Ostracoda, depositional environments and late quaternary evolution of eastern Nile Delta, Egypt

Abstract

Ostracode assemblages serve to refine the interpretation of the depositional environments during the late Quaternary in the northeastern Nile delta of Egypt. Nine radiocarbon-dated cores, specifically selected along a land-to-sea SW to NE transect across the northeastern delta plain, provide a representative and near complete sequence of alluvial to open marine lithofacies of late Pleistocene to Recent age. Holocene sections in six of these nine cores comprise 33 ostracode species. 30 of these live in various modern Mediterranean environments; three forms (Cytherella sp. 1, Loxoconcha sp. 1, and Sylvestra sp. 1) have not been recorded previously in this sea and are now in open nomenclature. We clustered selected species in six groups, plus a miscellaneous stock of species represented by allochthonous juveniles only. Together, these characterize different depositional environments, from lagoonal to open marine prodelta settings. Evaluation of the temporal and spatial distributions of ostracode faunae, in conjunction with petrological analysis of core sections, provides a basis to interpret the nature of Holocene deltaic fades which accumulated from about 7500 years B.P. The configuration of this region, including changes in position of the coastline, River Nile distributaries and delta lobes, is mapped for four time periods, from about 7500 years B.P. to 1500 years B.P., i.e. during the active progradation of the modern delta. Environmental markers, such as Basslerites berchoni, help recording progressive changes from marine to lagoonal settings. Other species appear responsive to climatic oscillations, such as Sylvestra sp. 1 whose distribution correlates well with a major change from wet to drier conditions at about 4000-3500 years B.P.