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Journal of Human Evolution 76 (2014) 1e25 Contents lists available at ScienceDirect Journal of Human Evolution journal homepage: www.elsevier.com/locate/jhevol Acheulean technological behaviour in the Middle Pleistocene landscape of Mieso (East-Central Ethiopia) * Ignacio de la Torre a, , Rafael Mora b, Adrian Arroyo a, Alfonso Benito-Calvo c a Institute of Archaeology, University College London, 31-34, Gordon Square, WC1H 0PY London, United Kingdom b Centre d'Estudis del Patrimoni Arqueologic de la Prehistoria, Facultat de Lletres, Universitat Autonoma de Barcelona, 08193 Bellaterra, Spain c Centro Nacional de Investigacion sobre Evolucion Humana (CENIEH), Paseo Sierra de Atapuerca S/N, 09002 Burgos, Spain article info abstract Article history: The Mieso valley is a new paleoanthropological sequence located in East-Central Ethiopia. It contains Received 10 February 2014 Middle and Upper Pleistocene deposits with fossil and lithic assemblages in stratified deposits. This Accepted 23 June 2014 paper introduces the Middle Pleistocene archaeological sequence, attributed to the late Acheulean. Low Available online 22 July 2014 density clusters of artefacts suggest short-term use of the landscape by Acheulean hominins. In Mieso 31, one of the excavated assemblages, refit sets indicate fragmentation of the reduction sequences and Keywords: enable study of the initial stages of biface manufacture. Mieso 7, also a stratified site, is primarily Early Stone Age characterized by a small concentration of standardized cleavers, and portrays another dimension of Acheulean fi East Africa Acheulean technology, that related to nal stages of use and discard of large cutting tools. Available Large cutting tools radiometric dates place the Mieso Acheulean around 212 ka (thousands of years) ago, which would make Mieso valley this sequence among the latest evidence of the Acheulean in East Africa, in a time span when the Middle Stone Age is already documented in the region. © 2014 Elsevier Ltd. All rights reserved. Introduction great ape fossils (Suwa et al., 2007). Mieso also lies between two sites discovered by Desmond Clark during his surveys across the Our knowledge of the Early Stone Age in East Africa has Main Ethiopian Rift in the 1970s (Clark and Williams, 1978), namely increased substantially over the last few decades. Intensive field- Aladi Springs (a stratified Middle Stone Age site 26 km to the north- work in Kenya, Ethiopia and Tanzania has enabled the establish- east), and Arba (an Acheulean surface site 30e40 km to the south- ment of a solid radiometric and archaeological framework for west). Despite its proximity to known archaeological sites, the Oldowan and Acheulean contexts. This is particularly true of the Mieso deposits nonetheless remained unreported until the begin- Ethiopian Rift Valley, where systematic surveys (e.g., Asfaw et al., ning of our field project. 1990) led to the discovery of key sites, unknown to paleoanthro- During our surveys across the Mieso valley, Middle and Upper pology prior to the 1990s (WoldeGabriel et al., 2000). Over the last Pleistocene deposits were documented including fossils and arte- few years, however, the pace of discovery of new sequences has facts attributable to the Acheulean, Later Stone Age and putatively slowed down, and a substantial part of archaeological fieldwork is also to the Middle Stone Age. The geology and chronology of the conducted in areas already known. Mieso Middle Pleistocene deposits are presented elsewhere Here we introduce the archaeological sequence of Mieso, (Benito-Calvo et al., submitted for publication), while emphasis will discovered during our surveys in 2008, and systematically inves- be given here to the archaeological contexts. Thus, this paper will tigated in consecutive field seasons between 2009 and 2012. The introduce the archaeological sequence of the Mieso valley, focusing Mieso valley is named after the town of Mieso (c. 300 km east of on the archaeo-stratigraphy of the Acheulean sites and, particularly, Addis Ababa), on the road from Awash town to Asebe Tefari and on the lithic assemblages. Our aim is to present a detailed account Dire Dawa (Fig. 1). The Mieso valley is located approximately 60 km of the Acheulean technology in this previously unreported Middle south-east of Chorora, well-known for the discovery of Miocene Pleistocene sequence, and discuss the significance of well- preserved low density assemblages for the reconstruction of Acheulean hominin behaviour. In this context, our technological * Corresponding author. analysis will discuss methods of handaxe production and data E-mail address: [email protected] (I. de la Torre). derived from refit studies, the implications of assemblage structure http://dx.doi.org/10.1016/j.jhevol.2014.06.008 0047-2484/© 2014 Elsevier Ltd. All rights reserved. 2 I. de la Torre et al. / Journal of Human Evolution 76 (2014) 1e25 Figure 1. A) Location of the Mieso study area and position of the archaeological sites on Google Earth imagery (see also video clip in SOM 3). B) General stratigraphic sequence of the Mieso valley, based on descriptions by Benito-Calvo et al. (submitted for publication). Legend: 1, sites; 2, surveyed outcrop areas; 3, yellowish-brown silty clays; 4, greenish-grey clays; 5, white calcareous tufas; 6, yellowish-brown sands; 7, gravels with yellowish-brown matrix; 8, light brownish grey clays; 9, light brownish grey sands; 10, gravels with light brownish grey matrix; 11, greyish-brown silty clays; 12, greyish-brown sands; 13, pale grey clays; 14, pale grey sands; 15, gravels with pale matrix; 16, volcanic tuffs (TBI, TAi, TAs and CB); 17, calcretes; 18, carbonated nodules; 19, pedogenetic features; 20, disconformities. and inter-site variability for the reconstruction of mobility patterns Fig. 1B shows the three sedimentary units documented in the across the Mieso landscape, and the relevance of the Mieso Mieso valley sequence (see details in Benito-Calvo et al., submitted Acheulean sequence for the understanding of Middle Pleistocene for publication). Unit I sits on bedrock, and contains four beds; GB human behaviour in East Africa. (boulder, cobble and gravel conglomerates, mainly), FA (silty clays, clays and sands), LC (clays, marls and tufas), and CD (silty clays with calcretes). Unit II sits discordantly over bed CD and contains three Chronostratigraphic context of the Mieso valley beds (A, B and C) separated by erosive contacts, mainly composed of silty clays, sands and gravels. The base of Unit III is also erosive, and The Mieso area is located in the foothills between the SE Ethi- overall the unit is of alluvial origin, with sands, grey silty clays and opian Plateau and the Afar Rift. In the escarpment, the bedrock gravel layers. comprises Mesozoic sedimentary rocks (Triassic, Jurassic and Unit III belongs to the Upper Pleistocene, as suggested by a Cretaceous) and Oligocene-Miocene volcanic rocks (basalts, rhyo- number of stratified Later Stone Age assemblages dated by accel- lites and trachytes), while the Rift includes the Afar Series (basalts erator mass spectrometry (AMS) to < 20 ka (thousands of years and rhyolites) and the volcanic edifices of Asebot (2539 m above sea ago) (Mora et al., in progress). Argoneargon (40Ar/39Ar) dating of level [a.s.l.]) and Afdem (2125 m a.s.l.). The foothill area (Mieso tuffs from Units I and II (Benito-Calvo et al., submitted for valley) is dominated by a gentle alluvial piedmont, which has been publication) indicates a Middle Pleistocene age for the sequence. incised by the Mieso River and its tributary, the Yabdo. These fluvial Tuff TA has yielded a date of 212 ± 0.016 ka, which provides a courses are currently eroding a Pleistocene sedimentary sequence minimum age for assemblages in Beds GB, FA and LC (see Fig. 1B). about 24 m thick, formed by alluvial, palustrine and volcanic ma- Acheulean assemblages above tuff TA are more recent than 212 ka. terials, where a number of fossil and/or artefact localities have been One of the samples (M43-CB) from the upper tuff (Tuff CB) has found (Fig. 1A). I. de la Torre et al. / Journal of Human Evolution 76 (2014) 1e25 3 Table 1 Trenches dug in the Mieso valley Middle Pleistocene localities. Density of lithics refers to stratified material only. Area Locality Surface Stratigraphy Area excavated (sq. m) Thickness (m) Density of lithics Density of lithics per area per cubic meter Fossils Lithics Fossils Lithics Area 1 MIE4 42 38 0 0 1 1.0 0.0 0.0 Mieso River MIE6B 39 82 5 2 2 0.6 1.0 0.8 MIE7 69 63 Trench 5 0 0 17 0.1 0.0 0.0 Trench 6 0 0 3 0.8 0.0 0.0 Trench 7 64 50 58 1.0 0.9 0.8 MIE48 40 12 38 0 14 1.2 0.0 0.0 Area 7 MIE31 7 160 Yabdo River Trench 1 9 179 41 1.2 4.4 4.2 Trench 8 0 0 1 0.5 0.0 0.0 MIE43 5 39 Trench 2 0 0 14 0.4 0.0 0.0 Trench 3 0 0 1.5 0.6 0.0 0.0 yielded a date of 800 ± 0.05 ka, which is likely due to contami- At those localities where trenches were dug (Table 1), relative nation of much younger ashes. In fact, another sample from the coordinate systems were created with a total station in order to same tuff and locality (M43-CB-1) yielded one peak at achieve higher resolution than from GPS networks. Within each of 760 þ 0.04 ka and another close to 210 ± 0.03 ka, which is the four local coordinate systems established (Mieso 4, 6, 6B and 7; consistent with the date from tuff TA (Benito-Calvo et al., Mieso 48; Mieso 7; and Mieso 43), modern terrain features were submitted for publication).