the wetland habitat of therats was probably located within a few kilometres ofthe cave itself. However, vlei rats are also eaten bypeople (Smithers, 1971) and it is possible that they werebrought in from a more distant area.Most of the fossil rodent genera may have living

counterparts in the general area of Drotsky’s Cave.However, in Botswana, the Angoni vlei rat is found tothe north of the study area along the Okavango River,and the large-eared mouse is found to the south ofabout 22)S longitude. The vlei rat has also been foundat the Tsodilo Hills White Paintings Shelter about50 km to the west of the Okavango (Robbins et al.,1994). It is probably significant that the vlei rat is notfound above the terminal Pleistocene deposits in morerecently deposited sediments. As discussed below, sedi-mentological and other evidence suggests that thelate/terminal Pleistocene was much wetter than today.The most notable extralimital taxon is the white-tailedrat (Mystromys albicaudatus) recovered between 110and 130 cm, which is currently not found in Botswana.This relatively rare rodent is confined mainly to high-veld and montane grasslands in the Transvaal, north-western Natal, the Orange Free State, Lesotho, and theeastern region and western Cape of South Africa. It isfound in the Southern Savanna Grassland and theSouth West Cape biotic zones (de Graaff, 1981).Nowak and Paradiso (1983) describe it as inhabitinggrassy flats and dry sandy areas.

Birds

The preliminary identifications of the birds fromDrotsky’s Cave are presented in Table 4. At the presenttime, in the absence of other sources of water, birds areattracted to the entrance of the cave to drink smalldroplets of water emerging from the stalactites. Thecave is also used by owls, as evidenced by castings(pellets). Two barn owls were observed in the cave in1993. They were seen in both entrances.Most of the bird remains were found below the main

occupation layer and are believed to represent natural

deaths rather than human food refuse. Although con-ditions were wetter in the late Pleistocene, with fre-quent and possibly at times perennial river flow in theGcwihaba Valley, no aquatic or marsh birds wererecovered. In this regard, it should be noted thataquatic birds, such as ducks, do frequent the westernKalahari pans at present when they contain waterduring the rainy season. The owl remains are mostlikely referable to the barn owl (Tyto alba). Furthercomparative study of the buttonquail (Turnix), bee-eater (Merops) and probably the doves (Columbidae)could result in identifications to the species level.

Bullfrogs

The most striking aspect of the faunal sample from thepoint of view of human subsistence and paleoenviron-mental conditions was the comparative abundance ofbullfrog (Pyxicephalus adspersus) bones recoveredfrom the deposits. A total of 129 bullfrog elementswere recovered representing a minimum of 40 individ-uals. While they were distributed in every 10 cm levelbetween 40 and 130 cm, 26 of the individuals (65%)were recovered from the terminal Pleistocene charcoallayer between 50 and 80 cm. These frogs most likelywere obtained from the terminal Pleistocene river inthe Gcwihaba Valley or from nearby pans. Pyxicepha-lus adspersus is one of the largest amphibians incentral/southern Africa. The elements represent largeadults, estimated to range in size from approximately13 to 20 cm in length.The skeletal element representation was strongly

biased towards cranial elements, with under-representation of appendicular elements as comparedto an average frog skeleton (Table 5). Part of this biasis undoubtedly due to better preservation of the bull-frog cranial elements, which are ridged and veryrobust. However, because the limbs are among themost edible parts of the frog, these bones may havebeen infrequently preserved because they were ingestedalong with the meat. Two of the elements (1·8% of thetotal) showed evidence of burning, suggesting that atleast some of the frogs were roasted before eating.Pyxicephalus adults are large, fat bullfrogs, which

inhabit arid/semiarid regions throughout much of theAfrican continent. They are a food source for severalmodern human populations, including groups ofKalahari San (Stewart, 1967; Lee, 1979). The frogs arefossorial, hibernating underground during the dryseason, often for 10 months. They could be captured atthis time, being sluggish, by digging them out of theirburrows. In this regard, an historical reference ispertinent. Livingstone (1859: 49) learned from the‘‘Bushmen’’ that the ‘‘matlametlo (bullfrog) makes ahole at the root of certain bushes and there ensconceshimself during the months of drought. As he seldomemerges, a large variety of spider takes advantage ofthe hole, and makes its web across the orifice. He isthus furnished with a window and screen gratis.’’

Paleoenvironment and Archaeology of Drotsky’s Cave 15

Page 10: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

Table4.Birdsfrom

the1991testexcavationsatDrotsky’sCave

0–10cm

10–20

cm20–30

cm30–40

cm40–50

cm50–60

cm60–70

cm70–80

cm80–90

cm90–100

cm100–110

cm110–120

cm120–130

cm

All

NISP/

MNI

Passeriformes(songbird):4(+)spp.

1/1

3/2

5/2

11/4

13/4

33/8

Turnicidae:Turnixsp.(buttonquail)

1/1

1/1

1/1

1/1

3/1

7/2

Falconidae:Falcosp.(falcon)2(+)spp.

1/1

3/3

4/3

Colum

bidae(pigeon/dove)

1/1

1/1

2/1

Tytonidae:Tytocf.T.alba(barnowl)

1/1

1/1

2/1

Accipitridae:Neophronperonopterus(Egyptianvulture)

1/1

1/1

Phasianidae:Coturnixsp.(quail)

1/1

1/1

Apodidae(swift)

1/1

1/1

Meropidae:Meropssp.(bee-eater)

1/1

1/1

‘‘Raptores’’(raptorialbirdclaw)

1/1

1/1

Avesindeterminate

1/1

1/1

2/1

TotalNISP/MNI

2/2

1/1

2/2

8/5

7/4

13/8

24/13

55/21

Note:ThenumberbeforetheslashistheNum

berofIdentifiedSpecimens(NISP)andthenumberaftertheslashistheMinimum

Num

berofIndividuals(MNI).

16 L. H. Robbins et al.

Page 11: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

Livingstone then noted that the ‘‘Bushmen’’ wouldlook for the webs to locate the frogs. Also possible istheir capture during the rainy season when they con-gregate in groups around waterholes. Because this istheir breeding period, they are highly aggressive andcan inflict serious bites. Silberbauer (1981) reports thatfrogs are considered to be a delicacy among the G/wi ofthe central Kalahari where they are caught betweenNovember and March. The highest totals are in the wetseason months of January, February, and March.The presence of bullfrog bones consistently over

several thousand years of occupation at Drotsky’sCave indicates the importance of these animals as afood source. It also indicates long-term familiarity withtheir seasonal behaviour.Interestingly, in addition to the bullfrogs, one right

ilium of another frog, Xenopus sp. was recoveredfrom between 120–130 cm. This specimen was eitherXenopus laevus petersii or Xenopus muelleri. This frog issignificant because it is highly aquatic. While it cansurvive in desert regions, a constant water source isrequired.

Reptiles

The distribution of reptile elements is presented inTable 6. The majority of remains were tortoise, withelements clustering around 50 to 60 cm and between 60and 70 cm. The clear association with the charcoallayer implies use as food by humans. Two speciesof tortoise were identified: (1) Gechelone pardalisbabcocki, represented by five costal bones frombetween 50 and 60 cm and one peripheral from 110 to120 cm, and (2) Kinixys belliana, including two left

scapulae from the 50–60 cm level and one peripheralfrom the 110–120 cm level. In addition to the above,the left scapula of a side neck turtle, Pelusios sp, wasrecovered from the 50–60 cm level. The pelomedusidturtles are not very tolerant of saline or alkaline waters.Although the species could not be identified, the mostlikely possibilities based on current distributions arePelusios subniger or Pelusios bechunanicus. The latterform, known as the Okavango Hinged Terrapin, is thegeographically nearest one. Interestingly, it is describedas ‘‘a deep-water terrapin restricted to the clear watersof the greater Okavango system on the Kalahari Sands(Auerbach, 1987: 74).’’Lizards were represented by one vertebra of Varanus

sp. recovered from between 50 and 60 cm in thecharcoal layer. This monitor lizard was either Varanusexanthematicus or Varanus niloticus. Monitor lizardsare a common food resource in Botswana and arefound at the White Paintings shelter, as are the tor-toises mentioned above (Stewart, Stevens & Robbins,1991).The final reptile specimen recovered was the vertebra

of a snake belonging to the Family Colubridae, Genusindeterminate. It was found in the 120–130 cm level.While snakes are eaten by Kalahari peoples, it isuncertain if this one was eaten, or whether it was theresult of predation or a natural death. The snake,lizard, and tortoise elements are all from families thatwould be expected for this region (Auerbach, 1987).

Cave Sediments and Valley Calcretes: thePaleoenvironmental RecordThe faunal record and archaeological informationdescribed above have provided one body of evidencebearing on late/terminal Pleistocene environmentalconditions. The long record of wet and dry periodspreserved in the cave clastic sediments and in theGcwihaba Valley calcrete sequence provides anotherunique body of evidence that can be used to elucidatepast climates/environments in the Kalahari.

Cave clastic sediments

A column of sediment was removed in increment of7·5 cm from the east wall of the excavation. Samplingextended to 135 cm providing 18 samples of about160 g in weight. Sediment colour was determined ondry, untreated samples using a Munsell colour chart.Each sample was split to obtain a representative 25 gsubsample. Macro-organic matter and human artefactswere first removed and then the sample was sieved toobtain particles coarser than "1 ö. These particleswere manually separated into weathered dolomiticmarble and soft nodules of secondary calcite. Bothfractions were weighed and then the secondary calcitewas returned to the sample. The samples were thentreated with 0·5 N hydrochloric acid to remove

Table 5. Bullfrog elements from the 1991 test excavations at Drotsky’sCave (identified by K. Stewart)

Drotsky’s CaveAverage frog skeleton

%N %

Cranial 49 53·3 17.8Axial 19 20·7 17·0Appendicular 24 26·0 65·2

Table 6. Reptile elements from the 1991 test excavations at Drotsky’sCave

Level (cm) Tortoise Lizard Snake

0–40 0 0 040–50 1 0 050–60 47 1 060–70 19 0 070–80 4 0 080–110 0 0 0110–120 3 0 0120–130 1 0 1

Paleoenvironment and Archaeology of Drotsky’s Cave 17

Page 12: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

carbonates and further organic matter was removed byoxidation with hydrogen peroxide. What remained ofeach sample was then dispersed in a solution of sodiumhexametaphosphate and wet sieved through a 4 ö sieveto remove silt and clay. Particles coarser than 4 ö,including the dolomitic marble gravel removed earlier,were dry-sieved at whole ö intervals in the range from"2 to 1 ö and at half ö intervals from 1 to 4 ö. The<4 ö silt and clay fraction was then subjected to pipetteanalysis. Withdrawals were taken to divide the sedi-ment at the 5, 6 and 9 ö size intervals. Mean grain size,sorting, skewness and kurtosis were determined by thegraphical method of Folk and Ward (1957).Based on the radiocarbon dates of 5,470&90 and

11,240&60 years , the rate of sediment accumula-tion in the depth intervals between 0 and 25 cm(4·57 cm/1000 years) and from 25 to 50 cm (4·33 cm/1000 years) was very similar, averaging 4·45 cm/1000year. The radiocarbon age of 12,450&80 years forcharcoal from 75 cm depth suggests a sediment accu-

mulation rate of 20·66 cm/1000 years in the depthinterval between 75 and 50 cm or 4·6 times the accu-mulation rate in the upper 50 cm of the sedimentprofile. Although such an accumulation rate ispossible, we favour the view that sedimentation ratesremained fairly constant throughout the period ofsediment deposition and that the charcoal dated at12,450&80 yr is a cultural feature related to inten-sive human occupation of the cave, as is much of thecharcoal in the charcoal rich horizon between 50 and80 cm depth. The chronology attached to the sedimentsequence and archaeological material is thereforebased on an assumed sediment accumulation rate of4·45 cm/1000 years. We recognize that because organicmatter of low density makes up between 4·5 and 15·7%(average 8·5%) by weight of the sediments in the 50 to80 cm depth range, estimated age for sediments below50 cm may be slightly too old.Sediment characteristics are shown in Figures 5 and

6. Mean grain size varies from 2·46 to 2·66 ö, which is

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa a aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa a aaaaaaaaaaa a aa aaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa85

135

Dep

th (

cm)

5

15

25

35

45

55

65

75

95

105

115

125

2.45

–2.7

5,470±90

11,240±60

12,450±80

Mea

n

0.85

–1.5

0.15

–0.4

1.5–

2.25 0.0–2.0 3.5–16.580604020

5/45/5

5/4

4/44/3

7.5 yr

10 yr 4/3.5

4/3

4/44.5/4

4/4

7.5 yr

Cumulative percent

Grain size characteristics (phi units)

Sortin

g

Skewnes

s

Kurtosis

Calcr

ete n

odules

%

Munse

ll co

lor

Organ

ic m

atte

r %

Coarse to very coarse sand plus gravel (<1 φ)

Medium sand (1–2 φ)

Fine sand (2–2.5 φ)

Fine sand (2.5–3 φ)

Very fine sand (3–4 φ)

Medium and coarse silt (4–6 φ)

Fine to very fine silt plus clay (>6 φ)

Layers containing abundant charcoal

Figure 5. Analysis of sediments from the 1991 test pit.

18 L. H. Robbins et al.

Page 13: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

in the range of fine sand. Sorting varied from 0·87 to1·42 indicating moderately to poorly sorted sediments.The sediments all exhibited a fine tail and so werepositively to very positively skewed (skewness between0·16 and 0·36) and were very to extremely leptokurtic(kurtosis from 1·51 to 2·55) reflecting relatively peakedparticle size distributions. Organic matter varied from3·21 to 15·69% by weight and, not surprisingly, washighest between 50 and 80 cm where the sedimentswere rich in charcoal and faunal remains. Calcretenodules coarser than "1 ö made up 0·01 to 1·7% ofuntreated sample weight.As Cooke (1975) has pointed out, clastic sediments

in Drotsky’s Cave are produced by processes operatingwithin the cave but are also derived from outside thecave, being carried in by wind and water. Cooke foundthat windblown sand had in the past entered Drotsky’sCave in large quantities being particularly thickclose to the two entrances and being finer and bettersorted than sediments derived from within the caveitself.Logically, finer-grained, better-sorted sediments at

the archaeological site should equate with drier con-ditions when more material was transported into thecave by wind. Under slightly wetter, possibly semiarid,conditions we might expect an increase in coarse andvery coarse sand and gravel derived from within andoutside the cave and having a sizable dolomitic marblecomponent. Some of these fragments would be derived

from the interior walls and ceiling of the cave, otherswould be washed into the cave from outside by runoffafter heavy rain. We might also expect a reduction inthe input of aeolian sand. Under conditions of evengreater wetness, the input of aeolian sand should bereduced still further due to a denser vegetation coveron the nearby dunes. Also, there should be a greateraccumulation of coarse material produced by increasedbreakdown within the cave and by increased runoffinto the cave carrying coarser particles not transportedeasily by wind. The particle size most easily entrainedby running water is 0·2 mm (fine sand, diameterbetween 2 and 3 ö) while that most easily entrained bywind is 0·08 mm (very fine sand, diameter from 3 to4 ö) (Bagnold, 1941; Sundborg, 1956). Furthermore,with increased moisture in the cave there is everylikelihood that fragments of dolomitic marble dis-lodged from the walls and ceiling of the cave will bereduced in size or totally removed by dissolution.Under this scenario, there should be an increase insediment grain size under moist conditions because ofan increase in very coarse and medium sand ratherthan because of an increase in very coarse sand andgravel.Figures 5 and 6 show that there was a major

decrease in the mean grain size of sediments accumu-lating at the site shortly after about 11,000 years andthat this was accompanied by an increase in sortingand kurtosis. In addition, material coarser than 0 ö

e

135

Dep

th (

cm)

5

Est

imat

ed a

ge o

f D

rots

ky's

Cav

ese

dim

ents

(yr

. B.P

.)

500

15

25

35

45

55

65

75

85

95

105

115

125

1 2 3 4 5 6 7 8 9

g

f

e

d

c

b

a

1 2 3 4 5

g

f

d

c

a

6 7 8 9 10 11

5,470±90

11,240±60

12,450±80

1.5φ

0φ 1φ

3 6 9A

ngo

ni v

lei r

at

Cli

mbi

ng

mou

se

Xen

opu

s sp

. (fr

og)

Bu

llfr

og

250045006500850010 50012 50014 50016 50018 50020 500

24 50026 50028 50030 500

22 500

b

Figure 6. Late Quaternary Paleoclimatic records from the region of Drotsky’s Cave and neighbouring region of southern Africa. /, wetperiods indicated by high lake levels, periods of speleothem and calcrete deposition, or cave clastic sediment texture; /, low lake levels;-, radiocarbon ages; a–g, possible matching peaks in columns 1 and 4.1: Cumulative percent by weight of grains <0ö, <1ö and <1·5ö, 2: Drotksy’s Cave clastic sediments (this paper), 3: Drotksy’s Cave faunalremains indicating past wetter conditions (this paper), 4: Number of 14C dates indicating past wetter conditions in the summer rainfall zone ofsouthern Africa (Deacon & Lancaster, 1988), 5: Makgadikgadi Basin lake levels (Cooke & Verstappen, 1984; Shaw & Cooke, 1986; Thomas& Shaw, 1991), 6: Ngami, Mababe and Caprivi Basin lake levels (Shaw, 1986; Shaw & Cooke, 1986; Shaw & Thomas, 1988; Thomas & Shaw,1991), 7: Drotsky’s Cave speleothem ages (Cooke & Verhagen, 1977; Shaw & Cooke, 1986; Brook et al. 1990), 8: Gcwihaba Valley calcrete ages(Cooke & Verhagen, 1977; this paper), 9: Dry valleys of the middle and southern Kalahari (Shaw et al., 1992), 10: Tsodilo Hills lake (Brooket al., 1992), 11: Dobe Valley lake at Gi (Helgren & Brooks, 1983).

Paleoenvironment and Archaeology of Drotsky’s Cave 19

Page 14: Paleoenvironment and Archaeology of Drotsky’s Cave: Western Kalahari Desert, Botswana

(very coarse sand and gravel) also increased substan-tially, much of this consisting of large fragments ofdolomitic marble. Figure 3 also shows that accom-panying the increase in coarse material after 11,000years was an increase in material finer than 2 ö, thatis fine to very fine sand, silt and clay. Together, thesechanges suggest that, overall, the period from 11,000years to the present was significantly drier than thepreceding 20,000 years. However, variations in grainsize also indicate that the periods c. 11,500–9000 and6500–3000 years were somewhat drier than theintervals 9000–6500 and 3000–1250 years whenincreased wetness is suggested.The sediment data suggest that the interval 18,000–

11,500 years was the wettest of the past 30,000years. This is indicated by the lowest percentages ofvery fine sand, silt and clay and maximum cumulativepercentages of medium sand, coarse sand andgravel. Prior to 18,000 years the wettest con-ditions occurred at 30,500–28,500, 25,000–23,500 and21,500–20,000 years with drier conditions centred at19,500, 22,500 and 27,000 years . However, thegenerally higher percentages of particles coarser than2·5 ö in sediments deposited prior to about 11,500years indicates that this entire period was wetterthan the Holocene. Finally, the percentage of second-ary calcrete nodules in the sediments increases sharplybelow about 75 cm depth with peaks of 1·15% at about79 cm and 1·69% at 116 cm depth. We believe thatthese nodules are of pedogenic origin and that theyaccumulated between 60 and 75 cm below the level ofthe cave floor during dry Holocene intervals centred at9500 and 4500 years .

Valley calcretes

Cooke (1975) reports four calcretes of different agealong the Gcwihaba Valley near Drotsky’s Cave.Radiocarbon ages indicate that the two oldest depositsare beyond the range of the method (i.e. they are>45,000 years old), while the youngest two depositswere laid down from 11,000–10,000 years (Cooke &Verhagen, 1977; Cooke, 1984). Cooke (1984) interpretsthe various calcretized sands and gravels in theGcwihaba Valley as evidence of ephemeral river flow ina sub-humid to semi-arid climate. In 1991 we collecteda sample of calcrete from the floor of the GcwihabaValley approximately 2 km up valley of Drotsky’sCave. The calcrete was radiocarbon dated to11,430&60 (Uga 6591) assuming that it contained15% old, dead carbon at the time of formation (Cooke& Verhagen, 1977).The calcrete contained 8·1 million diatom valves per

gram, thus providing important information aboutterminal Pleistocene conditions in the GcwihabaValley. Diatom preservation was good and there werefew other microfossils in the sample. Identification andinterpretation of diatoms were based on Gasse (1986)and Patrick and Reimer (1966, 1975). Six species made

up 78% of the 456 diatoms counted (Cymbella muelleri25%; Rhopalodia gibberula 24%; Gomphonema gracile9%; Cyclotella meneghiniana 8%; Navicula species 6%;Nitzschia cf fonticola 6%). Cymbella muelleri is typi-cally benthic, but has been found in plankton insignificant numbers. Gasse (1986) considers it broadlytolerant of alkalinities, pH, and mineral content.Rhopalodia gibberula is also tolerant of water con-ditions but Gasse’s (1986) survey of African lakesediments led her to suggest that it prefers stronglyalkaline waters, growing best in hyperalkaline lakes ofhigh conductivity, alkalinity and pH. Gomphonemagracile (variety intricatiformis) is pH-tolerant althoughGasse (1986) found it to be most common in water ofpH 7·0–8·7, pehaps of low nutrient content. Cyclotellameneghiniana is littoral or planktonic, and seems toprefer more saline waters (Gasse, 1986).Cemented into the outside of the calcrete was a shell

of Trachycystis sp., which is a terrestrial snail notnecessarily associated with water (Chris C. Appleton,University of Natal-Pietermaritzburg (pers. comm.1991). This confirms that the carbonate cement of thecalcrete formed under conditions of seasonal or evenephemeral stream flow. Thus, the diatom assemblage,which is older than the carbonate cement of thecalcrete, indicates that prior to c. 12,000 years therewas substantial stream flow in the Gcwihaba Valley.Stream flow may have lasted for a considerable portionof the year or even have been perennial. The age of thecarbonate cement of the calcrete, and the presence ofthe terrestrial snail shell, indicates that by c. 11,500years stream flow had become seasonal or evenephemeral.

Summary and ConclusionsThe sediment and faunal data from the Drotsky’s Caveexcavation are compared in Figure 6 with selectedpaleoenvironmental records for the Kalahari and withthe frequency of radiocarbon ages indicating wetterconditions in the summer rainfall zone of southernAfrica. The records are in broad agreement and thecorrelation between the sediment and radiocarbon agedata is particularly striking. The evidence indicates thatthe late/terminal Pleistocene from about 30,000 to11,000 years was substantially wetter and probablycooler than the ensuing Holocene and that the intervalbetween 17,500 and 11,000 years may have beenparticularly moist.Cooler conditions are indicated by the possible

presence of blesbok in the charcoal-rich layer (Yellenet al., 1987) and by the presence of white-tailed rat at130–110 cm depth. Neither blesbok nor white-tailed ratis found in the area today, the latter being confined tohighveld and montane grasslands. Wetter conditionsalong the Gcwihaba Valley in the late/terminalPleistocene are clearly suggested by the presence ofAngoni vlei rat, climbing mouse, the Xenopus frog, and

20 L. H. Robbins et al.

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the side neck turtle. The diatom assemblage in thecalcrete from the Gcwihaba Valley confirms that therewas more permanent river flow in late/terminalPleistocene times with calcretization of fluvial sedi-ments probably taking place as river flow becamemarkedly seasonal or even ephemeral c. 11,500years .It is perhaps significant that Drotsky’s Cave was

used more intensively from c. 12,500 to 11,000 years at the time of a major transition from cooler and wetterto warmer and drier climatic conditions. At this time ofmarkedly seasonal or ephemeral stream flow in thevalley the cave may have provided a dry shelter forhunter–forager groups utilizing the resources of theGcwihaba Valley. In addition, it is likely that drip-waters in the cave may have provided a source of waterduring dry periods. From c. 30,000 to 12,500 years the cave may have offered no special advantages givena relatively plentiful supply of water in the rivervalleys. Furthermore, being wetter and colder thannow it may not have been an ideal shelter. Duringthe Holocene, with little or no stream flow in theGcwihaba Valley, it is not surprising that the cave wasused sparingly, although dripwaters may have pro-vided water in the dry season. The fact that charcoaldeposits in the Drotsky’s Cave excavation (between 80and 50 cm, and c. 25 cm) occur at times of transitionfrom wetter to drier conditions suggests that the cavewas most attractive to hunter–forager groups at thesemarginal times when the cave was probably an idealshelter, provided water if needed, and was close to thewet-season resources of the Gcwihaba Valley.

AcknowledgementsWe thank the National Science Foundation for fund-ing and the National Museum of Botswana for facili-tating this research. We are especially grateful toA.C. Campbell, N. Walker, T. Mpulubusi, J. Clark,B. Smith, J.A. Holman, J. Yellen, G. Schneider,R. Hitchcock, K. Egan and H.J. Cooke. The analysesin the paper reflect a multidisciplinary effort and aredivided among researchers as follows: Robbins andMurphy, archaeology and general comments; Brookand Ivester, sediment analysis; Brook and Haberyan,diatoms, Klein and Milo, macromammals, Stewart,bullfrogs, Winkler, rodents, Matthiesen, identificationof the birds; Stevens, reptiles.

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22 L. H. Robbins et al.