Ash deposits in Hayonim and Kebara caves, Israel: Macroscopic, microscopic and mineralogical observations, and their archaeological implications

A study of the hearths and ash layers preserved in Hayonim and Kebara caves, Israel, showed that they are composed of one or several different minerals. These include the polymorph of CaCO3, calcite, a variety of phosphate minerals and a suite of siliceous minerals. The major component of the latter are siliceous aggregates that are present in wood. Detailed studies of the mineral associations in these fossil ash layers, as well as in fresh wood ash, using optical and scanning electron microscopy in the back scattered electron mode together with elemental analyses, showed that ash in these caves undergoes a series of diagenetic changes. The best preserved ash layers resemble fresh ash and are composed mainly of calcite with minor amounts of siliceous minerals. The calcite reacts with phosphate-rich solutions to form carbonated apatite and with time the latter dissolves and a variety of other phosphate-containing minerals form. With each diagenetic change, some of the more soluble minerals are lost and ultimately only the ash-derived siliceous minerals remain. In both caves there-are local accumulations of such siliceous minerals that are metres thick. In fact ash-derived minerals in general are major components of the sediments in both Kebara and Hayonim caves. Their diagenesis involves a hugh reduction in volume, which in turn may have important effects on the geological structures and stratigraphy of the sediments. The changing mineralogy of the sediments due to diagenesis complicates the use of present-day estimates of radiation content of the sediments for correcting age estimates by thermoluminescence and electron spin resonance. Finally, the presence of the relatively stable ash-derived siliceous minerals in a sedimentary layer in other caves, could be a useful means of identifying the presence of ash in other archaeological sites where macroscopic heart features are absent.