Relict and palimpsest depositional patterns on the Nile shelf recorded by molluscan faunas

Abstract

Infralittoral molluscs, whose normal living depths are less than 25 m, were recovered off the Nile delta between the coast and outer continental shelf and on the uppermost slope. At depths exceeding 25 m, these 13 species are interpreted as relict markers of former low sea-level stands of latest Pleistocene-to-Holocene age. Their concentration in coast-parallel belts also records the role of seafloor erosion by Holocene to modern bottom-current activity, and also displacement by bioturbation. Widespread distribution of reworked molluscan faunas and low rates (to <3 cm/1000 years) of sediment accumulation mapped on many parts of the shelf and upper slope record the overall sediment-starved nature of the Nile shelf: Where now concentrated in deep-water environments, infralittoral molluscs serve as markers to help define effects of the Holocene transgression, denote zones of intense erosion and biogenic reworking, and interpret both relict and reworked relict (palimpsest) patterns on. the modern Nile shelf.