A comparison of pleistocene gastropod distribution in both open shore and Lagoon at Ash Shaibah South Jeddah, Western Saudi Arabia

Abstract

An exposed succession of raised beaches at the lagoon (5.5m) and the open shore (4.5m), at Ash Shu’aybah area, 80 Km south of Jeddah City was studied from the Paleontologic point of view. The focus was carried out on gastropods collected from two sites to study their diversity and abundance. The studied raised beach at the lagoon is divided into four distinct layers: dolomitic algal limestone layer (1m); calcareous mudstone layer (2.5m); argillaceous limestone layer (1m); calcareous sandstone layer (1m). The open shore raised beach is divided into four distinct layers: dolomitic limestone layer (2m decreasing northward to 1m); limestone layer (1m increasing northward to 2m); argillaceous limestone layer (1m); calcareous sandstone layer (0.5m). The calcareous sandstone layer has high diversity and abundance of gastropods. The study led to the identification of 80 gastropod species belonging to 58 genera, 29 families and 7 orders. The succession at the lagoon has more species (76 species) than the succession at the open shore (27 species), some species are common between the two sites. This is due to the difference in energy (currents and waves) and substrate type. The species Conus auricomus is recorded in the Red Sea for the first time.