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Geoarchaeology | Prehistoric Archaeology | Rock Art | Historic Archaeology | Archaeobotany

Fig. 1 - Tin Lalan, travertine

Fig. 2 - Wadi Agmir, rockshelter
with dung deposit

Rock varnish is a fine film rich in manganese which covers the surface of sandstone exposed to the atmosphere. Its origins are generally attributed to microbial activity under humid conditions in the past. We have obtained some consistent radiocarbon datings for this substance (spanning the Early and Middle Holocene); however, it is not entirely clear what part of the varnish has been dated.

The rock varnish in the Messak Settafet, as shown by microscopy, is composed of three microlayers of different composition, belonging to three different phases of the Holocene.

The innermost layer is rich in alluvial clay, indicating humid conditions (Wet Holocene); the presence of P205 indicates biological activity during deposition.
The second microlayer is rich in manganese, and is of bacterial origin; the outer layer is made up of aeolian quartz dust, and was formed during the Late Holocene desertification (Fig. 3).

Fig. 3 - The landscape of the Messak
and (below) a thin section
of rock varnish

Fig. 4 - Erg Uan Kasa, lake deposit
underneath dunes

The anthropogenic cave deposits analysed date to between 9700 and 3800 years ago; these originate from human use of the rock shelters, and consist mainly of plant fragments, organic matter and animal dung. Besides their archaeological significance, these anthropogenic deposits represent one of the main sources of palaeobiological and palaeoenvironmental information for the Wet Early and Middle Holocene.

Micromorphological examinations show that the deposits of dung were laminated by trampling; they are composed of fragments of grass, seeds, mineral particles and coprolites, indicating that the shelters were used as stables. The dung frequently contains spherulites, typical of goats or sheep.
Currently, along lines recently proposed by Canti, our research concentrates on other types of dung, such as bird guano, well preserved in numerous shelters. Furthermore, fine sections have allowed us to identify the presence of phosphates and starch.

These deposits also contain well-preserved insect exoskeletons. Research is still in progress, but suggests that these are important indicators of the palaeoenvironment within caves and in their immediate surroundings. Coleoptera, Curculionidae and Hymenoptera Apoidea indicate the presence of living plants outside the shelter.
Some Coleoptera (Dermestidae, Ptinidae and Tenebrionidea) seem to be linked to the storage of wild cereals inside the caves. Other groups of Coleoptera are associated with animal dung (Fig. 2).

Fig. 5 - Erg Uan Kasa, sequence of lake deposit formation,
and sedimentary facies

Lake sediments found in the interdune corridors indicate the presence of palaeolakes in the ergs, the result of higher levels of rainfall. During the Holocene intense precipitation caused the oversaturation of the dunes and consequently a rise in the water table. Radiocarbon dating indicates the presence of lakes between 8400 and 4600 years BP.

The sedimentary facies, composed of peat, carbonated mud, and then a gypsum crust, shows the gradual rise in water levels in the lake, and the subsequent drying up of the basin.

The molluscs present in the sediment and the fragments of ostrich eggs near the deposits represent a register of the isotopic composition of the waters of the lakes, and of the rates of precipitation in surrounding areas.

Research on the isotopic composition of these is still in progress, but for the molluscs we can observe that they are isotopically very light at around 7000 BP (Figs. 4, 5, 6, 9).

Fig. 6 - Erg Uan Kasa, molluscs
and ostrich shells

Garat Ouda was a lake fed by a branch of the wadi Tanezzuft through a delta: the channels in the delta and the geomorphological features of the lake have been perfectly preserved. Hundreds of archaeological sites, consisting of thousands of fireplaces (3000 have been mapped), lie in close proximity to these channels.

On the basis of geomorphological and archaeological data, three different phases in the progradation of the lake have been identified; no date later than 4500 years BP was found for the archaeological material contextual to the delta sediments.

This date is therefore taken to be the point at which the lake dried up almost instantaneously, due to the diminished flow of the wadi Tanezzuft (Fig. 7).

Fig. 7 - Meandering palaeochannel
of the delta system

Fig. 8 - Door made of Cupressus Dupreziana
in Old Barkat.

Given that the width of the growth rings depends on the availability of water, this curve represents a detailed record of changes in rainfall levels over the decades.

Whilst there are some problems relating to dating, annual growth rates, and the indicization of the growth trend which still await a solution, the curve indicates that a severe arid episode at 5000 years BP was followed by several phases of higher precipitation (at 3000-2000 years BP, 3200-2400 calibrated years BP), and the onset of extremely arid conditions at 1500 years BP (1370 calibrated years BP).

These data are in good agreement with the local geological record, and consistent with palaeoclimatic proxies from equatorial Africa and the Middle East, and can therefore be regarded as relevant (Fig. 8).

Fig. 9 - Erg Uan Kasa, palaeosoil in
a fossil dune

During the last fieldwork season (January-February 2003), in the area of the erg Uan Kasa, some pre-Holocene deposits were discovered, indicating wet phases of the Pleistocene.

These consist of strongly cemented lake deposits and fossil dunes with deep clayey palaeosoils. In many cases these deposits are associated with Acheulean artefacts.

Early Palaeolithic artefacts (galets amenagees) have been found in connection with the deposits, alongside the fossilized remains of large mammals and reptiles. Uranium/thorium dating of the deposits is currently in progress.

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Geoarchaeology | Prehistoric Archaeology | Rock Art | Historic Archaeology | Archaeobotany