Polarizing Microscopy Identification of Chemical Diagenesis in Archaeological Cementum

Cementum increment analysis can potentially retrieve relatively complete, high-precision seasonality and mortality profiles from archaeological mammalian tooth assemblages. However, cementum exhibits many similarities to bone in composition, histology, ultrastructure, and even microstructure. Consequently, the mineralized dental tissue may be prone to the same processes of post-depositional chemical alteration that affect bone. This article reviews the issues surrounding chemical diagenesis in cementum and presents a new application to archaeological ungulate cementum of a polarizing microscopy technique that has previously been utilized to identify the effects of chemical diagenesis in archaeological bone and human cementum (Geusa et al., 1999; Gilbert, 1989; Watson, 1975; Zeder, 1978). It is argued that the post mortem leaching of collagen and the diagenetic growth of apatite crystallites can develop into banded features that mimic seasonal cementum increments. This pattern of diagenesis is demonstrated in multiple locations on a macroscopically well-preserved Upper Pleistocene-age archaeological tooth, which was previously interpreted by the author to exhibit biogenic seasonal cementum increments (Stutz, 1993; Stutz et al., 1995). It is suggested that if researchers seek to retrieve seasonality and mortality data from archaeological cementum, the microscopy analysis protocol must include screening of a pilot sample for the frequency and extent of chemical diagenesis.