RESPONSE OF DESERT OUTWASH SURFACES TO ENVIRONMENTAL CHANGES DURING THE LAST 55 000 YEARS

Evidence of climatic changes is preserved in central Saudi Arabia in the form of a series of outwash plains developed along the eastern edge of the Arabian Shield. The Al-Harmaliah is a fan-shaped outwash suggesting that the region had a considerably higher rainfall at some time during the late Quaternary. The evolution of this outwash fan during the last 55,000 years is analyzed based on data derived from OSL dating and supported by several published 14C data in the region. These data suggest wet phases at c. 55 to 47 ka BP., c. 40 to 19 ka B.P., c. 10 to 5 ka B.P. and c. 0.8 ka B.P. Periods of aridity probably occurred at c. 47 to 40 ka B.P., 19 to 10 ka B.P., and c. 5 to present.

The wetter conditions in central Saudi Arabia can probably be attributed to a shift of the monsoon northwards as a result of increased temperatures, a global rise in sea levels and increased evaporation of the oceans sometime during the late Quaternary.