Study of ash layers through phytolith analyses from the Middle Paleolithic levels of Kebara and Tabun caves

[eng] The Levant, and Israel in particular, possesses a rich archaeological record of prehistoric caves from the Middle and Upper Paleolithic periods. Some of these caves have been subjected to intensive multidisciplinary studies, providing information not only on the archaeological record, but also on the diagenetic processes that have affected this archaeological record through time.One of the most interesting remains preserved in these caves is the ashy features or hearths. They are usually abundant and often visually well preserved. Ash accumulations are sometimes meters thick. Their presence has made it possible to use and develop new techniques in order to obtain more information about the fire related activities carried out in the cave, the functionality of these hearths and their significance in the social life of past cultures.One of the techniques used for the study of hearths involves the analysis of phytoliths. Phytolith analyses in prehistoric hearths can be used for a variety of purposes. These include the identification of ash remains, even in locations where they are not visible to the naked eye due to diagenetic alteration; the identification, in a specific hearth, of the use of wood/bark as opposed to other types of vegetation such as grasses, and the identification of different species of trees and/or other plants used as fuel in a specific hearth. It is also conceivable that the latter two sources of information could provide indications of possible uses of fire (cooking, warmth, technical purposes, etc.) based on the different fuels used.An interpretation of the phytolith data from an ashy feature or hearth needs to be based both, on the morphological characteristics and the quantitative analyses of the phytoliths. This provides information on the absolute number of phytoliths produced by the trees and other plant taxa present in the area, and on the number of phytoliths per unit weight of sediment. This in tum may indicate, for example, the extent of mixing of ash with other soils, the relative proportions of say wood ash and grasses in a hearth, or the use of fruits from trees or other parts of the trees.This study focuses on the ash layers frorn two prehistoric caves in Israel, Tabun and Kebara, both located on Mount Carmel, Israel (Figure 1). Tabun was occupied during the Lower and Middle Paleolithic periods and Kebara was occupied during the Middle and Upper Paleolithic periods. Both caves have visible hearths, with those in Kebara being particularly impressive.Alternative modes of occupation of Tabun Cave during the deposition of the Mousterian Levels B and C, have been proposed. Garrod & Bate (1937) interpreted the archaeological record of both levels as being indicative of domestic occupationaI activities. Jelinek et al. (1973) proposed that the presence of articulated limb bones of "Dama mesopotamica" in the Level B sediments below the cave chimney, indicated that the cave was used as a natural game trap. They also noted that the white ash layers in Level C extended across the whole cave, and proposed that this was due to the burning of natural vegetation in the cave. The study carried out in Tabun cave aims at clarifying the modes of occupation during these periods.Level B sediments closely resembles the terra rossa soil, that is common in this region. Burning activity is inferred from charcoal fragments observed in thin sections. A minor wood ash component is present based on the preponderance of phytoliths with a variable, irregular morphology, produced mostly in wood and bark as compared to those with a consistent or characteristic morphology, as well as phytoliths with shapes characteristics of those formed in wood and bark of local trees. Thus fires were produced in the cave during this period. The cave may also have been used as a game trap.Level C is composed of multiple layers of brown, black and white sediments. Micromorphology, mineralogy and phytolith analyses all show that these layers are mixtures of terra rossa soil and ash, with the latter being abundant in the white layers. The phytoliths in these layers are derived almost entirely from wood and bark, and not from grasses. These observations are consistent with a domestic occupational mode.Kebara cave is a well studied archaeological site. It contains abundant visible hearths and ash-derived minerals that are the major component of the Mousterian sediments. The latter are in varying states of preservation. Furthermore, archeobotanic information is available from charred remains. Kebara cave is thus an ideal location to study the potential of phytoliths to provide information on the mode of fire used in the cave, to assess the input of other plant materials, as well as to determine the effects of diagenesis on phytolith preservation.Sixteen samples were analyzed in terms of their mineralogy, phytolith contents per unit weight of acid insoluble fraction, and phytolith morphologies. In general the preservation of the phytoliths is good, except for the two samples in which the mineral component at present is largely ash-derived calcite. The cave sediments contain about ten times more phytoliths than those present in the four samples analyzed from outside the cave. The major source of plant material input into the cave is clearly from the wood and bark used for the fuel for fires. The grass phytoliths present in the samples are also thought to have been brought into the cave mainly associated with the wood/bark fuel. Sediments from the hearths, as well as those between the hearths, contain abundant wood/bark phytoliths. The two samples of the latter contain also appreciable amounts of phytoliths not known to be present in wood and bark, as do other hearth-derived samples. Plant materials other than those used as fuel, were thus also brought into the cave.The study about Kebara cave shows that phytoliths analysis, in conjunction with detailed mineralogical, stratigraphic, archaeobotanic and field information, can provide a more complete understanding of the use of plant materials in prehistoric caves for both fuel and other purposes