Palynostratigraphy and paleoenvironmental significance of the Cretaceous succession in the Gebel Rissu-1 well, north Western Desert, Egypt

Abstract

Palynological investigation of the Cretaceous Abu Roash, Bahariya, Kharita, Alamein, Alam El Bueib and Betty formations, encountered in the Gebel Rissu-1 well, north Western Desert, Egypt yielded 27 species of pteridophytic spores, 24 of gymnosperm pollen, 25 of angiosperm pollen and 11 of dinoflagellate cysts in addition to some acritarchs, foraminiferal test linings and freshwater algae. This enabled us to recognize five miospore biozones arranged from youngest to oldest as: Classopollis brasiliensis– Afropollis cf. kahramanensis– Dichastopollenites ghazalataensis Assemblage Zone (Late Cenomanian); Elaterosporites klaszii– Sofrepites legouxae– Afropollis jardinus Assemblage Zone (Middle/Late Albian–Early Cenomanian); Pennipollis peroreticulatus– Duplexisporites generalis-Tricolpates Assemblage Zone (Early Aptian–Early Albian); Tucanopollis crisopolensis– Afropollis sp. Assemblage Zone (Barremian) and Appendicisporites cf. tricornitatus– Ephedripites spp. Assemblage Zone (Late Neocomian). The Early Cretaceous Kharita, Alam El Bueib and the Betty formations encountered in the Gebel Rissu-1 well are interpreted to indicate oxic proximal and distal shelf deposits, characterized by type III/IV, V kerogen, which is gas prone but having little potential to produce hydrocarbons. The Upper Cretaceous Abu Roash and Bahariya formations are characterized by a distal suboxic–anoxic and marginal dysoxic–anoxic environment, and their kerogen type III/II indicates gas/oil prone nature. The Bahariya and Kharita Albian–Cenomanian sediments in the present study witnessed the onset of a semi-arid to arid climate, with local or seasonal humid conditions, based on the continuous high abundance of the elaterates pollen and Afropollis-producing plants that inhabited the paleotropical humid coastal plains.