Geologic Contexts of the Acheulian in the Eastern Sahara

8/7/2019 Geologic Contexts of the Acheulian in the Eastern Sahara

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Geoarchaeology: An International Journal, Vol. 16, No. 1, 6594 (2001)2001 John Wiley & Sons, Inc.

Geologic Contexts of the Acheulian

(Middle Pleistocene) in the EasternSahara

Christopher L. HillIce Age Research Program, 600 West Kagy Blvd., Montana State University,Bozeman, Montana 59717-2730

The Bir Tarfawi and Bir Sahara East region of northeast Africa contains sedimentaryremnants

associated with Acheulian artifacts. The geology of these localities can be used to help ex-amine paleobiogeographic and taphonomic contexts and paleoclimatic chronologies relatedto Middle Pleistocene hominids. Recognized by the presence of handaxes, Acheulian occur-rences in the Eastern Sahara have been found with paleosols, cemented gravels, and tufas,and are often found as deationary lags. In the Tarfawi region, handaxes were found embed-ded in sands overlain by carbonates, embedded in limestones, and in deated contexts. TheseAcheulian sites likely date to before 300 ky B.P. The lithostratigraphic sequences indicatethat paleoclimatic conditions in the Sahara during the Pleistocene were wetter than in theHolocene. The geologic context (stratigraphy, sedimentology, dating) of the Acheulian in theEastern Sahara seems to indicate wet paleoclimatic intervals during the Pleistocene whenbiogeographic conditions were favorable for hominid habitation in the region. 2001 JohnWiley & Sons, Inc.

INTRODUCTION

Objectives

The geologic contexts of Acheulian (Lower Paleolithic) artifacts from southernEgypt (Figure 1) provide information useful for evaluating Middle Pleistocene land-scape (paleobiogeographic) settings and site formation (taphonomic) processesconnected with Middle Pleistocene hominids, as well as paleoclimatic chronologiesof northeast Africa. The objectives of this article are to provide a succinct reviewof Acheulian sites in the Eastern Sahara, briey describe and interpret the geologiccontext of Acheulian artifacts in the Bir Tarfawi-Bir Sahara region of southernEgypt, and place these discoveries in a tentative paleoclimatic chronologic frame-work.

The Bir Tarfawi-Bir Sahara area (Figure 2) is situated within the Darb el ArbainDesert, a term applied by C. Vance Haynes, Jr. to distinguish the most hyperaridregion of the Sahara (Haynes, 1987). The geologic record of this region preservesstrong evidence for dramatic changes in paleoenvironmental conditions. Thesechanges appear to have had an important inuence on Pleistocene biotic popula-tions that were sometimes able to exist in what is now the driest part of the largestdesert on Earth (Haynes et al., 1997).


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Figure 1. Map showing locations of some of the documented Acheulian sites in the Eastern Sahara. BirSahara and Bir Tarfawi are located in southern Egypt, just north of the border with Sudan. Inset mapindicates location of the Eastern Sahara in southern Egypt and northern Sudan (in northeastern Africa).

Review of Previous Work

The rst systematic investigation of Pleistocene geology and Acheulian artifactsin the Egyptian Sahara was by Caton-Thompson in the early 1930s, at Kharga Oasis(Figure 1) (Caton-Thompson, 1932, 1952). At about the same time, Myers studiedan Acheulian site at the Gilf Kebir as part of Bagnolds 19371938 expedition (Bag-nold et al., 1939). In the Bir Tarfawi region, Acheulian artifacts were rst studiedby the Combined Prehistoric Expedition (CPE) in the early 1970s (Schild and Wen-


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GEOLOGIC CONTEXTS OF THE ACHEULIAN IN THE EASTERN SAHARA

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL 67

Figure 2. Map showing the locations of three Acheulian sites at Bir Tarfawi and Bir Sahara East. SiteBS-14 is situated in the southern part of Bir Sahara East. There are two Acheulian localities at BirTarfawi; one is a limestone capped remnant in the central part of the depression, the other, designatedSite E-88-12, is situated in the south part of the depression. There are other deational basins in theregion, such as Little Bir Sahara. Besides sedimentary remnants with Acheulian artifacts, there are otherMiddle and Late Pleistocene remnants associated with Middle Paleolithic artifacts in the Bir Tarfawiregion. Map based on Figure 3.3 in Wendorf et al. (1993).

dorf, 1975, 1981; Wendorf et al., 1976). Acheulian sites have also been reportedfrom other locations in the Western Desert of Egypt and in the Saharan portionsof Sudan, Chad, and Libya. Figure 1 shows the general locations of selected Acheu-lian sites.

Acheulian sites from the Dakhla and Kharga region north of Bir Tarfawi (Figure1) are typically found with fossils springs, indicating a relationship with wetterclimates during the Middle Pleistocene (Caton-Thompson, 1952; Schild and Wen-dorf, 1977; Wendorf and Schild, 1980; Brookes, 1983; McDonald, 1982; Kleindienstet al., 1999; Kleindienst, 1999; Churcher and Mills, 1999; Nicoll et al., 1999). As anexample, the Evolved Acheulian assemblage at spring mound KO10 (Kharga Oasis10) is estimated to be older than 300 ky B.P. (Churcher et al., 1999). Wetter envi-


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ronments are also inferred along the eastern edge of the Kharga depression at Refuf Pass, where Acheulian artifacts are embedded in gravels capped with tufas (Caton-Thompson, 1952; Butzer and Hansen, 1968). The gravels seem to indicate increased

wadi deposition (Wendorf and Schild, 1980) while the ner clastics and carbonateswere deposited in slowly moving water, ponds, or springs. Tufa deposits at Refuf Pass and elsewhere near Kharga seem to be related to spring-fed alkaline streamenvironments (Nicoll et al., 1999). The Refuf Pass (Wadi el-Refuf) Acheulian assem-blages are placed in two categories: an Evolved or Upper Acheulian perhaps olderthan 400 ky B.P., and an Acheulio-Levalloisan, older than 300 ky B.P. (Caton-Thompson, 1952; Churcher et al., 1999; Churcher and Mills, 1999). Higher watertables and tufa deposition seems to have occurred at Refuf Pass at around 300,240, 198, 174, 138, and 125 ky B.P. (Nicoll et al., 1997), providing an indication of when wetter environmental conditions may have prevailed.

Acheulian artifacts are found elsewhere in the Eastern Sahara in geologic con-texts that also seem to imply paleolandscapes with wetter climates during the Mid-dle Pleistocene. For instance, in the vicinity of Wadi Midauwara, south of Kharga,Acheulian artifacts were reported as lags on tufa surfaces or in solution basins(Smith et al., 1999). North of Kharga, three Acheulian sites (KUWDE 30, 31, and34) were found on alluvial terraces associated with Pleistocene wadi courses (Sim-mons and Mandel, 1985) (Figure 1). Closer to the Nile at Kurkur (Figure 1), Acheu-lian bifaces were recovered from within a tufa (Hester and Hoebler, 1965; Hoeblerand Hester, 1969).

Between Bir Tarfawi and the Nile Valley, Late Acheulian bifaces are found onthe pediments in the Nabta area, in lag position near Bargat el Shab, and on the

surface of a red soil at the top of sands near Kiseiba. Late Acheulian artifacts arewithin basal sands along the southeastern bank of the Kiseiba Scarp (Wendorf etal., 1984), while other Acheulian artifacts are sand blasted (Haynes, 1985). An im-portant set of sites in geologic context have been documented near Kiseiba, southof Two Hills playa (Haynes et al., 1997). One of these, Kiseiba Acheulian site no. 1(KAS-1), contains Acheulian handaxes, cleavers, and other artifacts that do notappear to have been signicantly redistributed by uvial action (Haynes et al.,1997). Late Acheulian artifacts have also been reported on top of gravels at BirDibis southwest of Kiseiba (Wendorf and Schild, 1980).

In Egypt, south of Bir Tarfawi, Middle and Upper Acheulian artifacts were dis-covered near and in Wadi Arid, south of Wadi Arid, and around Bir Safsaf (Figure1). Some of these sites have been dated, and some are possibly in primary context.Others are in lag position, such as Middle Acheulian artifacts found on a deatedpetrocalcic paleosol (Haynes, 1985). Carbonate adhering to akes dated by uraniumseries to 212 ky B.P. provides a minimum age for the Acheulian at Site 84f21-7 AreaA (McHugh, 1988b; Szabo et al., 1989). At Site 84f21-7 Area Z (E-85-14 in Wendorf et al. [1987b]) Middle Acheulian artifacts were found embedded in slope-wash,which might indicate that, although in stratied geologic context, they have beentransported to some degree. Acheulian artifacts were also found on top of thetruncated calcied pebble gravel surface and partially embedded in gravels, and


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crude handaxes were embedded in the calcied pebble gravel at Wadi Arid(McHugh et al., 1988b). Middle Acheulian bifaces at Site 84F22-2 (E-85-13 in Wen-dorf et al. [1987b]) could be in primary context (McHugh et al., 1988a). Uranium-

series-dated carbonate nodules are chronologically inverted and provide ages of 212, 141, and 45 ky B.P. Also in the Wadi Arid region, Site E-85015 contains an earlyUpper Acheulian assemblage (Wendorf et al., 1987a, 1987b).

The Bir Safsaf area (Figure 1) contains several Acheulian sites on sandsheets orgravel covered hills (McHugh et al., 1988b). Site 84M9-12 (or E-85-12 in Wendorf etal., 1987a) consists of a surface collection of handaxes. Handaxes are embeddedin partially cemented sands and gravels or are on a surface deated from calichied(calcium carbonate cemented) alluvium (McHugh et al., 1988b). Late Acheulianartifacts at Site 84M9-3 in the Bir Safsaf area were found on the surface surroundinga remnant capped by kunkar (a calcareous duricrust) with rhizoliths (McHugh etal., 1988a).

At Dagdag basin, southeast of Bir Safsaf, Acheulian artifacts occur on the surfaceand within the top of sands and gravels containing calcareous concretions andplates (Wendorf et al., 1987b). There are two taxonomic components at Site E-85-2; most of the abraded artifacts are Middle Acheulian, while less weathered andfresh artifacts are Upper or Final Acheulian. On the northern edge of the Dagdagbasin, slope-wash deposits contain Late or Final Acheulian artifacts; artifacts fromE-85-15 were embedded in slope-wash sands and redeposited gravels (Wendorf etal., 1987b).

Acheulian sites are known from the Gilf Kebir region and the Great Sand Sea(Figure 1). Site 1000 is an extensive Late Acheulian scatter along the base of the

Gilf Kebir plateau (Bagnold et al., 1939; Wendorf and Schild, 1980). It lies in theuppermost stratum of a gravelly alluvial fan (Wendorf and Schild, 1980; Haynes,1983). The site may be contemporaneous with a period of increased wadi activity(Wendorf and Schild, 1980). In the Great Sand Sea region, Acheulian artifacts occuras surface lag and extend under sandy muds and derived sands reecting playaconditions (Haynes, 1982, 1985; Roe et al., 1982). Acheulian artifacts are also as-sociated with the contact between the surface of a dune ridge and alluvium, orolder playa deposits transitional to the alluvium (Haynes, 1982). A handaxe madeof Libyan glass was recovered in the Sand Sea area (Roe et al., 1982).

In Oyo, northwest Sudan (Figure 1), Late Acheulian handaxes and other EarlyPaleolithic artifacts have eroded from under lacustrine muds, diatomites, and marlscapping a mesa (Haynes, 1985). The artifacts may have been deated before thedeposition of the Pleistocene lake sediments. In some places, an erosional contactof reworked sandstone contains late Acheulian artifacts. These artifacts were sand-blasted while at the surface prior to burial (Haynes, 1985) or are in uvial sandsunderlying the Pleistocene lake beds (Haynes, 1989). In north central Sudan, se-verely eroded Lower Paleolithic sites occur in the Laqiya Depression (Figure 1). Atleast one Late Acheulian site is known from Prendergast Valley. Handaxes andother artifacts occur in a soil developed in alluvial sands and gravel (Haynes, 1985).

In southern Libya and northern Chad, Acheulian occurrences include Upper


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Acheulian (?) bifaces from the well at Sarra eroding from the surface of a soilcovered by eolian sands (Arkell, 1964). Arkell found an assemblage that could betransitional between the Lower and Middle Paleolithic at Little Wanyanga Lake.

Tillet (1985) considers that the sites near Wanyanga Kebir studied by Arkell rep-resent a very evolved stage of Acheulian.

In summary, artifacts taxonomically afliated with Middle, Upper, Late, andEvolved Acheulian have been discovered in both surface and subsurface contextsin the Eastern Sahara. Where there are unambiguous relationships between arti-facts and geologic contexts, the pattern that seems to emerge is that Middle Pleis-tocene hominids lived in the Eastern Sahara during times when the climate con-ditions were substantially wetter than at present. Populations were widespreadwithin the region but perhaps usually constrained to habitat settings connectedwith reliable sources of water. Acheulian artifacts within stratied deposits arerare. Detailed sedimentologic or taphonomic studies could help evaluate whetherartifacts found within stratigraphic sequences are in primary context or assist indetermining Pleistocene biogeographic settings.

METHODS

Studies of the geology of Acheulian sites in the Bir Tarfawi region were con-ducted as part of a broader project designed to (1) evaluate their paleogeographicsetting (landscape habitat), (2) assess whether the patterns of artifact taxonomiccomposition and distribution could be directly attributed to Pleistocene hominids,and (3) place the sites within a paleoclimatic-chronologic framework. The eld andlaboratory techniques used are described in more detail by Hill (1992). Field ex-amination and sampling included assessments of texture and composition, Munsellcolor (dry, Table I), coherence/cementation, prominent bedding or structures,thickness of deposits, character of stratigraphic boundaries, fossils, and artifactualcontent. Laboratory studies included particle size (wet sieving and pipette usingsodium hexametaphosphate as a dispersent, after removal of carbonates and or-ganics, Tables I III), loss-on-ignition (weight loss after heating to 550 C and 1025 Cto estimate organic and carbonate content, Table II), x-ray diffraction analyses, andpetrographic thin-section studies. The thin-section descriptions follow the carbon-ate classication of Dunham (1962) and were provided by McGillis (1993).

RESULTSAcheulian artifact assemblages, recognized by the presence of handaxes (mode

2 of Clark [1977]), were studied from three localities in the Bir Tarfawi-Bir Sahararegion (Figure 2). Several other occurrences or isolated bifaces also were found.These include a set of handaxes recorded during a walking survey of the areabetween Bir Tarfawi and Bir Sahara East by Hill and J. Saunders during 1986, andSites BS-5, BS-7, BS-9, BS-10, BS-20 discovered during the 1973 campaign of theCPE. Excavations recovered Acheulian artifacts in denitive subsurface geologiccontext at Site BS-14, situated at the south end of Bir Sahara East (Figure 2).


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GE OA R C H A E OL OG

Y : A N

I N T E R N A T I ON A L J OU R N A

L

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Table I. Compositional data.

Sample No.

Loss on Ignition500 C

(Organics)10025 C

(Carbonate)

HCl SolubleFraction

(Carbonate)

CarbonateEstimateAverage

PlasticComponent

Coarse F

BS 14-T1/88: 015 0.49 0.5 97.0 BS 14-T1/88: 016 4.94 5.0 89.0 BS 14-T1/88: 017 0.38 55.33 59.08 57.0 36.5 BS 14-T1/88: 018 28.31 28.5 67.0 BT-T3/87: 001 2.73 3.0 90.0 BT-T3/87: 002 92.83 93.0 3.5 BT-T3/87: 003 94.22 94.0 3.5 BT-T3/87: 004 1.39 93.58 88.61 91.0 5.0 BT-T3/87: 005 88.27 88.0 1.0 1BT-T1/87: 001 8.45 8.5 84.0 BT-T1/87: 002 14.54 14.5 77.5 BT-T1/87: 003 7.92 8.0 78.0 1BT-T1/87: 004 1.72 90.56 96.39 93.5 1.5

BT-T1/87: 005 17.76 18.0 57.5 2BT-T2/88: G1 0.12 0.1 95.0 BT-T2/88: G2 0.80 1.0 89.0 1E-88-12: A2 0.16 0.2 96.5

E-88-12: A4a 0.40 94.82 97.80 96.0 (4.0)


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Table II. Particle weight-size distribution data.

Sample No.

Coarse Siliciclastics

Gravel

VeryCoarseSand

CoarseSand

MediumSand

FineSand

VeryFineSand

FineSiliciclastics

Silt Clay

BS 14-T1/88: 015 0.74 31.05 34.51 17.10 8.58 5.24 1.85 0.93BS 14-T1/88: 016 5.64 25.88 15.66 21.21 15.56 9.73 2.43 3.89BS 14-T1/88: 017 3.65 19.24 16.25 18.41 15.27 12.14 5.23 9.62BS 14-T1/88: 018 0.50 20.27 20.56 21.57 19.26 11.29 1.51 5.04BT-T3/87: 001 0.00 2.97 10.89 38.44 29.97 10.00 3.00 4.86BT-T3/87: 002 0.00 0.00 2.55 17.56 16.68 9.65 30.73 22.83BT-T3/87: 003 0.00 0.00 30.30 9.70 8.48 11.52 18.18 21.82BT-T3/87: 004 0.00 1.70 6.25 18.75 15.35 11.93 40.00 6.25BT-T3/87: 005 0.00 0.00 1.39 2.87 2.77 2.78 0.00 90.28

BT-T1/87: 001 0.39 0.77 8.70 27.92 41.25 12.76 3.86 4.35BT-T1/87: 002 5.10 0.88 10.42 32.49 39.29 2.66 4.06 5.10BT-T1/87: 003 0.00 1.38 8.43 32.18 28.87 13.95 8.28 6.91BT-T1/87: 004 0.00 0.00 1.89 7.54 7.55 7.55 66.04 9.43BT-T1/87: 005 0.00 1.42 7.80 21.45 25.36 14.01 18.61 11.35BT-T2/88: G1 0.00 0.42 6.94 41.68 36.90 9.04 0.84 4.18BT-T2/88: G2 0.00 1.57 7.54 29.51 38.93 12.09 4.71 5.65E-88-12: A2 4.08 19.39 11.22 26.85 27.63 7.38 2.35 1.10E-88-12: A4a 0.00 0.58 1.92 3.27 5.38 10.00 78.85 0.00

Geologically in situ artifacts were recovered from Site E-88- 12, on the south endof Bir Tarfawi (Figure 2). In other instances, Acheulian artifacts were found on thesurface, although the artifacts were sometimes unweathered, presumably indicat-ing their fairly recent erosion from sediments.

Bir Sahara East (Site BS-14 Area)

Site BS-14 is the most thoroughly documented Acheulian locality in the region(Schild and Wendorf, 1975, 1981; Wendorf and Schild, 1980; Hill, 1992). The sedi-mentary mound at BS-14 has a substantial (ca. thicker than 80 cm) cap composedof cemented sandy carbonate (sandy limestone, calcrete). The carbonate cap thinsout toward the edges of the remnant and overlies clastic quartz sands (Figures 3and 4). Acheulian artifacts were recovered on and in the sands underlying thecarbonate (Figure 4). The excavations of M. Kobusiewicz as part of the CPE ex-cavations in the early 1970s found ostrich eggshell fragments in these sands.Bifaceswere recovered on top of the carbonate, and bones have been found embedded inthe carbonate (Schild and Wendorf, 1981). Three trenches were excavated into thecarbonate (Trenches 1/73, 2/73, and 9/88, Figure 3). Twelve other trenches(Trenches 3/73, 1-8/88, and 10-12/88) were placed on the edge of the carbonate capor excavated into the sands (Figure 3). Descriptions and proles of the trenchesare available in Hill (1992).


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Table III. Grain-size statistics.

Sample No. Mean Sorting Skewness Kurtosis

BS 14-T1/88: 015 0.70 1.32 0.28 1.05BS 14-T1/88: 016 1.18 1.99 0.22 1.10BS 14-T1/88: 017 1.71 2.56 0.29 1.34BS 14-T1/88: 018 1.44 2.18 0.27 1.49BT-T3/87: 001 2.06 1.68 0.35 2.12BT-T3/87: 002 4.94 2.98 0.21 0.64BT-T3/87: 003 3.73 3.94 0.17 0.67BT-T3/87: 004 4.04 2.59 0.20 0.77BT-T3/87: 005 8.89 1.53 0.37 2.81BT-T1/87: 001 2.30 1.59 0.23 20.7BT-T1/87: 002 1.96 1.87 0.11 2.68BT-T1/87: 003 2.47 1.92 0.38 1.82BT-T1/87: 004 5.34 2.32 0.11 1.02BT-T1/87: 005 3.69 2.73 0.48 1.07BT-T2/88: G1 2.06 0.96 0.13 1.10BT-T2/88: G2 2.35 1.75 0.30 2.28E-88-12: A2 1.33 1.52 0.14 0.83E-88-12: A4a 5.38 1.83 0.15 0.97

Compositional and textural attributes representative of the stratigraphyobservedat BS-14 are provided in Tables IIII and Figure 4. The lowest deposit consists of a quartz sand (sample 15, Figure 4) separated from the overlying deposits by anerosional unconformity. The basal sands are more than 90% coarse fraction clastics

(sand-sized or larger particles).The basal sands are unconformably overlain by an uncemented, poorly sorted

gravelly sand (sample 16, Figure 4) that contains Acheulian handaxes, retouchedakes, debitage, and some faunal remains. Laminae suggest that the depositionalenergy regime was not uniform. At times, transportational and depositional energylevels were relatively high; these deposits have more than 34 times as much gravelas the basal sand. The detrital component also contains more muds, indicatinglower energy depositional regimes on occasion. A trend from an overall higherenergy to lower energy system is reected by the decline in gravel content and anincrease in the amount of very ne sand, silt, and clay. This decrease in energy isalso reected in the increased mean grain size and sorting indices (Figure 4). Interms of depositional mechanics, the detrital component of these sands representsa uctuating, but gradually decreasing, energy regime. These clastic patterns areconsistent with a depositional setting along the margin of a shallow deationalbasin in which sands were being redeposited as wash or colluvium. The decreasingsize of the clastic fraction could be an indication that the upper sediments weredeposited in a quieter setting farther from the effective margin of the basin, possiblyin a groundwater-fed pool. The ning upward sequence could also indicate thatcoarse clastics were not being transported into the basin because of increasedvegetational cover. Trace fossils (rhizoconcretions) are present in the sands con-


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Figure 3. Plan view of the Site BS-14 sedimentary remnant (situated in the southern part of Bir SaharaEast, see Figure 2) showing the locations of stratigraphic test trenches. Trenches were excavated intothe limestone cap, along the edge of the limestone, and in the sands surrounding the limestone. Acheu-lian artifacts were found on the limestone, in deated position on the surrounding sands, and stratiedwithin sands underlying the carbonates.

taining Acheulian artifacts, and probably indicate either the presence of plants orinvertebrate fauna.

The upper deposits at BS-14 are sandy limestones. At Trench 1/88, the carbonateis about 30 cm thick, with medium blocky structure (sample 17, Figure 4). It iscomposed of about 60% carbonate. Based on petrographic thin sections (McGillis,1993), this is a calcite mudstone with 3 30% detritial quartz grains. Typically, theclastic component is bimodal, with smaller angular and subangular quartz grains,and larger rounded to well-rounded grains. Bivalve fragments, rare calcispheres,and some ostracods are present. In some instances, the ostracod wall structure hasrecrystallized to equant calcite. There are some possible pelecypods, gastropods,and forams. Patchy hematite stains and equant calcite cement crusts occur on someof the quartz grains.

These carbonate-rich sediments could be related to a rising groundwater table


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Figure 4. Stratigraphy and sedimentology of Trench 1/88, providing a representative prole for Site BS-14 (Bir Shara East). Basal sands are represented by sample 15 and contain no artifacts. An erosionalunconformity forms the boundary between the basal sands and the overlying deposits containingAcheu-lian artifacts. Basin wash sediments (sample 16) contain Acheulian artifacts and Pleistocene faunalremains. Trace fossils are also present. These sands are gradationally overlain by groundwater-formedcarbonates (samples 17 and 18). See Tables I-III for compositional and particle size data (particle sizestatistics refer to clastic or detritial component of the sediments).

within a shallow basin. Based on studies of nearby sediments, Pachur et al. (1987)used the term phreatogenic crusts to distinguish calcareous crusts formed bygroundwater or in lakes from pedogenic calcretes. The sandy limestones at SiteBS-14 seem to be the result of carbonate deposition related to a groundwater seep-age pool. The relatively high detrital content may indicate that the basin was small,that the groundwater level was not very high within the basin, or that there wasnot much vegetation surrounding the pool. The water level may have been justslightly higher than the ground surface or perhaps sometimes only saturating thesurface, causing carbonate deposition within the previously deposited clastics. If the clastics represent ongoing deposition into the basin, they may reect the ab-sence of dense plant cover, perhaps indicating relatively low or highly sporadiclocal precipitiation.

Other morphologically and lithologically different sedimentary remnantsare nearBS-14, and some have Acheulian artifacts scattered on them. These sedimentary


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remnants consist of cemented clastics (mostly sandstones). Issawi (1978) desig-nated remnants composed of a top section of carbonate as spring mounds, whilethose cemented by silica or Fe oxides were named ferrocrete mounds. Issawi sug-

gested that the mounds were formed during a dry phase after a more humid intervalassociated with the deposition of carbonates that form the surrounding plateau.The lithologic differences between the mounds may relate to local deposition of Fe or carbonate minerals in continuously drying ponds that formed by seepage(Issawi, 1978). These mounds could represent phreatophyte-induced accretionsaround semipermanent pools (Neal and Motts, 1967).

Since the episode of wetter conditions, several processes have modied the sed-imentary sequence. Some remnants are almost entirely lag features, the results of erosion by wind. Weathering has altered the top section of BS-14, the sandy lime-stone caprock. Where the underlying sands were not protected by indurated car-bonates, the smaller-sized clastics were selectively removed by wind, leaving thelarger particles (mostly handaxes and less resistant cemented rock fragments) asa deational lag surrounding the mound. On the margins of the BS-14 mound, thislag deposit has helped to protect the underlying sands from further erosion.

No direct ages are available for BS-14, but some nearby deposits were dated. Forexample, Szabo et al. (1995) provided a uranium-series date of about 277 ky B.P.on sandy limestone from west of Bir Sahara, although the sample is not directlyassociated with artifacts. Churcher et al. (1999) correlate the BS-14 artifacts withthe Upper Acheulian sensu stricto at Kharga dated at over 400 ky B.P., while Schildand Wendorf (1981) indicated some resemblance to the Acheuleo-Levalloisian fromRefuf Pass. The Acheulio-Levalloisan is estimated to be older than 300 ky B.P., but

it may consist of a mixture of Lower and Middle Paleolithic artifacts in geologiccontext (cf. Churcher et al., 1999).

Central Bir Tarfawi

Acheulian bifaces were recovered from the surface of a sedimentary remnant inthe central part of the Bir Tarfawi deational basin (Figure 2), near several impor-tant Middle Paleolithic sites (Wendorf et al., 1993). The collection ranged fromnearly unweathered to highly weathered, implying that the artifacts were exposedat the surface for varying amounts of time. Artifacts were not recovered from thestratigraphic trenches (Figures 5 and 6).

The remnant is a low plateau capped by very strongly cemented carbonates(limestones) and surrounded by small mounds composed of sandstones and mud-stones (indurated, cemented clastics) (Figure 5). Loose to slightly cemented quartzsands underlie the carbonate cap and clastic-dominated mounds. Acheulian arti-facts on the limestone and on the slopes of surrounding mounds were rst mappedin 1974 (Wendorf and Schild, 1980). During the 19861988 CPE campaigns, thespatial distributions of the Acheulian artifacts were recorded (Hill, 1992) along withthe description and sampling of the stratigraphic sequence and the surroundingmounds (Figures 57). No artifacts were recovered within these deposits, although


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Figure 5. Plan view of the Acheulian sedimentary remnant in the central part of Bir Tarfawi (see Figure2). The limestone plateau is outlined in black. It is interpreted as a remnant of a Middle Pleistocenelake. Diagonal patterns represent sedimentary remnants composed of indurated clastics on and sur-rounding the limestone plateau, interpreted as spring mounds. Acheulian artifacts were found on thesurface of the limestone plateau and associated with the spring mounds. Three trenches were excavatedon the plateau under the direction of R. Schild in 1988. Trench 1/87 is on the west edge of the remnant,Trench 2/87 was excavated between Trench 1/87 and 3/87, and Trench 3/87 was placed further to theeast closer to the center of the remnant. Two test pits (Trenches 1/88 and 2/88) were placed next to thetwo spring mound vents along the west side of the plateau (see Figure 6). Compositional and texturaldata for Trenches 2/88, 1/87 and 3/87 are shown in Tables I-III and Figure 7.


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Figure 6. Plan view of two spring mound vents situated on the west side of the Acheulian sedimentaryremnant in the central area of Bir Tarfawi. Trench 1/88 is situated on the north side of the south moundspring vent and Trench 2/88 is situated on the north side of the north spring mound vent. Compositionaland textural data for samples G1 and G2 are shown in Tables I-III and Figure 7.


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Figure 7. Sedimentology and stratigraphy of Trenches 2/88, 1/87, and 3/87, at the Acheulian-relatedsequence in the central part of Bir Tarfawi. Sediments from Trench 2/88 (samples G1 and G2) arerepresentative of basal sands. Redeposited basal sands are also found in the lower sections of Trenches1/87 and 3/87. The maximum lake stage near the margin of the basin is represented by sample 4 atTrench 1/87. Clay-rich sediments with high carbonate contents (samples 2-5, Trench 3/87) reect dep-osition nearer the center of the lake basin. Vertical and horizontal scales are the same.


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many of the handaxes found on the surface appeared to be slightly weathered andprobably were embedded in sediments until exposed relatively recently by dea-tion.

The sedimentary sequence appears to represent the remains of a small Pleisto-cene lake with spring mounds. Compositional and textural information are pro-vided in Tables I III and Figure 7. The sequence consists of lower basal sands andredeposited basal sands, and overlying deposits representing transgressive, maxi-mum, and regressive stages of a paleolake. The detrital component of the paleolakedeposits appears to be reworked basal sands.

The detrital component and the abundance of carbonate seem to reect slightlydifferent depositional regimes within a deationally formed basin. Initial sedimen-tation consisted of redeposited basal sands. These lowermost deposits are high inclastics; they seem to be sand that was washed into a deational basin during atime when there was little vegetation. There is an increase in carbonate towardsthe center of the basin.

The edge of the plateau remnant (Trench 1/87, Figures 5 and 7) appears to havebeen near the margin of a lake. The sequence is dominated by clastics. The maxi-mum lake stage is associated with high levels of carbonate deposition and endswith a return to clastic-dominated sedimentation of a regressive lake stage. Thetransgressive phase is indicated by a detrital component that shows an increase inthe proportion of silt and clay.

Nearer the center of the paleolake, at Trench 3/87 (Figures 5 and 7), detritalsediments deposited prior to the maximum lake stage have a substantial portionof silt and clay. This supports the idea that this area was closer to the deeper part

of the lake, in a lower depositional energy setting than deposits along the edge of the remnant. The lack of a transgressive trend might reect a more stable depo-sitional setting than deposits of the same lake stage nearer the lake margin. Themost striking difference between the lake margin and deeper water deposits priorto the maximum lake stage is the amount of carbonate. Near the lake margin, thecarbonate content is always below 15% while in the deeper part of the lake, car-bonate content is more than 90%.

The maximum lake phase represented by the high carbonate peak at the edge of the remnant (Trench 1/87, sample 4, Figure 7) is overlain by sediments that indicatea higher energy depositional regime and preserve evidence of a regressive lakestage. These deposits are dominated by clastics and seem to reect deposition inshallower waters, perhaps caused by a reduction in the size of the paleolake. Thecoarse to ne ratio and the carbonate content of the deposit seem to indicate thatthe paleolake was larger than the lake before the maximum lake stage.

Mounds composed of indurated clastics (quartzitic sandstones and mudstones)surround the limestone remnant (Figures 5 and 6) and appear to overlie basal sandsor slightly redeposited basal sands. In some places where the basal sands are ex-posed on the surface, an incipient soil horizon has developed. The top surfaces of these sands have a slightly increased ne fraction and carbonate (sample G2, Fig-ures 6 and 7). Acheulian handaxes were found on the surfaces of the mounds


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(Figures 5 and 6). Two types of mounds composed of siliceous minerals weredescribed by Neal and Motts (1967). Spring mounds form where mineralized ma-terial is deposited when groundwater emerges at the surface. These mounds sup-

port vegetation and, ideally, the height of the mound will approximate the piezo-metric surface (the height of the water table). Small conical mounds composed of siliciclastics on and adjacent to playas also form as a result of continual accumu-lation around plants. When the phreatophyte dies, a conical hill remains. Themounds at Tarfawi are morphologically somewhat similar to ferrocrete moundscomposed of quartz sandstone (Issawi, 1978) in the BS-14 area. Said (1975) de-scribes freshwater springs in southern Egypt containing carbonates in solution. Intheir last stages of activity, these springs produce mounds made of sandstone ce-mented by carbonate or nodules that form in association with vegetation. Robertsand Mitchell (1987) describe similar conical hillocks with or without central cratersconsisting of carbonate-cemented sand and silt.

An estimate of the age of this sedimentary remnant, and the associatedAcheulianartifacts, is approximately 450 500 ky B.P., based on uranium-series dating(Schwarcz and Morawska, 1993). This is about twice as old as the oldest remnantin the central area of Bir Tarfawi associated with Middle Paleolithic artifacts, es-timated to date to around 220233 ky B.P. based on samples 87BTF 21, 32, and 33in Schwarz and Morawska (1993) and sample 25-73Eg86 in Szabo et al. (1995).

South Bir Tarfawi (Site E-88-12)

Acheulian artifacts in the south area of Bir Tarfawi (Figure 2) were discovered

by the CPE during the 1975 campaign (Wendorf and Schild, 1980; Schild and Wen-dorf, 1981). The artifact assemblage from Site E-88-12 was analyzed by R. Schildand Hill (Hill, 1994). The main part of this sedimentary remnant consists of twotypes of indurated deposits: limestones and sandstones. Acheulian artifacts wereembedded within both lithologies as well as on the surface of the remnant. Thesandstones (poorly sorted, slightly gravelly sands, sample A2, Figures 8 and 9) areextremely hard and very strongly cemented by calcium carbonate. Bulk mineralogyx-ray diffraction analyses indicate that quartz is the principal mineral. The surfacesare weathered or are covered by a thin clay lm.

The limestones contain around 96% carbonate (sample A4a, Figures 8 and 9).Bulk mineral x-ray analyses indicates that calcite is the dominant mineral. Theresidual (clastic) component is a poorly sorted sandy mud. The exposed surfaceof these lithied carbonates are abraded and polished. Some surfaces are coveredwith a clay lm. Impressions of mollusc shells and handaxes were preserved in thelimestones. The mollusc impressions are probably Hydrobia or Melanoides. In thinsection, the calcite mudstones contain bivalve shells and possible ostracods(McGillis, 1993).

The two sedimentary rock types found at E-88-12 are interpreted as differentdepositional regimes, both of which were associated with Acheulian occupations.The sandstones, which underlie the limestone remnant, may be sand-sheet depos-


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Figure 8. Map showing geology of Site E-88-12, in the southern part of Bir Tarfawi (Figure 2) andsediment sample locations. Lithologies include limestones (sample A4a) and sandstones (sample A2).Acheulian handaxes are imbedded in the limestones and sandstones.

its. Postdepositional diagenetic processes cemented the deposits to form sand-stones. The bimodal grain size distribution of these deposits is similar to sandsheetsdescribed elsewhere in Egypt and usually regarded to be eolian deposits (Bagnold,1935; Maxwell, 1982; Breed et al., 1987).

The limestone at E-88-12 was probably biochemically precipitated as endogeniccarbonate mud near the center of a freshwater lake or pond. About 79% of thedetrital component consists of silt, indicating a very low-energy depositional re-gime. The impressions of what appear to be freshwater forms of gastropods maymean the paleolake had relatively low-salinity levels during at least some lakestages.

The highly indurated nature of these lithologies, the abraded and polished ex-posed surfaces, and the low relief of the exposed remnant all indicate that thislocality has been subjected to a higher degree of weathering and diagenesis than


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Figure 9. Compositional content (carbonate and clastic components) and grain-size histograms of thedetritial fraction of sediments from Site E-88-12. Sample A2 is dominated by clastics and has a bimodalgrain-size distribution, while sample A2 is composed almost entirely of carbonates and has a clasticcomponent dominated by silt.


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other Pleistocene remnants in the region. This could mean that the artifacts areperhaps some of the oldest recovered from the area. Two dating methods wereused to estimate the age of the E-88-12 sedimentary remnant. Quartz thermolumi-

nescence measurements of sand underlying the limestone provided an age of about165 ky B.P. (Bluszcz, 1993). Uranium-series determinations indicate deposition of the limestone prior to 350 ky B.P., perhaps around 600 ky B.P. (Wendorf et al.,1994). Although both methods indicate a Middle Pleistocene age for the associatedAcheulian artifacts, the older date may be more reasonable, or perhaps even aminimum age.

CONCLUSIONS

Paleogeographic Settings and Artifact Taphonomy

Based on the association of artifacts with particular geomorphic and depositional

contexts, we can make inferences about (1) the landscape setting and resourcesassociated with the hominid occupations and (2) the effect geologic processesmight have on transforming the original patterns of the hominid occupations intothe observable record (cf. Rapp and Hill, 1998). Inferences concerning landscapecontext, in turn, provide a framework for proposing models of adaptive systems(such as organizational and resource-use strategies, mobility patterns) employedby Paleolithic groups in the Eastern Sahara during the Middle Pleistocene. Like-wise, attempts to determine how the archaeological record has been affected bypostoccupational processes provide a way to evaluate whether the patterns ex-pressed by artifact assemblages can be reliably attributed to Pleistocene hominidbehavior. If the spatial distributions and artifact forms are probably related to theinitial occupation, and not the result of postoccupation agencies of accumulation,these patterns can be used to evaluate the duration and intensity of occupation,and the size of the prehistoric group involved. Furthermore, the meaning of theabsence or presence of specic forms of artifacts may become clear. Through thesemethods, it should be possible to begin to assess the prehistoric record in termsof its implications for Pleistocene hominid activities.

From the perspective of taphonomy and site integrity, some Acheulian artifactsat Site BS-14 may be essentially in primary context; it is possible that the initialhominid occupation record has not been severely affected by postdepositional pro-cesses. It may also be possible to evaluate the paleolandscape associated with theAcheulian occupations. At Bir Tarfawi and Bir Sahara East, the Acheulian occu-pations seem to be associated with emergent groundwater pools and the marginsof perennial lakes. These localities are far removed from any known lithic re-sources, and at Site BS-14 the typology and technology of the assemblage appearto reect its characterization as either a base camp or resource procurement lo-cality (Hill, 1992). The apparent presence of Acheulian lithic assemblages indicatingfunctionally specic reduction strategies in particular paleolandscape settings, mayreect Middle Pleistocene resource-based organizational strategies and mobility pat-terns in the Sahara, although more eld studies need to be undertaken to test this idea.

Acheulian artifacts in North Africa have been found with a wide variety of sed-


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imentary deposits (Hill, 1992). These sediments indicate some of the processes bywhich the artifact accumulation was formed, and, depending on taphonomic tra-jectories, the landscape setting, and potential resources associated with the hom-

inid occupation. In addition, some of the artifact accumulations are associated withother geologic resources, such as rock outcrops usable for obtaining raw materialfor the production of artifacts. A continuum of local geomorphic contexts andspecic depositional regimesranging from eolian sandsheets to settings associ-ated with playa and perennial lakes appear to have been present in the Bir Tar-fawi region during the Pleistocene (Hill, 1993). Paleolithic artifacts have been foundembedded or associated with almost every kind of depositional setting that hasbeen studied. These include settings associated with coarse siliciclastic deposition,with increased levels of mud (ne siliciclastics), and in settings associated withhigh carbonate deposition. For example, Acheulian artifacts are known to havebeen embedded in both sandstones and limestones.

Sands containing zones of thin, cylindrical calcite-cemented trace fossils occurin several contexts within the various Pleistocene sedimentary sequences. Theymay be the result of biologic activity and seem to imply the presence of nearbymoisture. Trace fossil horizons were observed within basal sands and in basin-wash deposits. Many of the trace fossil horizons appear to be the lateral faciesequivalents of hydromorphic deposits. These horizons could have developed as theresult of plant root systems (composed of horizontal root mats) formed within ormarginal to a shallow phreatic zone (Mount and Cohen, 1984). Others appear to bethe result of the development of grasses and other vegetation on the edges of waterbasins and on nearby eolian deposits (cf. Glennie and Evamy, 1968; Plaziat and

Mahmoudi, 1990). Some of the trace fossil horizons may be the result of aquaticmacrophytes and other biologic activity (including insects and small burrowingorganisms) within shallow lake margins.

Trace fossils were observed in the sands containing Acheulian artifacts at SiteBS-14; these sands were overlain by carbonates related to a groundwater pool. Interms of palegeographic interpretations, these trace fossil horizons imply stabilizedland surfaces or basinal margin settings. Taphonomically, artifacts embedded inthese bioturbated zones may have been vertically displaced. Thus, as with othersettings containing trace fossil concentrations, there is some question concerningthe temporal relation of these structures and the deposition of the artifacts. Theseemingly unabraded surfaces of the artifacts recovered within the sands, the pres-ence of a wide range of artifact sizes (chips to handaxes), as well as the apparenttechnological coherence implied by the presence of different forms of artifacts,suggests that this locality could contain a relatively intact record of Acheulianpresence in southern Egypt. If the sands are a result of basin-wash associated withdeposition in a groundwater pool, the artifact record may have been less affectedby postdepositional events than in a spring vent setting.

Coarse siliciclastic-dominated Pleistocene sediments can be separated into sev-eral sets based on specic microdepositional settings (Hill, 1993). One set consistsof clastics derived from the redeposition of basal sands and deposits probably


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initially derived from basal sands, such as eolian-related sediments. These includesands deposited along the margins of basins where only pelagic sedimentationoccurred (playa-pan settings and early stage perennial lake settings), as well as

sands deposited within the active beach/shore zones connected to maximum ex-pansion stages of lakes where carbonate deposition was occurring deeper in thebasin. Clastic deposition can also be related to the formation of dunes along themargins of the basins and eolian activity during drier climatic conditions.

Coarse-clastic-dominated deposits from the Acheulian Sites E-88-12 and BS-14contain embedded artifacts. At Site E-88-12, the coarse siliciclastics appear to besandsheet sediments deposited in a shallow basin and then buried by limestones.One set of Acheulian artifacts at Site E-88-12 may have been deposited in sandsheetdeposits unrelated to the subsequent lake deposits, while another set can be di-rectly connected to the presence of the limestone. At Site BS-14, the artifacts areembedded in sands deposited within and along the margins of a shallow basin,probably later submerged by a rise in the groundwater level. A calcareous sand-stone cap (calcrete) overlies these artifact bearing sands.

Artifacts of various sizes were deposited within the sands at BS-14. These sandscould have been associated with the run-off of sporadic rains or with the edge of a small groundwater-charged basin. The calcrete cap may be the result of carbonatedeposition after a period of increased moisture when rising water inundated theartifact-bearing sediments. The carbonate overlies these sands and appears to haveformed as a result of evapotranspiration of a groundwater/vadose zone-formedpool. The carbonate cap helped protect the underlying sands from erosion.

Along the periphery of the carbonate cap at BS-14, the sands containing Acheu-

lian artifacts were subsequently altered by the accumulation of pedogenic carbon-ates and reddened by incipient weathering and soil development. Unprotected ar-eas of these sands were weathered and deated, forming lag deposits of Acheulianhandaxes around the periphery of the limestone remnant (see Figure 44 in Schildand Wendorf [1981]). Smaller artifacts (debitage: chips) that were introduced intothe sediments as a result of Middle Pleistocene hominid activity were destroyed orweathered to various degrees. Artifacts found on top of the BS-14 remnant couldhave eroded out from portions of carbonate removed by deation, or from othersediments overlying the carbonate that were eroded away, or may remain wherethey were left by subsequent hominid activities.

The presence of apparently unabraded artifacts in basin-edge and basin-washsands and the occurrence of concentrations of rhizoconcretions suggests that arelatively undisturbed Acheulian artifactual record may be present at Site BS-14.The occurrence of both large and very small artifacts within the sands suggests thelikelihood that, assuming a groundwater pool context, the artifacts have not beensubstantially disturbed from their initial occupational context, at least in terms of horizontal displacement. For example, Schick (1992) used the absence of smalldebitage (less than 2 cm) as an indication of uvial sorting at an Acheulian site;the presence of small debitage at Site BS-14 might support the contention that thesite was not disturbed by water action.


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Some vertical dispersal of the artifacts at BS-14 is suggested by an ascendingvadose zone as well as by the presence of trace fossil concentrations, which indi-cate subsequent groundwater saturation of the deposits. The trace fossils likely

indicate the presence of a stabilized vegetated surface contemporaneous with ei-ther the Acheulian occupation episode and the initial deposition of the artifacts ora period of vegetative cover after the initial deposition of the artifacts. Bioturbationcould have affected the vertical placement of the artifacts.

The artifact component at Site BS-14 that was recovered embedded within thesands underlying the calcrete cap provides a critical record of the Acheulian oc-cupation of southern Egypt. It provides an essentially undispersed and, at least,technologically coherent Acheulian assemblage from the Eastern Sahara. The pres-ence of a technologically coherent assemblage (that is, an assemblage probablycontaining representative materials from all aspects of lithic reduction activitiesassociated with the occupation at the site) presents an opportunity to compare theresource and mobility strategies at Site BS-14 with other Acheulian assemblagesfrom southern Egypt. Succinctly, the artifacts at Site BS-14 could represent Acheu-lian occupations associated with strategies of raw material use apparently far fromthe sources of these materials, reecting patterns related to mobility and curation.In contrast, other Acheulian localities reect patterns associated with the directpresence of the lithic materials used to form the artifacts. The Site BS-14 Acheulianassemblage may reect Pleistocene hominid activities associated with use of pa-leobiogeographic contexts located away from lithic raw material resources.

The depositional setting directly associated with the biochemical precipitationof carbonate is similar to the setting associated with the deposition of ne silici-

clastics within a lake basin. Limestones and marls are generally deposited in quiet,low energy settings except for some types of travertines and tufas and spring ventsettings. The presence of artifacts embedded within lacustrine carbonate sedimentscould imply that these surfaces were subaerially exposed at the time Middle Pleis-tocene hominids were present. Artifacts were found embedded in marls and lime-stones at the Acheulian locality of Site E-88-12 in the south part of Bir Tarfawi. Theartifacts were buried by other lake sediments implying occupations duringdry seasons, possibly near dry-season pools of groundwater-fed perennial water-bodies.

The Pleistocene archaeological sites associated with perennial lake contexts(lake basins containing evidence of chemical deposition) are situated in transi-tional, potentially high energy, depositional settings along the margins of lake ba-sins (Hill, 1993). At the Acheulian sedimentary remnant in the central part of BirTarfawi, artifacts were found in several surface contexts. Bifaces were found ontop of the limestone remnant, on the sands surrounding the remnant, and on thesurface of mounds surrounding the remnant. These Acheulian artifacts, as well asthose embedded in limestones at the south area of Bir Tarfawi (Site E-88-12) pro-vide more evidence indicating that Acheulian occupations were associated withperennial lakes. The artifactual context at Site E-88-12 implies that some of theseoccupations coincided with regressive lake cycles, probably during the dry season,


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when some of the carbonate deposits were exposed and the lake was reduced insize. These might represent later stages of hominid presence within a major lakephase, in contrast to the emergent groundwater pool at Site BS-14.

Paleoclimatic and Chronologic Context

The presence of perennial lakes associated with the Pleistocene archaeologicaland paleobiotic record in southern Egypt contrasts with evidence for only playasettings during the early Holocene. While Pleistocene sites are in contexts associ-ated with both perennial lakes (e.g., carbonates deposited in groundwater-fed sys-tems) and seasonal playas (dominated by clastic transported by local rains), Ho-locene sites seem to be conned to playa settings. Thus it seems that Pleistocenepluvial events may have been connected with wetter climates than the earlyHolocene in the Sahara (cf. Haynes, 1980, 1987; Hill and Wendorf, 1991, 1997;McKenzie, 1993).

The relative and absolute chronologic placement of the Acheulian in the Saharahas relied on specic local and regional geomorphic/stratigraphic associations, cor-relations with dated sequences outside North Africa, and coupling (correlation) of sedimentary sequences with paleoclimatic models. The Lower Paleolithic in NorthAfrica extends back to at least the early Pleistocene (Clark, 1992; Sahnouni and deHeinzelin, 1998). In terms of absolute ages, Acheulian assemblages are estimatedto have been present prior to a million years ago (e.g., Isaac, 1972; Clark, 1998;Dennell, 1998; Rolland, 1998). In Kenya, Upper Acheulian artifacts have been esti-mated to date to around 230 ky B.P. (Isaac, 1972), and Final Acheulian artifacts

(from near Lake Ziway, Ethiopia) overlain by assemblages similar to Typical Mous-terian of Levallois Facies are in deposits dated to about 181 ky B.P. (Wendorf etal., 1975). This can be compared to the transition from Acheulian to Middle Pale-olithic in Europe, which may have occurred during isotope stage 6. Age estimatesfor the Acheulian of about 288240 ky B.P. have been correlated with isotopestages 7 and 8 (Schwarcz and Grun, 1983), while Middle Paleolithic artifacts havebeen dated to around 123 ky B.P. and correlated with istope stage 5e (Schwarczand Blackwell, 1983). Along the eastern Mediterranean, at Tabun Cave, the latestAcheulian may date to around 300 ky B.P. while the earliest Mousterian may beolder than 250 ky B.P. (Mercier et al., 1995). Throughout North Africa, Pleistocene-age sedimentary sequences provide evidence of episodic changes in paleoclimaticconditions which, when securely dated, provide the potential for evaluating thechronologic context of Paleolithic artifacts. The chronologic placement of theAcheulian in the Sahara is complicated by the rarity of stratigraphically superim-posed artifact sets, as well as the difculties involved in developing sedimentolog-ical and paleoclimatological interpretations with adequate age constraints.

At Bir Tarfawi and Bir Sahara East, geochronometric dating has provided ageestimates for deposits containing or related to the Acheulian that are at least 350ky B.P., and perhaps with the range from 600460 ky B.P. (Wendorf et al., 1994).Sedimentary remnants containing or associated with Middle Paleolithic artifacts


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range from more than 350 ky B.P. to less than 50 ky B.P.; however, the most feasibleestimates range from slightly older than 200 ky B.P. to around 70 ky B.P. (Miller etal., 1991; Wendorf et al., 1994).

The potential for interpreting North African sedimentary deposits in paleocli-matic terms and correlating these with other chronoclimatic sequences has beenrecognized and attempted (especially along the Atlantic and Mediterranean coastswhere direct connections with sea level changes can be made). These correlationshave become more reliable with the increasing dependability of direct dating mea-surements. Using a model based on external forcing by uctuations in solar inso-lation, threshold insolation values can possibly be used to predict the onset of monsoon conditions in North Africa, which would be recorded in the geologicrecord by the presence of lacustrine or other pluvial related deposits (e.g., Rossig-nol-Strick et al., 1998; Hill and Wendorf, 1991). An alternative approach is to cor-relate the sedimentary sequences with independently dated paleoclimatic se-quences; such as the Vostock ice core or the Devils Hole chronology (Winograd etal., 1997). Based on these types of correlations, any potential succession fromAcheulian to Middle Paleolithic in the southern Egyptian Sahara would have oc-curred during the interval from about 300200 ky B.P.

A postulated age for the end of the Acheulian and the beginning of the MiddlePaleolithic prior to 200 ky B.P. appears to conict with other proposed chronolo-gies for North Africa (Hill, 1999). While not negated by other age measurementsfrom southern Egypt (e.g., Szabo et al., 1989, 1991; Crombie et al, 1997; Sultan etal., 1997; Churcher et al., 1999), this age model is different from the chronologiesproposed elsewhere based on direct measurements or paleoclimatic correlations

with isotope stages. For instance, along the Atlantic Sahara Upper and EvolvedAcheulian artifacts are indirectly dated by correlation with isotope stage 5 (ca. 130100 ky B.P. [Barbey et al., 1991). In Libya, the Terminal Acheulian has been asso-ciated with lacustrine episodes centered on 130 ky B.P. (Petit-Maire, 1991; Petit-Maire et al., 1991), while in Tunisia the Final Acheulian may date to about 150 kyB.P. (Ballais and Heddouche, 1991). Whether the apparent differences in the agesof the end of the Acheulian and beginning of the Middle Paleolithic reect actualspatial variation for the transition, the relibility of geochronologic measurementsand correlations, or is a manifestation of the adequacy of existing lithic artifacttaxonomic categories still needs to be resolved. There does seem to be, however,a growing amount of geochronometric information which links the timing of Sa-haran pluvial events with interglacial climates; it seems that these pluvials werethe times when Middle Pleistocene biotic communities, including hominids usingAcheulian artifacts, would have been most viable in the Eastern Sahara.

Summary

The three sedimentary remnants from the Bir Tarfawi region associated withAcheulian artifacts share the following characteristics: They overlie basal sandsand/or redeposited basal sands constituting the lowermost part of the depositional


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sequences; the boundaries between the basal sands and the basin ll that form theremnants are at relatively high elevations (ca. 246248 m asl); and the remnantsare composed of extremely indurated limestones or sandy limestones. The char-

acter of the carbonate deposit at Site BS-14 is somewhat different from the lime-stone deposits at the Bir Tarfawi Acheulian localities. At Bir Tarfawi, the centralbasin limestones are indurated lime muds while at Bir Sahara East they contain amuch higher proportion of coarse detrital materials, probably indicating a shal-lower, smaller water body. Acheulian handaxes are commonly found in lag positionon the surfaces of the indurated detrital remnants. Acheulian artifacts also occuron the surfaces of the carbonate remnants at all three localities and are embeddedin carbonates at Site E-88-12. Acheulian artifacts were also recovered within sandsat Site BS-14 and E-88-12 and on the surface of sands in central Bir Tarfawi.U-series measurements indicate that carbonates associated with the Acheulian inthe Bir Tarfawi region may date to before 300 ky B.P. In terms of a paleoclimatechronology, the Acheulian in the Eastern Sahara seems to be linked to pluvialintervals associated with marine isotope stage 9 or older.

The studies summarized here were conducted while a member of the Combined Prehistoric Expedition,which has been jointly sponsored by Southern Methodist University, the Polish Academy of Sciences,and the Geological Survey of Egypt. The eld work could not have been initiated or completed withoutthe guidance and support of Fred Wendorf and Romuald Schild. George (Rip) Rapp, Jr. kindly allowedthe use of the facilities of the University of Minnesotas Archaeometry Laboratory. I am very gratefulto C. Vance Haynes, Jr. for providing valuable information pertaining to his studies, as well as B. Issawiand M. Kobusiewicz for sharing their knowledge about the geology and prehistoric archaeology of theEastern Sahara. This study was supported by National Science Foundation Grants BNS-8415650, BNS-8518574, and BNS-8718908 to F. Wendorf, and grants to C.L. Hill from Sigma Xi, the Scientic ResearchSociety, the Graduate Student Assembly of Southern Methodist University, the Institute for the Studyof Earth and Man (Southern Methodist University), and Montana State University. Tulane Universityprovided research assistant support. Funding from Department of Energy Grant DE FG05 90ER61015to W.A. Woodward, H.L. Gray, and R.F. Gunst provided support for assessment of the paleoclimatolog-ical and chronological context for a research group studying climatic change. Additional funds wereprovided by G. Rapp, Jr. and C.L. Matsch. I am very grateful to A. Freeman, K. Nicoll, V. Holliday, andR. Mandel for their very useful comments on an earlier version of this article. Special thanks to CherylHill.

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Received May 5, 2000

Accepted for publication August 1, 2000

Documents

Geologic Contexts of the Acheulian in the Eastern Sahara