AGE AND PALEOWIND REGIME OF LINEAR DUNES IN THE NORTHERN RUB AL KHALI

The Arabian Peninsula is dominated by extensive dune systems, including the world’s largest sand sea, the Rub al Khali. The northern parts of this sand sea exhibit a complex pattern of dune construction, reactivation, and stabilization in response to changes in sea level and climate. The complexity is manifested by up to six generations of dunes of different morphological types and composition. The largest and most widespread dunes in the area are west- to east- oriented 50 - 100 m high complex linear dunes with crescentic dunes superimposed on them in the north and east, and star dune peaks in the southeast part of their distribution. Dunes of this type are spaced 2 to 5 km apart and are found throughout the northern and eastern parts of the United Arab Emirates as well as in adjacent areas of Oman and Saudi Arabia. These dunes are composed mainly of reddish brown quartz sand with less than 10% carbonate grains, and are now being reworked in northern areas by NW winds into crescentic dunes and obliquely-oriented small linear dunes that are superimposed on the linear dunes and cross interdune corridors. Optical ages from exposures of these dunes at three locations range between 42 ka and 15.1 ka, with a clustering between 15.1 and 18.3 ka, suggesting their formation during period of the last Glacial Maximum. The superimposed crescentic dunes have ages between 0.5 and 0.11 ka. The gross bedform normal solution for dune trends indicate that the best fit for the west - east linear dune trend in the UAE involves a wind regime with increased sand transport from the northwest and west southwest. Such a wind regime likely resulted from the increased continentality of the region during a period of lower sea level and consequent desiccation of the Arabian Gulf. Our results combined with information from studies in other parts of the region indicate regional-scale synchroneity of episodes of aeolian construction and/or reworking. It appears that the linear dunes of this region were formed or reformed in the period spanning the last Glacial Maximum. There is some evidence to suggest that these dunes were also reworked during the Younger Dryas event (12.5 - 11.5 ka). Late Holocene dune activity has been restricted to reworking and modification of the older linear dunes by the dominant NW (Shamal) wind system.