Abu Quir Bay, a sediment sink off the northwestern Nile delta, Egypt

Abstract

Sectors undergoing erosion and/or sediment accretion in Abu Quir bay off the northwestern Nile delta, Egypt, are identified by distribution patterns of grain size, carbonate content and heavy minerals in beach and surficial bay and shelf samples. These data are used to interpret sediment dispersal patterns and to provide information on provenance of recent and relict sediments, including those from the Canopic distributary. The Canopic is a former major Nile distributary which once flowed in the western part of Abu Quir bay. Heavy mineral suites comprising opaques, hornblende, epidote, garnet and zircon are concentrated in areas subject to erosion, including the Rosetta promontory, Abu Quir headland and the Idku lagoon inlet (the latter is close to the mouth of the former Canopic branch). Proportions of these minerals diminish away from high energy zones and toward the center of Abu Quir bay. Conversely, proportions of augite increase toward the center of the bay. Distributions of texture, carbonate content and heavy minerals indicate sediment dispersal by both contour-following bottom and cross-shelf (seaward-trending) currents. Petrologic patterns define flow divergence away from high energy along the bay margins, and areas of flow convergence toward the center of the bay and northward on the shelf. Textural and mineralogical distributions are attributable to processes that erode the mouth of the modern Rosetta branch, transport carbonate sediments derived from the Abu Quir carbonate ridge, and rework relict sediment from the former Canopic channel and its subdelta. Transport patterns interpreted on the basis of petrology complement information determined from measurement of bottom currents and longshore transport. Together, this information indicates that much of modern Abu Quir Bay is a sediment sink on the Nile delta margin.