Stratigraphic and spatial variability in shell middens: microfacies identification at the ethnohistoric site Tunel VII (Tierra del Fuego, Argentina)

Based on ethnographic accounts from the eighteenth to the twentieth century, functional areas have been identified within Fueginian shell middens. In this context, archaeological microfacies acquire a functional meaning when the microscopic record is compared to information gathered from ethnology, macroscopic observations made during excavation, and experimental modern analogues. All these lines of evidence were combined for the first time at Tunel VII, an eighteenth/nineteenth century shell midden occupied repeatedly by Yamana people, the last hunter-gatherer-fisher groups of the Beagle Channel. The sampling strategy involved three sets of samples: (1) two stratigraphical columns taken from the hut "entrance" and from a portion of the shell midden (i.e., the surrounding refuse shell ring), (2) thin sections from five hearths representing successive phases of frequentation of the hut, and (3) experimental burnt valves of Mytilus edulis, the main malacological component of the site. Comparison of microfacies from groups (1) and (2) provided microscopic indicators to distinguish between shell dumping areas and occupation surfaces. Comparison of microfacies within columns from group (1) allowed recognizing periods of site abandonment and periods of more intense/longer site frequentation. The experimental samples from M. edulis served as a reference to characterize the five central hearths in terms of maximum burning temperatures reached. Different burning structures were correlated to the season of hut frequentation and to their location (and function) within different portions of the hut. The intra-site micromorphological comparison strategy within a well-documented ethnohistorical context provides valuable indicators for the identification of functional areas in archaeological contexts when ethnographical information is not available.