Sand dunes in Qassim region : geomorphological characteristics and economic value : an empirical study

الملخص EN

OSL dating technique has shown different periods of sand accumulation in the Qassim region.

The lithified basis of dune fields at depth more than 50 m under the general level were accumulated and formed during Pleistocene age (99.5 Ka).

Consequently, two different dune patterns were formed, the lower or older dunes at the early of Holocene (9.8 Ka), then the upper or recent ones were formed from 3.5 Ka until only 200 years ago.

Recent pattern is active and mainly formed from barchans and transverse types, but the older one is inactive and consists essentially of dome-shaped dunes.

Between them, there is a grassy surface at varying elevations above sea level.

This surface separates between to two different distinct sand faces as well as two different periods of dune formation.

The main geomorphological features of these dunes are discussed on the basis of dune type, origin, wind direction and velocities, wind ripples, internal structure and dune vegetation.

An attempt was made to differentiate between the two patterns of sand dunes as well as the sediments of Wadi ar Rumah’s floodplain.

The differentiation depends upon grain size distribution curves, statistical parameters, geochemical characteristics and OSL dating techniques.

The older dune sands are finer, more sorted, positive skewed and have slightly lower kurtosis values than the recent ones and also the Wadi ar Rumah floodplain.

On the other hand, the study of geochemical characteristics indicates that the older dunes and the floodplain of Wadi ar Rumah are more alkaline than the recent dunes.

While the EC and TDS tend to increase in the recent dunes than the older dunes and Wadi ar Rumah floodplain.

Carbonate, bicarbonate and chloride in general occur in narrow range as a result of weathering.

While the concentration of micronutrient metals (Fe, Mg, Zn and Cu) decrease significantly with the decreasing in finer fractions.