A snapshot into the Oligocene vegetation of the Tethyan southern shores: new fossil pollen evidence from North Africa (Egypt)

Abstract

A palynological investigation was carried out on 24 samples from the Oligocene Dabaa Formation, which cuts across the Amana-1X well, located in the Abu El Gharadig Basin, north Western Desert, Egypt. Palynological evidence presented here suggests an early Oligocene age for the studied Dabaa Formation. In addition, the palynological assemblages provide supplementary evidence for depositional environments. They are generally indicative of outer-shelf to upper slope environment under oxic to anoxic conditions for the lower part of the studied Dabaa Formation, but infrequent occurrences of more diverse assemblages suggest an inner neritic marine environment for strata at some levels in the upper part of the studied section. It was during the Oligocene that marked floral changes leading to the development of modern plant associations began such as temperate deciduous forests (with e.g., Acer and Betulaceae) which expanded greatly in the mid latitudes. A distinctive vegetational pattern could be outlined within the deposition of the Dabaa Formation. This pattern includes mangroves represented by taxa such as Zonocostites ramonae, Psilatricolporites crassus and Verrucatosporites usmensis. Another considerably different association with plenty of the freshwater algae Botryococcus and Pediastrum spp. at this level or tropical forests at slightly elevated altitudes (ever wet climate) are dominated by a variety of tropical forest taxa including Malvaceae and Striatricolpites, together with Retitricolporites irregularis, Psilatricolporites operculatus, Retibrevitricolporites ibadanensis, Retitricolporites spp. and Psilamonocolpites spp. in addition to ferns and tree ferns where tropical floras dominate. Also recognized are elements of savanna or open woodland (less humid climate) taxa like Poaceae pollen (grass) such as Monoporopollenites annulatus associated with Amaranthaceae (e.g., Chenopodipollis multiplex), Cyperaceae spp., Echiperiporites estelae, Proteacidites cooksonii, Cicatricosisporites dorogensis and Pteris. Finally, the montane ecosystems may have occurred at the slopes of mountains including rare pollen assigned to Sapotaceae (Psilastephanocolporites spp.) and Anacardiaceae (Retitricolpites simplex) which are probably part of the palynoflora due to long-distance transport.