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Accueil du site → Doctorat → Egypte → A multiproxy palynological-, stable isotope- and geochemical-based approach through the Upper Cretaceous of the Abu Gharadig Basin, North Western Desert, Egypt

Minia University (2019)

A multiproxy palynological-, stable isotope- and geochemical-based approach through the Upper Cretaceous of the Abu Gharadig Basin, North Western Desert, Egypt

Ibrahim, Ahmed Mansour Abdelmonem

Titre : A multiproxy palynological-, stable isotope- and geochemical-based approach through the Upper Cretaceous of the Abu Gharadig Basin, North Western Desert, Egypt /

Auteur : Ibrahim, Ahmed Mansour Abdelmonem.

Etablissement de soutenance : Minia University

Grade : Doctor of Philosophy (PhD) 2019

Résumé partiel
For the current study, thirty-one cutting rock samples from the Upper Cretaceous Abu Roash A Member in BED 2-3 well, drilled in the Abu Gharadig Basin in the North Western Desert, Egypt, have been investigated. Due to the lack of reliable age control for the Abu Roash A Member, a high resolution palynological processing has been carried out and led to the identification of a highly-diverse, rich and well-preserved palynomorphs assemblage compared to the previous palynological studies for the same succession that were lean. Around 218 species of reported palynomorphs, belonging to 123 genera was identified throughout the succession. The palynomorphs assemblage was dominated be marine dinocysts, mainly 157 species, and the MFTLs that were also abundant, whereas discrete abundances of pollen grains, spores, prasinophytes, acritarches, and fresh-water algae represented only a minor part. For the first time across the Egyptian platform in NE Africa, such rich assemblages led to construct three palynological assemblage zones to be recognized, based on the first downhole occurrence are ; I- Isabelidinium belfastense - Odontochitina operculata - Isabelidinium acuminatum Assemblage Zone (early Campanian). II- Dinogymnium acuminatum - Odontochitina porifera Assemblage Zone (Santonian). III- Cyclonephelium filoreticulatum - Spinidinium echinoideum Assemblage Zone (late Coniacian). A total of 16 species of dinocysts belonging to 13 genera are documented and identified, for the first time, in the Cretaceous (late Coniacian–early Campanian) record of Egypt. Various palynological parameters were used to reveal significant variations during deposition throughout the studied sequence. Therefore, two alternating palynofacies assemblages were recognised in the Abu Roash A Member, based on AOM, phytoclasts, M/T ratio, P:G ratio, MFTLs and freshwater algae. PFA-1 was deposited in a distal, middle neritic environment with a high primary productivity that maintained the preservation of high AOM content. PFA-2 was deposited in a slightly shallower, distal inner neritic environment compared with PFA-1. It was also observed that the bicavate Chatangiella and Isabelidinium groups have adapted and thrived in areas where shallower marine settings prevailed. The redox conditions were interpreted based on four approaches, the TS and TOC relationship, which indicated deposition during predominantly oxic to intermittently dysoxic conditions. The TS-TOC-FeT relationship that was in agreement with the results of the TS-TOC relationship ; however, two samples plotted above the pyrite line, reflecting deposition during OM-limited conditions and pyrite formation diagenetically in anoxic pore water. Trace element ratios, like the V/(V + Ni) ratio, suggested euxinic redox conditions, whereas the Ni/Co ratio showed that all samples were deposited under oxic conditions. The V/Cr ratio was the most reasonable and pointed to oxic and marginally dysoxic conditions. Therefore, the trace-elemental ratios indicated that cautions should be taken when applying multiple redox proxies.

Présentation étendue (EULC)

Page publiée le 15 décembre 2020