The Liwa area is located in the south-central parr. of the UAE along the no
rtheastern upwind margin of the Ar Rub' Al Khali sand sea and covers about
3694 km(2). It has one type of dunes: a mega-barchan that is compound and c
omplex in form characterized by the superimposition of smaller dunes. Due t
o the giant size of barchans, interdune areas appear as closed depressions
that vary in shape from irregular, elongate, triangular, to circular or sem
i-circular. These depressions are mostly covered with small barchans or sab
kha deposits with patches of gypcrete in their upper parts. Scattered flat-
top mounds are also observed in interdune areas. The size of dunes in Liwa
is directly controlled by Quaternary climatic changes: multiple generations
are superimposed on one another separated by calcretic horizons. The clima
te during dune formation alternated between relatively arid to humid. The d
une sands are unimodal with a modal class of fine sand, moderately to very
well sorted, and near symmetrical and mesokurtic. Quartz grains are mainly
subrounded to subangular. Based on the heavy-mineral suites, the sand came
mostly from the ultrabasic rocks that form the ophiolitic sequence of the O
man Mountains, the acidic rocks of Iran. and from the Arabian Shield. (C) 2
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