ABSTRACT
The housing for senior staff of PDO Ltd at Ras al Hamra, Muscat, is spread over a system of steep-sided ridges and intervening valleys built mostly of folded and faulted Lower Tertiary limestone. At many localities, these limestones are covered with the relics of a formerly more extensive cover of Quaternary carbonate-rich cemented dune sandstones that have a high content of Foraminifera, other biogenic fragments, and some ophiolitic material. Similar cemented aeolian sandstones on the NW coast of India and around the Arabian Gulf are known as Miliolite from their locally characteristic content of Miliolid Foraminifera. South of the Oman Mountains Miliolite also occurs beneath the southern Wahiba Sands and in the United Arab Emirates (UAE)inland from the Arabian Gulf.
The distribution and bedding attitudes of the cemented dune sandstones show that they draped much of the valley floor in the area, and indicate that the sand-transporting winds blew from the NNW towards the nearby Oman Mountains. At the eastern end of the Ras al Hamra beach, cemented aeolian dune sand extends below the current low-tide level. These observations imply that the source of the dune sands is now below sea level on the narrow continental shelf of the Gulf of Oman, which was being actively deflated at a time when global sea level was considerably lower than at present. A fall in sea level of up to 120 m occurred during the build-up of Late Pleistocene northern hemisphere glaciations, thereby exposing former shallow-marine sands to deflation.
Interpretation of regional desert data indicates that when the dune sands were deposited at Ras al Hamra, possibly some 150 ka BP, the climate was probably much more arid, and the winds stronger and more persistent than now. Once the supply of dune sand was cut off following the post-glacial rise in sea level, the area was probably subjected to deflation and to erosion by fluvial activity. During at least one inter-glacial period and the post-Glacial period of higher rainfall around 10–5 ka BP, the rainwater probably also led to leaching of unstable carbonate particles and to cementation of the sands. Arabia has become more arid during the last 5 ka, resulting in more recent deflation of the cemented sands by winds funneled between the ridges of Tertiary limestone.
