Textural and Compositional Characteristics of the Surficial Sediments on the Jizan Continental Shelf, Southern Red Sea coast, Saudi Arabia

Abstract This study investigates the sedimentological characteristics of the surface sediments on the seafloor of the southern Red Sea shelf. The study aims to provide valuable insights into the sedimentary processes and environmental conditions of the Red Sea continental shelf, compared to other modern continental shelves in the subtropical zone, and define implications that can enhance strategies related to offshore development in rift settings. Three research cruises were conducted to collect 192 samples from the Jizan continental shelf, which spans 77 km by 67 km. A Paterson grab sampler was utilized for sample collection; single beam echo sounders (model: ECHOTRAC MKIII) determined the water depths and GPS to decrement spot positions. Samples color, grain size, and composition were described and analyzed. Mechanically shaken and SediGraph technology were used for grain sizes. Statistical parameters: graphic mean, standard deviation, skewness, and kurtosis were calculated. X-ray analysis was conducted for 12 samples to determine the mineralogical composition. ICP-OES identified major and trace elements collected for selected samples. The Jizan continental shelf exhibits water depths ranging from 1 to 260 meters. The sediment composition analysis from the area revealed significant lateral grain size variations. The surficial sediments are classified into two main lithofacies: sand (gravelly muddy sand and muddy, gravelly sand) and mud (sandy mud and gravelly sandy mud). The sediment composition showed elevated Fe, Al, Mg, and Ti oxide concentrations and moderate SiO2 levels. This observation may indicate a source of basic igneous rocks in the coastal hinterland. The eastern nearshore part of the area receives detrital sediments characterized by decreasing oxide content as the carbonate minerals increase. Carbonate concentration appears low nearshore and becomes very high toward offshore sediments. Detrital minerals, such as quartz and feldspars, originate from the weathering of igneous and metamorphic rocks, while high carbonate content suggests erosion of marine limestone platforms. The sedimentary texture variation indicates different energy conditions across the shelf, with fine sediments dominating in calmer waters found in the protected area nearshore and deeper subtidal regions offshore. This study sheds light on sedimentary processes and environmental conditions shaping the Jizan continental shelf. The study emphasized the impact of both terrestrial and marine sources on sediment composition. No previous detailed textural and compositional characteristics of the surficial sediments have been conducted in the studied area. Consequently, this study can be used as an analogy to evaluate the surficial sediments of continental shelves in subtropical and rift settings.