Quaternary evolution of Dawhat Zulum (Half Moon Bay) region Eastern Province, Saudi Arabia

The Quaternary geology of the Half Moon Bay region, directly south of the Damman Peninsula, Saudi Arabia, has been mapped and is outlined in the present study. The bay is surrounded by sabkha plains and low sand dunes in a complex morphology which results from the interplay of global sea-level changes, local uplift of the Damman Peninsula, dune migration of the Jafurah Sand Sea, coastal sabka formation, and influx of the Al-Hasa perennial river. Half Moon Bay was emergent in the Late Pleistocene for at least 50,000 years, due to eustatic sea-level changes, but was inundated again during the Late Pleistocene/Holocene 'Flandrian' transgression that started about 12,500 years before the present (BP) and reached its culmination 4,000 years BP. The regional climate has fluctuated considerably in the geologic past, with colder, pluvial episodes occurring, amongst others, during the Early Pleistocene (1.6 to 0.7 million years BP), Middle Pleistocene (560,000 to 325,000 years BP), Wurm glacial (36,000 to 17,000 years BP) and Neolithic wet phase (10,000 to 6,000 years BP). Karstification and sinkhole hazards, present in all major carbonate units of the Eastern Province of Saudi Arabia, originated from dissolution during these past pluvial episodes. During the present-day hot and arid climate, torrential rains episodically cause overflow of the irrigation network of the Al-Hasa Oasis. The excess water fills large evaporation ponds which, in turn, feed a perennial river that transects the dune landscape for some 80 kilometers flowing towards Half Moon Bay.