Stone Tool Experiments and Reduction Methods at the Acheulean Site of Isampur Quarry, India

Article excerpt

Introduction

Stone tool technology has been used to make inferences about various aspects of hominin cognition, ranging from symbolism (e.g. Carbonell et al. 2003) to spatial awareness (e.g. Wynn 2002). Stone tool reduction experiments are an important methodology in archaeology as they allow us to infer aspects of behaviour which would be difficult to ascertain from the artefactual data alone. Lithic manufacturing experiments have been used to reconstruct specific reduction strategies employed at individual sites (Jones 1994; Madsen & Goren-Inbar 2004), and to compare the cognitive and skill demands of different knapping techniques (Edwards 2001; Stout et al. 2006). Stone tool experiments are therefore an important methodology for understanding hominin behaviour, and are here applied at the Acheulean site at Isampur Quarry.

Isampur Quarry is located in the Hunsgi-Baichbal Valley in the centre of peninsula India (see Figure 1). Over 15 000 artefacts have been recovered from the site, including limestone cores and debitage and a variety of hammerstones. It is apparent that the entire biface manufacturing sequence was carried out there, from extraction of the bedrock to the creation of finished handaxes and cleavers (Petraglia et al. 1999; Paddayya et al. 2006). Isampur Quarry occurs on a siliceous limestone pediment on the western edge of a 2-3m deep palaeo-drainage channel that has silted up since the hominin occupation (Paddayya et al. 2002). The limestone bedrock weathers in a predictable way leaving joint-bounded slabs of thicknesses varying from 20 to 200mm. The weathered form of the limestone makes it easy to procure and its highly siliceous nature (up to 18 per cent silica evenly distributed throughout the stone) gives it excellent Hertzian flaking properties, so it is an ideal material for lithic manufacture (Petraglia et al. 1999). The limestone, overlying an up-thrown fault block running near the site, has been chemically weathered to leave a residuum of chert cobbles, making a good supply of hammerstones. Other chert, basalt and quartzite hammerstones were also introduced to the site from 1-2km away.

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Our observations indicate that handaxes were predominandy made by reducing slabs of bedrock to leave the desired shape, while cleavers were mostly made from large flakes struck off slabs (Petraglia et al. 1999, 2005). Analysis of slab thickness showed that most of the thinnest slabs were not used by hominins, those from 30 to 80mm in thickness were reduced into handaxes, while those from 50 to 160mm were used as cores (Petraglia et al. 2005; Shipton 2007). Experiments were conducted to further explore these two reduction strategies.

The experimental design

Stone tool manufacturing experiments were conducted on natural limestone slabs at Isampur Quarry. Two analysts were involved in this research, Michael Noll, who performed the lithic experiments, and Michael Petraglia, who recorded relevant information. Based on observations and measurements of the chipped stone artefacts and hammerstones at Isampur Quarry, the analysts attempted to reproduce hominin reduction sequences. Two biface reduction methods were hypothesised at Isampur Quarry (Petraglia et al. 1999, 2005) the reduction of thinner limestone slabs to leave the biface form, and the striking of large flakes off thick core slabs to be used as biface blanks. Throughout this paper we refer to the former method as faconnage as it involves the shaping of a substrate by the removal of small pieces, and the latter method as debitage as it focuses on the removal of a single large piece of predetermined form. Once the biface blank has been created in the debitage technique final trimming and shaping is achieved through faconnage, however this process is not the main emphasis of the technique. Thirty-seven reduction experiments were carried out over a period of five days, producing 25 bifaces (see Table 1). …