Thermal alteration of bone : experiments in post-burial modification

Burned bone is a common component of archaeological deposits. Hearth features, fire-cracked rock, charcoal and ash are commonly associated with burned bone. However, such direct evidence of fire is not always present in the archaeological record. Nevertheless, burned bone has been associated with culinary activities, waste disposal, use as fuel, and as a by-product of naturally occurring fires. Such interpretations are based upon the assumption that the agents responsible for burning act upon the bone prior to deposition or burial. The sequential relationship between thermal alteration and deposition is continuously incorporated into the analysis of burned material. However, it has been suggested that post-burial alteration of skeletal material is not only possible, but may in fact, serve to explain the condition of burned material recovered in certain situations (see David 1990 and Lyman 1994). Furthermore, exposure to heat following deposition and or burial incorporates several additional variables. The sediment in which bone is deposited, duration of exposure to a heat source, and the interval between burial and burning are factors that affect the extent of thermal alteration. The focus of this research is to test the assumptions surrounding subsurface, (i.e., post-burial), alteration by surface fires. Experiments, both forensic and archaeological, have been conducted to determine features which characterize post-burial burning. Macroscopic and microscopic evaluation of these experimental materials with respect to the traits associated with bone burned through direct exposure to heat, yield intriguing and important results.