Nile delta margin: failed and fluidized deposits concentrated along distributary channels / La marge du delta du Nil : concentration de dépôts fracturés et fluidisés le long des paléo­chenaux fluviatiles

摘要

Abstract Previous sediment studies on the Holocene Nile delta margin have emphasized fluvial input and coastal processes, but have overlooked the failure of depositional sequences by syn- and post-depositional events. Herein, petrologic analysis of sediment sections in cores collected along the Nile delta margin indicates the presence of disturbed strata. These modified deposits are not randomly distributed, but are concentrated along former Holocene distributary channels, and generally absent between these Nile branches. Sediment failure involving fluidization, mass flow, and fault-offset prevailed from the mid- to late Holocene, especially since -4,500 years before present. Bedding disturbance was caused by deposition of sediment with high pore water pressure at and seaward of Nile distributary mouths, with flooding along channel mouths believed to be the major trigger of failure. These geohazards were responsible for destruction and partial submergence of the ancient cities of Herakleion and Eastern Canopus in western Abu Qir Bay from -100 B.C. to 741 A.D. Although floods no longer occur since the closure of the Aswan High Dam, some cities constructed on older water-saturated underconsolidated sediment along the modern delta coast remain prone to failure. Protection measures for expanding population centers on the Nile margin warrant thorough civil engineering surveys, including analyses of physical properties of the sediment substrate, with implementation of viable building codes.