A sedimentary depositional and diagenetic model of a Pleistocene/Holocene coastal formation in Alexandria, Mediterranean Sea, Egypt

Late Quaternary deposition along the northwest coastal plain of Egypt was influenced by sea level fluctuations as documented by a succession of Quaternary carbonate ridges (up to eight or nine) running parallel to the present shoreline. This study focuses upon depositional and diagenetic aspects related to the last glacial cycle and aims to the reconstruction of the coastal sedimentary paleo-depositional environments of the “Gabal El-Kor Island”, located along the Mediterranean coast of Egypt near Alexandria. The sedimentary succession cropping out at Gabal El-Kor Island is interpreted as a part of the Pleistocene second coastal ridge, dated at about 100 Ka. This study revealed that during the last interglacial period (Marine Isotopic Stage 5, MIS 5), marine deposits mostly made of bioclastic grains and ooids were formed and their early diagenetic alteration was achieved under marine subaqueous conditions. After marine regression, during glacial periods, a phase of subaerial exposure followed. This was associated with transport and accumulation of the exposed carbonate sands from the shore inland by wind action. In the postglacial, the sea level rose up to its present level and a lagoon formed behind Gabel El-Kor Island. The most relevant diagenetic events took place in three distinct stages: MIS 5, between MIS 4 and MIS 2, and during the early and middle Holocene MIS 1. Salient diagenetic events refer to vadose, meteoric, and marine phreatic environments respectively.