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EFCHED

Chronology, adaptation and environment of the Middle Palaeolithic in Northern Africa: implications for the dispersal of anatomically modern humans

Africa was a critical location in the emergence and dispersal of anatomically modern humans.

In particular, they appear to have evolved in central/southern Africa during the penultimate glacial-interglacial cycle and subsequently dispersed through Africa and into Asia, Australasia and Europe during the last glacial-interglacial cycle.

Understanding the timing and extent of climatic change in North Africa over the last glacial-interglacial cycle is therefore of critical importance in understanding human migration, since the Sahara forms a potential barrier to northerly population movement.

A robust and internally consistent chronological framework for the archaeological and climatic record of North Africa is therefore required.

We aimed to use optically stimulated luminescence (OSL) dating as a basis for temporal correlation between geographically widespread archaeological sites and the palaeoclimatic record.

Some of our major findings

Work on the North African palaeoclimate record concentrated on the Chad (Chad and Niger) and Fazzan (south-west Libya) closed basins in the Sahara, the largest desert on Earth.

Although mostly uninhabitable due to present day aridity, both basins contain extensive shoreline and lacustrine sediments, providing evidence that they contained very large lakes in the past.

Digital elevation model (Shuttle Radar Topography) and remotely sensed data (Landsat Thematic Mapper) were analysed to map shoreline and lacustrine deposits with unprecedented accuracy.

This analysis gave estimates of 350,000 km2 and 76,000 km2 for the ancient lakes in Chad and Fazzan basins respectively.

Key lake land-forms from within the basins were dated using OSL techniques, and provide a chronology for large scale humidity fluctuations in this portion of the Sahara.

Digital Elevation Model of North Africa showing possible large water bodies. Image: N Drake

Image:Digital Elevation Model of North Africa showing possible large water bodies.

The Fazzan lake, which formed in the largest basin fed exclusively by rainfall falling within the Sahara sensu stricto, was full at the beginning of the present and last interglacials.

We also identified four older lake phases, which we tentatively correlated with inter-glacial periods on stratigraphic grounds.

The northern, presently arid, basin of Lake Chad yielded a much shorter palaeoclimate history, beginning in the early Holocene.

OSL ages for lake shorelines and for barchan dunes buried by lacustrine sediments indicate that Chad experienced at least three rapid arid-humid transitions during the Holocene.

The existence of two large palaeolakes within the Sahara poses three key questions which our data might answer:

  1. What mechanism drives periods of North African humidity and associated lake phases?

  2. What is the regional climatic impact of large standing water bodies in the Sahara?

  3. Does synchronous humidity in the Chad and Fazzan basins provide a 'humid corridor' across the Sahara, allowing the migration of hominin populations out of central Africa?

Archaeological sites at Ounjougou, Mali and Sai Island, Sudan were also investigated during this study.

Both sites contain abundant lithic materials that document a history of punctuated occupation by Palaeolithic populations.

Ounjougou contains numerous geo-graphically dispersed sites containing lithic industries from the Lower Palaeolithic to the present. OSL dating was used to link these sites into a single, internally consistent chronology.

Hand axes from Fazzan. Image: N DrakeUnlike Ounjougou, site 8-B-11 on Sai Island contains artefacts in direct stratigraphic superposition. The artefacts range in age from Lower to Upper Palaeolithic and contain an unusual abundance of symbolic objects, notably ochre covered chert pebbles and a worked sandstone slab interpreted as a mortar.

Together these factors make Sai an important site for studying the origin of modern human behaviour. OSL dating indicates that the site is younger than previously thought, with the early Middle Palaeolithic material dating from the Last Interglacial.

The OSL chronologies for lithic industries at Ounjougou and Sai allow the population dynamics represented at these two sites to be explored for the first time.

This summary was compiled by Simon Armitage (Oxford). David Thomas (Oxford) is the PI for this project.

Regional investigations were carried out by:

Libya: Nick Drake (Kings College London), Simon Armitage (Oxford), Ahmed El-Hawat (University of Garyounis, Libya), Mustafa Salem (El-Fatah University, Libya), Kevin White (Reading), Peter Turner (Birmingham) and Sue McLaren (Leicester).
Chad: Charlie Bristow (Birkbeck, University of London), Simon Armitage and Nick Drake (Kings College, University of London).
Sudan: Sallie Burrough (Oxford), Stephen Stokes and Philip van Peer (Katholieke Universiteit Leuven, Netherlands).
Mali: Chantal Tribolo (Oxford), Stephen Stokes and Eric Huyescom (Geneva).

Additional funding: Great Man Made River Authority (Libya), National Geographic, The Royal Geographical Society and a Marie Curie Fellowship.