MICRO-FABRICS, MINERALOGY AND ISOTOPE COMPOSITION OF MANGROVE CARBONATE MUD IN THE AL-DAKHIRA MODERN LAGOON, NORTH QATAR

The present paper deals primarily with the micro-fabrics, mineralogy and oxygen and carbon stable isotope results of carbonate mud recovered from four short cores (60 cm) recovered from the Al-Dhakira modern lagoon in northern Qatar. The high sediment accumulation rates associated with sea level highstand during the last 1400 Yr must have affected the growth and development of mangrove ecosystem. Aragonite, which exists as acicular to bladed lath-like crystals as revealed by SEM studies, is the dominant CaCO₃ mineral (Av. 88.2%) with subordinate amounts of LMC (Av. 3.5%) and HMC (Av. 4.3%). The δ¹⁸O values (0.85 to -5.79‰PDB) of the studied aragonite mud show negative deviation from normal marine values. Strong negative excursions in δ¹⁸O in individual cores are observed as a consequence of diagenesis, meanwhile, variability along individual cores is comparably low (<1.2‰ PDB). Meanwhile, the δ¹³C values (3.6 to -1.7‰PDB) are indicative for precipitation from water comparable to unmodified marine water.