A Siliciclastic Coastal Sabkha, Red Sea Coast, Saudi Arabia سبخة شاطئية سليسية على شاطئ البحر الأحمر بالمملكة العربية السعودية

A modern, siliciclastic sabkha occupies the widespread, low lying and almost flat area to the east of AI-Kharrar lagoon on the west of Saudi Arabia. Four sedimentary facies were recognized in shallow cores: (1) surface sand layer associated with halite crust; (2) light brown clayeysandy unit displaying interstitialevaporatic minerals; (3) grey calcareous sandy unit which represents sediments accumulated during marine transgression; and (4) basal poorly sorted gravely-clayey sands of continental origin (Pre-Holocene alluvial deposits). The thickness of the sabkha and marine-lagoonal facies ~facies 1, 2, 3) in general decreases towards the south and east. There are two evaporative assemblages in the studied sabkha. The first assemblage occurs in the southern part and includes gypsum, high Mg-calcite and dolomite. It has formed through reworking of the sediments by flood water from the lagoon and subsequent rapid evaporation. The absence of aragonite in the surface sediments and its presence in those of the subsurface indicate that not only penecontempor3cneous alteration of aragonite to dolomite but also later diagenetic processes have been active. The second assemblage in the central and northern parts of the sa",kha is dominated by gypsum and high Mg-calcite in the surface sediments. Aragonite occurs only in subsurface sediments. Mg concentrations did not reach a level to initiate diagenetic dolomitization. The observed mineralogical distribution is typical for coastal-marine evaporative system. هناك سبخة شاطئية سليسية حديثة في منطقة منخفضة نسبيا ومسطحة تقريبا تقع شرق لا جون الخرار على الساحل السعودي للبحر الأحمر . ولقد أوضحت دراسة هذه السبخة أنها تحتوي على أربع سحن رسوبية هي كالآتي: