Late Holocene Red Sea Coastal Evolution: Evidence from Shallow Subsurface Sedimentary Facies, North Al-Wajh, Saudi Arabia

The stratigraphy of the late Holocene shallow subsurface coastal sediments, North Al-Wajh, Saudi Arabia was investigated to reconstruct the environmental evolution of the area in relation to sea-level changes. Five shallow cores (1.1 to 2.2 m long) were collected from the intertidal flat bordering the Dumaygh Lagoon, and the mouths of wadis Antar and Haramil. The cores exhibit siliciclastic-dominated sediments, in some parts containing reworked calcareous shell fragments of bivalves, gastropods and coral remains. The sediments were analyzed for grain size, loss on ignition (LOI), CaCO3 content, and bulk mineralogy. Mineralogically, the sediments were dominated by siliciclastic minerals (quartz, plagioclase, feldspars, and hornblende) followed by low Mg-calcite (LMC), high Mg-calcite (HMC) and aragonite. In addition, traces of mica, amphiboles, clay minerals, and dolomite were recognized. There is a slight lateral variation in the relative abundance of aragonite and high Mg calcite (HMC), particularly at the base of cores. The results provide a simple scenario for the late Holocene Northern Red Sea coastal evolution. Two vertically stacked sedimentary facies were recognized from the cores; grey mud-dominated lagoonal/bayfill at the base and yellowish-brown sand-dominated intertidal flat at the top. The vertical facies stacking suggests a forestepping pattern or progradational sequence possibly attributed to the late Holocene relative sea-level fall.