SHAPE OF PEBBLES AS AN INDICATOR OF CLIMATIC CHANGES DURING THE QUATERNARY IN MAKHTESH RAMON, NEGEV, ISRAEL

Nearly 8000 pebbles were analyzed in Makhtesh Ramon in an attempt to u se pebble shape as a lithostratigraphic tool and to explain the differ ences between morphometric indices of the pebbles for the different al luvial terraces. According to the values of morphometric indices, two groups of alluvial units were distinguished. The first group is charac terized by the lower values of indices. It corresponds with the Holoce ne alluvium (stream, flood plain and the terrace I), and to the terrac es III (8-10 m) and V (18-20 m above river bed). Lithological and poll en analyses show that the accumulation of the alluvium of the first gr oup corresponds with arid climatic conditions with an annual precipita tion of less than 200 mm. The highest values of morphometric indices w ere found in the alluvium of terraces of the second group: II (5-6 m), IV (13-15 m), and VI (25-30 m). The alluvium of this group contains c alcic paleosols and pollen spectra reflecting recurring periods of wet ter semi-arid climate in the past with annual rainfall exceeding 200-3 00 mm. Thus, particle shape may be used not only as a lithostratigraph ic tool, but also as an additional paleoclimatic indicator.