Sediment characteristics and molluscan fossils of the Farasan Islands shorelines, southern Red Sea, Saudi Arabia
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ORIGINAL PAPER
Sediment characteristics and molluscan fossils of the Farasan Islands shorelines, southern Red Sea, Saudi Arabia Rashad A. Bantan & Ramadan H. Abu-Zied
Received: 31 May 2012 / Accepted: 15 January 2013 # Saudi Society for Geosciences 2013
Abstract The Farasan Islands are located about 40 km offshore of Jizan area, southern Red Sea, Saudi Arabia. This is a preliminary study aiming to collect shoreline sediments from 17 stations to describe their main lithologic characters and identify the dominant molluscs that could help to evaluate the environmental conditions of these islands. Also, a sediment core FARA2 was collected from the intertidal area of Khor As Sailah Lagoon to see the development of shoreline sediments in this area with time. The results indicated that the shoreline sediments of the Farasan Islands comprised mainly of white, biogenic sand enriched in remains of corals, molluscs, calcareous algae, and benthic foraminifera. Thirty-four mollusc species were recorded from these sediments. Among them, Strombus fasciatus, Strombus tricornis, Chicoreus ramosus, Chicoreus virgineus, Tridacna maxima, and Tridacna squamosa were the most common molluscan in/near the shoreline sediments of Farasan Islands. Frequency abundances of sediment grain-size fractions in the core FARA2 indicated that the shoreline of the Khor As Sailah Lagoon is developing towards shallow intertidal setting due to high production of biogenic sediments by reefal communities. Metal concentrations (Fe, Mn, Cu, and Zn) in the sediment of the core FARA2 were stable throughout, showing no remarkable changes. This finding could indicate that flux of detrital components by fresh water runoff or wind-blown dust over the Farasan Islands was un-detectable during the deposition of these sediments. R. A. Bantan (*) : R. H. Abu-Zied Marine Geology Department, Faculty of Marine Science, King Abdulaziz University, P.O. Box 80207, Jeddah 21589, Saudi Arabia e-mail: [email protected] R. H. Abu-Zied Geology Department, Faculty of Science, Mansoura University, El-Mansoura 35516, Egypt
Keywords Farasan Islands . Heavy metals . Shoreline sediments . Gastropods . Pelecypods
Introduction The Farasan Islands are located in southern Red Sea, in the extreme southwestern side of the Saudi Arabia (Fig. 1). They have low topography varying from 10 to 20 m above sea level; however, a maximum elevation of 75 m occurs at the northwestern side of the Farasan Al-Kabir Island and Jabal Bottan (Bantan 1999). The surface of the islands is mainly composed of fossil reefal limestone with the oldest strata (early Pleistocene) in the center of the islands and the younger ones (late Pleistocene) occur near the low topography coastline (Dabbagh et al. 1984; Bantan 1999). This suggests that the Farasan Islands were formed during progressive uplift and relative sea level fall as indicated by the occurrence of shell middens of Holocene age (5,400 ± 250 BP) on a 2-m-high notch that occurs today at more than 50 m distance from the shore (Bantan 1999; Bailey et al. 200
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