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Article Dans Une Revue Journal of Human Evolution Année : 2023

On the age of Ain Hanech Oldowan locality (Algeria): First numerical dating results

Résumé

Our current understanding of early human settlements in North Africa relies on a few well-contextualized Oldowan and Acheulean sites (e.g., Ain Hanech, El Kherba, Ain Boucherit Lw and Up, Tighennif in Algeria; Thomas Quarry in Morocco). In particular, the site of Ain Hanech has documented for many decades the earliest evidence of human presence in North Africa (e.g., Sahnouni and de Heinzelin, 1998), until older stone tools were recently reported at the nearby Ain Boucherit locality (Sahnouni et al., 2018). While the Early Pleistocene antiquity of this Oldowan assemblage has never really been questioned, its exact age has, however, been discussed. In the early 2000s, a series of articles were published in this journal arguing either for an age of ∼1.8 Ma (Sahnouni et al., 2002, 2004) or much younger, around 1.2 Ma (Geraads et al., 2004). Although subsequent chronostratigraphic studies have provided additional evidence for the older age (Parés et al., 2014; Sahnouni et al., 2018; Duval et al., 2021), Ain Hanech site had never been numerically dated until now. Moreover, beyond the archeological relevance of the site, Ain Hanech faunal association has also long been used as a reference for biochronological inferences and comparative studies with other paleontological localities of the region (e.g., Geraads, 2002; Sahnouni et al., 2002; Van der Made and Sahnouni, 2013; Van der Made et al., 2021). In other words, the accuracy of North African biochronology over the Early Pleistocene timescale partly relies on the age of Ain Hanech. In this context, we present here the dating results from electron spin resonance (ESR) and uranium-series (U-series) methods tentatively applied to optically bleached quartz grains and fossil teeth from Ain Hanech and the nearby stratigraphically equivalent site of El Kherba (Sahnouni and de Heinzelin, 1998). Additionally, new paleomagnetic data were obtained for independent age control, complementing the magnetostratigraphic study of the Ain Hanech Formation by Parés et al. (2014). This combined dating approach enables us to securely constrain the age of the uppermost Oldowan level of the Oued Boucherit sequence. Ain Hanech is situated in Northeast Algeria 7 km northwest of El Eulma (Sétif; Supplementary Online Material [SOM] Fig. S1). The site is located near a small cemetery in a sedimentary outcrop exposed in a deep ravine of the Oued Boucherit. Its discovery was reported in the late 1940s by Arambourg, 1947, Arambourg, 1949. In 1992, Sahnouni and colleagues launched multidisciplinary investigations that resolved major questions surrounding the site including stratigraphy, age, and behavioral implications of the archeological occurrences (Sahnouni and de Heinzelin, 1998; Sahnouni et al., 2002). It also led to the discovery of El Kherba, a lateral extension of Ain Hanech, situated a few hundred meters south of it (SOM Fig. S1). Ain Hanech is part of the Oued Boucherit Plio-Pleistocene sequence that encases various paleontological and archeological deposits dated to between ∼3.8 and ∼1.7 Ma (Duval et al., 2021). This sequence hosts a unique succession of three Oldowan (from bottom to top: AB-Lw, AB-Up, Ain Hanech/El Kherba) levels and one Acheulean level (Ain Hanech) ranging from ∼2.4 to ∼1.7 Ma and distributed over a small area of <1 km2, offering an unprecedented opportunity to study in detail the onset and evolution of the Oldowan as well as the transition to the Acheulean culture in North Africa. The archeological localities are all contained in the 29-m-thick Ain Hanech Formation, which comprises six stratigraphic members (P, Q, R, S, T, and U) of fluvial origin (Sahnouni and de Heinzelin, 1998). The El Kherba and Ain Hanech deposits are encased in Member T, which is 4 m thick, mainly muddy, and light brown or pink in color with carbonated nodulations toward its top. Both correspond to the stratigraphically youngest Oldowan level of the sequence (Duval et al., 2021). The stratigraphy of Ain Hanech consists of seven layers (TI to TVII, from top to bottom) based on sediment texture, consistency, and color (Fig. 1; SOM S1). The associated fossil bones and Oldowan stone artifacts originate from three distinct archeological levels (A to C, top to bottom; Sahnouni et al., 2002). They are contained in layers TIV and TV (level A), TVI and upper TVII (level B), and lower TVII (level C; Fig. 1). For detailed information about the stratigraphy and sedimentary context of El Kherba, see Abdessadok et al. (2022) and SOM S2 (see also SOM Fig. S2). Major excavations were undertaken at Ain Hanech between 1992 and 2004, totaling a surface of 118 m2. The archeological levels yielded 1242 fossil bones (see faunal list in SOM S1) and 1232 stone artifacts >2 cm. The stone tools are made of limestone and flint and incorporate a range of Oldowan categories, including core forms, whole flakes, and retouched pieces (SOM S1). Likewise, excavations undertaken at El Kherba yielded faunal assemblages associated with Oldowan stone tools very similar to that of Ain Hanech. Both Ain Hanech and El Kherba lithic artifacts are very similar to those known from Olduvai upper Bed I (DK, FLK North) and lower Bed II (BK, TK, HWK East, MNK), especially in terms of flaking patterns and resultant artifacts forms (Sahnouni, 1993, 1998, 2006). The age of Ain Hanech locality has hitherto been inferred from biostratigraphy and estimated to be between ca. 2 Ma and <0.8 Ma, depending on the authors (see an overview in Van der Made et al., 2021 and references therein). However, given the scarcity of well-dated Pleistocene paleontological localities in North Africa, most correlations utilized East-African assemblages (e.g., Olduvai Bed 1, Shungura Formation; for details, see Van der Made et al., 2021) located thousands of km to the SE, thus strongly compromising the reliability and accuracy of the derived chronological constraints. A succession of magnetostratigraphic studies (Sahnouni et al., 1996, 2018; Parés et al., 2014) has progressively enabled to refine the chronostratigraphic framework of the whole Oued Boucherit sequence. In this context, an age estimate of 1.8 Ma was proposed by Sahnouni et al. (1996, 2002), whereas Geraads et al. (2004) claimed a younger age of about 1.2 Ma using faunal and archeological arguments. More recently, an age of 1.77 ± 0.03 Ma was extrapolated for Ain Hanech from the sediment accumulation rate and the associated age-depth model established for the whole sequence (SOM S1; Duval et al., 2021). Further details about the chronostratigraphic context may be found in SOM S1.
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hal-04116623 , version 1 (05-06-2023)

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Mathieu Duval, Mohamed Sahnouni, Josep Parés, Jian-Xin Zhao, Rainer Grün, et al.. On the age of Ain Hanech Oldowan locality (Algeria): First numerical dating results. Journal of Human Evolution, 2023, 180, pp.103371. ⟨10.1016/j.jhevol.2023.103371⟩. ⟨hal-04116623⟩
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