Temperature, compression and fragmentation: an experimental analysis to assess the impact of taphonomic processes on cha
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ORIGINAL PAPER
Temperature, compression and fragmentation: an experimental analysis to assess the impact of taphonomic processes on charcoal preservation Carla Lancelotti & Marco Madella & P. Ajithprasad & Cameron A. Petrie
Received: 7 April 2010 / Accepted: 9 August 2010 / Published online: 14 September 2010 # Springer-Verlag 2010
Abstract This paper explores how mechanical properties of different South Asian tree taxa might influence charred wood fragmentation and the composition of charcoal assemblages retrieved from archaeological contexts. The dataset is composed of selected plant species that were collected in Gujarat (Northern India) in September 2007 as part of the North Gujarat Archaeological Project. The taxa analysed represent the most common wood species found in the arid thorn scrubland formation in South Asia and are among the most abundant identified in Neolithic and Chalcolithic archaeological sites in this area. The specimens have been measured and subsequently charred at three different temperatures, under constant conditions. Afterwards, their resistance to compression has been measured on two planes, parallel and perpendicular to the direction of fibres, using a Hounsfield 5-kN machine. The tests were performed in order to understand the different response to compressive stress of wood that has been subject to a range of thermal degradations.
C. Lancelotti (*) : C. A. Petrie Department of Archaeology, University of Cambridge, Downing Street, Cambridge CB2 3DZ, UK e-mail: [email protected] M. Madella ICREA IMF-CSIC, c/Egipciaques, 15, 01800 Barcelona, Spain P. Ajithprasad Department of Ancient History and Archaeology, MS University of Baroda, Vadodara, India
The standardised treatment applied to the samples has permitted the comparison of results and the delineation of simple correlations and divergences among the species analysed. Furthermore, the utilisation of a relatively simple operating protocol easily allows the addition of further data in the future. The applied protocol was specifically designed to answer archaeological questions. Therefore, even though from a material science point of view some of the measurements were not taken according to the prevailing standard procedures, it offers valuable data for anthracological research applied to archaeology in arid zones. Keywords Wood . Charred wood . Charcoal . Taphonomy . Resistance to compression . Fragmentation . South Asia
Introduction Charcoal1 is one of the most ubiquitous plant remains found in archaeological excavations. Its importance for radiocarbon dating has long been recognised, and its adoption as a proxy for palaeoenvironmental reconstruction has increased exponentially in the past few decades (see discussion in Figueiral and Mosbrugger 2000; Smart and Hoffman 1988). Anthra-
1 Some authors consider 325°C as the minimum temperature for cell fusion and, therefore, charcoal formation (Jones and Chaloner 1991; Kim and Hanna 2006; Kwon et al. 2009; Scott 2010). Other scholars indicate the loss of volatiles that occurs above 400
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