Mobility and kinship in the prehistoric Sahara: Strontium isotope analysis of Holocene human skeletons from the Acacus Mts. (southwestern Libya)

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Abstract

The origins and development of pastoralism in Saharan North Africa involves societies and economies that, subjected to profound climatic changes and progressive desertification, came to be based on the movement of people and resources. The extreme conditions to which these groups were subjected made mobility a ‘resource’ in itself. Through the first analysis of Sr isotopes (87Sr/86Sr) in dental enamel of human skeletons from prehistoric burials of the Fezzan (southwestern Libya), we begin to investigate how mobility patterns changed with the onset of the desert. In combining our results with the archaeological evidence, we find that, the transformation in the economy of prehistoric groups correlated with a shift in mobility and possibly kinship systems.

Section snippets

Archaeological setting and theoretical premises

Across the prehistory of the Fezzan, as everywhere in Northern Africa, the alternation of wet and dry periods, over several millennia during the Holocene, profoundly affected food security and hence the economic strategies of the known human groups (e.g., Cremaschi and di Lernia, 1999, deMenocal et al., 2000, Gasse and Van Campo, 1994, Hassan, 1997, Wendorf et al., 2001). During the earlier phases (around 9800–7000 BP) there is a progressive shift from wet to drier conditions, under which Early

Geological setting and biologically available 87Sr/86Sr

As shown in Fig. 1, our study in the southwestern Fezzan consists of several main geomorphological features, including the Wadi Tanezzuft, the Acacus mountains, the Messak massif, and surrounding areas of dune-dominated sand seas (Cremaschi, 1998). These formations are basically underlain by sedimentary rocks, which are tilted in a monocline such that on the surface they become younger going from west to east. On the western side, lower Silurian sandstone and shales underlie the alluvial plain

Uan Afuda (UAF)

Three human teeth come from Uan Afuda, a cave showing Late Pleistocene (Aterian) occupation, later re-occupied during the Holocene (Epipaleolithic Early Acacus, 9800–9000 and Mesolithic Late Acacus, 9000–7000 years BP) (di Lernia, 1999b). These scattered remains, excavated in 1994 although not associated with properly defined burials, were attributed to three different individuals—H1, a young child of about 4 years; H2, a child of about 8 years; and H3, a mature adult more than 45 years old (

Sample and procedure

A total of 35 individuals from the listed sites could be sampled for dental enamel. Among them, seven adults were selected for bone (usually a rib). Not all sites provided fully complete skeletons so that only four of the seven contexts examined (i.e., Takarkori, Tanezzuft Transect Area, Site 96/129 and In Aghelachem) provide bone signature. For dental enamel either upper or lower molars were chose where possible, but otherwise the selection of tooth simply reflects what was available, given

Results and preliminary comments

Of the 35 individuals sampled for enamel, 27 gave results (Table 1) while all of the 7 individuals sampled for bone gave successful readings (Table 2). First, we see that data of the regional enamel samples show distinct 87Sr/86Sr signatures from individuals at the different locations (see Fig. 1). The signature from the Acacus mountains (UAF, UMG, and IMN) is below 0.711, while enamel 87Sr/86Sr from the Tanezzuft (TNZ and IN AGH) is usually above that value (Fig. 2). This is likely to reflect

Discussion

We have compared strontium isotope ratios from human burials of the Libyan Sahara, ranging chronologically from Late Acacus to Garamantian phases. While the sample was necessarily small and our conclusions speculative, this preliminary study presents sign of two main aspects.

First, earlier (Late Acacus) and later (Garamantian) phases show heterogeneous signal, while Pastoral contexts so far reveal a more restricted range of 87Sr/86Sr values (Fig. 4). This framework is easily explained for the

Acknowledgments

We warmly thank Francesca Ricci for useful comments and preliminary skeletal data, and Olga Rickards for providing genetic data in publication. We are grateful to Mauro Cremaschi for discussion on the geomorphology of the Libyan Sahara. Our deepest acknowledgments also go to the anonymous reviewers for useful comments and suggestions. Analyses were funded by the Italian MIUR granted to M.A.T.

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