Paleomagnetic analyses of the northern margin of Aïn Béni Mathar – Guéfait basin (Eastern Morocco)

Abstract

Dating Pleistocene occupations in the Circum-Mediterranean region plays a key role in the study of human evolution, as it is critical to establish an accurate time framework for better understanding how, when and why the first human expansions occured outside the African continent. In Eurasia this out of Africa expansion and colonization probabl occurred through the Middle East and along several pulses (Aguirre and Carbonell, 2001; Allué et al., 2013; Bermúdez de Catro and Madtinón-Torres, 2012; Carbonell et al., 2008; Toro-Moyano et al., 2013) as documented by sites such as Dmanisi, with an age of 1.7 to 1.8 Ma (Ferring et al., 2011; Lordkipanidze et al., 2007) or archeologcal sites presents in the Circum-Mediterranean basin such as Atapuerca, Pirro Nord, Ubeidiya, among others (Parés et al., 2011) with ages between 0.8 and 1.4 Ma. However, the chronology of deposits in North Africa such as Ain Hanech and E-Kerbha, shows that, the dispersal from Africa of genus Homo, egan earler than previosuly thougth, possibly since the beginning of the lower Pleistocene (Sahnouni et al., 2010; Parés et al., 2014). In this sense, the chronology of Paleolithic archaeological sites in Morocco, such as in the basin of Aïn Béni Mathar (easter Morocco), can be crucial to contextualize old human dispersal in Northern Africa. Sediments and terraces in the Aïn Béni Mathar area, in the basin if the same name, contain remains of both Acheulean (Mode II) and Oldowan (Mode I) stone tools that have been discovered in successive campaigns since 2006. In attempt to provide a first chronological context for these archaeological sites in Eastern Morocco, we have collected samples from two different yet related áreas within the basin fo paleomagnetic dating. The firs succesion is found near to the town of Aïn Béni Mathar, where 50 samples were obtaine along a sequence of about 80 meters and the second one, near to the town of Guéfait with a sequence of approximately 120 meters with 110 specimens. Palomagnetic analysis were carried out at both Universitiy of Burgos, and CENIEH, and all samples were demagnetized by stpewise progressive alternating field of therman demagnetization to determine the characteristic remanent magnetization (ChRM) directions. The paleomagnetic analysis of both sequenes have resulted in a two local magnetic magnetostratigraphies, where both normal and reverse polarities are observed. Due to the lack of bioestratigrpahic data, a conclusive correlation of the local magnetostratigraphy to the Geomagnetic Polarity Time Scale (GPTS) is not possible, although we will discuss possible options, wich are constrained by the presence of stone tools remains.