The Middle Palaeolithic site of Birzgane (Tebessa, Algeria): Rock magnetic property characterisation and past rainfall reconstruction

摘要

A new Middle Palaeolithic site was discovered at Birzgane, south of the city of Tebessa in eastern Algeria. The archaeological study revealed richness in archaeological artefacts, belonging probably to the Aterian culture, but an absence of pedunculates. The Aterian archaeological layer was assigned to the end of the Middle Pleistocene by uranium-thorium dating. The environmental conditions at the time were assessed by means of magnetic proxy data such as hysteresis parameters, magnetic susceptibility and remanent magnetisation. The magnetic fraction of the alluvial sediment contains mainly oxidised magnetite and smaller amounts of haematite and goethite; indicated by thermal demagnetisation curves of isothermal remanent magnetisation. Magnetic properties such as enhanced susceptibility, anhysteretic remanent magnetisation and frequency dependent susceptibility indicate that the upper part of the section was subjected to pedogenesis after deposition. A conceptual magnetic enhancement model was applied to reconstruct past rainfall quantities in the upper part, taking into account present day temperatures and rainfall, water saturation, soil moisture and magnetic susceptibility. A precipitation quantity of 560 ± 40 mm was estimated for the transition period from MIS 5 to 4, corresponding to the Saharan Pluvial, an extended humid climate period in northern Africa between 100,000 and 70,000 years before present.