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Palynological analyses of the Late Pleistocene, Early Holocene and Middle Holocene layers
... A more significant change towards aridity occurred during the Late Acacus, as was sedimentologically and stratigraphically attested to at Uan Tabu from Unit II to Unit I, which are both part of the Late Acacus horizon. Pollen spectra indicated a reduction of the savannahlike vegetation and an increase of shrubs, favoring a diversification of the habitats (Mercuri and Trevisan Grandi, 2001;Mercuri and Garcea, 2003). ...
... Herbs were dominant in the pollen spectra and were mainly harvested for food. No cereal pollen types were recovered in the Early Acacus deposit (Mercuri, 1999(Mercuri, , 2001Mercuri and Trevisan Grandi, 2001;Mercuri and Garcea, 2003). ...
... Unit II, dated to 8800-8900 B.P., indicated that a large spectrum of plant resources was exploited and the accumulation of plants doubled. Unit I showed a higher specialization over a slightly reduced spectrum of plant resources, with an intensive exploitation of cattails (Typha) (Mercuri and Trevisan Grandi, 2001). Cattails could have been used for food, bedding, weaving, and/or building. ...
Food production originated in various ways in different parts of the world. Plant domestication with the adoption of agriculture has been successful in some areas, but not in others, where animal domestication with nomadic pastoralism proved to be more effective. Likewise, the preceding phases of pre-adaptation and development of a broad spectrum of wild resource exploitation followed different pathways, according to the locally available resources, climatic and geographic conditions, and social organizations. Northern Africa greatly contributed to the understanding of the origin of food production under preconditions that differed from those in the Fertile Crescent. Apart from a narrow strip along the Nile valley, northern African lands are arid and scarcely productive for agriculture. Nevertheless, early studies interpreted northern African archaeological records of the Early and Middle Holocene according to the traditional north-western Mediterranean and Near Eastern frames of reference. Consequently, terms such as Epipalaeolithic, Mesolithic, and Neolithic were uncritically applied to northern African contexts. This paper compares and discusses the evidence for food production in the Near East and northern Africa, considering the question of introduction or local breeds of domesticated animals in the Maghreb and the Sahara. It then reviews the relevant data for long-held diffusionist models of pastoralism into Africa to provide a different perspective and the proper means of interpretation of the northern African archaeological records. Finally, it examines some recent findings from the Tadrart Acacus, in the Libyan Sahara, which contribute to clarification of distinctive African pathways and propose an alternative model for the beginnings of food production.
... Stratigraphic and artefactual changes evidenced the shift from the Early Acacus to the Late Acacus, whereas no environmental shifts appeared during this transitional phase (Cremaschi and di Lernia 1999). A climatic change towards aridity occurred during the Late Acacus with pollen spectra indicating a reduction of the savanna vegetation and an increase of shrubs (Mercuri and Trevisan Grandi 2001). Pottery occasionally appeared in the Early Acacus, but became common in the Late Acacus. ...
... With regard to subsistence base, Barbary sheep hunting predominated in the Early Acacus and decreased in the Late Acacus to about 45-60 per cent in favour of the Plate 1 Impressed pottery with dotted zigzags from Uan Tabu. exploitation of a broader faunal spectrum, Barbary sheep corralling and delayed and planned resource consumption of both animals and plants (Gautier 1987;di Lernia 1999di Lernia , 2001Mercuri and Trevisan Grandi 2001;Garcea 2003). The formation processes of the stratigraphic sequence at Uan Tabu, as well as at the nearby site of Uan Afuda, indicated that an organic colluviated unit was reworked with coprolites that accumulated during multiple colluviation phases (Cremaschi and Trombino 2001). ...
Early Holocene foragers in North Africa provide unique responses to adaptational patterns of non-agricultural societies and they can offer intriguing answers to questions regarding relationships between sedentism, economy and sociocultural complexity. Three points are of major relevance for understanding late foragers in North Africa: first, fishing, sustained by reduced mobility, was a common practice at sites located along perennial rivers, such as the Nile, or seasonal watercourses (wadis); second, the successive shift to a food-producing economy implied the acquisition of nomadic pastoralism; third, agriculture has never been a feasible economic practice in desert and peri-desert environments. The practice of fishing and the scarcity of moist lands away from watercourses encouraged more permanent settlement of sites by the water, which offered nutritional resources to plants, animals, as well as humans. The combination of these economic adjustments and environmental conditions favoured social organizations based on continual occupations of semi-permanent settlements and led to a population increase, which – in turn – triggered the rise of sociocultural complexity and new technological productions, such as pottery and groundstone, before the adoption of any form of food production.This paper presents the socioeconomic dynamics of Early Holocene foragers in North Africa and offers examples from the Central Sahara and the Upper Nile Valley, where the author has conducted research for almost two decades.
... Micromorphological studies have also demonstrated to be valuable for the analysis of site formation processes, to identify functional areas, and in the recognition of sin/post-depositional processes that shaped corral deposits (Canti 1998;Cremaschi and Trombino 1999;Karkanas and Goldberg 2013;Matthews et al. 2014;Shillito et al. 2018). As regards the site formation processes, micromorphology may be correlated with zooarchaeological and pollen analyses Mercuri et al. 1998;Mercuri and Trevisan Grandi 2001;Rasmussen 1993;Trevisan Grandi, Mariotti Lippi, and Mercuri 1998) to provide additional information. ...
The archaeological landscape of the Tadrart Acacus massif (SW Libya, central Sahara) is made of sites testimony of complex systems of cultural-specific settlement and economic strategies stretching over millennia of occupation. Here, caves and rock shelters represent the main physiographic features exploited by prehistoric herders. Climate fluctuations, settlement patterns and economic strategies regulate the depositional and post-depositional processes documented in the excavated sites. In this regard, the site of Takarkori, thanks to its well-preserved archaeological record, which was extensively excavated, represents a highly valuable archive of past societal activities. We show how a multifaceted analysis of deposits and sediments of anthropogenic and biogenic origin, like dung and coprolites accumulations, may broaden the reconstruction of the cultural dynamics and variability of the Saharan Late Pastoral Neolithic (5700-4650 cal BP). Analysis of spatial distribution coupled with micromorphological investigation increased the reconstruction of the shelter's organisation and use, including its deposit’ formation processes. Pollen analysis highlighted aspects of seasonality among Late Pastoral herders attending the site, also contributing to deepen our knowledge on palaeoenvironment of Middle Holocene Sahara.
Existing pollen datasets from northern Africa stored in the African Pollen Database were used to assess changes in landscape physiognomy at the end of the African Humid Period (AHP) from 5000 cal yr BP to the present using arboreal pollen percentages. The thirty-six sites available were used to map changes in arboreal cover at a sub-continental scale. Based on their location in present-day forested and non-forested areas and their relatively higher temporal reso- lution eight of them were selected to examine the timing and amplitude of the vegetation response in more detail, and particularly in the Sahel. In spite of low pollen production and dispersal of many tropical plants, which lead to the under representation of most of the trees relative to their abundance in the landscape, we were able to distinguish the geographical pattern and timing of vegetation changes. The landscape response to the end of the AHP was far from homogeneous particularly in the Sahel where a clear east-west gradient of changing tree cover is indicated with the central Sahel being notably species poor. In areas where forests were well developed during the AHP, i.e. in the south and west, the establishment of the modern landscape was abrupt with a threshold crossed between 3300 and 2500 cal yr BP according to local conditions. Elsewhere in northern Africa the switch from tree (C3) to grass (C4) dominated landscapes occurred more gradually during the same period. This review shows that the timing of the ecosystem response at the end of the AHP was remarkably synchronous throughout northern Africa.
Plant foods play an important role in the human diet and the ability to grow, store and extract nutritive potential from plants has had a transformative role in human history. During the Holocene, the invention of thermally resistant ceramic vessels, regarded as a crucial step in human technological progress, provided new opportunities to boil plants such as wild grasses, fully unlocking the potential of such plants as foodstuffs. This allowed a broadening of subsistence bases, increased dietary diversity, a greater variety of nutrients and more stable and palatable foods. Pottery was invented early in north Africa, at c. 12000 cal BP, where it was first made by semi-sedentary hunter-gatherers, raising questions as to what this early pottery was used for. Combined molecular and isotopic techniques revealed the presence of diagnostic plant lipids, including leaf waxes and seed oils, in pottery from Holocene sites in the Libyan Sahara and Mediterranean north Africa, suggesting the processing of grasses, seeds and aquatic plants. In combination with archaeobotanical evidence from sites across these regions, these data provide insights into the wide range of plants exploited in Holocene north Africa, providing information on dietary and subsistence practices of human groups across north Africa and confirming the importance of plant processing in the earliest pottery vessels in both regions.
A comprehensive understanding of the relationship between land cover, climate change, and disturbance dynamics is needed to inform scenarios of vegetation change on the African continent. Although significant advances have been made, large uncertainties exist in projections of future biodiversity and ecosystem change for the World’s largest tropical landmass. To better illustrate the effects of climate-disturbance-ecosystem interactions on continental-scale vegetation change, we apply a novel statistical multivariate envelope approach to subfossil pollen data and climate model outputs (TraCE-21ka). We target paleoenvironmental records across continental Africa, from the African Humid Period (AHP: c. 14,700-5,500 years BP) – an interval of spatially and temporally variable hydroclimatic conditions – until recent times, to improve our understanding of overarching vegetation trends and to compare changes between forest and grassy biomes (savanna and grassland). Our results suggest that although climate variability was the dominant driver of change, forest and grassy biomes responded asymmetrically: (1) the climatic envelope of grassy biomes expanded, or persisted in increasingly diverse climatic conditions, during the second half of the AHP whilst that of forest did not; (2) forest retreat occurred much more slowly during the mid to late Holocene compared to the early AHP forest expansion; and (3) as forest and grassy biomes diverged during the second half of the AHP, their ecological relationship (envelope overlap) fundamentally changed. Based on these asymmetries and associated changes in human land use, we propose and discuss three hypotheses about the influence of anthropogenic disturbance on continental-scale vegetation change.
During the ‘Green Sahara event’, water bodies developed throughout the Sahara and Sahel, reflecting the enhanced influence of the Atlantic monsoon rainfall. Major lakes then dried out between 6.5 and 3.5 ka. This study investigates land cover change and lacustrine environment during the Holocene at I-n-Atei, Southern Algeria, a desert region lying in the hyperarid core of the Sahara. This site is remarkable by its extent (up to 80 km2) and by the exceptional preservation and thickness of the lacustrine deposits (7.2 m). I-n-Atei was a lake from 11 to 7.4 ka, then it dried out and left place to a swampy environment. Charcoal concentrations show that the surroundings of the lake were vegetated throughout the wet period with two short phases of possible vegetation deterioration associated with a lowering of the lake level at 9.3 and 8.2 ka, coeval with well-known dry events in the tropics. The stable carbon isotope record reflects the penetration of C4 herbaceous populations in replacement of the original C3, typical of the regional vegetation at the time of the maximum lake expansion. The δ13C of charcoals increase non-linearly with the 14C-based ages from − 24.5‰ to − 13.0‰ (V-PDB). Assuming that these extreme values sample both C3 and C4 plant end-members, mass balance calculations suggest that C3 were replaced by C4 plants according to an exponential decay law with a half-life (t1/2) of 850 ± 110 years. The replacement of C3 by C4 plants occurred in two main steps: a mixed C3–C4 vegetation of “wooded grassland” type was present from 10 ka to 8.4 ka while a C4 exclusive vegetation developed after 8.4 ka. After the end of the lacustrine phase a catastrophic event (flooding?) provoked the lifting of most of the lacustrine deposits and their re-deposition above the lacustrine sequence.
Although past climate change is well documented in West Africa through
instrumental records, modeling activities, and paleo-data, little is
known about regional-scale ecosystem vulnerability and long term impacts
of climate on plant distribution and biodiversity. Here we use
paleohydrological and paleobotanical data to discuss the relation
between available surface water, monsoon rainfall and vegetation
distribution in West Africa during the Holocene. The individual patterns
of plant migration or community shifts in latitude are explained by
differences among tolerance limits of species to rainfall amount and
seasonality. Using the probability density function methodology, we show
here that the widespread development of lakes, wetlands and rivers at
the time of the "Green Sahara" played an additional role in forming a
network of topographically defined water availability allowing for
tropical plants to migrate north from 15 to 24° N (reached ca. 9 cal
ka BP). The analysis of the spatio-temporal changes in biodiversity,
through both pollen occurrence and diversity, shows that the core of the
tropical rainbelt associated with the Intertropical Convergence Zone was
centered at 15-20° N during the early Holocene wet period with
comparatively drier/more seasonal climate conditions south of 15° N.
Dendroclimatology of Cupressus dupreziana, the Tassili cypress, has been attempted on samples obtained from the door beams of the old cities of Ghat and Barkat located at the foot of the Tassili, where the cypress still lives. The tree rings of 20 samples were measured and dated by 24 AMS 14C dates. A mean ring-width chronology has thus been obtained, spanning, though discontinuously, 5220 to 100 14C BP (5990-65 cal. BP). As the tree-ring width in dry lands depends mainly on water availability, the mean ring-width chronology represents a detailed record of changes in rainfall on a decade scale for the middle and late Holocene of the central Sahara. It indicates main drought spells at 5200-5000 14C BP (5900-5760 cal. BP) and at 4350 BP (5120 cal. BP), followed by phases of enhanced precipitation and by the onset of extreme arid conditions at 1550 14C BP (1500 cal. BP).
Pollen analyses of 13 archaeological sites in the Wadi Teshuinat area, in southwestern Fezzan, Libya, were synthesised to explore the po-tential contribution of palynological investigation to archaeological research in this area. During the Holocene, the sites were occupied by pre-Pastoral (hunteregatherers) and Pastoral (pastoralists) cultures. Different pollen stratigraphies and floras characterised the diverse sites and the relevant cultural phases. Pollen data were reported by discussing the sites separately, and by combining them to interpret the regional data set. Emphasis was made on the anthropogenic pollen indicators and grasses, including large grass pollen grains (>40 mm), which were considered evidence of plant transport into the site. These were ethnobotanical markers, human-made evidence of plant harvesting by hunteregatherers, or of animal breeding by pastoralists. The disappearance of some wild cereals was also observed, consistent with increasing climate dryness and land exploitation. Macroremains were used as a parallel tool to better understand plant exploitation in the region.
a b s t r a c t Central Sahara rock shelters offer an early and middle Holocene environmental reconstruction. This paper summarises palynological research carried out within a multidisciplinary archaeological research project on the Wadi Teshuinat area (Tadrart Acacus Mts., in south-western Fezzan, Libya). The sites were occupied by hunter-gatherer and pastoralist cultures. On-site pollen data, treated as a single 'regional site', showed that different pollen stratigraphies and flora characterised the past phases. Plant macro-remains also helped to understand local plant exploitation and landscape evolution. Pollen spectra showed the following climate oscillations: wet and cool (approx. 8800–8250 cal. BC), dry and warm (approx. 7920–7520 cal. BC), wet (approx. 7550– 7200 cal. BC), dry (approx. 6340–6210 cal. BC—geoarchaeological evidence), wet and warm (approx. 6250–4300 cal. BC, including a wetter and warmer phase at approx. 5500–4600 cal. BC); dry and warm (approx. 4250–2900 cal. BC); drier and warm (approx. 2900–1600 cal. BC, up to the present). Since the early Holocene, both climatic and anthropic factors have played an important and strictly interconnected role in transforming the environment. Thus, while subsistence strategies were adjusting to climatic and environmental changes, the plant landscape was also being slowly and continuously shaped by humans.
In the Central Sahara lying approximately between 27° N and 18°
N, rains were primarily due to tropical depressions in the early
Holocene up to about 6500 BP. Then the monsoon rains of Sahelian type
dominated up to about 4400 BP.
Pollen analysis was made of sheep's faecal pellets, collected at various times during the period 1974–1977 from a paddock and from pastures, both near Bergen in western Norway. The results are compared with the available data for the seasonal pollen rain from the same area. No relationship was found between the pollen rain composition and the pollen content of dry fodder samples, harvested in the same area. Pollen analysis of faeces provide virtually no information about the quantitative composition of the vegetation of the sheep's environment, but do provide valuable information about their diet.
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 rcognitions et fouilles systmatiques ont t conduites dans le Tadrart Acacus et dans les zones circonvoisines; ces tudes ont donne des nouvelles information en ce qui concerne les changements climatiques et les dynamiques culturelles de cette rgion pendant l'Holocne. Dans ce papier, les vidences gologiques, gomorphologiques, et archologiques ont t intgres afin d'obtenir une synthse prliminaire sur la prhistoire de la rgion.
At Uan Afuda, and other Early Holocene sites of the Acacus mountains, in the Libyan Sahara, dung layers and plant accumulation are a major, but repeatedly neglected, feature of hunter-gatherer communities. To understand the formation and meaning of such features, a multidimensional analysis has been undertaken, combining micromorphological, palynological, botanical, archaeozoological, and archaeological data. The hypothesis here formulated is twofold: plant accumulations are evidence of anthropic activity aimed at the storage of fodder; and dung layers are related to a forced penning of a ruminant, very likely Barbary sheep (Ammotragus lervia). The exploration of these two features has hinted at the existence of a deep reciprocal relationship, which has been interpreted as the cultural control of wild Barbary sheep, leading to a delayed use of food resources. This behavior may be considered an opportunistic strategy adopted to minimize the effects of lean periods and implicates increasing cultural complexity within Late Acacus Saharan forager societies of the 9th millennium B.P.
This paper presents a compilation of eolian-based records of late Quaternary climate changes in the Sahara. Although the data are relatively sparse, when viewed as a whole, they reveal a general pattern of widespread eolian sediment mobilization prior to 11,000 cal. years bp, eolian sediment stabilization from 11,000 to 5000 cal. years bp, and a return to widespread eolian sediment mobilization after 5000 cal. years bp. Furthermore, an eolian-based record from southern Tunisia reveals the existence of millennial-scale changes in eolian sediment behavior. These millennial-scale variations provide examples of eolian sediment responses to climate changes at a scale intermediate between seasonal and orbital (‘Milankovitch’) changes, and they are also coincident with abrupt atmospheric and oceanic changes. The general synchroneity of the eolian stratigraphic records and their coincidence with various oceanic and atmospheric changes suggest that global forcing mechanisms have influenced late Quaternary eolian sediment behavior in the Sahara.
Following introductory comments on the nature of plant fossils (eg. how age is determined, systematic relationships, reconstruction and nomenclature), chapters trace the evolution of different forms from the Precambrian through to the 'living fossil', Ginkgo. The last 4 chapters provide overviews: discussion of the first coniferophytes; the diversification of conifers and taxads; the origin and early evolution of angiosperms; and major evolutionary events and trends - a summary. Throughout, description (including many line drawings) is linked with functional and evolutionary development. -P.J.Jarvis
Draws together information on how far archaeological sites, including occupation sites, may themselves serve as sources of pollen data that can be related directly to human activities in the past. Having reviewed the principles and techniques of soil pollen analysis, the author examines the opportunities provided by waterlogged sites, old land surfaces, open sites, and caves and rock shelters. Chapters outline both the scope for interpreting structures from pollen analysis, and the problems and challenges that arise from biased pollen spectra. -J.Sheail
Paleohydrology and paleoecology of the region around the Chemchane sabkha (Mauritania) are reconstructed from the comparative analyses of mineralogy, stable isotope ratios of bulk carbonates, and palynology from sediment cores. The age of the section is from ca. 13.5 ka to the middle Holocene. Maximum lake expansion between about 8.3 and 6.5 ka is recorded in a girdle of stromatolite carbonates. These document a lower-salinity lake concomitant with a general establishment of Sahel-Sudan vegetation. The Chemchane area is the northernmost (lat 21°N) occurrence of humid- phase elements that are related to maximum intensity of monsoon activity during the early Holocene.
Palaeoenvironments are reconstructed from the diatom flora of Holocene swamp and lacustrine sediments which lie in closed depressions of the Chad basin (Niger).
The geological and hydrological setting of the sedimentary profiles investigated is presented in section I. Three types of hydrological environments are considered: depressions which have been connected with L. Chad during the Holocene, small river-fed basins outside of the maximum extension of L. Chad, and depressions which have been mainly supplied by groundwater.
Methods used for palaeoecological reconstruction are discussed (section II) on the basis of the present-day distribution of diatom species and communities in the investigated zones. Attention is drawn to the diversity of the habitats in a given waterbody, and on the potential effects of seasonality and water stratification on the composition of diatom assemblages contained in the sediments. Because of the spatial and temporal changes in diatom communities, the sediment may integrate a mixture of communities with different ecological requirements. Thus, mean values of individual ecological variables deduced from a fossil assemblage are not sufficient to characterize a palaeoenvironment.
In section III, a classification of the palaeoenvironments is proposed. One attempts to distinguish the different communities contained in the fossil assemblages. The fossil communities are compared to diatom populations living today in the studied zones, or in other African sectors when no regional analogue has been found, and for which ecological conditions are known. This allows environmental characteristics to be inferred from sedimentary profiles. At a given time, the palaeosystems show the same ecological diversity as the modern ones.
The main status of the palaeoenvironmental evolution are then drawn for each stratigraphical profile (section IV), for an understanding of their causes. The major climatic tendancies affecting intertropical Africa have been chiefly responsible for the presence or absence of aquatic environments in the closed depressions. Superimposed to that, the diversity and the evolution of the individual palaeoecosystems have been controlled by local topographical and hydrological factors (origin of water, permeability of lake floor. . ). This is a common situation for waterbodies lying in tropical arid and semi-arid zones, and especially for palaeolakes associated to groundwater circulations. Therefore, palaeolimnological data can hardly serve as direct and accurate climatic indicators, if they are not corrected for the effects of local hydrology.
Palynological investigations of corings in the sebkhas of Taoudenni (N-Mali) and Segedim (N-Niger), archaeological excavations in the Acacus Mts. (SW-Libya) and charcoal records in the central Ténéré (Niger) give evidence for a northward shift of the desert-savanna boundary to 22°–20° N during the middle Holocene. Between Niger and S-Libya there was a ecological gradient from the sudanian, sahelian and saharan savannas to a denser saharan desert vegetation. After a transition phase between 6000 and 4000 BP the saharan desert vegetation was finally established in the Taoudenni and Segedim region and this degraded from ca. 2000 BP to its present condition.
During the middle Holocene the central Sahara had a monsoonal summer rain climate with an effective rainfall of 250–300 mm per year near the desert-savanna boundary (ca. 22° N). Interaction between the monsoon and the atlantic cyclones also allowed rainfall in other periods of the year.
Regions beyond the present or past penetration of the Indian and African monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14C kyr.Pollen and lake records from West Asia (Western Tibet and Rajasthan), East Africa (Ethiopia) and West Africa (Western Sahara, Sahel and subequatorial Africa) were selected on the basis of chronological control, sensitivity of both site and environmental indicators to climate change, the continuity of the record, and interdisciplinary control of the palaeoclimatic interpretation.Conditions wetter than those of today prevailed during the early-mid-Holocene period, but major dry spells are recorded at all sites during the intervals ∼ 11.0–9.5 kyr BP, ∼ 8–7 kyr BP and 3–4 kyr BP. Several records also suggest dry events of minor amplitude around 6 kyr BP. Potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed. The solar radiation accounts for the general envelop of the post-glacial monsoon fluctuations, but explains neither the timing nor the amplitude of the short-term changes. In spite of apparent covariation between fluctuations in sea surface conditions in the North Atlantic and the monsoon record, no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength. Changes in tropical land surface conditions (soil moisture negative feedback, and changes in CH4 production from wetlands) provide a more satisfactory hypothesis for explaining abrupt reversal events.
In the mountains of the central Sahara (lat ca. 20° to 22°N, long 16° to 19°E) and particularly in the Tibesti mountains, important lacustrine formations developed during the late Pleistocene, primarily during the Last Glacial Maximum (LGM). Two main phases, separated by a brief regression, intervened between ca. 20,000 and 15,500 BP, and between 15,000 and 12,500 BP. Pollen analyses were carried out on four samples of this formation. The high lacustrine levels were associated to both important precipitations and a reduced evaporation linked to lower temperatures. Similar lacustrine deposits were found in the Djebel Marra in the south of the Sahara. In the mountains of the central and eastern Sahara, during the same period and until the middle Holocene, the “Middle Terrace” Formation was deposited in the river valleys of the Tibesti, Hoggar, Air and the Red Sea Hills. Since the southern headwaters of the Nile were dry from ca. 20,000 to 12,500 BP, the fluviatile sediments deposited in the Nile valley in Nubia may have resulted almost entirely from the numerous wadis flowing from the Red Sea Hills.
The West Nubian Palaeolake is the most large-scale hydrographic evidence in the Eastern Sahara of the early to mid-Holocene wet phase that affected northern Africa. It is the result of a significant increase in local rainfall due to the northward shift of the tropical rainfall belt. A series of fieldwork-based differential GPS (DGPS) measurements along several profiles across the West Nubian Palaeolake basin provides the first precise topographic data from this up to a 5330 km2 large palaeolake feature. In combination with sedimentological, geochemical, and archaeological results, an almost complete picture of significant palaeoclimatic changes and human occupation during the early to mid-Holocene for this region is presented. Different stages of palaeolake evolution ranging from non-existence of the lake through stable freshwater conditions to its extinction were identified in the period from 9400 to 3800 14C yr BP. These lake stages coincide with phases of intensive human inhabitation between ca. 6300 and 3500 14C yr BP, and include at least four settlement phases distinguishable by style of pottery. These are known from adjacent areas of the palaeolake region, emphasizing strong prehistoric cultural connections in the Eastern Sahara. During the highstands of the palaeolake in the early to mid-Holocene, the Dotted Wavy-Line pottery relates to the Early Khartoum type culture with its supra-regional distribution from the Nile Valley to the Chad, and possibly with slightly different forms even to the Atlantic coast. Later in the Holocene, Western Nubia with its large palaeolakes and migration paths along palaeowadis, such as Wadi Howar, acted as an important natural and cultural link between the Nile Valley and the Chad Basin until the region was deserted during the fourth millennium BP.
Pollen and phytogeographic evidence provides a vegetational history of the Sahel for the period 0–18,000 yr B.P. The zonal vegetation fluctuated latitudinally and its most extreme positions occurred at 18,000 and 8500 yr B.P. The first involved a southward shift of the Sahelian wooded grassland to 10°N under the arid conditions of the last glacial maximum. The second change shows a rapid northward migration of humid vegetation: Guinean elements reach 16°N and Sahelo-Sudanian elements extend to the southern margin of the modern Sahara (21°N) when the Atlantic monsoon flux increased. In the middle Holocene the extensive spread of Sudanian elements into the modern Sahelian zone suggests the appearance of a markedly dry season. The modern Sahelian semiarid conditions appeared abruptly at 2000 yr B.P.
The present-day Sahara occupies an area of slightly over 8 million km2in Africa, between latitudes 16 and 32° N, circumscribed within the isohyet of 100 ± 50 mm mean annual rainfall. The hyperarid area alternately expanded and shrank on both sides of a seemingly narrow semi-permanent eremitic zone along the Tropic of Cancer during the course of the Quaternary epoch (1·7 Ma). The Cenozoic, Mesozoı̈c and Paleozoı̈c Sahara, in turn, has undergone drastic climatic changes as the African continent drifted northward from its Antartic position to reach its present latitudinal situation. But, seemingly the Sahara was never the large desert it now is, with the exception perhaps of the Upper Triassic Lower Liassic epochs. The Pleistocene and Holocene contrasting climate changes induced large variations in flora and fauna distribution, as well as in geomorphic processes.
Land-sea correlation off NW Africa is investigated from both modern and late Pleistocene/Holocene pollen records. Pollen spectra from modern soil surface samples from Senegal and Mauritania and from modern bottom sediment samples from the offshore eastern Atlantic (21-12°N) record accurately the latitudinal vegetation zonation of West Tropical Africa, by showing the maximum percentages of the phytogeographical groups and the same characteristic taxa as the adjacent vegetation zones. A strong correlation between marine (core M-16017-2 near Cap Blanc) and continental (sebkha of Chemchane, Mauritania) pollen signals is also observed for the evolution of the late Glacial/Holocene vegetation zonation at 21°N. The differing sensitivities of each sedimentary environment for recording local and/or subcontinental vegetation changes are discussed.
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Archaeology and Environment in the Libyan Sahara: the Excavations in the Tadrart Acacus, 1978-1983
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The Uan Afuda cave Hunter-gatherer Societes of Central Sahara, Arid Zone Archaeology, Monographs 1. All'Insegna del Giglio
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Some remarks on Saharan terminology. Pre-pastoral archaeology from the Libyan Sahara and the Middle Nile Valley
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