A siliciclastic coastal sabkha, Red Sea coast, Saudi Arabia

الملخص EN

A modern, siliciclastic sabkha occupies the widespread, low lying and almost flat area to the east of Al-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 clayey-sandy unit displaying interstitial evaporatic 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-cal-cite 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 penecontemporaneous alteration of aragonite to dolomite but also later diagenetic processes have been active.

The second assemblage in the central and northern parts of the sabkha 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 tnineralogical distribution is typical for coastal-marine evaporative system.