New insights into Coniacian-Santonian palynology in the Neo-Tethys (Egypt), with special emphasis on the ecological and depositional significance of the freshwater alga Pediastrum

Abstract

Integrated palynological and palynofacies investigation based on hundreds of samples recovered from surface and subsurface successions in Sinai and the Gulf of Suez, Egypt, offer reliable data on the depositional framework of the Coniacian-Santonian Matulla Formation. The results reveal that the palynofacies contents of the three members of the Matulla Formation differ in that the lower Matulla-3 Member is Pediastrum-dominated, Matulla-2 Member is phytoclast-dominated, and the upper Mautalla-1 Member is AOM-dominated. However, some gradational mixing is observed. The assumed subdivision is very important as the Matulla Formation is a significant hydrocarbon reservoir in the Gulf of Suez, especially since this subdivision is strongly correlated with previous informal lithostratigraphic units.Furthermore, the peak occurrence of Pediastrum and its allied colonial algae that dominate the palynological assemblage, especially in the lower member of the Matulla Formation (Matulla-3), which is marginal marine, clearly implies freshwater incursions. Hence, these fossil algae are useful tracers of river runoffs as well as suspended load, enabling reconstruction of paleo-river discharge and sediment source area determination, especially if they have a promising reservoir potential, as in this case. This noteworthy record may specify an important ecozone at this time, not only in Egypt but also regionally, based on similar records from neighboring North African regions. Ultimately, the presence of Pediastrum demonstrates a sea level fall and its good preservation argues for a deposition in lowstand system tracts, which greatly conforms to sequence stratigraphic data.