Discrimination of accreted and eroded coasts using heavy mineral compositions of the Nile Delta beach sands, Egypt



Coastal erosion has occurred on the beaches of the three major promontories of the Nile Delta of Egypt. The eroded sand is generally carried alongshore to the east, or locally to the west, from these promontories and is deposited in areas of beach accretion between promontories. In this study the heavy minerals of 150 samples have been investigated with the aim of differentiating between eroded and accreted beaches. Discrimination was achieved by using bivariate plots of the raw weight percentage data and Q-mode factor analysis. Factor analysis yielded two ‘mineral assemblages’: Factor 1 is dominated by augite, hornblende and epidote, while Factor 2 consists of opaque minerals, garnet, zircon, rutile and monazite. These two mineral factors are produced by the selective sorting of heavy minerals by natural processes of waves and currents. Minerals of Factor 2 are associated with high density opaques which tend to concentrate as a lag in areas of erosion. Conversely, the lower density minerals of Factor 1 are preferentially transported away from areas of erosion and carried to the accreted shorelines.