Geochemistry of Holocene Sediments from the Nile Delta

Abstract

Clay-size fractions of Holocene (to > 7,500 years BP) core samples (n = 173) from lagoonal/marsh, delta-front and prodelta facies in the northeast sector of the Nile delta were analyzed for 23 elements. The cores follow three distributary systems that were active at different times during delta evolution. The sediments are enriched in Fe, Mg, Ni, Cu and Zn with respect to the earth's continental crust. Factor analysis of the data show related element groups that may be interpreted as representing, for example, an aluminosilicate from a basic rock factor, a silicate-oxide factor, a clay mineralt paleosalinity factor, a biogenic factor, a redox factor and a sorption factor. The element enrichments and these factors record provenance (dominated by detritus and weathering products from the Ethiopian Highlands with its 75% Trap Series Basalts cover), physical, chemical and biological conditions in the depositional environments,  and geography as it relates, in part, to subsidence and northeast tilting of the delta. This tilting, coupled with rising sea level, affected Nile channel base levels and gradients during the Holocene. Binary plots of factor scores can differentiate between the < 2 µm size samples from the different environments represented in the deltaic sequence of each distributary.