Late Quaternary stratigraphy and paleogeography of the eastern Nile Delta, Egypt

Abstract

A petrological study of numerous sediment borings identifies the late Pleistocene and Holocene lithofacies in the northeastern Nile Delta of Egypt. A coarsening-upward sequence characterizes the major Holocene depocenters located along the northern margin of the present Delta. Stratigraphic correlation of radiocarbon-dated sections and mapping of key facies such as delta-front mud reveal the locations of four major Holocene delta lobes related to former distributary branches of the Nile River: Mendesian, Pelusiac, Tanitic and pre-modern Damietta. These lobes, formed primarily of marine prodelta and delta-front deposits, interfinger geographically, but radiocarbon dating indicates that their bases are not synchronous. Lobes developed for the most part since 8000 years B.P., i.e. as the rate of eustatic sea-level rise began to decrease. Climatic and sediment-discharge fluctuations, lateral migrations of distributaries, and isostatic subsidence of land are additional factors that affected the temporal and spatial distributions of the lobes. Paleogeographic maps reveal the changes with time in the distributions of different lobes and deltaic-plain environments (marsh, lagoons), and concomitant displacement of the coastline. Holocene sediment accumulation rates to 500 cm per 1000 years are calculated. This is 10 times greater than that on the Nile Cone and 50 times greater than on the Egyptian continental shelf. The delta coastal margin in the study area migrated northward by as much as 50 km during the past 5000 years, an average progradational rate of up to 10 m per year. The general configuration of the present delta developed during the past millennium. The major changes recently induced by man in this region, coupled with a series of continuing natural phenomena (slow rise in sea level, coastal erosion, subsidence) have markedly affected the evolution of the delta. Petrological study of the Nile Delta sediments provides baseline reference information to help recognize changes in the recent geological past, to help identify those taking place at present, and possibly to help predict those likely to occur in this region in the future.