The Bir (a bir is a well) Sahara and Bir Tarwafi are basins in the western desert of Egypt. This area was occupied by different groups from as long as 33,000 years ago to 5200 B.C. They were formed by deflation and have elongated oval shapes. They are about 10 meters below the level of the surrounding flat plain. The area was occupied only during time periods where there was a climatic change of a significant increase in moisture, causing the basins to fill with water. The Bir Sahara has spring vents surrounding it and a lack of a distinct peripheral drainage net. This suggests that the lake was fed by artesian springs associated with the aquifer in the underlying sandstone.
Both basins have irregular elongated outlines, about 8 km and 15 km in maximum length, and are oriented north-northeast to southwest. There are numerous bays, peninsulas and buttes. The central parts contain modern dunes, extensive patches of limestone and marl. There are shallow wadis surrounding the birs which disappear into the plain after a few hundred meters.
These two basins provide the basic sequence for the early Upper Pleistocene. Several distinct lithostratigraphic units from the framework for the sequence. It is composed of lacustrine and eolian events associated with human occupations as well as rich vertebrate and invertebrate faunas.
The first occupation is on plateau carbonates and the underlying sands. There are numerous Acheulian sites, and the tools found are characterized by less abraded tools, some have faces that are almost completely fresh. Next is a layer of limestone remains with deflated sands surrounding the limestone. Artifacts there consist of Upper Acheulian tools, mostly bifaces, all heavily abraded. Several of the tools found apparently represented artifacts that were worked or thrown in from the adjacent Acheulian campsites.
After this level is the final Acheulian springs, with occasional Acheulian bifaces found there. Some faunal remains found were ostrich eggshell, a tooth belonging to a warthog, and other bones. This period ended when the spring dried up. This was followed by a significant period of eolian erosion.
After this, a Mousterian culture existed during a period of dune formation. Therefore, the Mousterian artifacts are heavily sandblasted. The tools found were denticulates and notches. After the dune there was an intricate series of lacustrine, shore and inblown sediments. There are several Mousterian occupations. These people probably lived near a shoreline, and slight differences in elevations of artifacts may be accounted for by changes in the shoreline. There are several layers, a black layer, a sand layer, a vegetation layer, and silt layers separated by a burnt layer. After the silt layer is a layer of marl. Both the sand layer and the vegetation layer contain an extensive Mousterian settlement. The silt and marl units represent an expanding lake. After this, a dune began forming on the sites, which were then covered by new units of silts. Large amounts of mollusks including land snails were found here.
