Lithology, fauna and environmental conditions of the Late Pleistocene raised reefal limestone of the Jeddah coastal plai
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ORIGINAL PAPER
Lithology, fauna and environmental conditions of the Late Pleistocene raised reefal limestone of the Jeddah coastal plain, Saudi Arabia Rashad A. Bantan 1 & Ramadan H. Abu-Zied 1,2 & Rabea A. Haredy 1
Received: 8 May 2014 / Accepted: 12 March 2015 # Saudi Society for Geosciences 2015
Abstract The upper successions of the raised reefal limestone of Jeddah coastal plain, especially at Obhur area, were investigated through three temporary exposed geologic sections such as south and northeast Obhur and Al Salam Street. Uranium-series age datings of these successions indicated that their topmost parts were mostly deposited during the last interglacial marine isotope stage 5e (MIS 5e). Lithological–faunal analyses and field observations allowed the division of these successions into two distinct layers: white limestone (lower) and brown shell-rich calcareous clay (upper). The lower layer is enriched with in situ coral boulders of Porites sp. and faviids, as well as with the foraminifers Amphistegina sp., indicating deposition near fore reef and reef crest environments. The upper layer is enriched with molluscs, echinoids, branched (and dwarfed faviids) corals, and the foraminifers Elphidium striatopunctatum and Challengerella bradyi, indicating deposition in back reef, lagoonal environments. The boundary between these two layers is very sharp and irregular, suggesting that the transition from the fore reef to lagoonal conditions was very rapid and catastrophe on coral reef ecosystem due likely to sea-level changes accompanied with warming and increased water runoff. The upper surface of the shell-rich calcareous layer seems to be truncated, but its microfossils could indicate that it was deposited when the sea level was higher than the present mean sea level (MSL) by at least 7 m.
* Rashad A. Bantan [email protected] 1
Marine Geology Department, Faculty of Marine Science, King Abdulaziz University, P.O. Box 80207, Jeddah 21589, Saudi Arabia
2
Geology Department, Faculty of Science, Mansoura University, El-Mansoura 35516, Egypt
Keywords MIS 5e . Sealevel . Benthic foraminifera . Raised carbonate terrace . Coral reef
Introduction The study area The study area is located on the coastal platform of north of Jeddah City (Obhur) between latitudes 21° 40′ 12″ to 21° 45′ N and longitudes 39° 05′ 24″ to 39° 07′ 49″ E (Fig. 1). Within this area, three geologic sections were investigated. The south of Sharm Obhur section (SSO) occurs at the Faculty of Marine Science Lab between latitude 21° 42′ 31.60″ N and longitude 39° 5′ 52.07″ E (Fig. 1). The northeast of Sharm Obhur section (NSO) occurs on the eastern side of Sharm Obhur and far from the shoreline by about 300 m (Fig. 1). It is located at latitude 21° 44′ 51.58″ N and longitude 39° 8′ 6.83″ E. The Al Salam Street section (ASS) is far from the Red Sea coast of Jeddah City by about 2.7 km (Fig. 1) and is located at latitude 21° 40′ 4.02″ N and longitude 39° 7′ 19.66″ E (Fig. 1). The study area is a part of the carbonate platform that extends to cover mos
