Taphonomic impact of prolonged combustion
on bones used as fuel
Sandrine COSTAMAGNO, Isabelle THÉRY-PARISOT,
Delphine KUNTZ, François BON, Romain MENSAN
The combustion of bones results in numerous processes whose impact on the representivity of fossil bone assemblages is increasingly well known due to the multiple experimental approaches developed over the last ten years. Recent experiments conducted with outdoor hearths have shown the consequences of prolonged combustion on bone combustion residues.
The average loss of bone mass after combustion is 65 %. The weight of the fine fraction (ashes and fragments less than 2 cm) corresponds to more than one quarter of the residual mass of the remains collected, while the mass of calcined (i.e. white) bone represents an average of 77.2 % of the residues. Finally, the residual bone mass is not correlated with the duration of use of a hearth, but with the manner in which it is maintained. These experiments thus clearly document the significant role of fire maintenance methods on the nature and form of bone residues.
To cite this article
Costamagno S., Théry-Parisot I., Kuntz D., Bon F., Mensan R., 2010 – Taphonomic Impact of Prolonged Combustion on Bones Used as Fuel, in Théry-Parisot I., Chabal L., Costamagno S., The taphonomy of Burned Organic Residues and Combustion Features in Archaeological Contexts, Proceedings of the round table, May 27-29 2008, CEPAM, P@lethnology, 2, 169-183.
The action of weathering on burned bone:
an Experimental Approach
The alteration of bones following exposure to weathering is today well known, but it is possible that burned bones do not suffer the same type of changes since their physicochemical properties are modified by combustion. A series of experiments has been carried out with the aim of better understanding these reactions. These experiments form part of a more widespread attempt to better understand the impact of taphonomic agents on burned bones in order to estimate the distortions between bone material originating from experimental combustion and the fossil material.
Five experimental series resulting from the combustion of fresh cow humeri were exposed for eighteen months to weathering in a Mediterranean context. Several criteria were observed in order to highlight the impact of this exposure on the burned bones: degree of fragmentation, loss of bone mass, alteration of bone surface, influence of the degree of combustion (carbonised vs charred) and of the bone tissue (spongy vs compact) on the preservation of the material.
The results of these experiments mainly show a high fragmentation of the material (the small burned bones being in the majority), associated with a reduction in bone mass. In addition, spongy and charred bones have an increased sensitivity to the action of weathering, leading to their destruction. A preferential preservation of charred compact bone is thus expected.
To cite this article
Gerbe M., 2010 – The Action of Weathering on Burned Bone: an Experimental Approach, in Théry-Parisot I., Chabal L., Costamagno S., The taphonomy of Burned Organic Residues and Combustion Features in Archaeological Contexts, Actes de la table ronde, 27-29 mai 2008, CEPAM, P@lethnology, 2, 185-196.