Palynomorph biostratigraphy, palynofacies, thermal maturity and paleoenvironmental interpretation of the Bajocian-Aptian succession in the OBA D-8 Well, Matruh Basin, Egypt

摘要

A palynological study of 35 cutting samples from the Middle Jurassic-Lower Cretaceous section encountered in the OBA D-8 Well in the north Western Desert of Egypt yielded palynomorphs and particulate organic matter used to interpret the biostratigraphy, palynofacies, paleoenvironment, thermal maturation, and hydrocarbon potential of the Matruh Basin. The stratigraphically significant dinoflagellate cyst and sporomorph taxa recovered, which include Murospora florida, Aequitriradites spinulosus, Pilosisporites trichopapillosus, Callialasporites trilobatus, Tenua anaphrissa, Muderongia simplex, Systematophora sp., Gonyaulacysta jurassica, Korystocysta gochtii, Pareodinia ceratophora, and Dissiliodinium sp., permit an age assignment of the studied section as Bajocian to Aptian. Seven formal dinoflagellate cyst zones and four formal sporomorph zones are proposed for this time interval, in addition to differentiating four palynofacies assemblages and using the Rock-Eval Pyrolysis method to visually and geochemically evaluate the source rock potential. The 0.45-2.82 wt% TOC values of the studied samples indicate fair to good source rocks. An inner neritic depositional environment due to relatively high sea level is deduced for the Khatatba and Masajid formations using palynological proxies, as reflected in the lower percentages of sporomorphs relative to dinoflagellate cysts. During the Lower Cretaceous, a predominance of terrestrial sporomorphs in the Alam-El Bueib Formation suggests the advance of a fluvio-deltaic environment, possibly related to a significant sea level fall and regressive phase.