地球科学与气候变化杂志

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Palynological and Paleoenvironmental Investigation of Middle Miocene-Late Pliocene-Sediments from Well-X, Agbara Field between Intervals (2240 ft-3320 ft and 5260 ft-6160 ft), Shallow Offshore Depobelt, Niger Delta, Nigeria

Soronnadi Ononiwu, Didei Innocent

Thirty-two (32) ditch cutting samples composited at 60 ft intervals from Well-X, shallow offshore Niger Delta were subjected to lithological and palynological analyses using the conventional maceration technique for recovering of acid insoluble organic- walled microfossils from sediments. The lithological analysis was done with the aid of the gamma ray log of the well sections and physical description. The samples consist of fine to medium grained shale and sandy shale suggesting that the analysed section belongs to the paralic Agbada Formation. A total of 183 (one hundred and eighty-three) palynomorphs consisting of 51 fungal spores, 23 pollens and 109 spores were obtained between 2240-3320 ft interval. A total of 64 species of palynomorphs were identified from 5260-6160 ft. The diagnostic palynomorphs recovered permitted the dating and paleoenvironmental interpretation of the section and included. Verrucatosporites usmensis, Selaginella sp, Laevigatosporites haaditii, Deltoidspora minor, Monoporites sp, Acrostichumaurem, pteris sp, Elaeis guineensis, Classopollis sp. Maximum abundance of palynomophs were encountered at depth range (2300-2360 ft), equal occurrence of pollen, spore, and fungal spores occur at (2660-2770 ft). A middle Miocene to Early Pliocene age was assigned to the studied section based on the co-occurrences of Stereisporites sp, Nympheapollis clarus, Cypereaopollis sp, Retistephanocolpites gracillis and Podocarpus milanjianus, and the absence of Gemmamonoporites sp. Palaeoenvironmental interpretation was conducted by grouping the palynomorphs recovered from the well section into their various paleoenvironmental groups. The results showsshow that the palynomorphs were dominated by fresh water and coastal swamp indicators with low occurrences of marine forms, suggesting deposition within the Delta plain to Delta front, within the foreshore to upper shoreface paleoenvironment.