Clay-mineral variations in the northeastern Nile Delta, as influenced by depositional processes

Abstract

A study of five Holocene sections cored in the northeastern Nile Delta, Egypt, indicates that smectite and kaolinite dominate the clay-mineral assemblages, that illite is of lesser importance, and that proportions of chlorite are usually very low. Of note is the poor or lack of correlation among the clay-mineral assemblages and time-related stratigraphic position in the cores, and the moderate to good relationships among mineral assemblages, grain size and geographic location. Of the three major minerals, illite appears most closely related with grain size. We suggest that changes in deposition, particularly those related to transport processes and flocculation effective in former Nile delta-front environments, best explain upcore fluctuations in the proportions of clay minerals observed in the five cores. The percentages of kaolinite in the delta clay-mineral assemblages are generally higher than those recorded in the Nile River and in distal offshore Nile Cone and Levantine Basin regions. This probably resulted from selective entrapment of kaolinite relative to smectite near former coastlines, and by-passing of the latter mineral to sectors beyond the delta-front. Moreover, smectite values are highest in one core located south of Lake Manzala, a site near what may have been the mouth of a former branch (Tanitic) of the Nile which flowed east of the present Damietta branch. Climate and related paleoceanographic conditions fluctuated markedly in the eastern Mediterranean during the Holocene. It is concluded, however, that depositional processes rather than climate have been largely responsible for observed vertical and lateral changes in clay-mineral proportions in deposits accumulating in these sedimentologically active Nile fluviomarine environments.