ABSTRACT

Bardawil lagoon is a body of water about 600 km², it is about 80 km long and its maximal width is approximately 18 km. The lagoon is separated from the Mediterranean by a sand barrier.

Waters and sediments of the lagoon were analysed. The decrease in specific alkalinity of the waters with increasing distance from the inlets and with increasing chlorosity suggest that authigenetic carbonates are precipitating at present from the lagoon waters.

The predominant type of sediment is sand, covering all the nearshore and nearbar areas; clayey sand covers the deepest and the most distant parts from the inlets, which connect the lagoon with the Mediterranean.

The western-arm sediments, composed of sand containing marine diatoms and pelecypods, show that the region was under marine conditions throughout the period represented by the column of sediments studied.

In the main lagoon a change from marine condition, represented by sand and marine shells found in the deeper portions of the cores to lagoonal evaporitic ones in the upper sediments (gypsum and clayey sediments present), is clearly demonstrated.

At the present the salinities of the lagoon waters do not permit the precipitation of gypsum. This shows a restoration of the connection between the lagoon and the Mediterranean leading to the dilution of the highly saline lagoon waters and hence to the cessation of precipitation of gypsum.

The relative abundance of the sand, the spatial distribution of gypsum and marine and lagoonal diatoms suggest that the sedimentary column studied was formed under marine to lagoonal conditions and that no streams entered the lagoon during this period. The sediments were brought to the lagoon from the Mediterranean. The Nile branches (including the Pelusiac) brought the sediments to the Gulf of El Tina in the Mediterranean and long shore west-east currents brought the sediments to the lagoon.