Maryut lagoon (Nile Delta, Egypt) hydrological and biosedimentary budget from 8000 to 3200 years cal. B.P.

Maryut lagoon is situated on the north-western margin of the Nile Delta, near Alexandria in Egypt. Its evolution has been reconstructed through the biosedimentological study often radiocarbon-dated borings. The lagoon was formed at about ∼8,000 years cal. BJ., during the marine transgression, before being rapidly isolated from the sea by a sand barrier during the progradation of the Nile Delta coastline. A first biofacies highlights confined ecological conditions until ∼4,800 years cal. B .P., followed by a second biofacies that records a more open lagoon until ∼3,200 years cal. B.P. Transition towards a more open lagoon is recorded when the Nile's discharge strongly decreased during a period of regional aridification. Then, we describe the alternation of two biofacies with a much finer resolution, each lasting several decades. This phase of environmental change appears to be correlated with higher fluctuations in Nile discharge. Our study refines the chronology and the hydrosedimentary specificity of the northwestern delta margin.