EOLIAN CHRONOLOGY AND PALEOWIND VECTORS IN THE NORTHERN RUB AL KHALI, UNITED ARAB EMIRATES

The Quaternary history of northern parts of the Rub al Khali sand sea of Arabia exhibits a complex pattern of dune construction, reactivation, and stabilization in response to changes in sea level and climate. The complexity is manifested by: (1) multiple generations of dunes of different morphological types and (2) the stratigraphic record of partially to completely lithified carbonate-rich eolian sediments (eolianites), which underlies many areas of the dune system.

Stratigraphic evidence from exposed sections and clustering of OSL dates from the eolianites indicates that dunes were formed during the periods 129-164, 99-113, 34-64 and 22-18 ka from bioclastic sediments deflated from the shelf areas of the Arabian Sea during periods of low sea levels. Wind directions during these periods of dune construction were from the NW-NNW.

OSL dating of the large quartz rich E-W to SW-NE-trending linear dunes which are superposed on the eolianites, provides evidence for their formation in the periods 31-42, 15 –18, and 12- 9 ka. The change from a carbonate-dominated to a quartz-dominated eolian system after about 18 ka suggests depletion of sediment supply from the Arabian Gulf, perhaps accompanied by a change in the wind regime to a more westerly orientation.

In the Liwa area to the south, large quartz-rich compound crescentic dunes overlie inland sabkas. Stratigraphic and geomorphic evidence, together with OSL dating of eolian sands indicate periods of dune accumulation around 141, 106, 40, 26, 12, and 4-6 ka. The lack of coincidence of many of these dates with those from the eolianites closer to the Arabian Gulf suggests that dune activity in this area was controlled by climate rather than sea level. Radiocarbon and OSL dates indicate that the widespread calcareous-cemented interdune sediments in the Liwa area (many of which now cap mesas in an inverted topography) formed between 29 and 41 ka, when the water table in this area was several meters higher than present, possibly as a result of increased precipitation during MIS 3.