Heavy mineral composition and texture of the recently formed fluvial delta sediment of Lake Nasser/Nubia, Egypt and Sudan

摘要

Surficial sediment samples collected from the recently formed fluvial delta in Lake Nasser/Nubia(Egypt and Sudan)in conjunction with data on bottom current and depth soundings are examined to interpret hydraulic-sorting processes and transport/depositional patterns.The~500 km long northeastwardtrending lake,lies within Egypt and Sudan,is created as a result of the construction of the Aswan High Dam in 1964.The original grain-size distribution and heavy mineral compositions of these samples help to characterize the classical depositional features of the recently formed underwater delta-front and prodelta depocenters.Starting from the south,those delta-front deposits,which floor most of the narrow-shallow basin of Lake Nubia,are characterized by thick coarse-grained sandy deposits,rich in heavy minerals(averaged 12.8%).This delta-front is followed to the northeast by thin layers of prodelta mud,poor in heavy mineral contents(averaged 0.6%).These layers cover the entire broad basin of Lake Nasser.The northeasterly downslope fining-trend,along with a continuous decrease in heavy mineral composition,along the length of the lake,are attributable to processes of grain sorting,which take place due to contrasting densities and grain sizes.These processes lead to the concentration of heavy mineral placer,mostly in the delta-front samples.The sorting mechanism,in turn,is controlled by the interplay of unidirectional-directed northeastward current,physiographic characteristics of the lake,including topographic configuration,geometry(cross-section),and floor topography(slope gradient).In terms of mineral exploration,the highest proportion of mineral grades in the delta-front sediments is likely to be considered as a viable source for economic placers that require more planning initiatives for industrial and commercial evaluation.