Sediment Distribution Pattern in the Al-Shoaiba Lagoon, Red Sea Coast of Saudi Arabia
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The Al-Shoaiba coastal lagoon located on the eastern side of the Red Sea is covered mostly with calcareous sand and muddy sand. Wind derived quartz is the most abundant detrital component in the surficial sediments of the lagoon. The lagoon is veneered with sediments of biogenic, aeolian and/or of evaporitic origin. Tidal, wind and wave generated currents play an important role in the redistribution of sediment at the mouth of the lagoon. The fine sediments at the mouth are resuspended by tidal currents and transported into the lagoon. Although the lagoon is very shallow^ the wind and wave generated currents have little impact on the redistribution of sediment except at the entrance. The tidal current moves in the northeastern direction resulting in the winnowing of the fine sediment, leaving the coarser material as lag deposits. Carbonate is abundant in the form of aragonite and high-Mg calcite with subordinate calcite and dolomite. Halite is transported to the lagoon during ebbing from the surrounding low-lying sabkhas. The presence of gray to blackly freckled shell fragments and the presence of authigenic pyrite may be taken as an evidence for reducing condition in some parts of the lagoon.