Level U3.1, a new archaeological level discovered at BK (upper bed II, Olduvai Gorge) with evidence of megafaunal exploitation
Introduction
The Bell Korongo (BK) site was discovered by L. Leakey in 1935, and was intensely excavated from 1952 to 1958, uncovering remains of a minimum of 24 individuals of Pelorovis olduwayensis (Leakey, 1954). Initially, L. Leakey interpreted the site as a megafaunal mass killing site, whereas later in the sixties M. Leakey classified the site as a swamp to which most of these animals were driven, dispatched and consumed by hominins (Leakey, 1971). However, modern taphonomical analyses carried out by Monahan (1996), Egeland and Domínguez-Rodrigo (2008) and Domínguez-Rodrigo et al. (2009a) have shown that the assemblages have a diachronic history in which hominin and non-hominin agencies intervened (frequently independently) and affected the archaeofaunal concentration.
Excavations carried out by TOPPP (The Olduvai Palaeoanthropology and Paleoecology Project) between 2006 and 2012, following the archaeological levels and stratigraphic sequence described by M. Leakey revealed that Levels 1, 2 and 3 were characterized by anthropic activity on medium and small sized animals (size 1–3 according to Bunn, 1982) and on large sized animals (sizes 4–5 according to Bunn, 1982) in the lower Levels 4 and 5 (Domínguez-Rodrigo et al., 2009a, 2014a; Organista et al., 2015). Taphonomic analyses revealed primary early human access to small, and medium carcasses and very likely, an early access to large carcasses also (Monnahan, 1996; Egeland and Domínguez-Rodrigo, 2008; Domínguez-Rodrigo et al., 2009a, 2014a; Organista et al., 2015).
Very large mammal such as hippopotamids, giraffids, and large bovid exploitation as seen at BK is common in the Lower Pleistocene at Olduvai Gorge. Several sites throughout the gorge show this kind of behaviour: hippopotamus bones at SHK known as Sam Howard Korongo (Domínguez-Rodrigo et al., 2014b) and, large bovid bones in the lower Bed II site of FLK known as Frida Leakey Korongo West (FLKW; Díez-Martín et al., 2015). Furthermore, several sites from other African archaeological localities also present anthropogenic traces on large mammal bones. For instance, El Kherda in Algeria (Sanhouni et al., 2013), Koobi Fora in Kenya (Bunn, 1994) and Buia in Eritrea (Fiore et al., 2004) revealed hippopotamus carcass remains bearing cut marks, and at Peninj (Tanzania), cutmarks are found also on giraffid remains (Domínguez-Rodrigo et al., 2002). Alongside these sites, there are others with association of megafaunal remains and lithic industry, although cutmarks are not visible on the bones. Such is the case of FLKN 6 in uppermost Bed I, Olduvai Gorge, where elephant bone remains show no evidence of anthropic activity (Domínguez-Rodrigo et al., 2007) or TK known as Thiongo Korongo in Bed II-III, Olduvai Gorge (Yravedra et al., 2016).
During the 2016 field season, excavations at BK were resumed. Although the original aim of these excavations was to proceed with the study of the lower levels described by Organista et al. (2015), a new level was discovered before reaching them. This fortuitous find motivated the present study, which has as its main aim to describe geologically and archaeologically this newly discovered level. Furthermore, a taphonomical analysis of the remains embedded in this level has been conducted in order to better understand the formation of this archaeological assemblage. Although samples presented in this work are not abundant, an extensive excavation of the encountered level is logistically unviable at the moment. Since further excavations of this level will not be carried out in the near future, a report of this new geological and archaeological level with evidence of megafaunal exploitation was deemed necessary.
Olduvai Gorge is located on the western margin of the southern bifurcation of the Gregory Rift, the eastern branch of the East African Rift in northern Tanzania (Hay, 1976, Fig. 1). The site is situated on the South wall of the Side Gorge, 3 km upstream from its junction with the Main Gorge (Fig. 1). The Side Gorge is only 20 m deep in the BK area and therefore only the uppermost part of Bed II, small sections of Bed III and Ndutu are naturally exposed (Hay, 1976). The present study focuses on the westernmost section of the site, in Trench 14 (Fig. 2).
Stratigraphically, BK is situated directly above Tuff IID (Hay, 1976), which was recently dated at 1.338 ± 0.024 Ma (Domínguez-Rodrigo et al., 2013)) and a few meters underneath the Bed II –Bed II limit, dated 1.15 ± 0.10 Ma (Hay, 1976). The site is placed in a large meandering river, where most of the archaeological levels are found in the point-bar and the thalweg (Uribelarrea and Domínguez-Rodrigo, 2017). The channel deposit consists of three sedimentary Lateral Accretion (LA) units of low-energy fluvial deposits (LA Units 1–3) overlain by a channel macroform (CH Unit 4) filling the channel with very fine overbank sediments (Fig. 2, Uribelarrea and Domínguez-Rodrigo, 2017). The two lowermost LA units (LA Units 1 and 2) contained the only archaeological levels known before this study: Levels 3a, 3b, 4a and 4b (Domínguez-Rodrigo et al., 2014a) along with Levels 4c and 5 (Organista et al., 2015, 2017) are found in LA Unit 1, whereas Levels 1 and 2 (Domínguez-Rodrigo et al., 2009a) in LA Unit 2. These five archaeological levels are found in fluvial deposits mainly composed of clay, silt and sand (ranging from very fine to very coarse sand). The archaeological levels vary in thickness, from 15 cm to 1 m with different concentration patterns (Domínguez-Rodrigo et al., 2009a, 2014a; Organista et al., 2015, 2017).
Section snippets
Geology
Stratigraphical levels and LA unit limits in Trench 14 (Fig. 2) were measured and georeferenced with sub-centimetre precision using a laser total station (TOPCON) and correlated to previous levels and their uncovered boundaries as measured and described by Uribelarrea and Domínguez-Rodrigo (2017) throughout the rest of the site. Macro and microscale stratigraphical and sedimentological features of the profile were logged in detail and photographed.
Zooarchaeology and taphonomy
Additionally, a taphonomical and
Geology
Level U3.1 is a 40–60 cm tuffaceous silt level found overlying a 3–4 cm white and heavily cemented carbonate hard pan (Fig. 3). This is carbonate level transition into to a chute channel erosive surface into a 10–40 cm clayey silt layer, part of the LA Unit 2 as described by Uribelarrea and Domínguez-Rodrigo (2017).
The uppermost surface of the LA Unit 2 is undulated, especially towards the thalweg (westwards), where swales and irregular depressions are found, corresponding to small chute
Discussion
Level U3.1 was deposited in decantation facies, such as those explained by Uribelarrea and Domínguez-Rodrigo (2017) for archaeological sites in meandering rivers. These quick and low energy sedimentation processes furnished ideal conditions for preservation. The low percentage of abraded (Stage 2, according to Alcalá, 1994) remains reinforces this interpretation. Level U3.1 is the first documented archaeological level to be found in this type of facies at BK, which although are theoretically
Conclusions
Level U3.1 was deposited by a quick and low energy sedimentation processes in decantation facies inside a meandering river channel. This level is the first documented archaeological level to be found in this type of facies at BK and is the youngest archaeological assemblage found at the site, since it is found in LA Unit 3.
Taphonomically, the predominance of unweathered remains and the homogeneous distribution of the remains on top of the same isochronal layer suggest that the assemblage is
Acknowledgements
We thank COSTECH and the Antiquities Unit (Ministry of Natural Resources and Tourism) of Tanzania for permission to conduct research at Olduvai. DMMP acknowledges an FPI postgraduate fellowship associated to Project CGL2015-68333-P. MSD acknowledges a postdoctoral fellowship under the program “Marie Sklodowska-Curie Individual Fellowships” (European Commission). We would like to thank the Spanish Ministry of Education, Culture and Sports, the general direction of Fine Arts and Cultural Heritage
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