Response of Clay Chemistry to Extreme Heating during Fire Events: Applications to Archaeology

Fire in the natural environment has been shown to play a role in altering the mineralogy of the geologic material in which it comes in contact. Our work seeks to utilize the nature of these changes in mineralogy on a small scale to seek a relationship between fire intensity and clay mineralogy in the landscape. The Hopi Indian Tribe had a settlement named Chevelon located near Winslow, Arizona. Due to abundant ash deposits and the highly oxidized nature of some of the walls of this structure, it is thought this location was burned and subsequently abandoned near 1400 AD. To help understand the burning process, archeologists created and intentionally burned the Homolovi structure, which is a modern day analogue to the Chevelon structure. Samples were collected from both structures to help find possible correlations that could explain the type of fire that occurred at the Chevelon site. Our research is using clay chemistry as a tool to investigate fire intensity in an archeological context. Powder XRD and SEM were used to help identify clay mineralogy. Standards of the resulting minerals were then burned at temperatures simulating a high fire. The clay morphological changes of these minerals at increasing temperatures were studied and then compared to the samples from the Chevelon and Homolovi structures to get an understanding of both fire intensities. Our work suggests that there are progressive changes in O/Si ratios with temperature in silicates that may be useful in tracing temperature of the sediments during fire events