Mineral Assemblages in Theopetra, Greece: A Framework for Understanding Diagenesis in a Prehistoric Cave

Prehistoric cave sediments are often subjected to severe mechanical and chemical alteration, making it difficult to interpret aspects of their archaeology. Theopetra cave offers unique opportunities to resolve aspects of this problem, particularly in relation to chemical changes, because it has a relatively well defined stratigraphy and its older deposits have been subjected to unusually severe diagenesis. A study of the mineralogy and micromorphology of the sediments, and in particular the phosphatic minerals that formed in the sediments after deposition, shows that each stratigraphic unit has its own pattern of authigenic mineral distribution. In some units these patterns vary sequentially in both lateral and vertical directions. These variations reflect changing degrees of diagenesis and the observed patterns imply that every unit obtained its diagenetic fingerprint fairly soon after burial. The prominent ash layers in the older sediments were subjected to unusually severe diagenetic alteration, such that most of the relatively stable siliceous components of ash decomposed into amorphous silica. An intimate association between ash minerals and the K, Fe-phosphate mineral leucophosphite was also observed. The sequential changes in authigenic mineral assemblages in Theopetra are basically similar to those observed in several caves in Israel, raising the possibility that common processes are involved and that information obtained from these detailed studies can be applied to other caves in diverse geographic regions. ? 1999 Academic Press