A mineralogical and phytolith study of the Middle Stone Age hearths in Sibudu Cave, KwaZulu-Natal, South Africa : Sibudu Cave

Sediments from Middle Stone Age hearths and burnt deposits in Sibudu Cave (KwaZulu-Natal, South Africa) were analysed for their mineral and phytolith contents. The mineral compositions were determined by FT-IR spectroscopy. The phytoliths were classified and counted by transmitted polarized light microscopy. Burning experiments using wood and grasses from species native to the cave's environment yielded the reference ashes. The visible hearths and ash dumps contain phytolith assemblages characteristic of wood fuel. A significant portion of the phytoliths of hearths and ash layers display morphologies related to intense heating. This finding is suggestive of long-burning wood fires and/or reuse of the same fireplace. The heat-altered phytoliths are useful in tracing fires, especially if hearth structures are not preserved and ash deposits have been diagenetically and heavily altered. The phytolith contents and mineralogical composition of the ash deposits and the surrounding sedimentary matrix are very similar. This feature suggests that the sedimentary matrix originally contained fireplaces and ash deposits, whose structures were destroyed shortly after deposition, presumably by trampling. The intact circular hearths are most likely the product of intense fires. Similar results from hearths and their surrounding matrix have been reported from Middle Palaeolithic cave sites in Israel.