The North African earliest Pleistocene faunal sequence: from biostratigraphy to biochronology

Abstract

The Early Pleistocene faunal record in North Africa is well known from classic localities, documented already in the 19th century and earlier part of the 20th century, such as Aïn Boucherit and Aïn Hanech. In the second half of the 20th century, radiometric dates became available and correlations were used to estimate the ages of the earliest Pleistocene North African sites. However, isolation and long-distance correlations were not favourable for a precise chronology of the North African fossil record, leading to major discrepancies on the ages of the sites, with age estimates differing as much as one million years. Such a situation hampers research on prehistory and the correlation of observed faunal change to the published detailed climatic and environmental records.The Aïn Hanech and Oued Laatach Formations crop out in the small Oued Boucherit, where a series of fossiliferous and archaeological sites are situated in superposition in the lithostratigraphic sequence. These include the classic sites of Aïn Boucherit and Aïn Hanech, as well as the more recently discovered El-Kherba, a new fossiliferous level at Aïn Boucherit, as well as various minor localities. These sites are in a section or can be correlated to it, which has been dated using a combination of magnetostratigraphy, Electron Spin Resonance (ESR) applied to optically bleached quartz grains, sediment accumulation rates and biostratigraphy. The oldest fossiliferous site is situated in the Gilbert Chron and has an age exceeding 3.58 Ma, while the estimated ages of the archaeological sites are between 2.44 to 1.7 Ma. With these dates, biostratigraphy of this part of the North African record turns into biochronology. The lower paleontological and archaeological level at Aïn Boucherit has an inferred age of about 2.44 Ma and is, thus not more than about 140 ka, younger than the oldest sites with widely accepted stone tools, such as Gona EG10 and 12, and OGS 6 and 7 in Ethiopia, which are situated just above the Gauss.