Abstract
Coral reef area in northwest of the Arabian Gulf was investigated for mineralogy and geochemistry to throw lights on such unique Iraqi Marine Environment; six specimens of two main species of coral reefs, Platygyra pini Chevalier, 1975 and Octocoral Menella were collected at two sites. While eight samples of the surrounding sediments are chosen from other two sites. The mineralogy is determined by XRD, and reveals that calcite, low magnesium-calcite, and aragonite are the main minerals that comprise the Octocoral Menella in site 1, whilst aragonite and calcite are dominate in the P. pini coral reef at site 4. The non–carbonate fractions indicate that these coral reefs contain quartz, anorthite feldspare , halite, and gypsum; the highest content of aragonite was observed in the P. pini compared to calcite. The abundance of carbonate minerals (92.1%) in the P. pini is in contrast to (73.1%) in the Menella. The main minerals in the sediments of site 2 are represented by chlorite and talc, whereas quartz and phengite are the most prominent minerals that diagnose in sediments of site 3; phengite mineral is a first discovery in the sediments of Arabian Gulf, whilst talc is a first detection in Iraqi marine sediments. The concentration of CaO is the most abundant oxide in all the analyzed specimens of the coral reef followed by SiO2. There are high proportions of calcium oxide in P. pini Chevalier coral (56.65 %) than the Menella (48.81%). There are some special pattern of distribution for major and trace elements in coral reef area based on calcium content. Most of the silica came from quartz, phengite and clay minerals; the highest concentrations of Al2O3, Fe2O3, K2O, Na2O, MgO, SiO2, TiO2, V2O5, Cr, Ni, Cu, Rb and Zr are found in the sediments of site 2 as opposed to the other sites. These results could affect the association of these elements with clay minerals through adsorption or absorption, the highest content of P2O5, Ga, W and As in the sediments of site 3 may reflect the adsorption of these elements on surface of the quartz and phengite; from the other hand, the highest concentrations of Sr, Zn, Br, Sn, Ta, and Pb in the P. pini may indicate the relative effects of the environmental variation within the studied area.
Highlights
Coral reefs are among the greatest keys to unlock our understandings of a marine ecosystem (Perkol – Fenkel and Banayahu, 2007); this organism lives within exclusive temperature conditions and the sea water varieties survive between 14 to 34 0C (Coles and Fadlallah, 1991)
The bulk mineral components and the relative abundance of each mineral have been considered on the basis of peak high measurements of a 100% reflection peak; the data attained are summarized in Table (2) and selected X-ray diffractograms are provided in Diagrams (1, 2, 3, and 4); carbonate minerals obtained in the Menella sp.l (Site 1) are calcite, low Mg-calcite, and aragonite
Aragonite and calcite could be the main carbonate minerals of the P. pini in site 4, it formed more than 92% from the total minerals of this reef, and recorded here dominates over calcite, quartz and halite are recorded at lower constituents regarding this species of coral reef
Summary
Coral reefs are among the greatest keys to unlock our understandings of a marine ecosystem (Perkol – Fenkel and Banayahu, 2007); this organism lives within exclusive temperature conditions and the sea water varieties survive between 14 to 34 0C (Coles and Fadlallah, 1991). Coral reefs of the Arabian Gulf and Oman Sea are serious habitats of cultural, socio-economic, and scientific importance. Corals in the Arabian Gulf are exposed to great summer sea temperatures compared with other tropical regions, with temperatures above 34°C for several months annually and summer maxima rising above 36°C (Coles and Riegl, 2013; Burt et al .,2015). Salinity in the Arabian Gulf is very high, generally between 35- 46 ppt in Iraqi marine environments (Al-Dabbas and Al-Jaberi, 2015) , while in the shallow waters between Bahrain and Qatar, salinity often exceeds 50 ppt; these waters have the potential to offer important insights into how corals respond to temperature and salinity stress (Smith et al, 2017). In most areas of the Arabian Gulf, corals do not form true reefs, but are better described as ‘coral carpets’, where separate colonies a raise on exposed rocky substrates rather than building on older dead coral skeletons (Burt et al.,2015)
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