Étude expérimentale de l'action du gel sur les restes fauniques. Premiers résultats.
Résumé
The recognition of human action on prehistoric bones hoards is one of the basic problems in taphonomy. In an archaeological site the fragmentation of bones and/or teeth is not only anthropic since natural factors are involved in the breaking up. Among these natural factors we can distinguish the climate effects and especially those of frost breaking in a cold chamber in the “Centre de Géomorphologie du CNRS” of Caen in collaboration with J.-Cl. Ozouf director of the cryoclastism laboratory.
Since four years teeth, long bines, short bones, antlers have been subjected to daily cycles of frost/thaw between -5°C and +12°C. At 1012 cycles we observe that:
1 – Frost effect is, to some degree, independent of the degree of humidity;
2 – A great variability in frost effect.
The preliminary study of the results of the experimental frost breaking suggests that the fragmentation, in an archaeological site, is not only anthropic as previously noted. However as we are unable to compare the experimental frost fractured chips to the archaeological fragments, we do create an experimental site in an area subject to frost/thaw cycles (solifluction, cryoclastism, frost splitting, ...). Archaeologists, archaeozoologists, geologists and palynologists from the “Centre de Géomorphologie du CNRS” of Caen and of the “Institut du Quaternaire, UMR9933 du CNRS” have a great interest in this pluridisciplinary research program named “TRANSIT” (J.-P. Texier dir.). In the perspective of this project, the artificial site will be composed of five identical squares in which some specific objects (flint and faunal remains) are perfectly located. Each year we shall excavate one square in order to analyze the modifications (solifluction ... in the soil, movement and weathering of the samples). To complete the results, we shall add a seventh square in which the soil will be very disturbed (trampling, fire-place ...). Finally, this last square will be excavated at the end of the program. Then all faunal fragments will be compared on the one hand to those treated in the frost chambers and on the other hand to the archaeological fragments.
Since four years teeth, long bines, short bones, antlers have been subjected to daily cycles of frost/thaw between -5°C and +12°C. At 1012 cycles we observe that:
1 – Frost effect is, to some degree, independent of the degree of humidity;
2 – A great variability in frost effect.
The preliminary study of the results of the experimental frost breaking suggests that the fragmentation, in an archaeological site, is not only anthropic as previously noted. However as we are unable to compare the experimental frost fractured chips to the archaeological fragments, we do create an experimental site in an area subject to frost/thaw cycles (solifluction, cryoclastism, frost splitting, ...). Archaeologists, archaeozoologists, geologists and palynologists from the “Centre de Géomorphologie du CNRS” of Caen and of the “Institut du Quaternaire, UMR9933 du CNRS” have a great interest in this pluridisciplinary research program named “TRANSIT” (J.-P. Texier dir.). In the perspective of this project, the artificial site will be composed of five identical squares in which some specific objects (flint and faunal remains) are perfectly located. Each year we shall excavate one square in order to analyze the modifications (solifluction ... in the soil, movement and weathering of the samples). To complete the results, we shall add a seventh square in which the soil will be very disturbed (trampling, fire-place ...). Finally, this last square will be excavated at the end of the program. Then all faunal fragments will be compared on the one hand to those treated in the frost chambers and on the other hand to the archaeological fragments.
La fragmentation observée dans un gisement archéologique ne peut s'expliquer uniquement en termes d'action anthropique. Nous avons donc procédé à des expériences de gel d'os et de dents pour essayer de caractériser les gélifracts et les distinguer des autres types de fragments. Le bilan de la gélifraction au terme de 1012 cycles expérimentaux de gel/dégel nous permet de mettre en évidence les effets du gel mais, ne pouvant comparer directement les gélifracts expérimentaux et les fragments osseux archéologiques, nous avons, dans le cadre du programme de recherche pluridisciplinaire TRANSIT, placés des restes fauniques dans des sites artificiels naturels dans les Alpes du Sud.
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