Pleistocene Stephanodiscaceae Diatoms from Deposits in El Fayoum Depression, Egypt

Abstract

Diatomite samples in the Pleistocene deposits collected from three different localities in El Fayoum depression, reveal the predomi-nance of Cyclostephanos and Stephanodiscus from Stephanodiscaceae. Stephanodiscus spp. were regarded with high frequencies in the western region of Lake Qarun and the dominan-cy is lowered in the eastern part while Cyclo-stephanos was present with less frequency. Stephanodiscus was represented by two species S. aegyptiacus and S. minutulus while Cyclo-stephanos found as one species C. dubius. Mor-phological variations of fossil species were de-scribed using light and scanning electron mi-croscopy. The results show both morphological differences and similarities between the ob-served species. Observing the investigated taxa with light microscope they show similarities, while observation with the SEM shows distinct differences. The presence of Stephanodiscus minutulus with large number indicates that the paleoecological environment was alkaline fresh-water nature and also suggested that the lake at this time was a different water levels or different degree of transparency. Recording of Cyclo-stephanos dubius in the diatomaceous earth of the studied site proved that this area was char-acterized by both high conductivity and high nutrients concentration during the Pleistocene era.