Pleistocene Stephanodiscaceae Diatoms from Deposits in El Fayoum Depression, Egypt

摘要

Diatomite samples in the Pleistocene deposits collected from three different localities in El Fayoum depression, reveal the predominance 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 Cyclostephanos was present with less frequency. Stephanodiscus was represented by two species 5. aegyptiacus and S. minutulus while Cyclostephanos found as onespecies C. dubius. Morphological variations of fossil species were described using light and scanning electron microscopy. The results show both morphological differences and similarities between the observed 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 freshwater nature and also suggested that the lake at this time was a different water levels or different degree of transparency. Recording of Cyclostephanos dubius in the diatomaceous earth of the studied site proved that this area was characterized by both high conductivity and high nutrients concentration during the Pleistocene era.