Holocene Climatic Changes and Cultural Dynamics in ... - Springer Link

African Archaeological Review, Vol. 16, No. 4, 1999

Holocene Climatic Changes and Cultural Dynamics in the Libyan Sahara M. Cremaschi1 and S. Di Lernia2,3

Systematic surveys and excavations were carried out during the 1990—1996 field seasons in the Tadrart Acacus and surrounding areas, shedding new light on the climatic changes and cultural dynamics which occurred during the Holocene. In this paper, the geological, geomorphological, and archaeological evidence is assembled in order to provide a preliminary synthesis on the prehistory of the area. Pendant les saisons de terrain du 1990 au 1996, des recognitions et fouilles systematiques ont ete conduites dans le Tadrart Acacus et dans les zones circonvoisines; ces etudes ont donne des nouvelles information en ce qui concerne les changements climatiques et les dynamiques culturelles de cette region pendant l'Holocene. Dans ce papier, les evidences geologiques, geomorphologiques, et archeologiques ont ete integrees afin d'obtenir une synthese preliminaire sur la prehistoire de la region. KEY WORDS: Late Pleistocene; Holocene; Libyan Sahara; palaeoenvironment; cultural dynamics.

Libycae quod fertile terrae est vergit in occasus; sed et haec non fontibus ullis solvitur (...). In nullas vitiatur opes; non aere nec auri excoquitur, nullo glaebanum crimine pura el penitus terra este. Anneo Lucano, Farsalia IX

INTRODUCTION The mountain ranges of the Libyan Sahara are known as areas of remarkable interest for prehistoric art (e.g., Barth, 1857; Mori, 1965; Lutz, 1995) and 1 C.N.R.C.G.A.Q.,

Universita di Milano, Milano, Italy; e-mail: [email protected]. di Scienze Storiche, Archeologiche e Antropologiche dell' Antichita, Universita degli Studi di Roma "La Sapienza," Via Palestro 63, 00185 Rome, Italy; e-mail: [email protected]. 3To whom correspondence should be addressed. 2 Dipartimento

211 0263-0338/99/1200.0211$16.00/0 C 1999 Plenum Publishing Corporation

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Cremaschi and Di Lernia

Fig. 1. The area licensed to the Italo-Libyan Joint Mission. Squares indicate the sampling areas of systematic surveys performed in the 1990-1996 field seasons (georeferenced map, edited in Autocad).

for their rich archaeological record (e.g., Mori, 1965; Barich, 1987; Lupacciolu, 1992). However, past research in the Tadrart Acacus and the Messak Settafet has favored rock art, with only a few isolated archaeological excavations. In addition, systematic investigation on a regional scale has been practically missing. This paper presents the results of the regional survey carried out by the Italo-Libyan Joint Mission directed by Prof. Fabrizio Mori, from 1990 to 1996. The survey took place mainly in the central Acacus, but also, in the wadi Tanezzuft (Tahala area), in the Messak Settafet, in the erg Uan Kasa, and in the Edeyen of Murzuq (Fig. 1), which were previously unknown from an archaeological point of view. The area is roughly delimited by coordinates latitude 24°30'-26°N and longitude 10-12°E; it presently has a hyperarid climate, with a mean annual precipitation of 10 mm and a mean annual daily maximum temperature of 30°C (Walter and Lieth, 1960) and it is composed of a wide range of physiographic features. The Tadrart Acacus consists of a deeply dissected mountain range composed mainly of Permian and Carboniferous sandstone. The Messak Settafet represents a relict plateau, cut in Cretaceous sandstone, and the erg Uan Kasa and the Edeyen of Murzuq are sand seas, which show a dune-dominated landscape and also include fluviatile and lacustrine deposits. This paper presents the results of a regional survey conducted from a geoarchaeological perspective, i.e., archaeological and palaeoenvironmental research

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Climate and Cultures in Libyan Sahara Table I. Name, Surface Area, and Percentage of the Surveyed Areas Survey area

1 2

3 4 5

Region Central Tadrart Acacus Central Erg Uan Kasa Central Messak Settafet Northern Edeyen of Murzuq Northern Wadi Tanezzuft (Tahala)

Approximate sampled area (km 2 ) 3,000 1,600 3,500

625 500

Approximate dimensions (km 2 ) Ca. 50 Ca. 75 Ca. 50 Ca. 25 Ca. 25

x 60 x 20 x 95 x 25 x 20

Approximate surface area (km 2 ) 15,000 7,500 18,000 61,000 2,000

Ratio (%)

20.0 21 3 19.5

1.1 25.0

conducted by the same team operating in the field (Cremaschi and Di Lernia, 1996b, 1998). The total surface area of the survey is approximately 9225 km 2 . The size of the surveyed area and percentage on the total region are reported in Table I. More than 450 archaeological sites were identified, spanning a period from the Early Stone Age to Late Pastoral cultures. In this paper we discuss the Late Quaternary environmental changes and cultural dynamics of the human groups. The dating of the occupation of these Holocene sites is supported by a large number of radiometric dates. As samples for 14C dating were collected, in most cases, from archaeological contexts, we can consider this continuity of dating as corresponding to human occupation. SOME METHODOLOGICAL ISSUES The geoarchaeological survey and the environmental research were carried out simultaneously, with the aim of detecting the environmental changes which took place during the Late Pleistocene and throughout the Holocene. Our map references were based on a satellite Landsat image. Generally, each cluster of archaeological material has been recorded as a site. This is a broad definition, including both multistratified cave sites, as well as open-air sites with only a few finds. The archaeological visibility of the sites varied according to the different physiographic units. When available, 14C radiocarbon datings are indicated. Uncalibrated conventional 14C datings (C13 corrected) indicated as BP are used. The sites, classified as Lower Palaeolithic, are mainly of the Late Acheulean phase; those of the Middle Palaeolithic were prevalently of the Mousterian and Aterian facies. The Holocene sites with extractive economic basis have been classified as "Epipalaeolithic" or "Early Acacus" and "Mesolithic" or "Late Acacus"; those with food-producing economy, as Early, Middle, and Late Pastoral Neolithic. The lithic industries were classified according to Bordes (1961) for the Pleistocene lithic industries and according to Tixier (1963) for the Holocene industries. The typology developed by Caneva (1987) was used to analyze ceramic decorations. The chronocultural attribution was based on several types of archaeological indicators: the lithic assemblages were sampled in order to define tool-kit

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and chaine operatoire; all the lithologies were sampled. A significant number of pottery samples were collected for decoration analysis. Spatial configurations of archaeological structures (pits, fireplaces, etc.), when preserved, were mapped and sampled. Particular attention was also addressed to the presence of residual strips of stratigraphy, faunal remains, and grinding equipment. We would like to draw attention to the terminology used: this is a timeconsuming issue, which probably should be addressed elsewhere. However, in order to avoid confusion with the use of terms like "Epipalaeolithic," "Mesolithic," and "Neolithic" (Cremaschi and Di Lernia, 1995; Di Lernia and Cremaschi, 1996a; Di Lernia, 1996; Di Lernia and Garcea, 1997), we propose a terminology based on local fades, referred to the regional Holocene cultures, awaiting the general consensus of scholars (e.g., Sinclair et al., 1993; Aumassip et al., 1996; various informal meetings). The long "pre-Pastoral" occupation of the Acacus has been subdivided into two distinct phases on the basis of the stratigraphic sequence of Uan Afuda (Cremaschi and Di Lernia, 1995). This differentiation was analyzed on a regional scale, giving consistent results (Di Lernia, 1996,1997a, 1998b) and used as a mean to suggest the new terms for the early Holocene extractive communities, i.e., Early and Late Acacus, instead of "Epipalaeolithic" and "Mesolithic" (Di Lernia and Garcea, 1997). In order to determine the more ancient phases of pottery production in contexts with extractive economy (i.e., generically "pre-Pastoral"), the presence of rocker-decorated fragments and particular syntactic motives, such as the Dotted Wavy Line and packed zigzags (Caneva, 1987), have been taken in consideration to define a "Mesolithic" or "Late Acacus" occupation. Regarding the distinction between the different Pastoral phases, in the nonstratified contexts we must note the difficulty to assign these sites to a determined chronological phase. This is due also to the general apparent uniformity of the pottery, which is usually the most frequent archaeological indicator. In any case, a first, coarse distinction can be made between Early-Middle Pastoral and Late Pastoral contexts. The Early-Middle Pastoral complexes are dated between ca. 7500 and 5000 BP, and characterized by "Return" and "Alternately Pivoting Stamp" techniques (Caneva, 1987), with significant percentages of "Rocker" decoration in the earliest phases. The Late Pastoral contexts are associated with an arid phase, whose beginning is dated from ca. 5000 BP, and are characterized by the "Simple Impression" technique, with undecorated sherds prevailing (see also Ponti et al., 1998).

HOLOCENE ENVIRONMENTAL CHANGES IN SOUTHWESTERN FEZZAN The main sources of evidence for palaeoclimatic reconstruction in the area are the cave and shelter fills in the mountain ranges and lacustrine or marsh deposits in the interdune corridors located in the erg areas. In the reconstruction of

Climate and Cultures in Libyan Sahara

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environmental changes, TL-, OSL-, U/Th-, and radiocarbon-dated geological and geoarchaeological evidence has been used (Cremaschi, 1998a,b). Fossil dune remnants discovered within the mountain range and dated—by TL and OSL—at the base of some of the cave fills (Martini et al., 1998) indicate strong desert conditions since 90,000-70,000 years BP, which may correspond to the beginning of the Ogolian desert encroachment in the area (Fig. 2). The travertine deposits discovered in caves and shelters of the Acacus mountains are the oldest evidence for post-Ogolian wet conditions (Carrara et al., 1998). They represent the recharge of the hydrographic net in the mountains, were sedimented

Fig. 2. The stratigraphic sequence of Uan Afuda cave, located in the central Acacus. (1) Weathered bedrock and lower paleosol; (2) aeolian sand and top soil; (3) Unit 2, colluvial deposits and gypsum lenses; (4) organic rich deposits; (5) hearth; (6) deposits with slightly decomposed plant remains; (7) present aeolian sand.

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from 14,000 up to 9700 years BP as indicated by U/Th dating, and are indicative of a substantial increase in precipitation during the late Upper Pleistocene and at the very beginning of the Holocene. Since there was no subsequent travertine deposition, this period has to be interpreted as the wettest phase of the late Quaternary. The Holocene fill of the caves and shelters in the area is mainly of anthropogenic origin, as it consists mainly of plant remains, transformed to some extent by fire, organic material addition, trampling, etc. The way by which the organic fraction was preserved appears to be strictly climate dependent; within the Holocene a twofold trend of aridification can be seen (Cremaschi et al., 1996). In the early Holocene, the deposits of Uan Afuda cave (Fig. 2) (Cremaschi and Di Lernia, 1995; Di Lernia, 1997a,b) and Uan Tabu shelter (Garcea, 1996) are of a colluvial nature at their base, whereas at the top, the plant remains and matter are progressively better preserved, lacking of bacterial activity, and therefore indicating an increasing aridification. A sedimentary gap in the cave fills may be related to an erosional phase in a dry environment, which occurred after 8000 and before 7500 years BP. Around the same period (8100-7200 years BP), an aeolian sand ingression clearly connected to a dry period is recorded in the Ti-n-Hanakaten sequence (Aumassip, 1984). This indicates that this dry period may have regional relevance, centered on ca. 7400 BP (Gasse and Van Campo, 1994; Lamb et al., 1995). The second phase spans from about 7500 to 5000 years BP. The older deposits have suffered clear humification of the organic matter and movement of solutes, which are indicative of water percolation. This picture of wet conditions is further confirmed by pollen analyses both of the base levels of the Uan Muhuggiag shelter (Fig. 3) (Mercuri et al., 1998) and of the Mathendush cave, which indicate a wet savannah plant cover (Trevisan et al., 1995). In the late seventh millennium BP, humification and solute movements were progressively reduced. Erosional surfaces, deposition of aeolian sand inside caves and shelters, and the collapse of shelter roofs indicate the onset of severe dry conditions after 5000 years BP. After this date, shelter and cave deposits consist mainly of dung, which is composed of unaltered plant and grass remains, cemented by animal excrement. This material did not suffer any bacterial degradation and should be attributed to a subdesertic dry environment. Pollen grains also indicate a dry steppe environment (Trevisan etal., 1998). There is geological evidence for the existence of Holocene lakes and swamps both in the Erg Uan Kasa (Fig. 4) and in the Edeyen of Murzuq (Fig. 5) (Cremaschi, 1994; Cremaschi and Di Lernia 1996a,b). Only the lakes at the western fringe of the erg Uan Kasa were directly fed by tributaries, whereas the others inside the interdune corridors were derived from a rise of the water table. In both cases, the formation of the lakes was a consequence of increased precipitation which occurred both locally and in the surrounding mountain ranges. The formation of lakes and ponds was delayed in comparison with the mountain range, since the recharge of erg acquifers probably took longer.


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Fig. 3. The stratigraphic sequence of Uan Muhuggiag shelter. (1) Loose aeolian sand; (2) slightly cemented sand and coprolites: dung; (3) hearths; (4) hearths in slightly humified organic sand and lenses of fresh plant remains; (5) humified organic sand, (6) strongly humified organic sand and gypsum concretions.

Fig. 4. Schematic stratigraphic sequence of a lacustrine basin in the Erg Uan Kasa. (1) Bedrock; (2) fossil dune including Acheulean artifacts; (3) bleached bedrock; (4) "Early Acacus" artifacts; (5) sand ridge; (6) green sand; (7) organic mud; (8) calcareous silt, including mollusk shell; (9) gypsum crust; (10) Acacia tree.

Radiocarbon dating of lacustrine deposits suggest that lakes existed from 8445 to 5500 years BP, but indications of lake level fluctuation are poorly known at present. At 8445 BP lakes existed and were probably rising (Cremaschi, 1998a,b). An important break in lake sedimentation followed this phase, but it is still poorly dated. This is evidence that an erosional phase affected deposits at around

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Fig. 5. Schematic stratigraphic sequence of a lacustrine basin in the Eyeden of Murzuq. (1) Dune ridge; (2) bleached sand; (3) upper terrace; (4) organic mud interpreted as shore deposits; (5) calcareous silt including mollusk shell and base peat; (6) "Pastoral" sites; (7) "Early Acacus" sites.

8000 years BP. The lake level was gradually rising at 7300 years BP, reaching the maximum level at 6600-6000 years BP. As yet, there is no more recent data for lacustrine deposits, even if a high concentration of pastoral sites around the lake shores suggest the existence of ponds up to 5000 years BP. However, along the valley of wadi Tanezzuft, which is the western margin of the surveyed area, fluvial activity is still recorded up to 3800 years BP. These data also indicate that in the central Sahara at latitude 24-25°N, in a previously poorly understood area from a paleoenvironmental point of view, there is clear evidence of a long Holocene wet period, which produced lakes and ponds in lowlands and savannahs inside the mountains. This confirms the picture of a continuous belt of wet landscape during the Holocene "interglacial" (Street and Grove, 1976; Lezine et al., 1990) from the Sahelian area to the Northern fringe of the Sahara. The trend of environmental change is quite similar to that of the surrounding area, but the timing appears to be somewhat different. The peak in precipitation, as recorded by the travertine deposition in the mountain range, preceded the rising of


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the Malian lakes (Oxnevad, 1993; Petit-Maire, 1991; Petit-Maire, 1993), the onset of wet conditions in western Sahara (Lezine et al., 1990), in the Egyptian desert (Kroepelin, 1987), and in western Nubia (Pachur and Hollzman, 1991) by about a thousand years. However, it appears to be contemporary with the Ethiopian lakes, particularly Lake Afar (Gasse, 1980). The onset of outstanding dry conditions began around 5000 years BP, contemporaneous with the western areas of the same latitude (Kroepelin, 1987) yet not as late as the Ethiopian lakes that began to drop at 4500 years BP. However, the aridification began earlier here in comparison with the southern Malian belt, with the area of the lake Tauodenni drying at 3800 years BP and with the northern fringe of the Sahara where aridification is recorded at about 3000 years BP. EARLY HOLOCENE HUMAN OCCUPATION (CA. 9800-7400 YEARS BP) "Epipalaeolithic" or "Early Acacus" Hunter-Gatherers (Ca. 9800-8900 Years BP) The post-Ogolian wet period started in the area some 1000 years before the start of the Holocene. Travertine deposition inside the Acacus mountain range is indicative of a clear increase in precipitation from 14,000 to 10,000 calendar years BP, as indicated by U/Th dating. There is no evidence of human occupation in the area recorded at the beginning of this interval. This gap is consistent with the data from other North African contexts (Petit-Maire, 1993; Close, 1992; Gabriel, 1987), and therefore it can be considered representative of the time necessary for a full biological recolonization of a region (Cremaschi and Di Lernia, 1996b). The oldest "Epipalaeolithic" or "Early Acacus" site was recorded inside the Uan Afuda cave (9765 ± 105 BP; GX-20750), with archaeological material included in colluvial sediments, evidence suggesting wet palaeoenvironmental conditions (Fig. 2). Several other sites were located in the Acacus mountains, and artifacts were systematically associated with the top of the red aeolian sand formation. The archaeological record of "Early Acacus" sites in the Acacus range is unfortunately less rich in information than those located near the ancient lake basins. However, it has become possible to hypothesize the existence in the mountain range of multiactivity base camps, based mainly on the evidence from Uan Afuda cave. They are characterized by stone structures, shallow hearths and a quantity of lithic artifacts, struck from different raw material (Fig. 6). Grinding equipment, although present, seems to be less impressive here than in other, subsequent archaeological phases. Actually, "Early Acacus" sites were widely attested in the erg Uan Kasa and inside the Edeyen of Murzuq. These sites were probably located close to lakes existing at that time inside the dune corridors. The lake surfaces were in a

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Fig. 6. "Early Acacus" lithic industry from a base camp (Uan Afuda cave) located in the mountain range.


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transgressional state, as several sites were buried by lacustrine organic sediments at around 8500 years BP. The stratigraphical context of these sites appears to be systematically related to the basal hydromorphic sand, which was subsequently buried by organic deposits usually dated at the ninth millennium BP, therefore giving a terminus ante quem for the "Early Acacus" occupation in these lake areas. It is interesting that sites of this period have not yet been found on the Messak plateau. These "Early Acacus" sites of the lowlands are generally small (diameter 10 mm) and the frequent use

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Fig. 9. Different motifs of rocker decoration from a "Late Acacus" site (Uan Afuda cave). (1) A typical Dotted Wavy Line motif (actual size).

of vegetable tempers. The "rocker" technique is widely attested, mostly with the packed zigzag motif and more rarely with the Dotted Wavy Line syntax (Fig. 9). Pottery production is documented in the central areas of the Acacus from the first half of the ninth millennium BP at Uan Afuda (Cremaschi and Di Lernia, 1995) and Uan Tabu (Garcea, 1996). The analysis of pottery from the surface sites (Ponti et al., 1998; Cremaschi and Di Lernia, 1998) confirmed a scarce presence of "Late Acacus" pottery in the dune zones. This could be associated to a probable procurement of raw material and other resources by the ephemeral sites located in the ergs (indicating movement toward the quartzite outcrops of the Messak?). The substantial abandonment of the dune zones in favor of those mountainous was confirmed by many indicators of increasing sedentism that came from the Acacus shelters like Uan Afuda, UMG-wadi, Uan Tabu, and others, where there were important modifications in


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the material documentation. Organization of lithic technology, grinding equipment, and pottery seem to be the main indicators of increasing sedentism. We noted an increase in the macrolithic part of the industries, which was almost exclusively struck from silicified sandstone, the strong decrease in the blade and bladelet component, the healthy increase in the grinding equipment and the important production of pottery. Regarding the lithics, we still recorded an important component of backed tools, which seems to represent an element of continuity with the "Early Acacus" production. The increase in geometries (mostly lunates, but also triangles) seems to represent a trend which began with the former cultural phase. An important restructuring of the economic strategies was noted during the "Late Acacus." They changed from an economy of specialized hunting of Barbary sheep and modest use of plants during the "Early Acacus" to a more diversified economic base during this phase (Table II), with hunting of both small and large mammals, fish, birds and, above all, with a flourishing of wild cereal exploitation (Fig. 10) (Di Lernia, 1996; Castelletti et al., 1998). We registered at Uan Afuda (and probably also at Uan Tabu) interesting modalities of exploitation of Ammotragus lervia, with forms of cultural control documented by the forced enclosure of these animals between 8500 and 8000 BP, as seen in the accumulations of dung and forage in the more internal parts of the cave. It seems possible to hypothesize the containment of Barbary sheep and periodical slaughtering of the animals in particular periods (Cremaschi et al., 1996; Di Lernia and Cremaschi, 1996b; Castelletti et al., 1998; Di Lernia, 1998a). The absence of "Late Acacus" sites in the Tanezzuft and in the Messak seems to point to a privileged territory in the Acacus mountain range, with specific models of adaptation to a drying environment.

MIDDLE HOLOCENE OCCUPATION (CA. 7400-3500 YEARS BP) Early Pastoral (Ca. 7400-6400 Years BP) All available evidence indicates wet conditions mainly in the second half of the period (around 6900-6400 years BP), both in the mountain range and in the sand seas. Wet conditions coincide with a dense occupation of both areas as well as the Messak plateau. This fact is supported by the type of sediments in the cave (organic sand and humified organic matter) and pollen contents from the Mathendush cave (Trevisan et al., 1995) and Uan Muhuggiag shelter (Mercuri et al., 1998), which indicate a wet savannah at 6800 and 6900 years BP. Lake basins reached the highest stand, indicated by well-preserved strand lines both in the erg Uan Kasa and in Edeyen of Murzuq, at about 6600-6500 years BP. A continuity in the settlement system seems to be documented between the "Late Acacus" phases and the Early Pastoral. Actually, the distribution of sites

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Fig. 10. Basketry remains (58 x 33 mm) with Brachiaria/Umchlea seeds: (1) Front view; (2) back view. Provenance: Uan Afuda cave; layer 3mb, 14C dated to 8790 ±95 years BP—GX 20751.

seems to indicate a preference for the interior areas of the mountain range, probably for specific environmental conditions. The oldest contexts are indicated by several factors: most of the pottery was decorated by rocker technique and a different circulation of the lithic raw materials has been recorded (Di Lernia et al., 1997). It must be underlined that at the end of the eighth millennium BP, food production is

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attested at Uan Muhuggiag (Gautier, 1987), even if hunting activity (Gautier, 1987; Corridi, 1998) and exploitation of wild cereals are also well attested (Wasylikowa, 1992; Mercuri et al., 1998). The settlement pattern still has to be completely understood, but an articulated system seems to exist, which was probably based on movement between the mountains and the lowlands, according to seasonal variations. Middle Pastoral (Ca. 6100-5000 Years BP) The environment was quite similar to that of the previous period. However, a slight shift toward drier conditions can be seen, both from pollen diagrams indicating a dry savannah environment and from cave deposits, where organic matter was better preserved than before. The archaeological transition from the Early to the Middle Pastoral cannot be associated to any environmental change in the geological record. Actually, a break in 14C datings from 6410 to 6082 BP is present (Fig. 11), as also attested by the gap in their standard deviation. Due to the large number of datings, this gap cannot be considered as a random bias, but it could be cautiously related to a drop in human occupation. The causes of this phenomenon are still unclear. It could be due to a short-term dry period, which has not yet been found in the geological record. It is tempting to associate this break to the short or abrupt dry period recorded in several areas across the

Fig. 11. Chart with published and unpublished 14C datings from the Tadrart Acacus and Messak Settafet mountain ranges (after Cremaschi and Di Lernia, 1998).


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northern Africa (e.g., Hassan, 1996, 1997). We should also note the impact of some Saharan influences in the decoration techniques of the pottery found in the Nile Valley, as at Shagadud and Kabbashi (Caneva and Marks, 1990; Caneva, 1996). More information is necessary to comprehend fully this crucial period of Nilo-Saharan contact. A clear increase in well-defined sites in the lake zones, as well as an expansion into the easternmost areas of the Acacus is recorded during the Middle Pastoral, which is characterized by a marked presence of "Alternately Pivoting Stamp" decoration on the pottery. Raw material circulation also seemed to undergo important modification, with the increase in exotic raw materials (quartzite, flint) coming from the lake environment, represented largely in the mountains and many artifacts of silicified sandstone from the mountains present in the lake sites (Di Lernia el al., 1997). The mountainous sites are characterized by archaeological deposits consisting of alternating lenses of hearths that point to a continuous but intermittent occupation of these areas. These contexts could be attributed to seasonal, probably winter occupations by shepherds (Cremaschi et al., 1996; Mercuri et al., 1998), with an important frequency of ovicaprines (Gautier, 1987; Corridi, 1998). These sites are also distinguished by a coarse lithic industry, mostly on silicified sandstone, and by the recurrent presence of arrowheads of varied morphology. The economic base was integrated with hunting activity, with particular emphasis of rock hyrax (Procavia capensis), hare (Lepus capensis), hedgehog (Paraechinus cf. aethiopicus), porcupine (Hystrix cristata), dorcas gazelle (Gazelta dorcas), dama gazelle (Gazella dama), and Barbary sheep (Ammotragus lervia) (Corridi, 1998). In contrast, it is possible to identify in the lake areas several large sites (> 1 ha), whose size was obviously due to reoccupation, but where the recurrence of structural facilities seems to point to some kind of semisedentism, which was part of an east-west transhumance. The existence of structural facilities in the sites (fireplaces, waste pits) indicates new evidence for the lifestyle of these pastoral groups. Moreover, it is interesting to observe that domestic cattle was the most represented animal species in the archaeozoological record of these contexts. It is quite difficult to assign precisely the age of death to these animals (Corridi, 1998), which is essential for the analysis of the breeding strategies of these human groups (i.e., primary versus secondary use). In any case, the fact that the presence of cattle remains constant during the sixth millennium BP is of great interest. The pits found in the dune areas were used for the placement of ceramic containers, even of large dimensions (Fig. 12), and very rarely, a few lithic artifacts occur. A particular form of pit utilization was documented in some sites (e.g., 94/3), where they were used as hiding places for a few grinding-stones and hand querns. Furthermore, the beginning of systematic and intensive forms of raw material exploitation, particularly along the wadi scarps of the Messak Settafet has been recorded during the Middle Pastoral phases. Tens of quartzite quarries were

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Fig. 12. Middle Pastoral restored vessels unearthed from site Th 110 (1), in the Acacus mountain range; and at MT 127 (2), in the edeyen of Murzuq. (1) Height, 34 cm; (2) height, 29 cm.

identified, associated, in some cases, to specialized workshops (Di Lernia and Cremaschi, 1997). The circulation of artifacts (cores and blanks) coming from these specialized sites was once again found to be in relation to the sites of the lowlands, where, in fact, cores manifested a high degree of exploitation and a huge quantity of quarried lithics were found. Mining areas of silicified sandstone were recorded also in the Acacus, although quarries were less impressive and abundant than those recorded in the Messak (Di Lernia and Cremaschi, 1997; Di Lernia et al., 1997). The Middle Pastoral phase seems well documented also in the fluvial valleys of wadi Tanezzuft; however, the human groups seem to gravitate toward other, yet investigated territories. Indications of this phenomena came from the used raw materials, where a type of quartzite not recognised in the outcrops of the Messak Settafet was present (Di Lernia et al., 1997), which could be related to different areas. To sum up, the Middle Pastoral phase presents a complex dynamic that, on one hand, seems directed toward more "stable" ("semisedentary") settlements in the ergs, reoccupied several times, while, on the other, shows the use of the mountainous zones, which implies a connection to sheep and goat shepherds, which reach the mountains during the winter seasons. The scarcity of cattle in the


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Acacus archaezoological record can be explained by the contextual presence of sites with abundant recoveries of these animals in the ergs, whose consumption almost exclusively took place in the dune areas. Finally, the increasing number of sites could be testimony of possible demographic growth. Late Pastoral (Ca. 5000-3500 Years BP) The most dramatic environmental change in the area, related to the onset of dry conditions, took place at around 5000 years BP. The mountain range and, namely, the Messak Settafet plateau were covered by desert varnish, which is indicative of a moderately dry climate and corresponds to a dry steppe plant cover (Cremaschi, 1996;Trevisan et al., 1998). Dryness induced the collapse of cave and shelter vaults in several localities along wadi Teshuinat and surroundings. The dung deposits inside were preserved in an unweathered state, as the dry environment prevented any bacterial activity (Cremaschi et al., 1996). Aeolian sand intercalated with the dung deposits confirms a desert landscape and indicates a discontinuous use of shelters by nomadic communities. Even if no direct dating has been available up to now, it is highly probable that the greater part of the lakes transformed into sabkhas at that time. Fluvial activity and water availability are attested at 3800 years BP along the wadi Tanezzuft at the western margin of the studied area. Drying was certainly completed by 2300 years BP. From 5000 BP, which could be used as a conventional beginning date for the Late Pastoral, a large number of dry season sites have been recorded in the mountain range (Cremaschi and Di Lernia, 1996a; Trevisan et al., 1998). The elevated frequency of these sites, however, is essentially due to both visibility and a good state of preservation of organic matter (i.e., dung). The diversified use of the shelters, the increase in the undecorated pottery, the exclusive use of ovicaprines, and the specialized forms of pastoralism, are all distinctive features of this phase. The lake areas were almost completely abandoned with the presence of ephemeral camps, with few stones relative to hearths and scarce lithics being recorded. The manufacture of the lithic industry was almost exclusively of quartzite, and a notable increase in exotic elements, such as polished tools and axes on metamorphic/volcanic rocks (Di Lernia et al., 1997), and many "predynastic" tools was recorded. Hence, the high mobility practiced during this period can be seen in the presence of raw materials and tools deriving from contexts even some hundreds of kilometers away, and also by the specific characteristics of the sites. It is possible to hypothesize an ample year-round regional circulation for these Pastoral groups, as attested by ethnographic studies on Tuareg people effected in the southern Sahara (Smith, 1980). In an environment ever more dominated by increasing aridity, fluvial valleys, and their paleo-oases became a focal point of human concentration, which may have favored some forms of sedentism, with intensive use of plant resources.

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GENERAL OVERVIEW At the end of the Pleistocene and beginning of the Holocene, the Tadrart Acacus and surrounding areas show wet conditions, and a subsequent progressive climatic decline. This process was interrupted by at least one arid oscillation, which is documented both in the mountain ranges and in the lake basins in the lowlands. It is still difficult to date this dry peak precisely, considering the available data: probably, it is placed between 8000 and 7300 years BP. The onset of wet conditions in the Acacus and surroundings seems to precede, by at least 1000 years, the humid periods of the other Saharan areas, as well as the onset of aridity, which seems to precede the drying of other regions. At the margins of the study area we have evidence of fluvial activity at wadi Tanezzuft at 3800 years BP. Human groups appear to track the climatic episodes, giving origin to significant adaptations to the general palaeoenvironmental conditions. Actually, we would like to stress that no ineluctable coincidence exists between climatic changes and cultural dynamics: environmental change does not directly determine any human adaptations; instead, cultural responses varied depending on specific external and internal cultural factors, with different times and modalities of realization. Probably, only the onset of dramatic arid conditions produced effective changes in human occupation during the Late Pastoral. The general framework summarized herein provides a preliminary contribution to the understanding of the cultural dynamics in the area, through a regional scale of analysis. The first Holocene occupation of the area does not appear to be related to any Pleistocene occupation, but rather to the arrival of human groups, probably following the Sahelian belt. Evidence of a northward shift of the monsoon is well attested across the Sahara (Hassan, 1996), and we cannot discard the hypothesis of a southern provenance for the aceramic "Early Acacus" human groups (Di Lernia, 1997b, 1999). Unfortunately, no funerary remains belonging to this first Holocene phase of occupation have yet been found and therefore it appears difficult to provide further support to this hypothesis. The general features of the lithic industry do not show strict relationships with other lithic complexes since emphasis on a backed tool-kit is a general feature of early Holocene North African assemblages, as stressed by Close (1987). Therefore, it seems still premature to refer these assemblages to some specific North African lithic facies. The environmental conditions of this phase seem to have favored an abundance of resources, making specialized forms of hunting possible. However, this phase lasted around 1000 years, and fluctuations may have affected the economic strategies. Even if relationships between base camps in the mountains and the small specialized sites in the lowlands, around ponds and shallow lakes, remain hard to decode, they may be related to the existence of a differentiated exploitation of the environment. It is tempting to suggest a dispersion of groups during the wet seasons (i.e., summer) and their aggregation during dry seasons (i.e., winter) being indicated by the greater size of settlements, formation processes, and quantity of


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artifacts. We have to take into consideration the possible existence of base camps also in the lowlands, probably in relation to permanent water reserves. In this way, the sites of Edeyen of Murzuq, which do not show any relationship to the nearby plateau of Messak Settafet, may present some interesting differences in settlement systems. At the end of the "Early Acacus" phase, ca. 9000-8900 years BP, we have evidence of increasing aridity, indicated by the increase in the aeolian sand fraction in the layers of Uan Afuda cave. The "Late Acacus" hunter-gatherers reoccupied the same areas in the mountain range, but not extensively in the lowlands. The "Late Acacus" phase is recognized archaeologically by the presence of specific indicators, i.e., ceramic sherds with rocker decoration, and by a shift in the organization of lithic industry. We cannot discount the possibility of having underestimated the numerical frequency of this phase in the dune areas, but a general trend seems to emerge. Human groups were concentrated in the mountain areas, practically ignoring the lowlands and the Messak Settafet plateau, and an important shift is recorded in site formation processes. They were probably larger than the previous "Early Acacus" sites and are now formed by massive accumulations of plant remains. A different intrasite organization is evident in the formation of specialized areas for fire, fodder stocking, and probably animal corralling. Uan Afuda seems to be the most interesting site, but several other sites in the Acacus, yet to be excavated, show similar features. In the Acacus range, starting from ca. 8800 years BP, there is a general trend toward more wild cereal exploitation (Urochlea/Brachiaria type) and the use of grinding equipment. This cultural phenomenon may be, in part, related to the drying process of the environment. The progressive drying of ponds and shallow lakes in the lowlands, which may have been avoided by humans for health reasons, are among the possible effects of such a transition. We are not able to link climatic and cultural processes precisely, but it is tempting to suggest a progressive concentration of people in the mountain range, leading to intragroup stress and competition and a different approach to resource exploitation. A shift toward a broad spectrum of resources and forms of planned exploitation are a typical response of hunter-gatherers in a critical situation, such as increasing density or imbalance between population and resources (e.g., Binford, 1983). In the Acacus, we have some evidence of storage (pottery, rock-pits, basketry), but more interestingly, the cultural control over wild animals, such as Barbary sheep (Di Lernia and Cremaschi, 1996b; Di Lernia, 1998a). The slaughtering of animals in certain periods of the year may have favored some forms of (also ideological?) control over animals and then favored the introduction of domesticated animals into the economic basis. The relationships between "Early Acacus" and "Late Acacus" huntergatherers are still to be completely understood. Until recently, the "prepastoral" phase in this region was considered a cultural continuum (Barich, 1987), but differences in site formation processes, settlement patterns, economic basis, and material culture seem to be sufficient to suggest a cultural discontinuity. Whether this

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discontinuity has to be referred to as "simple" cultural adjustments to a stress by the same people or to a real external influence is uncertain. Theoretically, we are inclined to favor the first hypothesis, even if some evidence of external influence may exist, as the introduction of pottery in the archaeological record seems to show. Radiocarbon dating is indicative of a first local ceramic production in the southern Saharan sites (9500-9000 years BP) and a northern shift some hundreds of years later (starting from ca. 8800 years BP), but the forms of transmission of this new technology are still hard to decode (Di Lernia, 1999). A site with both a prepastoral and a pastoral phase has yet to be excavated in the central Acacus. The understanding of such a crucial stage of the local history is based on sites belonging to different phases, and the relations between them are still merely speculative. Actually, there is no continuity in the archaeozoological record of the "Late Acacus" and "Early Pastoral" phases. This seems to suggest an external provenance of domestic cattle, even if the antiquity of some faunal assemblages led to the earlier hypothesis of a local autonomous domestication in the area (Mori, 1965; Barich, 1987). An eastern introduction of cattle seems to be the most plausible hypothesis: moreover, a contemporaneous introduction of cattle and ovicaprids may be possible, rather than first the introduction of cattle and then a subsequent addition of domestic sheep and goats: the contemporaneous presence of cattle and ovicaprids in the most ancient Pastoral layers (Uan Muhuggiag; Uan Telocat) seems to confirm the former hypothesis. The increasing cultural complexity of "Late Acacus" hunter-gatherers and their cultural control over Barbary sheep may have favored the introduction of domesticated animals, whose frequency in the faunal record grew quickly (Di Lernia, 1998a, 1999). The settlement system of these Early Pastoral groups seems to prefer the interior areas of the mountain, even if the ponds in the lowlands were also frequented. It is tempting to suggest a preferential exploitation of the mountain areas, with some forms of seasonal transhumance in the lowlands. The climatic amelioration of the first half of the seventh millennium BP led to a flourishing of sites, with a progressive expansion in the lowlands. A short dry period may have occurred at the end of the seventh millennium BP, indicated by a drop in the number of the radiocarbon dates, which may be carefully considered as evidence of a less dense human occupation. It would be quite interesting to look for such a gap in the archaeological record of the surrounding regions, identifying the possible spread of pastoral groups across the Sahara. Whether the gap has to be considered as a hiatus in human occupation or as a flaw in 14C sampling, the Middle Pastoral seems to show some elements of continuity, with regard mainly to the material culture. Conversely, by considering the regional analysis of site distribution, a different settlement system seems to emerge. Sites are larger and more numerous in the lowlands, located along the shores of the ancient lakes, in the period at their maximum level. Sites in the mountains are smaller, and characterized by thin layers mostly of ashes and hearths, the material culture is scanty, and the economic basis shows an integration of


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herding and hunting activities. The hypothesis of an East-West transhumance on a seasonal basis seems to be consistent with the available data. There are several clues indicating that the Middle Pastoral was a "new" development in the area. For the first time in local history, the lowlands predominate on the mountains, and human groups seem to control regularly all the territory in a cultural network testified by the capillary expansion of the sites to the first and second terraces of the mountains and in each of the corridors of the dune areas. The systematic exploitation of raw material in the Messak and Acacus and the new forms of cultural expression such as site organization and funerary practices also indicate this "new" period. The onset of the dramatic arid conditions led to a more effective relationship between climate and humans in this area. Progressive desiccation of ponds and shallow lakes made these areas inhospitable and unhealthy, and only small transient camps still survived in the dune areas. Sites were reduced to a few fireplaces, with scanty archaeological finds. Rock shelters and caves in the mountain ranges were used as dwellings for sheep and goats, and cattle almost disappear from the archaeozoological record. The sites were used during the dry seasons, when the mountain ranges were more favorable to human and animal occupation, a sort of refuge in a dramatic landscape. Cultural response, in this case, seems to be really related to environmental forcing, and high mobility seems to represent the best adaptation to the environment. Large-scale movements are evident in the archaeological record, suggesting relations with the mountain ranges of the Tibesti and possibly farther eastward with the Nile Valley. But cultural responses may differ, even if environmental conditions are the same, and the increasing sedentism recorded in the paleo-oases located in the fluvial valleys may represent a different human strategy in adapting to an ever-drier climate. ACKNOWLEDGMENTS This research has been done within the Italo-Libyan Joint Mission. We wish to thank Ali Khadduri, Director of the Department of the Antiquities, and Fabrizio Mori, Director of the Joint Mission, for their help and friendship. Special thanks go to Ebrahim Azzebi and Mohammed Meshai for their support in the fieldwork. REFERENCES CITED Aumassip, G. (1984). Le site de Tin Hanakaten et la neolithisation sur les marges orientales du Sahara central. Cahiers ORSTOM, Ser. Geol. 14(2): 201-203. Aumassip, G., Clark, J. D., and Mori, F. (eds.) (1996). The Prehistory of Africa, XIII Congress UISPP, Colloquium XXX, Vol. 15, ABACO, Forli. Barich, B. E. (ed.) (1987). Archaeology and Environment in the Libyan Sahara. The Excavations in the Tadrart Acacus, 1978-1983, BAR International Series, 368, Oxford. Barth, H. (1857). Reisen Entdeckungen in Nord und Central Afrika, Perthes. Binford, L. R. (1983). In Pursuit of the Past, Thames and Hudson, London.

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