The Middle Stone Age sediments at Sibudu: results from FTIR spectroscopy and microscopic analyses

Abstract

We present results from Fourier transform infrared spectroscopy (FTIR), transmitted polarising light and scanning electron microscopy (SEM-EDAX techniques), as well as phytolith analyses applied to sediments from Sibudu Cave. The Middle Stone Age sediments at Sibudu show minor degrees of diagenesis. This is demonstrated by the rarity of authigenic phosphate minerals, the occurrence of gypsum and calcite, and the absence of plant ash residues enriched in phytoliths and siliceous aggregates. Little loss of bone due to dissolution can be expected in such a sedimentary milieu. Therefore unearthed bones are likely to be in situ. The dry sediment conditions, which can be deduced from the stability of gypsum and calcite, make Sibudu a key site for faunal studies. Nevertheless, microscopic evidence of bone fragmentation through gypsum crystallization suggests that much of the mechanical bone destruction above layer GR is related to the growth of secondary gypsum. Furthermore, the comparatively dry sedimentary milieu at Sibudu is responsible for the good preservation of the fire-related structures. Hearths and ash dumps frequently show sedimentary compositions and phytolith contents similar to those of the sediments around them.